Project (Final)

MSc Project

Zinc Nickel Plating for Hot Forming Steel in

Automobile Applications

Nihaad Pooloo

P10528585

2

Abstract

These days in the automotive industry there is a high interest in the production in high strength car

frame parts by means of hot forming. During the hot forming process the metal is exposed to the air

and reacts to the oxygen in the atmosphere causing scaling and at even higher temperatures it causes

decarburisation. These effects reduce the quality of the material and hence they must be protected

against exposure to oxygen so the material can retain its high quality properties. However scaling and

decarburising happen at very high temperatures (such as 920oC). Zinc Nickel coatings are known for

their corrosion and het resistance. This coating will be applied to a steel specimen and tested to see if

it is acceptable for hot forming in automobile applications.

3

Acknowledgements

I would like to express my greatest gratitude to my supervisor Dr Yong Sun who helped and provided

support for my Project and also to the lab technicians who left the laboratory open a little after hours

and also opened them during the holidays so I could finish my tests.

I wish to give special thanks my parents for supporting me and bearing with me throughout this

project.

4

Table of Contents

Abstract .................................................................................................................................................. 2

Acknowledgements ............................................................................................................................... 3

Introduction ......................................................................................................................................... 10

Literature Review ............................................................................................................................... 11

Methodology ........................................................................................................................................ 13

Results .................................................................................................................................................. 17

1. Zinc Nickel Coatings .............................................................................................................. 18

1.1 Zinc Nickel Coated Specimen Thicknesses .......................................................................... 18

1.2 Zinc Nickel Coated Specimen Surface Observation ........................................................... 25

1.3 Hardness of Steel under Zinc Nickel Coated Specimens .................................................... 30

2. Specimen I .............................................................................................................................. 34

2.1 Specimen I Coating Thickness .............................................................................................. 34

2.2 Specimen I Surface Coating Observation ............................................................................ 36

2.3 Hardness of Steel under Specimen I’s Coating ................................................................... 37

3. Pure Nickel Coatings ............................................................................................................. 38

3.1 Pure Nickel Coated Specimen Thicknesses ......................................................................... 38

3.2 Pure Nickel Coated Specimen Surface Observation ........................................................... 42

3.3 Hardness of Steel under Pure Nickel Coated Specimens ................................................... 44

4. Mass Difference of all Specimens Before and After Heat Treatment Procedure ............. 46

Discussion ............................................................................................................................................ 48

Conclusion ........................................................................................................................................... 49

Recommendation ................................................................................................................................. 50

Appendix .............................................................................................................................................. 51

Predicted Gantt Chart ........................................................................................................................ 72

Actual Gantt Chart ............................................................................................................................. 73

References ............................................................................................................................................ 74

5

List of Figures

Figure 1 ................................................................................................................................................ 51

Figure 2 ................................................................................................................................................ 51

Figure 3 ................................................................................................................................................ 52

Figure 4 ................................................................................................................................................ 52

Figure 5 ................................................................................................................................................ 53

Figure 6 ................................................................................................................................................ 53

Figure 7 ................................................................................................................................................ 54

Figure 8 ................................................................................................................................................ 54

Figure 9 ................................................................................................................................................ 55

Figure 10 .............................................................................................................................................. 55

Figure 11 .............................................................................................................................................. 56

Figure 12 .............................................................................................................................................. 56

Figure 13 .............................................................................................................................................. 57

Figure 14 .............................................................................................................................................. 57

Figure 15 .............................................................................................................................................. 58

Figure 16 .............................................................................................................................................. 58

Figure 17 .............................................................................................................................................. 58

Figure 18 .............................................................................................................................................. 58

Figure 19 .............................................................................................................................................. 58

Figure 20 .............................................................................................................................................. 58

Figure 21 .............................................................................................................................................. 59

Figure 22 .............................................................................................................................................. 59

Figure 23 .............................................................................................................................................. 59

Figure 24 .............................................................................................................................................. 59

Figure 25 .............................................................................................................................................. 59

Figure 26 .............................................................................................................................................. 59

Figure 27 .............................................................................................................................................. 60

Figure 28 .............................................................................................................................................. 60

Figure 29 .............................................................................................................................................. 60

Figure 30 .............................................................................................................................................. 60

Figure 31 .............................................................................................................................................. 60

Figure 32 .............................................................................................................................................. 60

Figure 33 .............................................................................................................................................. 61

6

Figure 34 .............................................................................................................................................. 61

Figure 35 .............................................................................................................................................. 61

Figure 36 .............................................................................................................................................. 61

Figure 37 .............................................................................................................................................. 61

Figure 38 .............................................................................................................................................. 61

Figure 39 .............................................................................................................................................. 62

Figure 40 .............................................................................................................................................. 62

Figure 41 .............................................................................................................................................. 62

Figure 42 .............................................................................................................................................. 62

Figure 43 .............................................................................................................................................. 62

Figure 44 .............................................................................................................................................. 62

Figure 45 .............................................................................................................................................. 63

Figure 46 .............................................................................................................................................. 63

Figure 47 .............................................................................................................................................. 63

Figure 48 .............................................................................................................................................. 63

Figure 49 .............................................................................................................................................. 63

Figure 50 .............................................................................................................................................. 63

Figure 51 .............................................................................................................................................. 64

Figure 52 .............................................................................................................................................. 64

Figure 53 .............................................................................................................................................. 64

Figure 54 .............................................................................................................................................. 64

Figure 55 .............................................................................................................................................. 64

Figure 56 .............................................................................................................................................. 64

Figure 57 .............................................................................................................................................. 65

Figure 58 .............................................................................................................................................. 65

Figure 59 .............................................................................................................................................. 65

Figure 60 .............................................................................................................................................. 66

Figure 61 .............................................................................................................................................. 66

Figure 62 .............................................................................................................................................. 66

Figure 63 .............................................................................................................................................. 66

Figure 64 .............................................................................................................................................. 66

Figure 65 .............................................................................................................................................. 66

Figure 66 .............................................................................................................................................. 67

Figure 67 .............................................................................................................................................. 67

Figure 68 .............................................................................................................................................. 67

Figure 69 .............................................................................................................................................. 67

7

Figure 70 .............................................................................................................................................. 67

Figure 71 .............................................................................................................................................. 67

Figure 72 .............................................................................................................................................. 68

Figure 73 .............................................................................................................................................. 68

Figure 74 .............................................................................................................................................. 68

Figure 75 .............................................................................................................................................. 68

Figure 76 .............................................................................................................................................. 68

Figure 77 .............................................................................................................................................. 68

Figure 78 .............................................................................................................................................. 69

Figure 79 .............................................................................................................................................. 69

Figure 80 .............................................................................................................................................. 69

Figure 81 .............................................................................................................................................. 69

Figure 82 .............................................................................................................................................. 69

Figure 83 .............................................................................................................................................. 69

Figure 84 .............................................................................................................................................. 70

Figure 85 .............................................................................................................................................. 70

Figure 86 .............................................................................................................................................. 70

Figure 87 .............................................................................................................................................. 70

Figure 88 .............................................................................................................................................. 70

Figure 89 .............................................................................................................................................. 70

Figure 90 .............................................................................................................................................. 71

Figure 91 .............................................................................................................................................. 71

8

List of Tables

Table 1 .................................................................................................................................................. 14

Table 2 .................................................................................................................................................. 14

Table 3 .................................................................................................................................................. 17

Table 4 .................................................................................................................................................. 20

Table 5 .................................................................................................................................................. 20

Table 6 .................................................................................................................................................. 21

Table 7 .................................................................................................................................................. 22

Table 8 .................................................................................................................................................. 25

Table 9 .................................................................................................................................................. 25

Table 10 ................................................................................................................................................ 26

Table 11 ................................................................................................................................................ 26

Table 12 ................................................................................................................................................ 27

Table 13 ................................................................................................................................................ 27

Table 14 ................................................................................................................................................ 28

Table 15 ................................................................................................................................................ 28

Table 16 ................................................................................................................................................ 30

Table 17 ................................................................................................................................................ 30

Table 18 ................................................................................................................................................ 31

Table 19 ................................................................................................................................................ 31

Table 20 ................................................................................................................................................ 31

Table 21 ................................................................................................................................................ 31

Table 22 ................................................................................................................................................ 32

Table 23 ................................................................................................................................................ 32

Table 24 ................................................................................................................................................ 34

Table 25 ................................................................................................................................................ 34

Table 26 ................................................................................................................................................ 36

