EFFECT OF WELDING PARAMETERS ON MECHANICAL … · aluminium and magnesium. In this present...

http://www.iaeme.com/IJMET/index.asp 564 [email protected]

International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 6, June 2017, pp. 564–574, Article ID: IJMET_08_06_059

Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=6

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

EFFECT OF WELDING PARAMETERS ON

MECHANICAL PROPERTIES OF FRICTION

STIR WELDED JOINTS OF AA6082 AND AA6061

ALUMINIUM ALLOYS

P. Radha Krishna Prasad and P. Ravinder Reddy

Department of Mechanical Engineering,

CBIT - Chaitanya Bharathi Institute of Technology, Hyderabad, India

K. Eshwar Prasad

JNTU - Jawaharlal NehruL Technological University Hyderabad, India

ABSTRACT

The need of the hour in aerospace and military structures is the joints between

dissimilar aluminium alloys. Friction stir welding (FSW) is a novel solid state joining

technology especially developed for joining low melting temperature alloys like

aluminium and magnesium. In this present investigation, AA6082 Aluminium alloy is

friction stir welded with AA6061 Aluminium alloy for different combination of tool

rotation speed, tool feed and tool tilt angle. A cylindrical tool with a square frustum

probe is employed for friction stir welding. For each of the three factors rotational

speed, tool feed and tool tilt angle two levels are selected. Eight experiments are

designed on full factorial concept and FSW carried out for 8 runs. The tensile

properties and microhardness were measured by UTM and Vickers hardness tester

respectively. Using analysis of variance (ANOVA) optimum parameters are obtained

and presented.

Key words: Friction stir welding, Dissimilar alloys, AA6082, AA6061, ANOVA.

Cite this Article: P. Radha Krishna Prasad, P. Ravinder Reddy and K. Eshwar Prasad.

Effect of Welding Parameters on Mechanical Properties of Friction Stir Welded Joints

of AA6082 and AA6061 Aluminium Alloys. International Journal of Mechanical

Engineering and Technology, 8(6), 2017, pp. 564–574.

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=6

1. INTRODUCTION

Recent trend in the automotive world has been transition from conventional materials to

light materials like Aluminium[1]. Due to the demands for a lower environmental impact

through improved fuel efficiency, weight reduction and load capacity Aluminium is being

used more widely in the auto industry, aerospace and marine structures [2] because of its light

weight. Modern structural concepts demand reductions in both the weight as well as the cost

of production. Fabrication of Aluminium alloys by riveting results in stress concentration and

P. Radha Krishna Prasad, P. Ravinder Reddy and K. Eshwar Prasad


increase of the weight of the structure. Therefore, welding processes have proven more

attractive and there is an urgent need to study their potential [3].

Conventional fusion welding methods for joining similar Aluminium materials and

dissimilar Aluminium materials producing joints with defects like porosity, hot cracking and

distortion. Friction stir welding has been found as a best alternative to produce the joints free

from the defects which are generally induced by fusion welding processes since FSW does

not involve melting and recasting.

Friction stir welding is a solid state joining process considered to be the significant

development for the past two decades which was invented and patented by The Welding

Institute (TWI), United Kingdom in the year 1991[4]. FSW involves in employing non-

consumable rotating tool with a shoulder terminating in a profiled pin. The tool rotates and

traverses along the butting surfaces of two plates are shown in Fig. 1. The heat for welding is

produced due to the relative motion between the tool and the two interfaces being joined. The

localized heating softens the material in the vicinity of the pin and combination of tool

rotation and translation results in movement of material from the front of the pin to the rear of

the pin where it is forged into a joint [5].

Figure 1 FSW process

Selection of process parameters plays a pivotal role in producing the sound joints. The

influence of process parameters like tool rotational speed, tool feed and tool design on FSW

have been studied previously [6]. The data reported on optimization of process parameters

tool rotational speed, tool feed and tilt angle using square frustum probe tool on FSW of

dissimilar Aluminium alloys is scanty. Thus, in this investigation parametric optimization on

FSW of AA6082 and AA6061 dissimilar aluminium alloys using a tool of square frustum pin

has been studied.

1.1. Taguchi

Taguchi method is a disciplined technique for implementing improvements in products,

processes, materials, equipment and facilities. These improvements are aimed at improving

the desired characteristics and simultaneously reducing the defects by studying the key

variables controlling the process and optimizing the process or design to achieve the best

results.

