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
Specimen Cross Section Position
Thickness (µm)
Average 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
Pre Heat Treatment Steel Hardness (HV) Post Heat Treatment Steel Hardness (HV)
126 120
476 476
129 462 473
119 441
Average = 125.00 Average = 475.00
Table 16
Specimen A Steel Hardness
Table 17
Specimen B Steel Hardness
31
Specimen C
Pre Heat Treatment Steel Hardness (HV) Post Heat Treatment Steel Hardness (HV)
153 473 470
142 476
144 427
Average =146.33 Average = 473.00
Specimen D
Pre Heat Treatment Steel Hardness (HV) Post Heat Treatment Steel Hardness (HV)
144 252
142 325
137 262
Average = 141.00 Average = 279.67
Specimen E
Pre Heat Treatment Steel Hardness (HV) Post Heat Treatment Steel Hardness (HV)
138 136 271 325 239
135 351 211
124 406 269
Average = 136.33 Average = 277.67
Specimen F
Pre Heat Treatment Steel Hardness (HV) Post Heat Treatment Steel Hardness (HV)
128 135 262 315 251
132 301 326 242
134 265 280 260
Average = 134.00 Average = 278.22
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
Pre Heat Treatment Steel Hardness (HV) Post Heat Treatment Steel Hardness (HV)
143 134 425 400 465
145 132 484 449 370
133 473 499 407
Average = 134.00 Average = 450.50
Plain Steel (no coating)
Pre Heat Treatment Steel Hardness (HV) Post Heat Treatment Steel Hardness (HV)
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
Coating Thicknesses measured under a Microscope (Pre Heat Treatment):
Specimen
Specimen Cross Section Position
Thickness (µm)
Average 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
Specimen Cross Section Position
Thickness (µm)
Average 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
are anomalies and were not included in the Average Results):
Specimen I
Pre Heat Treatment Steel Hardness (HV) Post Heat Treatment Steel Hardness (HV)
151 141 249 266 245
142 142 239 233 225
128 252 309 294
Average = 141.67 Average = 256.89
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
Coating Thicknesses measured under a Microscope (Pre Heat Treatment):
Specimen
Specimen Cross Section Position
Thickness (µm)
Average 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
Specimen Cross Section Position
Thickness (µm)
Average 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
are anomalies and were not included in the Average Results):
Specimen J
Pre Heat Treatment Steel Hardness (HV) Post Heat Treatment Steel Hardness (HV)
122 125 413 400 537 459
131 122 355 606 487
135 404 439 449
Average = 123 Average = 421
Specimen K
Pre Heat Treatment Steel Hardness (HV) Post Heat Treatment Steel Hardness (HV)
124 126 523 480 523
126 527 586
124 517 517
Average = 125 Average = 521.4
Specimen L
Pre Heat Treatment Steel Hardness (HV) Post Heat Treatment Steel Hardness (HV)
134 144 132 473 484 505
136 126 126 454 454
127 125 481 476
Average = 129.43 Average = 470.33
Specimen M
Pre Heat Treatment Steel Hardness (HV) Post Heat Treatment Steel Hardness (HV)
125 137 121 473 493 499 470
125 131 511 476 493
163 126 484 502 446
Average = 127.50 Average = 484.70
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
Specimen C Surface Coating 100 ×
magnification
Figure 61
Specimen C Surface Coating 400 ×
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
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