Table 27 ................................................................................................................................................ 37

Table 28 ................................................................................................................................................ 38

Table 29 ................................................................................................................................................ 39

Table 30 ................................................................................................................................................ 39

Table 31 ................................................................................................................................................ 40

Table 32 ................................................................................................................................................ 42

Table 33 ................................................................................................................................................ 42

9

Table 34 ................................................................................................................................................ 43

Table 35 ................................................................................................................................................ 43

Table 36 ................................................................................................................................................ 44

Table 37 ................................................................................................................................................ 44

Table 38 ................................................................................................................................................ 44

Table 39 ................................................................................................................................................ 44

Table 40 ................................................................................................................................................ 45

List of Charts

Chart 1 ................................................................................................................................................. 23

Chart 2 ................................................................................................................................................. 23

Chart 3 ................................................................................................................................................. 32

Chart 4 ................................................................................................................................................. 33

Chart 5 ................................................................................................................................................. 35

Chart 6 ................................................................................................................................................. 37

Chart 7 ................................................................................................................................................. 40

Chart 8 ................................................................................................................................................. 45

Chart 9 ................................................................................................................................................. 47

List of Equations

Equation 1 ............................................................................................................................................ 18

Equation 2 ............................................................................................................................................ 19

Equation 3 ............................................................................................................................................ 19

Equation 4 ............................................................................................................................................ 30

10

Introduction

Cold forming is a manufacturing process that shapes metals at room temperature using a punch and

die (see Figure 1). Hot forming is a similar process to cold forming but however involves heating the

component. The temperatures used to heat the component ranges from 600˚C to 980˚C depending on

the required specifications and the material used. The heat applied softens the metal making it easier

to be shaped. A hot die and punch tool is used to apply pressure to the hot metal forming it to the

desired shape. [1], [2]

Hot forming process improves ductility and reduces the springback effect of a metal. Springback

effect is the extent to which a metal shifts back to its original shape after a forming process (see

Figure 2). This effect is inevitable when forming some metals. However this can be compensated by

altering the die design causing the part to over bend and the resulting springback is to the required

shape. [3]

Hot forming achieves its desired shape with lower pressure and less residual stress than cold forming.

It also produces higher grain flow and microstructure that improves the parts mechanical properties.

[2], [4]

Some disadvantages of hot forming include poor surface finish, surface oxidisation (formation of

scales), decarburisation and shorter tool life. Poor surface finishes can easily be grinded away after the

hot forming process. [4]

Scaling occurs when a metallic part is heated above 560oC. The oxygen in the atmosphere reacts to

the surface of the metal diffusing ion the metal and in the case of steel the iron (Fe) diffuses outwards.

This creates a layer of iron oxide (FeO) on the surface of the metal. The iron oxide acts as a layer of

protection for the metal against atmospheric corrosion provided that there is no break in the oxide

layer. Scaling can be removed from steel surfaces with simple methods such as shot blasting or leave

it to be weathered off. However this also means that scaling changes the chemical composition of the

original material at its surface. Hence it alters the material properties at its surface. [5]

Decarburisation is the oxidisation at the surface of the carbon which is dissolved in a metal lattice at

temperatures of above 910oC. During decarburisation gaseous products are developed (CO and CO2).

However this is only possible when the gaseous products can escape. For example when the pressures

of the carbon oxides are high enough to break the scale layer or the scale layer is porous. Hence

decarburisation also changes the chemical composition of the original material and hence also alters

the material properties. [5]

Since scaling and decarburisation can affect the properties of the material this means that the material

might not be up to required standard. Scaling and decarburisation both occur due to the reaction of the

metal to the oxygen if the atmosphere at high temperatures. Therefore this Project will focus on

creating and testing a coating that is resistant to temperatures of 920oC for steel application.

The coating chosen of this Project is Zinc Nickel given it is known for its corrosion, abrasion and heat

resistance properties in the automotive industry. [6], [7]

11

Literature Review

Hot Forming in Automotive Industry

In the automotive industry there is a high interest in the production in high strength car frame parts by

means of hot forming. The production of high strength steel sheet frame components formed by hot

forming process contributes to the mass reduction of vehicles. This reduces fuel consumption and

improves crash safely. Initially if steel alloys strength are increased, deformability is reduced and

brittleness in increased. In order for the forming of high strength steels to be possible hot forming was

developed. This process does not only allow the forming but the also the improvement of the strength

of the steel. [8]

Plastic deformation of metals is determined by the arrangement and movement of dislocations.

Dislocations are deflects in the metal’s crystal lattice (see Figure 3). They are the reason why the

metal is malleable and ductile. Hence any changes in the property of the metal have to be explained

by changes in dislocation density. Dislocation density rises during deformation at low temperature

which is why strain hardening takes place. Strain hardening is a metal is strained beyond its yield

stress and an increase in stress in needed to produce more plastic deflection. This makes the metal

stronger and difficult to deform. [9], [10], [11]

During the lowering of the dislocation density through recovery, dislocations of opposite signs

annihilate each other and the remaining dislocations rearrange themselves to form subgrain

boundaries. Recovery is when deformed grains reduce their stores energy by removal of dislocations

introduced by plastic deformation. After deformation, recovery rearranges the dislocations in a

preferable arrangement. This process is called polygonisation (see Figure 4). [9]

Recrystallization is the formation of a new set of grains. Upon heating the metal a new set of gains are

formed that contain low dislocation densities. The heat treatment (annealing or forging) allows the

atoms of the grains to move into more desirable low energy configurations. Recrystallization only

occurs if a minimum dislocation density is available. Hence a degree of deformation must be

exceeded to attain that. High previous deformation will result in low recrystallization temperature. If

the annealing time is increased, recrystallization can be achieved at lower temperatures. After

recrystallization the grain size are larger and hence the smaller the deformation the higher the

annealing temperature has to be. [9], [13]

Hot forming process starts with the blanked metal being heated up to its austenite temperature or

higher. The metal is then extracted from the heating furnace and placed onto a pressing machine. It is

pressed to the desired shape with dies at room temperature. The sheet is held under pressure in the

pressing machine for fast cooling. The metal sheet is then placed through a heat treatment where a

martensite transformation occur which improves the strength and hardness of the material. [8]

For uncoated high strength steel hot forming the heat treatment takes place in a shielded gas

environment in order to prevent scaling (oxidisation). However scaling cannot be prevented during

the transfer from the furnace to the pressing machine where it is in direct contact with the oxygen in

the atmosphere. Scaling causes material hardness which in turn causes wear hence scaling must be

removed by means such as shot blasting. [8]

12

Zinc Coating

Pure zinc coatings are usually applied to steel coatings by means of electroplating (see Figure 5) or

hot dip methods (galvanising).

The electroplating method involves submerging the component which needs to be coated (i.e. Steel

plate) along with a piece of Pure Zinc Anode (see Figure 6) in a Zinc based electrolyte solution with

the component connected to the negative side of a power supply (cathode) and the piece of Pure Zinc

connected to the positive side of the power supply (Anode) (see Figure 5). When the circuit is closed,

particles from the Pure Zinc Anode will transfer to the surface of the component (i.e. Steel).

Hot dip galvanising involves immersing the steel component in a bath of molten zinc with a

temperature of around 450oC. The electroplating method applies a coating thickness of 4µm - 13µm

and usually gives a more uniform coating than hot dipping method. The hot dip method gives a

coating of 6µm - 20µm thick. Hot dip coatings are less expensive than electroplated coatings. Pure

zinc coatings (galvanising) are widely used in construction and the automotive industries. [14], [15]

Nickel Coating

Nickel plating is mostly known of its corrosion resistance and decorative purposes. However Nickel

plating has many applications in the Engineering Field. This coating was first used to reclaim

components which had been worn or corroded in service or incorrectly machined during manufacture.