1.2. Analysis Of Variance (ANOVA)

ANOVA was developed by Sir Ronald Fisher in the year 1930 as a way to interpret the results

from agricultural experiments. It is an objective decision-making tool for detecting any

differences in average performance of the groups of items tested. The decisions are arrived

Effect of Welding Parameters on Mechanical Properties of Friction Stir Welded Joints of AA6082

and AA6061 Aluminium Alloys


taking variation into account rather than using pure judgement. The purpose of ANOVA is to

determine the significant factor statistically. This gives a clear picture as to what extent the

process parameter influences the desired response and the level of significance of the factor

considered. ANOVA is a mathematical technique which breaks total variation down into

accountable sources. Some of the components in ANOVA are discussed.

1.2.1. Sum of Squares

The magnitude of each error value can be squared to provide a measurement of total variation

present. This is known as “Sum of Squares”. The basic ANOVA is that the total sum of

squares is equal to the sum of sum of squares due to known components as shown in Eq. 1.

�� = �� + �� (1)

Where,

SST - Total sum of squares.

SSm - sum of squares due to mean.

SSe - sum of squares due to error.

1.2.2. Variance Due To Error

Error variance, usually termed just variance, is equal to the sum of squares of error divided by

the degree of freedom of error. Error variance is a measure of variation due to all the

uncontrolled parameters, including measurement of error involved in a particular experiment.

1.2.3. Test of Comparison

The F-test is simply a ratio of sample variances as shown in Eq. 2.

� = �� / ��

� (2)

When this ratio becomes large enough, the two sample variances are accepted as being

unequal at some confidence level. To determine whether an F ratio of two sample Variances

are statistically large enough, three pieces of information are considered. These are the

confidence level, degree of freedom associated with the sample variance in the numerator and

degree of freedom associated with sample variance in the denominator. F-test values are

found from F-test table.

1.2.4. Percent Contribution

The portion of the total variance observed in an experiment attributed to each significant

factor and/or interaction is reflected in the percent contribution. The percent contribution is a

function of sum of squares of significant factor. The percent contribution indicates the relative

power of factor and/or interactions to reduce variation.

2. EXPERIMENTAL PROCEDURE

2.1. Welding

Rolled plates of AA6061-T6 and AA6082-T6 Aluminum alloys of 4mm thickness were used

in this investigation. Composition and mechanical properties of alloys AA6082-T6 and

AA6061-T6 are presented in tables 1 and table 2 respectively. Plates of equal size

160mm×80mm×4mm were cut and cleaned. The welding was carried out in butt joint

configuration of 160mm×160mm×4mm by placing AA6082-T6 on advancing side and

AA6061-T6 on retreating side. A milling machine modified for friction stir welding was used

to carry out the welding. A tool made of H13 tool steel having square frustum profile pin

shown in Fig. 2 was used for welding. Experiment set up for welding was illustrated in Fig.3.



In this investigation three factors and each of them at two levels are taken and illustrated in

Table 3. L8 standard orthogonal array matrix presented in Table 4 has been selected to

conduct the welding trails. The orthogonal array after assigning the values of factors

presented in Table 5. Welding was performed according to the matrix given in Table5. For

each run three specimens were welded.

Table 1 Composition of Parent Materials

S. No Material Si Fe Cu Mn Mg Cr Zn Ti Al

1 AA6061 0.6 0.23 0.25 0.12 1.04 0.12 0.017 0.007 REM

2 AA6082 1.07 0.3 0.046 0.58 0.96 0.021 0.014 0.006 REM

Table 2 Mechanical properties of Parent Materials

S. No Parameter AA6061-T6 AA6082-T6

1 Tensile strength (MPa) 292 332

2 0.2% Proof strength(MPa) 202 314

3 Elongation (percent) 24 13.5

4 Hardness-HV5 102 113

Figure 2 FSW tool

Figure 3 FSW set-up




Table 3 Factors and their levels

Table 4 L8 Orthogonal Array

RUN ROTATION SPEED

A

WELD SPEED

B

TOOL TILT ANGLE

C

1 1 1 1

2 2 1 1

3 1 2 1

4 1 1 2

5 2 2 1

6 2 1 2

7 1 2 2

8 2 2 2

Table 5 L8 Orthogonal array after assignment of factors

S.No ROTATION SPEED A

(rpm)

