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http://www.iaeme.com/IJMET/index.asp 528 [email protected] `International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 11, November 2017, pp. 528–534, Article ID: IJMET_08_11_056 Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=11 ISSN Print: 0976-6340 and ISSN Online: 0976-6359 © IAEME Publication Scopus Indexed INFLUENCE OF PROCESS PARAMETERS ON MECHANICAL PROPERTIES OF FRICTION STIR WELDING OF AA 6061-T6 ALLOY D.Raghavendra Assistant professor in S R Engineering College S.Sravya Assistant professor in S R Engineering College ABSTRACT: This paper includes butt joining of 5 mm of AA 6061 plates. The present study investigates the influence of welding parameters on microstructure and mechanical properties of friction stir welded AA 6061-T6 Alloy was studied. An attempt is made here to review the fundamental principle of this process its tensile strength and examination of its metallurgical consequences. An improved milling machine is fabricated for performing friction stir welding and its effectiveness in joining Al 6061- T6 Alloy plates is demonstrated in the current work. The FSW Process has proved to be very efficient and has immense potential for future application. Present investigation is to find out the optimum mechanical properties of friction stir welding of Al 6061-T6 alloy. In this present study an attempt has been made to study the effect of tool rotational speed(RPM), welding speed(mm/min),tool geometry and D/d ratio on FSW zone transformation in Aluminium alloy. For three different tools, rotational speeds, and three different tool D/d ratios, one tool pin profile have been used to fabricate the joints. Tensile properties, toughness and microstructure of the joint were evaluated and correlated as received Al 6061-T6 alloys. The joints fabricated using rotational speed of 900rpm, a welding speed of 60 mm/min, taper thread pin profile and tool shoulder diameter of 18 mm, (D/d)=3.0 showed higher tensile properties compared to other joints. Keywords: Aluminium alloy, Friction Stir Welding, Microstructure, AA 6061, Mechanical properties Cite this Article: D.Raghavendra and S.Sravya, Influence of Process Parameters on Mechanical Properties of Friction Stir Welding of Aa 6061-T6 Alloy, International Journal of Mechanical Engineering and Technology 8(11), 2017, pp. 528–534. http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=11
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INFLUENCE OF PROCESS PARAMETERS ON MECHANICAL PROPERTIES OF FRICTION STIR WELDING … · 2017. 11. 28. · Keywords: Aluminium alloy, Friction Stir Welding, Microstructure, AA 6061,

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Page 1: INFLUENCE OF PROCESS PARAMETERS ON MECHANICAL PROPERTIES OF FRICTION STIR WELDING … · 2017. 11. 28. · Keywords: Aluminium alloy, Friction Stir Welding, Microstructure, AA 6061,

http://www.iaeme.com/IJMET/index.asp 528 [email protected]

`International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 11, November 2017, pp. 528–534, Article ID: IJMET_08_11_056

Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=11

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

© IAEME Publication Scopus Indexed

INFLUENCE OF PROCESS PARAMETERS ON MECHANICAL PROPERTIES OF FRICTION

STIR WELDING OF AA 6061-T6 ALLOY

D.Raghavendra

Assistant professor in S R Engineering College

S.Sravya

Assistant professor in S R Engineering College

ABSTRACT:

This paper includes butt joining of 5 mm of AA 6061 plates. The present study

investigates the influence of welding parameters on microstructure and mechanical

properties of friction stir welded AA 6061-T6 Alloy was studied. An attempt is made

here to review the fundamental principle of this process its tensile strength and

examination of its metallurgical consequences. An improved milling machine is

fabricated for performing friction stir welding and its effectiveness in joining Al 6061-

T6 Alloy plates is demonstrated in the current work. The FSW Process has proved to

be very efficient and has immense potential for future application. Present

investigation is to find out the optimum mechanical properties of friction stir welding

of Al 6061-T6 alloy. In this present study an attempt has been made to study the effect

of tool rotational speed(RPM), welding speed(mm/min),tool geometry and D/d ratio

on FSW zone transformation in Aluminium alloy. For three different tools, rotational

speeds, and three different tool D/d ratios, one tool pin profile have been used to

fabricate the joints. Tensile properties, toughness and microstructure of the joint were

evaluated and correlated as received Al 6061-T6 alloys. The joints fabricated using

rotational speed of 900rpm, a welding speed of 60 mm/min, taper thread pin profile

and tool shoulder diameter of 18 mm, (D/d)=3.0 showed higher tensile properties

compared to other joints.

Keywords: Aluminium alloy, Friction Stir Welding, Microstructure, AA 6061,

Mechanical properties

Cite this Article: D.Raghavendra and S.Sravya, Influence of Process Parameters on

Mechanical Properties of Friction Stir Welding of Aa 6061-T6 Alloy, International

Journal of Mechanical Engineering and Technology 8(11), 2017, pp. 528–534.

