Characterization of Mechanical Properties of

Aluminum (AA6061-T6) By Friction Welding

E.Ravikumar, N.Arunkumar, and Sunnapu Gunhie Samhit

Abstract---The main objective of this investigation was to apply

friction welding (FW) for joining of 24mm dia of Aluminum rod AA6061-T6. In the present study an experimental friction welding setup, in which continuous drive friction welding used. At first optimum parameters were obtained to join parts having equal diameter (24mm). In the second part of the study, the effect of welding parameters on welding strengths was investigated. Later the mechanical properties of joints were examined by using tensile test and hardness test, macro & micro analysis. Finally the results obtained were compared and discussed.

Keywords-- Aluminum alloy, Friction welding, Mechanical properties, Heat affected zone.

I. INTRODUCTION RICTION welding is a solid state welding technique which is being used in recent times to weld similar as well as dissimilar metals so that a defect free weld can be

obtained. Many combinations like Low carbon to Stainless steel, Austenitic to Ferrite Stainless Steel, Aluminum to Copper and Titanium to Aluminum or steel have been tried out by various solid state welding processes with reasonably good results. 6061 Aluminum alloys are widely used for structural & marine applications. They have the advantage of being light while at the same time exhibiting good tensile strength.

II. LITERATURE REVIEW Mumim Sahin [1] has welded a variety of combinations of

materials. Equal and unequal diameters of austenitic stainless steel have been studied and their tensile properties and hardness variation have been researched upon . [2] H.Khalid Rafi, G.D.Janaki Ram, G.Phanikumar, K.Prasad Rao have used Taguchi techniques to determine the optimum friction welding parameters to weld similar 7075 joints.[3] Mumim Sahin, Int .J. Adv Manuf Technol Aluminum has been joined to Copper with reasonable good strength and the presence of intermetallic phases has been established here.[4]

E.Ravi Kumar is with the Mechanical & Production Department, Sathyabama University, Chennai, Tamil Nadu, INDIA. (ramakrishnar2009@gmail.com).

N.Arun Kumar is with the Mechanical Department, St.Josephs College Of Engineering, Chennai, Tamil Nadu, INDIA (n.arunkumar@rediff mail.com).

S.Gunhie Samhit is student of Mechanical & Production Department, B.E., Sathyabama University. Chennai, Tamil Nadu, INDIA (samhit389@gmail.com)

Most of the works on Aluminum 6061 alloy concerns with friction stir welding. Jiahu Ouyang, Eswar Yarrapareddy, Radovan Kovacevic, have studied friction stir welding of Al 6061 to Copper and have noticed the formation of Cu Al, CuAl2 and other similar intermetallic phases. [5] In a study by G.Liu, L.E.Murr, C.S.Niou, J.C.McClure, and F.R.Vega, The friction-stir weld zone in 6061-T6 aluminum seems to be characterized by what appears to be a dynamic continuous recrystallization microstructure. Second-phase particles in the work piece are essentially “stirred” into the weld zone where the residual hardness varies from 55 H.V. at the vicinity of the top zone & 65H.V, few m.m. from the bottom. In contrast the work piece hardness which varies between 85 H.V. and 100 H.V. [6] Micro structural characteristics and Mechanical properties of Alumina- 6061 alloy were studied by M.N.Ahmed Fauzi , M.B.Uday, H.Zuhailawati, A.B.Ismail. The study of the interface of ceramic/metal alloy friction welded components has been studied for understanding the quality of bonding between two dissimilar materials. Optical, electron microscopy as well as four-point bending strength and micro hardness measurements have been used to evaluate the quality of bonding of alumina and 6061 aluminum alloy joints produced by friction welding. [7]Dissimilar welding of 6061-T6 alloy with 1018 steel has also been reported by Emel Taban, Jerry E.Gould, John C.Lippold.[8]Takeshi Investigated the influenced of welding parameters on tensile properties of friction welded joints by similar materials of spheroidal graphite iron casting and gray iron casting. [9] The quality and the strength of the weld depend on the correct choice of these parameters. For example Ozdemir has joined AISI340 Laustenitic stainless steel and AISI4340 steel by friction welding using different rotational speed in these studies. He found that the tensile strength of joints was markedly affected by joining rotational and speed selected Ozdemir.N [10]. Ozdemir.N, Sarsilmaz.F, Hascalik.A, have also studied the effect of rotational speed on the interface properties of friction welded of different kind of steel. They observed that the width of the full plastic deformed zone (FPDZ) has an import taunt effect on the strength of friction welded samples and the strength increases with increase of the rotational speed.