WELD SPEED B

��

TOOL TILT ANGLE C

( 0 )

1 900 80 1

2 1400 80 1

3 900 100 1

4 900 80 2

5 1400 100 1

6 1400 80 2

7 900 100 2

8 1400 100 2

2.2. Tensile Test

Tensile specimens were prepared as per ASTM E 8 standard shown in Fig4. The tensile tests

conducted using 25KN, Universal tensile testing machine. A sample of tensile test specimen

before and after the test are shown in Fig5. and Fig.6 respectively. The mechanical properties

ultimate tensile strength(UTS), 0.2% yield strength and percentage elongation obtained from

experimentation are presented in Table 6.

(All dimensions are in mm)

Figure 4 Tensile specimen

FACTOR LEVEL 1 LEVEL 2

Speed (rpm) 900 1400

Feed(mm/min) 80 100

Tilt angle (degree) 1 2



Figure 5 Tensile specimen before test

Figure 6 Tensile specimen after test

2.3. Microhardness Test

The microhardness tests were performed using Shimadzu, Japan, model HMV-G on a cross

section perpendicular to the weld line at mid thickness across the weld zone applying 200gf

load for a dwell time of 10sec.

2.4. Microstructure

Microstructural examination conducted using the Metascope metallurgical microscope. For

the microstructure, the samples were cut in the direction perpendicular to the welding

direction. These samples were then polished successively on the Sic papers of grit 220 to 600.

Then samples were polished on a disc polishing machine to obtain mirror finish. The samples

were then etched using a solution of Keller’s reagent. Keller’s reagent is a mixture of

Hydrogen fluoride (HF) of 1ml, Hydrochloric acid (HCL) of 1.5 ml, Nitric acid(HNO3) of

2.5ml and Distilled water (H2O) of 95ml. Samples were prepared as per ASTM E407.

3. RESULTS AND DISCUSSIONS

3.1. Tensile Strength

Tensile strength and percentage elongation obtained for three samples of each run are shown

in table 6. Runs 1,3,5,6 and 7 have been found defect free and produced higher UTS. Among

these runs 3 and 6 gave superior tensile strength over the other runs and got joint strength of

65%. The true stress and true strain diagram for runs 3 and 6 is shown in Fig.7.The UTS

obtained for all the welds depicted in Fig.8.




Table 6 L8 MATRIX with UTS and %elongation

Run Rotation

speed A

(rpm)

Weld

speed

B

��

Tool

tilt

angle

C

( 0 )

UTS (MPa) %elongation

T1 T2 T3 T1 T2 T3

1 900 80 1 162.637 183.48 172.115 13.161 13.046 13.317

2 1400 80 1 147.422 154.018 150.321 11.261 12.738 12.012

3 900 100 1 168.598 188.397 178.469 14.137 14.502 14.353

4 900 80 2 156.255 149.295 156.188 14.606 13.407 14.217

5 1400 100 1 170.524 175.03 178.288 11.321 11.701 11.476

6 1400 80 2 177.254 163.076 189.671 9.126 9.714 10.681

7 900 100 2 171.234 177.905 175.081 12.345 12.945 13.702

8 1400 100 2 120.123 117.402 115.836 5.456 5.711 5.231

Figure 7 True stress and strain diagram for runs 3 and 6

Figure 8 UTS obtained for the welds

-50

0

50

100

150

200

250

1

83

16

5

24

7

32

9

41

1

49

3

57

5

65

7

73

9

82

1

90

3

98

5

10

67

11

49

12

31

13

13

13

95

14

77

15

59

16

41

17

23

18

05

18

87

19

69

20

51

21

33

Tru

e s

tre

ss(M

Pa

)

True strain (mm)

X3 X3 X6 X6



3.1.1. ANOVA Result Discussion

ANOVA is carried out to find out the most influencing parameters and their relative

influence. From the ANOVA results table 7 for UTS, it is observed that the most dominant

influencing factor for the strength is the combination of speed and tilt angle with a

contribution of 44.5% with a confidence level of 99%.The next influencing factor on UTS is

combination of speed and feed with a contribution of 13.46% at a confidence level of

99%.The next factor which influences UTS is combination of feed and tilt angle with a

contribution of only 11.78% at a confidence level of 99%.Among the individual effects of

speed, feed and tilt angle only feed has influence on UTS with a contribution of 10.56%,

whereas the other two factors have an insignificant(dismal) effect on UTS. The individual

effects of speed, feed and tilt angle on UTS is negligible when compared with interaction

effects of factors.