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=11

Page 2: INFLUENCE OF PROCESS PARAMETERS ON MECHANICAL PROPERTIES OF FRICTION STIR WELDING … · 2017. 11. 28. · Keywords: Aluminium alloy, Friction Stir Welding, Microstructure, AA 6061,

D.Raghavendra and S.Sravya

http://www.iaeme.com/IJMET/index.asp 529 [email protected]

1. INTRODUCTION

In 1991 a new process for welding of aluminium alloys was invented by The Welding

Institute, Cambridge, UK. The process was duly named friction stir welding (FSW), and The

Welding Institute filed for world-wide patent protection.This welding process has made

possible to weld a number of aluminum alloys that were previously not recommended (2000

series & copper containing 7000 series aluminium alloys) for welding [3] Consistent with the

more conventional methods of friction welding, which have been practiced since the early

1950s, the weld is made in the solid phase, that is no melting. After the invention of process,

it has received attention and today most of the companies are using the technology in

production, particularly for joining aluminum alloys.

Friction-stir welding (FSW) is a solid-state joining process in which (the metal is not

melted) that uses a third body tool to join two flat surfaces. During the process the region

between the material and the FSW tool softend due to the heat is generated between the tool

and material. It then mechanically intermixes the two work pieces of metal at the place of the

join, then the softened metal (due to the elevated temperature) can be joined using mechanical

pressure which is applied by the movement of tool, much like joining clay, or dough. It is

primarily used on aluminum, and most often on extruded aluminum (non-heat treatable

alloys), and on structures which need superior weld strength without a post weld heat

treatment. The process of Friction Stir Welding process has been widely used in the industries

and aerospace many applications. It is used mainly because of many of its advantages over the

conventional welding techniques[5]. Friction stir welding joints exhibits better mechanical

properties compared to other welding process and they are free from blowholes or porosity

compared to the other conventionally welded materials. The schematic Diagram of Friction

Stir Welding process is shown in figure 1

Figure 1 Schematic Diagram of Friction Stir Welding process

Aluminium alloys have light weight and higher strength to weight ratio due to this reason

alluminium alloys find wide applications in aerospace, automobile industries, railway

vehicles, bridges, offshore structure topsides and high speed ships. Welding is the primary

joining method in all cases which has always shows a great challenge for designers and

technologists. The main problem is lots of difficulties are associated with this kind of joint

process, mainly related to the presence of a tenacious oxide layer, high thermal conductivity,

high coefficient of thermal expansion, solidification shrinkage and, above all, high solubility

of hydrogen, and other gases, in the molten state . Further problems occur when attention is

focused on heat-treatable alloys, since heat, provided by the welding process, is responsible

for the decay of mechanical properties, due to phase transformations and softening. AA 6061

aluminium alloy containing magnesium and silicons as its major alloying elements is the most

widely used medium strength aluminium alloy, and has gathered wide acceptance in the

Page 3: INFLUENCE OF PROCESS PARAMETERS ON MECHANICAL PROPERTIES OF FRICTION STIR WELDING … · 2017. 11. 28. · Keywords: Aluminium alloy, Friction Stir Welding, Microstructure, AA 6061,

Influence of Process Parameters on Mechanical Properties of Friction Stir Welding of Aa 6061-T6

Alloy

http://www.iaeme.com/IJMET/index.asp 530 [email protected]

fabrication of light weight structure. 6061 is resistant to corrosion even when the surface is

abraded and more easily worked[2].

The tool serves three primary functions; the heating of the workpiece, the movement of

material to produce the joint, and the containment of the hot metal beneath the tool shoulder

[1]. The heat generated during the FSW process is often assumed to occur predominantly

under the shoulder; due to its greater surface and to be equal to the power required to

overcome the friction forces between the tool and the workpiece [3]. To an extent, with the

increase in the shoulder diameter the heat input into the welds increases 4]. To study the heat

input into the welds while varying the process parameters the three different shoulder

diameters are used.

2. EXPERIMENTAL PROCEDURE

The experimental study includes the butt joining of 5mm AA 6061 flat plates. The welding

process is carried out on a vertical milling machine. Tool is hold in a tool arbour. Special

welding jigs and fixtures are designed to hold on two plates of 250mm X 60mm X 5mm

thickness combinations of the tool rotational speed(RPM), welding speed(mm/min), tool

geometry and diameter of the tool shoulder to the diameter of the tool pin (D/d) FSW

experiment is performed on AA 6061 by keeping welding speed (40mm/min) constant and by

changing three rotational speeds(900,1120 and 1400) rpm’s and by using stainless steel tool

having screwed taper pin profile with three D/d ratios(ratio of diameter of tool shoulder to the

tool pin).The diameters of tool shoulder(D) were 18mm,21mm and 24mm and that of insert

pin diameter(d) and pin length(L) are 6mm and 4.8mm respectively[7].