Nickel Plating was performed similarly to Pure Zinc Plating with the added difference of a Nickel

based electrolyte solution and a piece of Pure Nickel Anode (see Figure 7) is used instead of Zinc

ones. Heavy Nickel plating was used to the either build up whole or just the affection area of the

unserviceable component to a size greater than required. The coating would then be machined off to

the desired dimensions. Operations such as turning, milling and grinding were suitable for this

coating. [16]

Nickel Coatings are often applied to newly forged iron or steel components to prevent corroding or

suffering damage cause by normal wear and tear experienced in some uses. The thicknesses of the

nickel deposition vary from 50µm to 500µm depending on the operation it is required for. [16]

Nickel coating prevents basic metals from corroding therefore it reduces the danger of corrosion

products of these substrates being produced which might contaminate other materials being processed

in various apparatuses. This property preventing metallic contamination along with its non toxicity

made Nickel Electrodeposits ideal for the food handling industry. [16]

Zinc Nickel Coating

Zinc nickel plating coatings contain roughly 10% - 14 % nickel and the typical electroplating

thickness is ranges from 3 µm - 6 µm. This coating is mostly used in automotive industry for panels

which need painting afterwards, areas near the engine and the exhaust because of their superior heat

resistance, weldability, corrosion resistance and formability over pure zinc coatings. [14], [17]

13

Methodology

Specimen preparation

1. Mild steel specimens were cut to dimension of 25mm by 15mm by 1 mm.

2. Steel specimens were polished on all sides using the grinding and polishing apparatus

Minitech 265 (see Figure 8).

3. Grinded the steel specimens from coarsest to finest grain with the multi jet spray on the

Minitech 265 permanently switched on during the grinding procedure to act as lubricant.

Grain coarseness: 120, 240, 400.

Electrolyte Bath preparation

The electrolyte solution is quite corrosive and can cause skin irritation and even burn. The

mixing is best done in a well ventilated area as some fumes might be given off. Hence

protective gear such as goggles, gloves and dust mask was worn at all times. For this project

5L of electrolyte solution was created.

1. 4L of warm distilled or deionised water was added to a plastic bucket preferably made of

polypropylene.

2. 600g of Ammonium Chloride.

3. 220g of Nickel Chloride.

4. 250g of Zinc Chloride.

5. 150mL of Zylite MB Make up (shake well before pouring into mixture).

6. 5mL of Zylite MB Maintenance (shake well before pouring into mixture).

Apparatus set up

1. Lowed Zinc plate (see Figure 6) and Nickel Foil (see Figure 7) into beaker containing

electrolyte solution each attached to a titanium wire and joined together using copper taping

(the Nickel Foil and the Zinc Plate constitute as the anode).

2. Lowered Steel Plate into electrolyte solution held by crocodile clip attached to clamp and

attached to ring stand.

3. Connected positive electrode to anodes with crocodile clip and connected negative electrode

to steel specimen also with crocodile clip.

4. Power supply apparatus was switched on to begin electroplating.

5. 4 of each specimen type were created.

6. Specimen types were as follows:

14

Zinc Nickel Coating

Specimen

Current (A)

Time (min)

A 0.16 30

B 0.20 30

C 0.16 60

D 0.10 60

E 0.12 60

F 0.14 60

G 0.18 60

Pure Nickel Coating

Specimen

Current (A)

Time (min)

H 0.08 60

I

(Pure Nickel coating topped

with a Zinc Nickel coating)

0.14 (for both coatings)

60 (for each coating)

J 0.14 60

K 0.14 45

L 0.14 30

M 0.14 15

Electroplating Pre Treatment Procedure

1. Dipped steel specimen in 10% NaOH (Sodium Hydroxide) Alkaline solution for 10 min [20].

2. Rinsed with water followed by distilled water.

3. Dipped specimen in 15% HCl (Hydrochloric Acid) solution for 30s (no more or specimen

starts to etch) [20].

4. Rinsed with water then by distilled water.

Electroplating Post Treatment Procedure

1. Rinsed with a tap water (Avoid contact with plated specimen by using gloves).

2. Rinsed with ethanol.

3. Rinsed with distilled water.

4. Rinsed with ethanol again.

5. The dry specimen using the Metaserv Specimen Dryer.

Table 1

Zinc Nickel Coating Specimens

Table 2

Pure Nickel Coating Specimens

15

Heat Treatment Procedure

1. Set furnace to 900oC

2. Place Ceramic Block into furnace to be heated up (see Figure 9) with tongs. A ceramic block

was used as a support to hold up specimens in furnace since ceramics do not expand or

contract under temperature changes and it would not react with metals (corrosion).

3. Specimen is placed in furnace on the ceramic black with tongs for 3mins.

Pre Mounting Procedure

1. Cut plated specimen in half using hack saw.

2. Grinded the cut cross section to a flat surface on the Minitech 265 (see Figure 8).

Mounting Procedure

1. Switched on the Mecapress 3 (see Figure 10) mounting apparatus.

2. Pressed: Mounting then Program Mode. Select

3. Opened the compression chamber (see Figure 11).

4. Raised the platform from the chamber (see Figure 11)

5. Placed specimen with cut cross sectional surface facing down on platform held up right using

a plastic support (see Figure 12).

6. Lowered platform into chamber.

7. Added acrylic powder into chamber (enough to cover specimen in chamber entirely).

8. Closed chamber.

9. Ran program.

Post Mounting Procedure

1. Grinded mounted specimen from coarsest grain to finest grain using the Minitech 265:

Grain size: 120, 240, 400,600 and 1200.

2. Polished mounted specimen:

6µm diamond Polisher

1µm diamond polisher

(Apply lubricant if needed)

16

Steel Hardness Measurement

1. A mass of 0.3 kg was set on the apparatus to be applied to the surface of each specimen.

Hence a load of 2.943 N was applied

2. The specimen is placed onto the platform (see Figure 13)

3. The camera must be in the position shown in Figure

4. Once in place the apparatus indented the specimen it showed the live image of the indentation

on a monitor.

5. On the program loaded on the monitor were 2 vertical lines one had to be placed on the left of

the diamond indentation and the other line on the right of the indentation this was done so by

turning the dials on the side of the camera (see Figure 13)

6. Once the lines are on the sides of the indentation the red button on top of the camera was

pressed.

7. The camera was then rotated 90o and the vertical lines on the monitor were aligned to the

sides of the indentation again and the button was pressed again. The apparatus automatically

calculated the hardness of each specimen and displayed it on the screen below (see Figure 14)

8. The hardness test was performed at random points on each specimen to do so the specimen

was moved by turning platform adjusters (see Figure 13)

9. This process was repeated for each specimen.

17

Results

Average Total Surface area of Mild Steel Specimens:

Mild

Steel

Specimen

Length

(mm)

Width

(mm) Depth (mm)

Total Surface Area

(mm2)

1 26 14 1.144 819.52

2 24.8 14 1.14 782.864

3 24.2 13.65 1.123 745.6711

4 25 13.1 1.148 742.4776

5 24.7 14.55 1.149 808.9665

6 25 14.3 1.123 803.2678

7 26.3 15.3 1.145 900.044

8 25 12.75 1.143 723.7965

9 25 14.1 1.124 792.8968

10 24.55 13 1.095 720.5345

11 26.75 13 1.157 787.4815

12 25 12.8 1.14 726.184

Average Total Surface Area

(mm2)

779.4753583

Average Total Surface Area

(cm2)

7.794753583

Table 3

Specimen Average Total Surface Area

18

1. Zinc Nickel Coatings

1.1 Zinc Nickel Coated Specimen Thicknesses

Coating Thickness Estimate for Zinc Nickel Coatings:

Current density =

Equation 1

Current density range for Zinc Nickel Plating is from 0.1 A/dm2 to 4 A/dm

2. [18]

Hence since the current density for Zinc Nickel plating is between 0.001 A/dm2 and 0.04 A/dm

2 the

current range to be used on the specimens would be:

Current range to be used in Electroplating:

From:

0.001 =

Current = 0.00779 A

To:

0.04 =

Current = 0.3116 A

Current range to be used in Electroplating of mild steel specimens are between 0.00779 A and

0.3116 A.

19

Predicted Coating Thickness for Specimen D (see Table 1):

Time of Electroplating Procedure = 3600 s

Nickel Atomic Mass = 58.69 amu

Zinc Atomic Mass = 65.38 amu

Nickel Charge Number = +2

Zinc Charge Number = +2

Faraday’s Constant = 96500 C/mol

Density of Nickel = 8.91 g/cm3

Density of Zinc = 7.14 g/cm3

Total Surface Area of Mild Steel Specimen = 7.79 cm2 (see Table 3)

Current = 0.10 A

Faraday’s Law:

Mass of Coating =

Equation 2

Atomic Mass of Zinc Nickel =

= 62.035 amu

Charge Number of Zinc Nickel =

= + 2

Mass of Coating =

= 0.115712953 g

Assuming electroplating is 80% efficient Mass of Coating = 0.092570363 g

Coating Thickness (cm):