Table 7 ANOVA result table for UTS

Source SS DOF V F P%

Speed 24.95532204 1 24.95532204 0.451722856 0.247019541

Feed 1066.78667 1 1066.78667 19.31018645 10.55955734

S XF 1359.903095 1 1359.903095 24.61596405 13.46096189

Tilt angle 146.41666 1 146.41666 2.650326522 1.449301122

SXT 4495.385676 1 4495.385676 81.37215998 44.49744654

FXT 1189.717772 1 1189.717772 21.5353947 11.77638734

SXFXT 935.48858 1 935.48858 16.93352515 9.259906953

SST 10102.56998 23

SSE 883.9162047 16 55.24476279 8.749419271

From the ANOVA results table 8 of %elongation it is evident that the most dominant

factor on %elongation is the combined effect of speed and feed with a contribution of 51.55%

at the confidence level of 99%. The individual influence of feed, speed and other factors of

%elongation has been found as 2nd

and 3rd

ranking factors with a contribution of 15.43% and

12.499% respectively at a confidence level of 99%.

Table 8 ANOVA result table for %elongation

Source SS DOF V F P

Speed 22.61265067 1 22.61265067 84.34167865 12.49913215

Feed 27.915894 1 27.915894 104.1219535 15.43049744

S XF 93.2598375 1 93.2598375 347.8447247 51.54933184

Tilt angle 18.9783735 1 18.9783735 70.78638868 10.49028713

SXT 5.841066667 1 5.841066667 21.78627243 3.228646886

FXT 5.396016667 1 5.396016667 20.12630498 2.982645705

SXFXT 2.620204167 1 2.620204167 9.772955019 1.448316636

SST 180.9137658 23

SSE 4.289722667 16 0.268107667 2.371142211

3.2. Microhardness

The microhardness variation measurement help the interpretation of microstructure and

mechanical properties. Microhardness tests were performed in order to characterize the

hardness in the vicinity of the weld affected area and help determine to what extent the HAZ

has been spread. The microhardness variation tests were conducted on a cross section

perpendicular to the weld line, at mid thickness across the weld zone applying load of 200gf

for a dwell time of 10 seconds. The variation of microhardness for runs 3 and 6 was illustrated

in Fig.9 and Fig.10 respectively.




The microhardness variation reveals that the microhardness values in the nugget region

were close to the parent metal AA6061-T6 and less than parent metal AA6082-T6. The

hardness recorded in the nugget zone higher than that of the TMAZ and HAZ of either side.

The average hardness in the nugget region of run 3 when compared to other runs. Better

hardness is attributed to fine grains which are resulted due to better mix and flow of metal in

weld nugget. The hardness on the advancing side and retreating side depicts that hardness

decreased from the nugget zone towards TMAZ and HAZ. The hardness observed on

advancing side in the NZ, TMAZ and HAZ region are more than the retreating side. The

lowest hardness observed on the HAZ of AA6061 which is the softest region where tensile

fractures occurred.

Figure 9 Microhardness variation for run 3

Figure 10 Microhardness variation for run 6

3.3. Microstructure

Microstructural examination revealed that there are three distinct microstructural zones weld

nugget zone (WNZ) or stir zone(SZ), thermomechanically affected zone(TMAZ) and heat

0

20

40

60

80

100

120

-22 -19 -16 -13 -10 -7 -4 -1 0 1 4 7 10 13 16 19 22

Mic

rohar

dnes

s hv 2

00gf

Distance from center of the weld (mm)

0

20

40

60

80

100

120

-22 -19 -16 -13 -10 -7 -4 -1 0 1 4 7 10 13 16 19 22

Mic

rohar

dnes

s hv 2

00gf

Distance from weld center(mm)



affect zone(HAZ) were present in the weld. The weld nugget zone (WNZ) the central portion

of the weld (i.e pin influenced region) is characterized by the mixture of the two alloys. The

nugget zone undergoes greater strain and is liable to recrystallization. TMAZ is at the two

sides of the nugget zone which terminates at the tool shoulder. TMAZ is subjected to heat and

severe plastic deformation marked by the highly deformed grains. The region outside TMAZ

which is affected only by the heat but not plastic deformation is HAZ.

