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International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 12, December 2017, pp. 173–183, Article ID: IJMET_08_12_018

Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=12

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

© IAEME Publication Scopus Indexed

DETERMINATION OF MECHANICAL

PROPERTIES OF FRICTION STIR WELDED

JOINT FOR ALUMINIUM ALLOY 6351 (HE-30)

B.Praveen Kumar, N.Samba Siva Rao and M.Mohith

Asst. Prof, Talla Padmavathi College of Engineering

P.Srikanth

Professor, KITS Warangal

ABSTRACT

Friction stir welding is a solid state welding process this process uses non-

consumable tool to generate frictional heat in the abutting surfaces. The welding

parameters such as tool rotational speed, welding speed, axial force etc., and the tool

pin profile plays a major role in deciding the weld quality. The main objective of

thesis is investigation of mechanical properties of friction stir welded aluminium alloy

6351 (HE30). Analysis of effect of tool pin profile on mechanical properties of

aluminium alloy. Heat treatment improves tensile strength, ductility, hardness.

Tapered Cylindrical tool pin profile gives higher tensile strength. Square tool pin

profile gives higher hardness. Triangular tool pin profile gives higher percentage of

elongation.

Keywords: Friction Stir Welded, Mechanical Properties, Aluminium Alloy 6351

Cite this Article: B.Praveen Kumar, N.Samba Siva Rao, M.Mohith and P.Srikanth,

Determination of Mechanical Properties of Friction Stir Welded Joint for Aluminium

Alloy 6351 (He-30), International Journal of Mechanical Engineering and Technology

8(12), 2017, pp. 173–183.

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=12

1. INTRODUCTION

Friction Stir welding (FSW) is a novel welding technique invented by the welding Institute

(TWI) in 1991 (Cary H.B., 1979) [1] FSW is actually a solid State joining process that is a

combination of extruding and forging and is not a true welding process. FSW is a derivative

of conventional friction welding. The FSW is a derivative of conventional friction welding.

The FSW process involves the translation of a rotating cylindrical tool along the interface

between two plates. The weld is formed by the deformation of the material at temperatures

below the melting temperature. FSW does not create a Heat effected Zone nor does it use

welding consumables. Since traditional heating methods are not employed. The properties of

the metal in the joined area are higher than those from any other known welding process and

distortion is virtually eliminated (Weisheit A at all, 1998, Juttner, 1998) [2].

Determination of Mechanical Properties of Friction Stir Welded Joint for Aluminium Alloy 6351

(He-30)


2. LITERATURE REVIEW

2.1 Friction Stir Welding in 1XXX Series Aluminium Alloys

Sato Y.S. et all (2003) studied a friction stir welding of ultrafine grained A1 alloy 1100

produced by accumulative roll bonding. FSW resulted in reproduction of fine grains in the stir

zone and small growth of the ultrafine grains of the material just outside the stir zone. FSW

suppressed large reductions of hardness in the material, although the stir zone and the TMAZ

experienced small reductions of hardness due to dynamic recrystallization recovery.

Consequently, FSW effectively prevented the softening in the alloy.

2.2 Friction Stir Welding in 5XXX Series Aluminium Alloys

Peel M. (2003) studied a microstructure, mechanical properties and residual stresses as a

function of welding speed in aluminium AA5083 friction stir welds. It has been found that the

weld properties have been dominated by the thermal input rather than the mechanical

deformation by the tool. The main results have been obtained that the recrystallization results

in the weld zone having considerably lower hardness and yield stress than the parent AA5083.

During tensile testing, almost all the plastic flow occurs within the recrystallized weld zone.

The peak longitudinal stresses increase as the traverse speed increases. This increase is

probably due to steeper thermal gradients during welding and the reduced time for stress

relaxation to occur. The base material is in an extremely work hardened state and this is

reflected in the hardness profiles.

3. MATERIAL SELECTION AND TOOL DESIGN

Material selection in Friction Stir welding is an important role, the aluminium alloys have

gathered wide acceptance in the fabrication of light weight structures requiring a high strength

to weight ratio and good corrosion resistance. Compared to the fusion welding processes that

are routinely used for joining structural aluminium alloys.

3.1 Friction Stir welding tool pin profiles:

Pin profile plays a crucial role in material flow and in turn regulates the welding parameters

of the FSW process. Friction stir welds are characterized by well-defined weld nugget and

flow contours. Almost spherical in shape, these contours are dependent on the tool design and

welding parameters and process conditions used.

Figure 1

B.Praveen Kumar, N.Samba Siva Rao, M.Mohith and P.Srikanth


4. EXPERIMENTAL DETAILS

Details of base metal composition, friction stir welding processes, mechanical testing and

metallographic techniques are described in the following.