A milling machine have spindle that is positioned vertically and a worktable that is

parallel to the ground. The vertical milling machine used to fabricate friction stir welding

joints was shown in figure 2 and the experimental tool set up is shown in figure 3

Figure 2 image of Vertical Milling Machine Figure 3 image of experimental tool set up

The materials used for the welding are similar AA 6061 alloy, and tool used is stainless

steel. AA 6061 plates before performing friction stir welding are shown in figure 4 and taper

screwed pin profile of stainless steel tools of three D/d ratio tools are shown in figure 5

The chemical composition of AA 6061is shown in fallowing table 1

Element Mg Si Cu Zn Ti Mn Cr Al

Amount(Wt%) 0.85 0.68 0.22 0.07 0.05 0.32 0.06 Balance

Table 1 Chemical composition of AA 6061 alloy

Page 4: INFLUENCE OF PROCESS PARAMETERS ON MECHANICAL PROPERTIES OF FRICTION STIR WELDING … · 2017. 11. 28. · Keywords: Aluminium alloy, Friction Stir Welding, Microstructure, AA 6061,

D.Raghavendra and S.Sravya

http://www.iaeme.com/IJMET/index.asp 531 [email protected]

Figure 4 AA 6061 work piece material Figure 5 Stainless steel tools of screwed taper pin profile

The initial joint configuration was obtained by securing the plates in position using

mechanical clamps. The direction of welding is normal to the rolling direction and single pass

FSW used to fabricate the joints and the three weld joints are in figure 6

Figure 6 Image of AA 6061 after fsw

3. RESULTS AND DISCUSSION

3.1. Tensile test on welded joints

Tensile test, also known as tension testing, and it is a destructive testing method that measures

and provides valuable information of the strength of a particular material, part, sample, weld

or other items. is a traditional materials science test in which a sample is subjected to ultimate

failure by performing the increasing the load capacity on the sample. The tensile test can be

commonly used to predict how a material will react under other types of forces or loads and to

select a material for an application, for quality control. In this paper the properties that are

directly measured by using tensile test are ultimate tensile strength, percentage of elongation

and yield strength. From these measurements the following properties can also be determined:

Young's modulus, Poisson's ratio and strain-hardening characteristics[6]. A tensile specimen

has a standardized sample cross-section,it has two shoulders and a gauge in between the

shoulders. The tensile specimen is shown in figure 7

Figure 7 Tensile test Specimen

Page 5: INFLUENCE OF PROCESS PARAMETERS ON MECHANICAL PROPERTIES OF FRICTION STIR WELDING … · 2017. 11. 28. · Keywords: Aluminium alloy, Friction Stir Welding, Microstructure, AA 6061,

Influence of Process Parameters on Mechanical Properties of Friction Stir Welding of Aa 6061-T6

Alloy

http://www.iaeme.com/IJMET/index.asp 532 [email protected]

3.2. Impact test on welded joint

In the impact test, the test specimen is provided by a V-notch. The amount of energy absorbed

by a material during fracture when a external force is applied was calculated. This absorbed

energy is a measure of a given material's notch toughness and acts as a tool to study

temperature-dependent ductile-brittle transition. Impact is a high force or shock applied on

two or more bodies collide over a short time period. Such a force or acceleration usually has a

greater effect than a lower force applied over a proportionally longer time period of time.The

impact specimen is shown in figure 8

Figure 8 Impact specimen

The results of tensile properties, yield strength, percentage of elongation and impact

strength are given in the table 2

S.NO Rotation

speed(RPM) D/d

ratio Ultimate Tensile

Strength(N/mm2) Yied

Strength(N/mm2)

PERCENTAG

E Of Elongation

Impact Sterngth

Weld

1 900 3 190.33 139.59 8.22 20

Weld

2 1120 3.5 169.75 138.63 8.56 20

Weld

3 1400 4 167.92 134.64 7.62 20

Table 2 A graph is drawn between weld joints and tensile strength is shown in figure 9[7]

Figure 9 weld jonts vs tensile strength

UTS(N/mm2)

weld1

weld2

weld3

Page 6: INFLUENCE OF PROCESS PARAMETERS ON MECHANICAL PROPERTIES OF FRICTION STIR WELDING … · 2017. 11. 28. · Keywords: Aluminium alloy, Friction Stir Welding, Microstructure, AA 6061,