Coating Thickness =

Equation 3

Density of Zinc Nickel =

= 8.025 g/cm3

Coating Thickness =

= 1.480776 × 10

–3 cm

= 14.808 µm

20

These calculations were repeated for Specimens A to G on Excel:

Specimen Coating Thickness (µm)

A 11.846

B 14.808

C 23.692

D 14.808

E 17.769

F 20.731

G 26.654

Coating Thicknesses measured under a Microscope (Pre Heat Treatment):

Specimen

Specimen Cross Section Position

Thickness (µm)

Average Thickness (µm)

A

Edge 1 8.400

7.575

Center 1 6.000

Edge 2 9.600

Center 2 6.300

B

Edge 1 9.600

8.800 Center 1 6.900

Edge 2 11.700

Center 2 7.000

C

Edge 1 16.500

16.326

Center 1 14.103

Edge 2 20.700

Center 2 14.000

D

Edge 1 6.000

5.375 Center 1 4.800

Edge 2 6.000

Center 2 4.700

E

Edge 1 8.484

6.621

Center 1 4.800

Edge 2 8.400

Center 2 4.800

F

Edge 1 12.000

13.327 Center 1 17.700

Edge 2 6.607

Center 2 17.000

G

Edge 1 15.000

11.900

Center 1 8.100

Edge 2 16.500

Center 2 8.000

Table 4

Predicted Zinc Nickel Coating Thickness

Table 5

Measured Zinc Nickel Coating Thickness (Pre Heat Treatment)

21

Coating Thickness Percentage Difference:

Data Analysis

These large Percentage differences could be attributed to the fact that Nickel is a Transition Metal and

hence has variable charge ranging from +2 to +4. In the Faraday’s Equation the Charge for Nickel

used was +2 to gain a prediction of the Zinc Nickel coating thickness.

Also the Density of the Zinc Nickel plated was an Average between the Density of Zinc and the

Density of Nickel. The density of a Zinc Nickel coating was unknown. The Total Surface Area of the

Mild Steel Specimens (Table 3) was an Average of 12 different Mild Steel Specimens meaning the

Total Surface Area used in the Coating Thickness Equation (Equation 3) and the specimens used in

the experiment was not 100% accurate to the required 25mm by 15mm by 1mm dimensions.

Specimen Predicted Coating

Thickness (µm)

Actual Coating

Thickness (µm)

Percentage Difference

(%)

A 11.846 7.575 36.054

B 14.808 8.800 40.573

C 23.692 16.326 31.091

D 14.808 5.375 63.702

E 17.769 6.621 62.738

F 20.731 13.327 35.715

G 26.654 11.900 55.354

Table 6

Zinc Nickel Coating Thickness Percentage Difference

22

Coating Thicknesses Measured under a Microscope (Post Heat Treatment):

Specimen


Thickness (µm)


FA

Edge 1 8.400

6.625

Center 1 6.000

Edge 2 6.000

Center 2 6.100

FB

Edge 1 11.977

9.744 Center 1 9.600

Edge 2 8.400

Center 2 9.000

FC

Edge 1 14.400

14.533

Center 1 14.400

Edge 2 15.648

Center 2 13.684

FD

Edge 1 -

- Center 1 -

Edge 2 -

Center 2 -

FE

Edge 1 11.400

2.85

Center 1 -

Edge 2 -

Center 2 -

FF

Edge 1 9.300

9.913 Center 1 8.400

Edge 2 12.300

Center 2 9.650

FG

Edge 1 36.120

9.03

Center 1 -

Edge 2 -

Center 2 -

(Specimens with F before their designated letter are Post Heat Treated Specimens i.e. Specimen FC )

Table 7

Measured Zinc Nickel Coating Thickness (Post Heat Treatment)

23

Representation of Results from Tables 5 and Table 7:

0

2

4

6

8

10

12

0.16 (Specimen A) 0.2 (Specimen B)

Co

ati

ng

Th

ick

nes

s (µ

m)

Current (A)

Pre Heat Treatment

Post Heat Treatment

0

2

4

6

8

10

12

14

16

18

Co

ati

ng

Th

ick

nes

s (µ

m)

Current (A)

Pre Heat Treatment

Post Heat Treatment

Chart 2

Zinc Nickel Coating Thickness vs. Electroplating Current (Specimen C – G)

Chart 1

Zinc Nickel Coating Thickness vs. Electroplating Current (Specimen A – B)

24

Data Analysis

Specimens A and B were not included in Chart 1 because they were both electroplated for 30 minutes

each. Chart 1 represents specimens electroplated for 60 minutes each (Specimens D, E, F, C and G in

ascending current respectively).

Specimen A showed a reduction in coating thickness after the Heat Treatment as expected (see Chart

1 also see microscope pictures Figure 14 - 19). High temperatures inside the furnace must have

oxidised the surface of the coating and worn some of it off.

Specimen B showed an increase in coating thickness after the heat treatment (see Chart 1 also see

microscope pictures Figure 20 - 25). This increase in coating thickness could be an anomaly.

Unfortunately the same specimen used for Pre Heat Treatment microscopic analysis cannot be the

same one used for the Post Heat Treatment microscopic analysis since the specimens had to be cut in

half before being mounted and analysed under a microscope hence leaving one side of the specimen

without coating protection from the high temperatures inside the furnace. Hence a different specimen

must be used for the Heat Treatment. Some specimens might have had thicker coatings depending

where they were cut in half and mounted. If the specimen was cut at the centre the coating would

appear much thinner than a specimen that was cut nearer to an edge since the current density during

electroplating is highest near sharp edges making the coating thicker at the edges. This anomaly could

be attributed to human error.

Specimen C also shows a reduction in coating thickness after the Heat Treatment (see Chart 2 and

also see microscope pictures Figure 26 - 31) same as specimen A the high temperatures inside the

furnace must have oxidised the surface of the coating and worn some of it off.

Specimen D however showed that there was not coating to be found on the mild steel specimen after

the Heat Treatment (see Chart 2 and also see microscope pictures Figure 32 - 37). It was however the

thinnest of the Zinc Nickel Coatings. Its coating was not thick enough to protect the mild steel for the

furnace temperatures.

Specimen E also had a loss in coating thickness after the Heat Treatment (see Chart 2). But on second

observation of Table 7 and microscope pictures Figure 38 - 43 it was noticed that there was only 1

edge on the specimen with coating still left on it. The rest of the specimen’s coating was absent. This

coating’s thicknesses was also not thick enough.

Specimen F showed a reduction in coating thickness after the Heat Treatment as well (see Chart 2 and

also see microscope pictures Figure 44 - 49). However unlike specimen E this coating had a full

coating still left on the mild steel (see Table 7). This coating was thick enough to withstand the heat

from the furnace.

Specimen G also shows a reduction in coating thickness after the Heat Treatment (see Chart 2 and

also see microscope pictures Figure 50 - 55). But its coating before the Heat Treatment itself was

lower than that of specimen F even though specimen G had a higher current used in the electroplating

procedure that specimen F. This leads to the conclusion of poor anodes used in the electroplating

procedure (Nickel foil used as anode was starting to deplete).

25

1.2 Zinc Nickel Coated Specimens Surface Coating Observations

No Coating

Pre Heat Treatment

Post Heat Treatment

Observation:

After the Heat Treatment the specimen came out dark colour with an a layer of Iron Oxide (FeO) on

its surface.

Specimen A (electroplated at 0.16A for 30 min)

Pre Heat Treatment

Post Heat Treatment

Observation:

After the Heat Treatment process some of the coating was still left on the specimen. There were a

couple of areas of oxidation. Also there were some areas where the coating turned yellow and it had a

very rough surface. These rough yellow patches are the Zinc Nickel coating but heavily oxidised since

both zinc and Nickel turn yellow when oxidised in the air

Table 9

Specimen A Coating Comparison

Mark left by

crocodile clip

during

electroplating

process

Iron

Oxide Zinc

Nickel

Coating Rough

Surfaces

Iron

Oxide

Smooth

surface

Table 8

No Coating Specimen Comparison

26

Specimen B (electroplated at 0.2A for 30 min)

Pre Heat Treatment

Post Heat Treatment

Observation:

After the Heat Treatment process the specimen was heavily oxidised with some patches of the yellow

rough surfaces and very little coating left.

Specimen C (electroplated at 0.16A for 60 min)

Pre Heat Treatment

Post Heat Treatment

Observation:

After the Heat Treatment process there were some patches of oxidation but less than specimen B.