4.1. Base metal

The aluminium alloy studies in the present work are 5 mm thick plate of AA 6351 (HE30)

whose chemical composition and mechanical properties are listed in table 1 and 2.

Table 1 Chemical composition (Wt.%) of 6351 (HE 30) Aluminium alloy.

Cu Mg Si Fe Mn Zn Cr Ti Others

0.1 0.4-1.20 0.60-1.3 0.60 0.4-1.0 0.1 0.25 0.20 0.20

Table 2 Mechanical Properties:

Mechanical Property UTS (N/mm2) YS (N/mm

2) % of Elongation

6351 (HE 30) 285 240 8

The rolled plates of 5 mm thickness, AA6351 (HE30) aluminium alloy, have been cut into the

required size (100x60 mm) by power hacksaw cutting. Square butt joint configuration has

been prepared to fabricate FSW joints. The initial joint configuration is obtained by securing

the plates in position using fixture and mechanical clamps. The direction of welding is normal

to the rolling direction. Single pass welding procedure has been followed to fabricate the

joints. Non-consumable tools made of high speed steel (HSS) have been used to fabricate the

joints as shown in fig.2. An indigenously designed and developed CNC milling machine has

been used to fabricate the joints.

Figure 3 FSW tool dimensions and shapes


(He-30)


Figure 4 Welded Sample by Tapered Cylindrical and Triangular Tool

Table 3 Welding parameters during FSW Operation on CNC milling machine

Sample Material Type of tool Speed

RPM

Feed

mm/min.

% of

spindle

load

Pin

depth

(mm)

Opera-

tion time

(min)

Sample 1 6351 Tapered

Cylindrical 800 14 15-20 4.7 8.8

Sample 2 6351 Triangular 1000 12 20-25 4.7 10.5

Sample 3 6351 Square 1200 10 20-25 4.7 11.9

5. TESTING METHODS

In this investigation mechanical properties such as yield strength, tensile strength and

percentage of elongation of FSW joints have been evaluated.

5.1. Tensile Test

American Society for Testing of Materials (ASTM) guidelines are followed for preparing the

test specimens. Test has been carried out in 400 KN, Universal Testing Machine. The

specimen finally fails after necking and load versus displacement has been recorded. The

ultimate tensile strength and percentage of elongation have been evaluated for tapered

cylindrical tool pin as shown in Table 4, Triangular tool pin as shown in Table 5 and square

tool pin as shown in Table 6.

Table 4 Tensile strength obtained by Tapered Cylindrical tool pin profile

PWHT UTL(N) UTS (N/mm2) Yield load (N)

Yield Stress

(N/mm2)

% of

Elongation

Without HT 20560 179.104 19640 171.095 2.860

With HT

(Aircooling) 25134 300.341 24640 250.125 1.00

Base Metal 23000 285.00 22000 240.00 8



Figure 5 Y-Axis (N) Vs. X-Axis disp. (mm) for tapered cylindrical tool pin

Figure 6 Y-Axis (N) Vs. X-Axis disp. (mm) for triangular tool pin

Table 5 Tensile strength obtained by Triangular tool pin profile

PWHT UTL(N) UTS

(N/mm2)

Yield load

(N)

Yield Stress

(N/mm2)

% of

Elongation

Without HT 25560 258.819 24000 242.206 1.220

With HT

(Aircooling) 30560 352.132 29000 320.00 1.00

Base metal 28000 285.00 26000 240.00 8

Table 6 Tensile strength obtained by square tool pin profile

PWHT UTL(N) UTS (N/mm2) Yield load (N)

Yield Stress

(N/mm2)

% of

Elongation

Without HT 18000 171.00 17000 150.00 1

With HT air

cooling 25000 228.00 24000 215.0 1

Base Metal 22000 285.00 20000 240.00 8


(He-30)


5.2. Brinnel Hardness Test

Table 7 Hardness varying with Tapered Cylindrical tool pin profile.

Distance from weld

centre, mm

Brinnel hardness

Without HT With HT (AC) Base metal

0

5

10

15

20

84.9

80.2

80.2

80.0

82.0

86.0

82.0

85.0

82.0

84.0

80

78

78

79

78

Table 8 Hardness varying with Triangular tool pin profile.

Distance from

weld centre, mm

Brinnel hardness


0

5

10

15

20

84.9

81.0

80.3

80.0

81.0

86.0

82.0

84.0

82.0

84.0

80

78

78

79

78

Table 9 Hardness varying with Square tool pin profile.