D.Raghavendra and S.Sravya

http://www.iaeme.com/IJMET/index.asp 533 [email protected]

3.3. Microstructure

The optical micrographs of all Aluminum 6061-T6 alloy (Exp.1-3) are shown in Fig.1.It show

the optical micrographs of the heat affected zone of all the samples. Significant grain

refinement can be noticed in the alloy on FSW in the first joint. Since the second phase

particles were not visible by optical microscopy. Density of precipitates has decreased as a

result of coarsening; Grain boundary precipitates have also coarsened. The effects of process

and tool parameters on macrostructure of the friction stir welded joints. It is generally known

that the fusion welding of aluminum alloys accompanied by the defects like porosity, slag

inclusion, solidification cracks, etc., deteriorates the weld quality and joint properties.

Generally, friction stir welded joints are joined in solid state due to the stirring action of tool

on the work. so joints are free from solidification related defects but FSW joints had defects

like pin hole, tunnel defect, piping defect, kissing bond, Zig-Zag line and cracks, etc., due to

bad consolidation of metal in the weld region and improper flow of metal and insufficient

consolidation of metal in the weld region.

The particles of Mg and Si were observed to be dispersed uniformly in the NZ for all the

conditions of composites made by FSP due to rotating tool gives sufficient heat generation

and a circumferential force to distribute the reinforcement particles to flow in wider area. It is

found that the sample made at 900rpm and D/d=3 shows severe plastic deformation and

frictional heating in the heat affected zone during FSW resulted in generation of a

recrystallized equiaxed microstructure. The microstructure specimen is shown in figure 10

After FSW, microstructural observations were carried out at the cross section of heat

affected zone zone(HAZ) of aluminum 6061-T6 alloy normal to the FSW direction,

mechanically polished and etched with Keller’s reagent (2 ml HF, 3 ml HCl, 20 ml HNO3 and

175 ml H2O) by employing microscope(OM)

Figure 10 Microstructure specimen

Microstructure obtained at heat affected zones at 100µm are shown in figure 11 to 13

Figure 11 AA 6061at 900rpm and D/d ratio 3 Figure 12 AA 6061at 1120rpm and D/d ratio 3.5

Figure 13 AA 6061at 1400rpm and D/d ratio 4

Page 7: INFLUENCE OF PROCESS PARAMETERS ON MECHANICAL PROPERTIES OF FRICTION STIR WELDING … · 2017. 11. 28. · Keywords: Aluminium alloy, Friction Stir Welding, Microstructure, AA 6061,

Influence of Process Parameters on Mechanical Properties of Friction Stir Welding of Aa 6061-T6

Alloy

http://www.iaeme.com/IJMET/index.asp 534 [email protected]

4. CONCLUSION

Aluminium alloys 6061 and was successfully welded.The influence of rotational speed and

D/d ratio on mechanical properties of Aluminum alloy 6061-T6 joined via Friction Stir

Welding were investigated and the following conclusions are obtained.

At rotational speed 900 rpm, welding speed 60mm/min and D/d ratio 3,the weld joint 1

exhibits maximum tensile properties compared to other joints.

It is found that the weld joint made at 900rpm and D/d=3 shows severe plastic

deformation and frictional heating in the heat affected zone during FSW resulted in generation

of a recrystallized equiaxed microstructure.

REFERENCES

[1] Thomas W. M, Nicholas E. D., Needham J. C., Murch M. G., Templesmith P. and Dawes

C. J. Improvements relating to Friction Welding. International Patent Application,

PCT/GB92/02203 (Patent) December 1991.

[2] Friction stir welding of aluminium. Online Available: http://www.alcotec.com Assessed

May 2012.

[3] Introduction to Friction Stir Welding Handbook, ESAB

[4] Blignault C, A friction stir weld tool-force and response surface model characterizing tool

performance and weld joint integrity. D.Tech dissertation, Nelson Mandela Metropolitan

University, Port Elizabeth, South Africa. 2007.

[5] Matrukanitz RP (1990) Selection and weldability of heat-treatable aluminum alloys.

ASM Handbook-Welding, Brazing and Soldering 6:528–536Google Scholar.

[6] Senthil Kumar T, Balasubramanian V, Sanavullah MY (2007) Influences of pulsed

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[7] Puneet Rohilla, Narinder (IJITEE) ISSN: 2278-3075, Volume-3, Issue-3 Experimental

Investigation of Tool Geometry on Mechanical Properties of Friction Stir Welding of

AA6061

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

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

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

[9] K. Sandeep Kumar, G. Chandra Mohana Reddy, Y. Laxmipathi and Dr. J Krishna Raj,

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[10] Sailaja C, N. Anuradha and B. Ramgopal Reddy, Experimental Analysis of Friction Stir

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