However there were more rough patches than specimen B and more coating left onto the specimen.

Mark left by

crocodile clip

during

electroplating

process

Zinc Nickel

Coating

Rough

Surface

s

Mark left by

crocodile clip

during

electroplating

process

Zinc Nickel

Coating

Rough

Surface

s

Iron

Oxide

Iron

Oxide

Table 10

Specimen B Coating Comparison

Table 11

Specimen C Coating Comparison

27

Specimen D (electroplated at 0.10A for 60 min)

Pre Heat Treatment

Post Heat Treatment

Observation:

This specimen had a lot of surface area that exposed after the Heat Treatment process. The Zinc

Nickel coating could have melted on the furnace and came off the steel surface during quenching.

Specimen E (electroplated at 0.12A for 60 min)

Pre Heat Treatment

Post Heat Treatment

Observation:

After the Heat Treatment of specimen E there was a large area of exposed steel. A lot of iron oxide

and rough surfaces. Coating must had fallen off during quenching for the exposed steel.

Mark left by

crocodile clip

during

electroplating

process

Rough

Surface

s

Exposed

Steel

Iron

Oxide

Table 12

Specimen D Coating Comparison

Mark left by

crocodile clip

during

electroplating

process

Rough

Surface

s Exposed

Steel Iron

Oxide

Table 13

Specimen E Coating Comparison

28

Specimen F (electroplated at 0.14A for 60 min)

Pre Heat Treatment

Post Heat Treatment

Observation:

The Post Heat Treated specimen was heavily oxidised at the top and bottom edges. Some of the

coating was still present at the centre on the specimen but the top end of the specimen had a yellow

rough surface and the bottom end on the specimen was heavily oxidised.

Specimen G (electroplated at 0.16A for 30 min)

Pre Heat Treatment

Post Heat Treatment

Observation:

Barely any coating left on the specimen after the Heat Treatment process. Lots of iron oxide areas and

rough areas.

Table 14

Specimen F Coating Comparison

Rough

Surface

s

Zinc Nickel

Coating Iron

Oxid

e

Rough

Surface

s Zinc Nickel

Coating Iron

Oxide

Table 15

Specimen G Coating Comparison

Mark left by

crocodile clip

during

electroplating

process

29

Data Analysis

Specimens A and B were both electroplate for the same amount of time however with different

currents. Specimen B even thought it had a thicker coating due to the higher current used in the

electroplating process than specimen A, its surface was more oxidised than that of specimen A (see

Table 9 and 10). Higher currents used for the electroplating process would seem to promote oxidation.

Lower currents would seem to provide better Heat resistant coating.

These rough yellow coloured patches were actually Zinc oxide when heavily oxidised in open air

(Zinc melts at 419.5oC and Nickel melts at 1455

oC). These rough surfaces however are not ideal for

hot forming processes. Rough surfaces can damage the Hot Forming Dies or Punches also the angles

required for the client’s specifications will not be accurate.

The rough Zinc Oxides and Iron Oxide patches were concentrated along the edges of the specimens

since that’s where the temperatures were highest.

All specimens after the Heat Treatment either had their coating fallen off after quenching or oxidised

iron or rough heavily oxidised zinc. The Zinc Nickel coating failed to protect the steel from oxidising

and failed to have a smooth surface for the Hot Forming processes which would follow unless the

specimen was hot rolled before hot forming however it is an additional and unnecessary process to the

steel since its surface was oxidised either way.

30

1.3 Hardness of Steel under Zinc Nickel Coated Specimens

Hardness is the resistance to deformation or the resistance to deformation under stress. The hardness

of the steel was measured using the Zwick Roell ZHV1-PC apparatus (see Figure 13). The apparatus

uses Vickers Hardness method.

Vickers Hardness Method

Vickers hardness method uses a diamond indenter in the shape of a four sided pyramid. The

pyramid’s opposite faces are 136o apart (see Figure 56). Once the specimen is placed under the

indenter a load is applied to the indenter. The full load is applied for a time of 10 to 15 seconds. The

lengths of the sides of the diamond shaped indentation left on the surface of the object after the

indenter has been removed (see Figure 57) is measured using microscope and their average is

calculated. The Vickers Hardness value is calculated using the equation: [19]

Where:

F is the load applied

d is the average of d1 and d2 (see Figure 13) Equation 4

Hardness of Zinc Nickel Coated Steel Before and After Heat Treatment (numbers marked in red

are anomalies and were not included in the Average Results):

Specimen A

Pre Heat Treatment Steel Hardness (HV) Post Heat Treatment Steel Hardness (HV)

134 131

134

135

513

143 463

139 480

Average = 133.50 Average = 485.33

Specimen B


126 120

476 476

129 462 473

119 441


Table 16

Specimen A Steel Hardness

Table 17

Specimen B Steel Hardness

31

Specimen C


153 473 470

142 476

144 427

Average =146.33 Average = 473.00

Specimen D


144 252

142 325

137 262


Specimen E


138 136 271 325 239

135 351 211

124 406 269


Specimen F


128 135 262 315 251

132 301 326 242

134 265 280 260


Table 18

Specimen C Steel Hardness

Table 19

Specimen D Steel Hardness

Table 20

Specimen E Steel Hardness

Table 21

Specimen F Steel Hardness

32

Specimen G


143 134 425 400 465

145 132 484 449 370

133 473 499 407


Plain Steel (no coating)


465 517 554

130 543 459 484

543 470 548

Average =130 Average = 509.22

Representation of Results from Tables 16 – 23:

0

100

200

300

400

500

600

Plain Steel (No Coating)

A B C

Vic

ker

s H

Ard

nes

s (H

V)

Specimen

Pre Heat Treatment

Post Heat Treatment

Table 22

Specimen G Steel Hardness

Chart 3

Zinc Nickel Coating Steel Hardness (Specimen A - C)

Table 23

Plain Steel Hardness

33

Data Analysis

Specimens A, B and C were not included in Chart 4 as there was a flaw during the electroplating of

these specimens. The Anodes (Zinc and Nickel) were not properly connected to the power source

hence the resulting coatings had an uneven amount of Zinc and Nickel. There was more Zinc plated

onto the coatings than Nickel since the coating after the electroplating procedure was reddish in

colour (see Figure 58 - 60). This issue was resolved by applying copper taping where the anodes

intersected to allow even distribution of current to both Zinc and Nickel.

Specimens A, B and C in Chart 3 all have high steel hardness after the Heat Treatment close to the No

Coating Specimen. This could be attributed to the poor electroplating process (lack of Nickel in the

coating). Zinc melts at around 419.5oC. It can be deducted that the coating with an abundance of zinc

melted off during the Heat Treatment and left the steel exposed inside the furnace hence hardening the

metal to hardenesses as high as a specimen without a protective coating.

Specimens G in Chart 4 had a high steel hardness after the Heat Treatment. This can be due to poorly

coated specimen. Chart 2 shows Specimen G having a thinner coating than Specimen F and C even

though the current used for electroplating Specimen G was higher than both. The Nickel used during

this electroplating process was poor hence the coating was lacking in Nickel which exposed the steel

to the High temperatures of the furnace making the Post Heat Treated Specimen G have such a high

hardness value.

Specimens D, E and F all have low Post Heat Treatment Steel Hardness. These specimens had well

distributed Zinc and Nickel coating deposited onto the coating. This resulted to a lower Post Heat

Treated Steel Hardness.

0

100

200

300

400

500

600 V

ick

ers

Ha

rdn

ess

(HV

)

Electroplating Current (A)

Pre Heat Treatment

Post Heat Treatment

Chart 4

Zinc Nickel Coating Steel Hardness (Specimen C - G)

34

2. Specimen I

With the repeated failures of the Zinc Nickel coating specimens a new type of coating was created.

Specimen I was a mild steel specimen coated with 2 different types of coatings. The fir coating

applied to the mild steel was a Pure Nickel Coating electroplated at 0.14A for 60 min, followed by a

Zinc Nickel Coating electroplated at 0.14A for 60 min as well (see Table 2).

2.1 Specimen I Coating Thickness


Specimen


Thickness (µm)


I

Edge 1 46.200

34.801

Center 1 24.602

Edge 2 43.200

Center 2 25.200

Coating Thicknesses measured under a Microscope (Post Heat Treatment):

Specimen


Thickness (µm)


I

Edge 1 37.500

26.551

Center 1 21.900

Edge 2 26.400

Center 2 20.402

Table 24

Measured Thickness (Pre Heat Treatment)

Table 25

Measured Thickness (Post Heat Treatment)

35

Representation of Results from Tables 24 and 25:

Data Analysis

Specimen I clearly shows a reduction in Coating Thickness after the Heat Treatment process (see

Chart 5 and see also microscope pictures Figure 61 - 66). The high temperatures inside the furnace

wore off some of the zinc nickel coating.