Distance from

weld centre, mm

Brinnel hardness


0

5

10

15

20

85

82

81

81

82

84

83

84

82

83

80

78

78

79

78

6. RESULTS AND DISCUSSIONS

Hardness

Recent investigations show that the bonded structure has periodic variation in grain size, a

clearly defined difference in both particle distribution and also hardness variation. Fig.4

presents Rockwell hardness results from straight lines at Z=00 mm on vertical transverse

cross section in FSW for AA 6351. The two welds exhibit a W-shaped hardness distribution

that is characteristic of many friction stir welds in precipitation hardening aluminium alloys.

Here the hardness data shows that the weld nugget is significantly harder than the thermo

mechanically affected region immediately outside the nugget boundary. Moving outwards

from the nugget centerline towards the advancing side of the weld, the profiles encounter the

distance minimum at location of 5 mm.

Tapered Cylindrical tool pin profile

At the weld centre the hardness is more in case of PWHT for air cooling (24 hours) than base

metal and others as shown in fig 7 for Tapered Cylindrical tool profile due to sufficient time

allowed to obtain fine grain structure. At the interface also, the hardness is more than base



metal others due to tool pin rotate uniformly in the metal with very fast and at interface grains

are properly adjusted with adjacent region.

Figure 7 Hardness variation from Weld centre for Tapered Cylindrical Tool pin

Triangular tool pin profile

At the weld centre the hardness is more in case of PWHT for air-cooling (24 hrs.) than base

metal and others as shown in fig.8. For triangular tool pin profile due to sufficient time

allowed to obtain fine grain structure. AT the interface, the hardness is approximately equal to

hardness without heat treatment. Due to tool pin is not rotate uniformly in the metal with low

speed. At the interface, the metal is cut by tool because sharp edges and it gives poor mixing.

Figure 8 Hardness variation from Weld centre for Triangular tool pin

Square tool pin profile


(He-30)


At the weld centre the hardness is more in case of without heat treatment than base metal and

others shown in Fig.16. For square tool pin profile. At the interface, the hardness is more in

cse of with heat treatment for air tooling than others, but it is more than base metal due to tool

pin is not rotate uniformly in the metal with low speed. At the interface, the metal is cut by

tool because sharp edges and it gives poor mixing. Due to sharp edges, the metallic bond is

poor and it loses hardness in heat treatment condition.

Figure 9 Hardness variation from Weld Centre for square tool pin

Comparison of tool pin profile

The hardness is high in weld zone in heat treatment condition (Air cooling) in Tapered

Cylindrical tool pin and in triangular tool pin and the hardness is high in weld zone in square

tool pin without heat treatment condition. In all the condition the hardness is higher than base

metal.

Tensile results for welded specimen

The welded sample of AA 6351 has a ultimate tensile strength in all conditions is less than the

base metal. The total elongations and strains to fracture are similar in both nuggets, interface

and base metal. Overall, it can be stated that the tensile properties of the weld nuggets and of

the corresponding base metals are very similar to each other.

Tapered Cylindrical tool pin profile

The tensile strength is approximately equal to base metal in heat treated condition with air

cooling and tensile strength is poor in without heat treatment. Due to air cooling for 24 hrs.,

the grain settle in their positions properly because sufficient time allowed and tool rotate

uniformly with high speed in the metal, the welded metal gives high tensile strength. Tensile

strength of welded sample is poor than the base metal due to rotational speed of tool pin

profile is low i.e. 800 rpm. Due to that the bond integrity is poor in weld metal as shown in

figure10.



Figure 10 Tensile strength varying with heat treatment process for Tapered cylindrical tool

Triangular tool pin profile

The tensile strength of friction stir welded sample using triangular tool in without heat treated

condition is less than base material and tensile strength is height than in heat treated condition

with air cooling. In heat treated condition with air cooling due to improper mixing of weld

metal because sharp edges of pin profile. Tensile strength of welded sample is poor than the

base metal due to rotational speed of tool pin profile is low i.e. 1000 rpm. Due to that the

bond integrity is poor in weld metal as shown in Fig. 11.

Figure 11 Tensile Strength varying with Heat treatment process for Triangular Tool

Square tool pin profile

The tensile strength of friction stir welded sample using square tool inwith heat-treated

condition is less than base material and the tensile strength is higher than in without heat

treated condition due to sharp edge and low speed. The tensile strength is poor in without heat

treated condition. So heat treatment process is required for square tool. Tensile strength of


(He-30)


welded sample is poor than the base metal due to rotational speed of tool pin profile is low i.e.

1200 rpm. Due to that the bond integrity is poor in weld metal as shown figure 12.