HAZ 6061 consists of elongated grains in the direction of rolling with randomly dispersed

particles of FeSiAl, MgSi. TMAZ 6061 consists of elongated grains in the direction of stirring

with coarse and fine particles (FeSiAl, MgSi) aligned in the direction of stirring. WELD

NUGGET consists of fine equiaxed recrystallized grains with randomly distributed particles

in the matrix. TMAZ 6082 consists of elongated grains with coarse and fine FeSiAl, MgSi,

AlMn particles aligned in the direction of stirring. HAZ 6082 consists of elongated grains

with mixture of coarse particles of FeSiAl, MgSi and AlMn aligned in the direction of rolling.

From the microstructure study of weld samples, we can find that finer and equiaxed grains

were present in the run 3 and run 6 welds nugget zone when compared with the runs of other

runs. The fine grain structure in WNZ may be due to the good mix of parent metals into the

weld nugget and the uniform homogeneous material flow. The microhardness readings in the

nugget zone of runs 3 and 6 are also higher. Run 3 tensile fracture occurred in HAZ of

retreating side. The HAZ of retreating side of run 3 weld grain size is smallest when

compared to the HAZ retreating side of other sides characterized by higher UTS. Hence a

good correlation is observed between mechanical tests and microstructure. As a sample

microstructures of weld nugget zones of runs 3 and 6 presented in Fig. 11 and Fig.12

respectively.

Figure 11 Microstructuree of WNZ of run 3

Figure 12 Microstructuree of WNZ of run 6




4. CONCLUSIONS

In the present work the effect of speed, feed and tilt angle on mechanical properties of friction

stir welded AA6082-T6 and AA6061-T6 alloy joints was studied. The following conclusions

are drawn.

1. The optimum parameters for the ultimate strength are with the rotational speed of 900rpm,

feed of 100mm/min and tilt angle of 10. In this condition optimum, tensile strength is

189MPa.

2. The most significant contributing factor for UTS has been found to be the combination of

speed and tilt angle.

3. The most dominant factor for percentage elongation is the combination of speed and feed.

4. The lower speed, higher feed, lower tilt angle or the higher speed, lower feed and higher tilt

angles results in superior joint strength welds and characterized by fine equiaxed grain in the

nugget zone.

REFERENCES

[1] Praveen P, Yarlagadda PKDV, Meeting challenges in welding of Al-alloys through pulse

gas metal arc welding. Journal of material processing technology, 164, 2005, pp.1106-

1112.

[2] Mathers G., The welding of Aluminum and its alloys, Wood head publishing ltd, England,

2002, pp.4-5.

[3] Thomas WM, Nicholas ED, Needham JC, MurchMG, TemplesmithP, Dawes CJ., Friction

Stir Butt Welding, GB Patent No. 9125978.8, 1991.

[4] Dawes CJ, Thomas WM, Friction Stir Welding of Aluminium Alloys, TWI Bulletin,

1995, pp.6: 124-127.

[5] Nandan R, DebRoy T, Bhadeshia HKDH, Recent Advances in Friction Stir Welding

Process, Weldment Structure and Properties, Progress in Material Science, 53, August,

2008, pp. 980-1023.

[6] Mishra RS, b Ma, ZY, Friction stir welding and processing, Materials Science and

Engineering R: Reports, 50(1-2), 2005.

[7] M. Satya Narayana Gupta and K. Shiva Shankar, Evaluation of Electro-Mechanical

Properties of Friction Stir Weld ed Al/Cu Bimetallic Lap Joints. International Journal of

Civil Engineering and Technology, 8(4), 2017, pp. 1967-1976

[8] Rajiv Ranjan Kumar, Ashok Kumar and Shalendra Kumar. Evaluation of Processes

Parameter and Mechanical Properties in Friction Stir Welded Steels. International Journal

of Mechanical Engineering and Technology, 8(2), 2017, pp. 183–193.

Date post:	19-Mar-2020
Category:	Documents
Upload:	others
View:	1 times
Download:	0 times

EFFECT OF WELDING PARAMETERS ON MECHANICAL … · aluminium and magnesium. In this present...

Documents