0

5

10

15

20

25

30

35

40

0.14 A for each coating (Specimen I)

Co

ati

ng

Th

ick

nes

s (µ

m)

Current (A)

Pre Heat Treatment

Post Heat Treatment

Chart 5

Zinc Nickel Coating Thickness vs. Electroplating Current (Specimen I)

36

2.2 Specimen I Surface Coating Observation

Specimen I

(Pure Nickel coating followed by Zinc Nickel Coating both electroplated at 0.14A for 60 min each)

Pre Heat Treatment

Post Heat Treatment

Observation:

The Post Heat Treatment specimen has areas of heavily oxide Zinc (Rough Surfaces) and some of the

Zinc nickel coating was still present on the specimen. However during quenching some of the Zinc

Nickel coating fell off revealing the Pure Nickel coating to be intact and not oxidised.

Data Analysis

Beneath the Zinc Nickel coating the Pure Nickel coating appeared un oxidised as it was still had a

shiny surface and the microscope picture Figure - it was revealed that the Pure nickel coating to be

still present With some Zinc Nickel coating still present and more importantly there were no iron

oxides.

Table 26

Specimen I Coating Comparison

Mark left by

crocodile clip

during

electroplating

process

Rough

Surface

s

Zinc Nickel

Coating

Pure Nickel

Coating

37

2.3 Hardness of Steel under Specimen I’s Coating

Hardness of Zinc Nickel Coated Steel Before and After Heat Treatment (numbers marked in red


Specimen I


151 141 249 266 245

142 142 239 233 225

128 252 309 294


Representation of Results from Table 27:

Data Analysis

Specimen I had an even lower Post Heat Treatment Steel Hardness than Specimens D, E and F (see

Chart 4 and 6). This could de due to the combination of 2 coating thicknesses which stopped the steel

hardness to rise as high as Specimens D, E and F after its Heat Treatment.

0

50

100

150

200

250

300

Specimen I

Vic

ker

s H

ard

nes

s (H

V)

Pre Heat Treatment

Post Heat Treatment

Table 27

Specimen I Steel Hardness

Chart 6

Specimen I Steel Hardness

38

3. Pure Nickel Coatings

Since the Pure Nickel coating remain intact in Specimen I it was logical to produce and test some mils

steel specimens with Pure Nickel coating. 4 types of Pure Nickel specimens were created (see Table

2). All having the same electroplating current but different electroplating times to determine the

minimum thickness needed to protect mild steel from oxidation and decarburisation while providing a

smooth surface finish on the mild steel which can be applied for hot forming procedures.

3.1 Pure Nickel Coated Specimen Thicknesses

Predicted Coating Thickness for Specimen J (see Table 2):

Time of Electroplating Procedure = 3600 s

Nickel Atomic Mass = 58.69 amu

Nickel Charge Number = +2

Faraday’s Constant = 96500 C/mol

Density of Nickel = 8.91 g/cm3

Total Surface Area of Mild Steel Specimen = 7.79 cm2 (see Table 3)

Current = 0.14 A

Mass of Coating =

= 0.153263005 g (using Equation 2)

Assuming electroplating is 80% efficient Mass of Coating = 0.122610404 g

Coating Thickness =

= 1.766493982 × 10

–3 cm (using Equation 3)

= 17.665 µm

These calculations were repeated for Specimens J to M on Excel:

Specimen Coating Thickness (µm)

J 17.665

K 13.249

L 8.832

M 4.416

Table 28

Predicted Pure Nickel Coating Thickness

39


Specimen


Thickness (µm)


J

Edge 1 24.900

19.350

Center 1 15.300

Edge 2 24.000

Center 2 13.200

K

Edge 1 23.400

18.600 Centre 1 15.300

Edge 2 20.400

Center 2 15.300

L

Edge 1 15.000

14.025

Center 1 12.900

Edge 2 16.500

Center 2 11.700

M

Edge 1 10.800

9.900 Center 1 9.600

Edge 2 11.100

Center 2 8.100

Coating Thickness Percentage Difference:

Specimen Predicted Coating

Thickness (µm)

Actual Coating

Thickness (µm)

Percentage Difference

(%)

J 17.665 19.350 9.53863572

K 13.249 18.600 40.38795381

L 8.832 14.025 58.79755435

M 4.416 9.900 124.1847826

Data Analysis

Looking at Table 29 as the Pure Nickel coating thickness decreased the Percentage Error increased. It

could be that the equation is suitable for coating thicknesses of 20µm and above.

Table 29

Measured Pure Nickel Coating Thickness (Pre Heat Treatment)

Table 30

Pure Nickel Coating Thickness Percentage Difference

40

Coating Thicknesses measured under a Microscope (Post Heat Treatment):

Specimen


Thickness (µm)


FJ

Edge 1 20.100

17.400

Center 1 13.500

Edge 2 22.200

Center 2 14.100

FK

Edge 1 19.500

18.075 Centre 1 16.500

Edge 2 21.300

Center 2 15.000

FL

Edge 1 12.900

10.950

Center 1 9.300

Edge 2 11.700

Center 2 9.900

FM

Edge 1 10.800

9.375 Center 1 8.100

Edge 2 9.900

Center 2 8.700

Representation of Results from Table 29 and 31:

0

5

10

15

20

25

15 (Specimen M) 30 (Specimen L) 45 (Specimen K) 60 (Specimen J)

Co

ati

ng

Th

ick

nes

s (µ

m)

Time (min)

Pre Heat Treatment

Post Heat Treatment

Chart 7

Pure Nickel Coating Thickness vs. Electroplating Time (Specimen J - M)

Table 31

Measured Pure Nickel Coating Thickness (Post Heat Treatment)

41

Data Analysis

All specimens had a thinner coating after the Heat Treatment process due to the high temperatures in

the furnace. Specimen L lost more than the average coating (see Chart 7). This could be due to a poor

specimen preparation.

Unlike Specimen F which was a Zinc Nickel electroplated coating Specimen J had a thicker coating

after the electroplating process and less coating thickness removed from its surface after the Heat

Treatment even though both were electroplated at 0.14A for 60 min (see on Charts 2 and 7).

All Pure Nickel coated specimens had their coating still on the surface of their mild steel after the

Heat Treatment unlike some Zinc Nickel Coatings such as Specimen D, E and G (see Table 7 and

microscope pictures Figure 32 - 37 for Specimen D, Figure 38 - 43 for Specimen E and Figure 50 - 55

for Specimen G)

42

3.2 Pure Nickel Surface Coated Specimens Surface Coating

Observations

Specimen J (electroplated at 0.14A for 60 min)

Pre Heat Treatment

Post Heat Treatment

Observation:

The surface of the specimen darkened all over (Nickel Oxide). However looking at the cross section

microscope pictures Figure 67 - 72. It was concluded that the Pure Nickel coating was still present

and protected the mild steel from oxidation and decarburisation. The Post Heat Treated specimen had

a smooth surface hence making it ideal for Hot Forming processes afterwards.

Specimen K (electroplated at 0.14A for 45 min)

Pre Heat Treatment

Post Heat Treatment

Observation:

Post Heat Treated specimen had a darker surface but the Pure Nickel coating was still present and

protected the mild steel from oxidation and decarburisation (see Figure 73 - 78). Its surface was also

smooth after the Heat Treatment process.

Mark left by

crocodile clip

during

electroplating

process

Table 32

Specimen J Coating Comparison

Table 33

Specimen K Coating Comparison

43

Specimen L (electroplated at 0.14A for 30 min)

Pre Heat Treatment

Post Heat Treatment

Observation:

The Post Heat Treated specimen had a darker surface to its Pre Heat Treated surface appearance but

the Pure Nickel coating was still present and protected the mild steel from oxidation and

decarburisation (see Figure 79 - 84). Its surface was smooth after the Heat Treatment process.

Specimen M (electroplated at 0.14A for 15 min)

Pre Heat Treatment

Post Heat Treatment

Observation:

The Post Heat Treated specimen had a darker surface to its Pre Heat Treated surface appearance but

the Pure Nickel coating was still present and protected the mild steel from oxidation and

decarburisation even though this specimen had the thinnest coating of the 4 (see Figure 85 - 90). Its

surface was smooth after the Heat Treatment process.