Figure 12 Tensile strength varying with Heat treatment process for square tool pin

Comparison of tool pin profile

Tensile strength is high in case of Tapered Cylindrical tool with heat treatment for air cooling

and tensile strength is high in case of triangular tool without heat treatment. In case of square

tool the tensile strength is high with heat treatment in air cooling.

7. CONCLUSIONS

The hardness is high in weld zone in heat treatment condition (Air Cooling) in Tapered

circular tool pin and in triangular tool pin and the hardness in high in weld zone in square tool

pin without heat treatment condition. In all the condition the hardness is higher than base

metal. Tensile strength is high in case of Tapered Circular tool with heat treatment for air-

cooling and tensile strength is high in case of triangular tool without heat treatment. In case of

square tool the tensile strength is high with heat treatment in air cooling.

REFERENCES

[1] Gary H.B., 1979, Modern Welding Technology Prentice Hall, inc., Engelwood Cliffs,

New Jersey, PP223

[2] Juttners, Fabr. 1998, Weld met; 66:11

[3] Dawis C.T. and Thomas W.M., 1996, Friction Stir Process Welds Aluminium Alloys, a

New Friction Welding Technique Allows Easy Welding of normally difficult to join

materials, Welding Journal, 75 (3), PP 41.

[4] Lee W.B., Yeon Y.M. and Jung S.B., 2003. The improvement of Mechanical properties of

friction stir – welded A 356, PP. 154-159.

[5] Benavides S., Li Y., Murr L.E., Brown D. and Mcclure JC, 1999 Low Temperature

Friction Stir Welding of 2024 Aluminium, Scripta Materialia, Vol. 41. No.8 PP.809-815.

[6] Fonda R.W., Bingert J.F. and Colligan K.J., 2004, Development of Grain Structure during

Friction Stir welding, Scripta Materialia 51, PP.243-248.



[7] Dickerson T.L. and Przy Datek J. 2003, Fatigue of friction stir welds in Aluminium alloys

that contain Root Flaws International Journal of Fatigue, 25, PP 1399-1409.

[8] Liu G., Murr L.E., Niou C.S., Mcclure J.C. and vega F.R., 1997, Mcrostructural aspects of

the Friction Stir Welding of 6061 – T6 Aluminium, Scripta Materialia Vol.37, No.3, PP

355-361.

[9] Lee W.B., Yeon Y.M., Jung S.B., 2003, The Joint Properties of Dissimilar Formed Al

Alloys by Friction Stir welding according to the fixed location of materials Scrpta

Materialia, 49, PP 423-428.

[10] Cavaliere P., Nobiler, Panella F.W. and Squillace A., 2006, Mechanical and

Microstructural Behaviour of 2024-7075 Aluminium Alloy Sheets Joined by Friction Stir

Welding, International Journal of Machine Tools & Manufacture, 46, PP.588-594.

[11] JATA K.V. and SEMIATIN S.L., 2000, Continuous Dynamic Recrystallization During

Friction Stir Welding of High Strength Aluminium Alloys Scripta Materialia, 43, PP 743-

749.

[12] LI Y, Murr L.E. and Mcclure J.C., 1999, Flow visualization and Residual Microstructures

Associated with the Friction – Stir – Welding of 2024 Aluminium to 6061 Aluminium

materials Science and Engineering, A271, PP 213-223.

[13] Chao B.Y.J., Wang Y and Miller K.W., 2001, Effect of Friction Stir welding on Dynamic

Properties of AA 2024-T3 and AA 7075-T.7351 Journal of material processing and

manufacturing, 7(2), PP.215-233.

[14] Chen C.M. and Kovacevic R., 2004, Joining of Al 6061 to ALSI 1018 Steel by combined

effects of Fusion and solid state welding, International Journal of Machine Tools and

Manufacture.

[15] Sreeharan B N, Dr. Kannan T and Aravind P, Process Optimization of GMAW over

Aa6351 Aluminium Alloy Using Ann, International Journal of Civil Engineering and

Technology, 8(9), 2017, pp. 208–218.

[16] Ragip Hadri and Ali Muriqi, Aluminum Alloys and Behavior under Cyclic Loading in

Joints of Truss Structures, International Journal of Civil Engineering and Technology,

8(11), 2017, pp. 746–752

[17] R. MuthuVaidyanathan, MahaboobPatel, N. SivaRaman and D. Tedwors, Effects of

Process Parameters on Friction Stir Welding of 6063 Aluminum Alloy, International

Journal of Design and Manufacturing Technology (IJDMT), Volume 6, Issue 1, January -

April (2015), pp. 01-09

determination of mechanical properties of friction … · 2017-12-30 · cite this article:...

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