Data Analysis

Though the Post Heat Treated specimens all appear darker in colour unlike the Zinc Nickel specimens

it left a smooth surface which is ideal for Hot Forming Applications. And the Pure Nickel coatings

also did not wear off or left the steel exposed to the atmosphere to be oxidised.

Table 34

Specimen L Coating Comparison

Mark left by

crocodile clip

during

electroplating

process

Table 35

Specimen M Coating Comparison

44

3.3 Hardness of Steel under Pure Nickel Coated Specimens

Hardness of Pure Nickel Coated Steel Before and After Heat Treatment (numbers marked in red


Specimen J


122 125 413 400 537 459

131 122 355 606 487

135 404 439 449

Average = 123 Average = 421

Specimen K


124 126 523 480 523

126 527 586

124 517 517

Average = 125 Average = 521.4

Specimen L


134 144 132 473 484 505

136 126 126 454 454

127 125 481 476


Specimen M


125 137 121 473 493 499 470

125 131 511 476 493

163 126 484 502 446


Table 36

Specimen J Steel Hardness

Table 37

Specimen K Steel Hardness

Table 38

Specimen L Steel Hardness

Table 39

Specimen M Steel Hardness

45

Representation of Results from Tables 36 – 39:

Data Analysis

Specimen K would appear to be an anomaly since it is not following the negative correlation of the

other Pure Nickel specimens (Specimen J, L and M). As their Electroplating Time was increased their

steel’s hardness after the Heat Treatment decreased. The thicker the coating the less hard the metal

becomes after the Heat Treatment.

Though all the Pure Nickel coated specimens did not expose their steel to the atmosphere to react with

the oxygen their hardness values are quite similar to that of a specimen without coating (see Chart 8).

The reason for the steel hardness to be so high without being directly exposed to the high

temperatures of the furnace could be due to the fact that Nickel is a very good Thermal Conductor.

The thermal conductivity of Nickel is 91 W/m.K, 1% Carbon Steel is 43 W/m.K and Zinc is 116

W/m.K.

0

100

200

300

400

500

600

Vic

ker

s H

ard

nes

s (H

V)

Electroplating Time (min)

Pre Heat Treatment

Post Heat Treatment

Chart 8

Pure Nickel Coating Steel Hardness (Specimen J - M)

46

4. Mass Difference of all Specimens Before and After Heat Treatment

Procedure

When mild steel is heated up in a furnace it reacts with the oxygen in the air and produces iron oxide

(FeO). This reaction with the oxygen causes the metal to gain mass. Hence to determine if the mild

steel under their coating was oxidised or not the masses of each specimen was measured before and

after the Heat Treatment. A gain in mass would indicate a reaction of the specimen and the oxygen in

the air. This experiment was created to seek out the specimen with the least mass gained meaning the

least reaction with the oxygen in the air (no oxidation).

Masses of specimens before and after the Heat Treatment

Mass (g)

Pre Heat

Treatment

Post Heat

Treatment

Mass

Difference

Plain Steel (No

coating) 2.961 3.0002 0.0392

Specimen A 2.98685 2.95965 -0.0272

Specimen B 2.8897 2.83505 -0.05465

Specimen C 2.9037 2.86215 -0.04155

Specimen D 2.994 2.9819 -0.0121

Specimen E 2.7013 2.7022 0.0009

Specimen F 2.6562 2.6563 0.0001

Specimen G 2.7015 2.6893 -0.0122

Specimen I 2.9273 2.903 -0.0243

Specimen J 3.1911 3.1924 0.0013

Specimen K 2.7356 2.7375 0.0019

Specimen L 2.7493 2.7507 0.0014

Specimen M 2.7441 2.7459 0.0018

Table 40

Specimen Mass Difference

47

Representation of Results from Table 39:

Data Analysis

The Plain Mild Steel Specimen with no coating clearly depicts the result of the reaction of the iron in

the steel and oxygen. Without any coating to protect the specimen from oxidation its mass increased

after the Heat Treatment process.

Specimen A instead of increasing in mass its mass decreased. This happened because the Zinc Nickel

coating which was meant to protect the coating form oxidation fell off during quenching after the

Heat Treatment procedure. Hence the loss in mass, Specimen B, C, D,G and I all experienced the

same problem, their Zinc Nickel coating fell off after quenching.

Specimen E however showed promise in Chart 9. The small amount of mass gained would indicated a

very small reaction of the specimen to oxygen. Hence this would have made it an ideal Heat Resistant

coating. However while observing the surface of Specimen E after the Heat Treatment (see Table 13).

There were areas of exposed steel and iron oxide. This would mean that the specimen gained mass

while in the furnace when the mild steel to its High Temperatures and loss that mass amount of mass

during quenching. Meaning this result was misleading and the same thing happened to Specimen F

(see Table 14).

The Pure Nickel specimens on the other hand showed no cracks, no exposed steel and had a smooth

surface and yet their mass gain was minimal (see Chart 9). Meaning there was a very small reaction

with oxygen.

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

Ma

ss (

g)

Chart 9

Specimen Mass Difference

48

Discussion

The Zinc Nickel coatings cannot protect mild steel form being exposed to oxygen regardless of

coating thickness (see Tables 9 – 15). Even thought the current was increase to promote thicker

coating thicknesses it proved useless against the Heat Resistance Test. Some coating was left at the

centre of the specimen but near the edges of the specimens there were heavily oxidised Zinc (rough

surfaces) and Iron oxide (FeO). The aim of this project was to test if Zinc Nickel Coatings would be

capable of being applied to steel for Hot Forming Applications in the Automotive Industry to stop the

oxidation of the metal (FeO). Hot Forming Applications require the steel to be heated to temperatures

ranging from 600oC to 980

oC. At temperatures of 900

oC the Zinc Nickel specimens all failed to

protect their steel form oxidation. Even if there was a coating thick enough to protect the steel form

oxidation the rough surfaces of the heavily oxidise Zinc made it in applicable for Hot Forming. These

rough surfaces will damage the punch and die during the Hot Forming process and it will be difficult

to determine the angle of rough surface steel that will be created in the pressing apparatus.

Unfortunately the Zinc Nickel Coating is not acceptable as a surface coating for steel that can be used

in Hot Forming procedures to stop oxidation and decarburisation of the metal.

Pure Nickel coatings however would prove to be a very good Heat Resistant coating. This coating

would barely wear off after the Heat Treatment. No coating came off so steel was exposed to the

atmosphere even after quenching hence no oxidation of the metal. It left a smooth surface finish after

the Heat Treatment which is acceptable for Hot Forming Procedures. After the Heat Treatment there

was barely any change in the masses of the Pure Nickel specimens meaning the Nickel barely reacted

with oxygen (Nickel melting temperature 1455oC). The thinnest coating created was Specimen M

which had a coating thickness of 9.9µm still protected the mild steel from oxidation meaning that the

coating thickness could be made thinner and still stop the metal form oxidation in the furnace.

Also since Nickel is such a good conductor of heat the steel beneath the Pure Nickel coating hardens

similar to steel without any oxidation protective coating. Meaning to attain a similar hardness level as

plain steel without an anti oxidation coating the furnace temperature will not need to be raised higher

to achieve similar hardness unlike the Zinc Nickel Specimens D, E and F whose hardness remained

low after the Heat Treatment Procedure.

49

Conclusion

This experiment was designed to apply and test the heat resistance of Zinc Nickel onto a mild steel

specimen. Its goal was to stop the oxygen in the atmosphere from reacting with the metal surface

while in the furnace with temperatures ranging from 600oC to 980

oC (temperatures for Hot Forming

Processes) or after being removed from the furnace. The results from the experiment proved to be

disappointing. At 900oC the specimen would melt in the furnace and detach itself from the steel

surface upon quenching. Some of its surface was oxidised (FeO) and some resulted in a rough surface

with very little Zinc Nickel coating still left on the specimen itself. It was clear that the Zinc Nickel

coating was unsuitable for Hot Forming Applications.

Specimen I however showed that Pure Nickel could be used as a potential anti oxidation coating in the

furnace. The Pure Nickel specimens did not melt while in the furnace, the also did not detached

themselves from their steel plate upon quenching and when analysed under the microscope the Pure

Nickel coating was still present across the coating after the Heat Treatment meaning oxygen could not

have reacted with the steel metal plate. Pure Nickel coating have very good corrosion and wear

resistance meaning it can be put through a pressing apparatus after its Heat Treatment and the Pure

Nickel coating would still be present on the steel plate. Pure Nickel coating can be use for Hot

Forming Applications to stop steel from oxidation and decarburisation.

50

Recommendations

Pure Nickel is a good coating to prevent steel form oxidation and decarburization.

However it is always best to explore other better and cheaper oxidation and

decarburization preventing coatings.

More time could have been given to repeat the Heat Treatment Procedure on all

specimens to provide a more reliable set of results

Better apparatus could have been used to detect the presence and content of the

coatings to discover if there were any reaction between the coatings and the metal

surface.

51

Appendix

Punch

Die Metal Plate

Figure 1

Punch and Die set

Figure 2

Springback effect

Metal Sheet

Intended Shape

Actual Shape

Springback Angle

52

Figure 3

Dislocation [12]

Figure 4

Bent Crystal Polygonisation [9]

Dislocation arrangement before

polygonisation

Dislocation arrangement after

polygonisation

53

Anode Cathode

Electrolyte Bath Particle movement

Power

supply

Figure 5

Electroplating Procedure

Figure 6

Piece of Pure Zinc

54

Figure 7

Piece of Pure Nickel Foil

Figure 8

Grinding and Polishing Apparatus

55

Figure 9

Ceramic Block Specimen Support

Figure 10

Mecapress 3 Mounting Apparatus

Steel Specimen

Ceramic Block

56

Raised Platform

Figure 11

Mecapress 3 with Raised Platform

Figure 12

Mecapress 3 with Raised Platform Close up

Raised Platform

Specimen

Plastic Support

57

Platform

Camera Camera dials

Platform

adjusters

Figure 13

Zwick Roell ZHV1-PC Hardness Testing Apparatus

Figure 14

Zwick Roell ZHV1-PC Hardness Testing Apparatus Hardness Display Screen

Display

Screen

58

Figure 15

Specimen A Edge 1 Pre Heat Treatment

Figure 16

Specimen A Centre Pre Heat Treatment

Figure 17

Specimen A Edge 2 Pre Heat Treatment

Figure 18

Specimen FA Edge 1 Post Heat Treatment

Figure 19

Specimen FA Centre Post Heat Treatment

Figure 20

Specimen FA Edge 2 Post Heat Treatment

Coating

Coating

Coating Coating

Coating Coating

59

Figure 21

Specimen B Edge 1 Pre Heat Treatment

Figure 22

Specimen B Centre Pre Heat Treatment

Figure 23

Specimen B Edge 2 Pre Heat Treatment

Figure 24

Specimen FB Edge 1 Post Heat Treatment

Figure 25

Specimen FB Centre Post Heat Treatment

Figure 26

Specimen FB Edge 2 Post Heat Treatment

Coating Coating

Coating Coating

Coating

Coating

60

Figure 27

Specimen C Edge 1 Pre Heat Treatment

Figure 28

Specimen C Centre Pre Heat Treatment

Figure 29

Specimen C Edge 2 Pre Heat Treatment

Figure 30

Specimen FC Edge 1 Post Heat Treatment

Figure 31

Specimen FC Centre Post Heat Treatment

Figure 32

Specimen FC Edge 2 Post Heat Treatment

Coating

Coating

Coating

Coating

Coating Coating

61

Figure 33

Specimen D Edge 1 Pre Heat Treatment

Figure 34

Specimen D Centre Pre Heat Treatment

Figure 35

Specimen D Edge 2 Pre Heat Treatment

Figure 36

Specimen FD Edge 1 Post Heat Treatment

Figure 37

Specimen FD Centre Post Heat Treatment

Figure 38

Specimen FD Edge 2 Post Heat Treatment

Coating

Coating

Coating

62

Figure 39

Specimen E Edge 1 Pre Heat Treatment

Figure 40

Specimen E Centre Pre Heat Treatment

Figure 41

Specimen E Edge 2 Pre Heat Treatment

Figure 42

Specimen FE Edge 1 Post Heat Treatment

Figure 43

Specimen FE Centre Post Heat Treatment

Figure 44

Specimen FE Edge 2 Post Heat Treatment

Coating

Coating

Coating Coating

63

Figure 45

Specimen F Edge 1 Pre Heat Treatment

Figure 46

Specimen F Centre Pre Heat Treatment

Figure 47

Specimen F Edge 2 Pre Heat Treatment

Figure 48

Specimen FF Edge 1 Post Heat Treatment

Figure 49

Specimen FF Centre Post Heat Treatment

Figure 50

Specimen FF Edge 2 Post Heat Treatment

Coating Coating

Coating

Coating

Coating

Coating

64

Figure 51

Specimen G Edge 1 Pre Heat Treatment

Figure 52

Specimen G Centre Pre Heat Treatment

Figure 53

Specimen G Edge 2 Pre Heat Treatment

Figure 54

Specimen FG Edge 1 Post Heat Treatment

Figure 55

Specimen FG Centre Post Heat Treatment

Figure 56

Specimen FG Edge 2 Post Heat Treatment

Coating Coating

Coating

Coating

65

136o in-between opposite faces

Diamond indenter

Specimen Surface

coating

Figure 57

Indenter

Figure 58

Diamond shaped Indentation

d1

d2

Figure 59

Specimen C Surface Coating 40 ×

magnification

66

Figure 60


magnification

Figure 61


magnification

Figure 62

Specimen I Edge 1 Pre Heat Treatment

Figure 63

Specimen I Centre Pre Heat Treatment

Figure 64

Specimen I Edge 2 Pre Heat Treatment

Figure 65

Specimen FI Edge 1 Post Heat Treatment

Coating

Coating

Coating

Coating

67

Figure 66

Specimen FI Centre Post Heat Treatment

Figure 67

Specimen FI Edge 2 Post Heat Treatment

Figure 68

Specimen J Edge 1 Pre Heat Treatment

Figure 69

Specimen J Centre Pre Heat Treatment

Figure 70

Specimen J Edge 2 Pre Heat Treatment

Figure 71

Specimen FJ Edge 1 Post Heat Treatment

Coating Coating

Coating

Coating

Coating

Coating

68

Figure 72

Specimen FJ Centre Post Heat Treatment

Figure 73

Specimen FJ Edge 2 Post Heat Treatment

Figure 74

Specimen K Edge 1 Pre Heat Treatment

Figure 75

Specimen K Centre Pre Heat Treatment

Figure 76

Specimen K Edge 2 Pre Heat Treatment

Figure 77

Specimen FK Edge 1 Post Heat Treatment

Coating Coating

Coating

Coating

Coating

Coating

69

Figure 78

Specimen FK Centre Post Heat Treatment

Figure 79

Specimen FK Edge 2 Post Heat Treatment

Figure 80

Specimen L Edge 1 Pre Heat Treatment

Figure 81

Specimen L Centre Pre Heat Treatment

Figure 82

Specimen L Edge 2 Pre Heat Treatment

Figure 83

Specimen FL Edge 1 Post Heat Treatment

Coating

Coating

Coating Coating

Coating

Coating

70

Figure 84

Specimen FL Centre Post Heat Treatment

Figure 85

Specimen FL Edge 2 Post Heat Treatment

Figure 86

Specimen M Edge 1 Pre Heat Treatment

Figure 87

Specimen M Centre Pre Heat Treatment

Figure 88

Specimen M Edge 2 Pre Heat Treatment

Figure 89

Specimen FM Edge 1 Post Heat Treatment

Coating

Coating

Coating

Coating

Coating

Coating

71

Figure 90

Specimen FM Centre Post Heat Treatment

Figure 91

Specimen FM Edge 2 Post Heat Treatment

Coating Coating

72

Predicted Gantt Chart

Objectives

Academic Week

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51

Steel plate

specimen

preparation

Zinc Nickel

Bath

Preparation

Apparatus set

up

Electroplating

Specimen

Mass

Difference

Analysis

Specimen

Coating

Analysis

Specimen

Hardness

Analysis

Dissertation

Writing

73

Actual Gantt Chart

Objectives

Academic Week

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51

Steel plate

specimen

preparation

Zinc Nickel

Bath

Preparation

Apparatus set

up

Electroplating

Specimen

Mass

Difference

Analysis

Specimen

Coating

Analysis

Specimen

Hardness

Analysis

Dissertation

Writing

74

References

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