III. EXPERIMENTAL WORK A. Description of friction welding machine The friction welding machine “FWG 20/300-S” is a

machine capable of operating with high precision and with excellent repeatability of all weld parameters. The spindle is

F

3rd International Conference on Mechanical, Automotive and Materials Engineering (ICMAME'2013) April 29-30, 2013 Singapore

127

driven by an AC spindle motor. Friction and upset forces are read by a load cell and precisely controlled by a hydraulic servo valve. The machine is controlled by an individual computer and the data of every weld is recorded. There is provision for retrieval of weld data. The machine has a stroke of 300 mm and maximum upset force of 200 K.N. The spindle motor is of 20 HP, 3 phase AC and operating speed can be varied from 1 to 2500 RPM. In the entire test the friction period is determined by the burn -off length control device which indicate the forge and arrest period when pre set amount of axial shortening has taken place.

The combination of rotational speed, friction load and burn off length which give welds ability to satisfy the mechanical tests. Before welding, the surface of the aluminum specimen were freshly machined by lathe, and degreased immediately prior to welding.

Fig. 1 Friction welding machine

I. Chemical Analysis was done using optical emission spectrometer. The welding parameters used in Model M/V/L, Magellan Friction m/c are as shown in the Table.

TABLE I FRICTION WELDING PARAMETERS

During welding, the primary parameters (friction pressure, forge pressure, burn of length and rotational speed) were continuously monitored. More trials have been carried out with different parameters in order to get defect free weld.

IV. RESULTS AND DISCUSSION TABLE II

MECHANICAL PROPERTIES OF BASE METAL Mechanical Property

Yield Strength (MPa)

Ultimate Tensile Strength(MPa)

% Elongation

Hardness HV

Value 326 353.6 17.6 96.5

Table-4 given below gives the mechanical properties of the welded specimens.

TABLE III MECHANICAL PROPERTIES OF WELD

S No Yield Strength (MPa)

Tensile Strength (MPa)

%Elongation

Location of fracture

1 135.75 219.61 3.68 Weld 2 150.58 214.70 5.3 Weld 3 131.38 149.61 3.9 Weld 4 144.32 230.65 6.52 Weld 5 137.45 222.52 7.84 Weld 6 149.08 238.17 13.28 Weld 7 143.99 234.27 13.26 Weld 8 136.89 238.56 14.00 Weld

It is seen that all the specimens failed at the weld

irrespective of the friction welding parameters. It is evident that the hardness of the fusion zone is lower which resulted in lower tensile value. A maximum Tensile strength of 238.56 MPa has been obtained for the parameter 8 which is listed below in the Table 5

TABLE IV OPTIMUM WELDING PARAMETERS

Friction Pressure (MPa)

Upset Pressure (MPa)

Burn-off length (mm)

Speed (RPM)

1 3 2 2000 It is seen that tensile strength is almost same irrespective of

parameters except sample 3 where the HAZ width is also more and the tensile strength is quite low compared to other samples. This can be attributed to a defect in the weld which can be clearly seen in the microstructure seen below.

S No Friction Pressure (MPa)

Upset Pressure (MPa)

Burn-off Length (mm)

Speed (RPM)

1 1 1 1 1000 2 1 1 1 2000 3 1 1 2 1000 4 1 1 2 2000 5 1 3 1 1000 6 1 3 1 2000 7 1 3 2 1000 8 1 3 2 2000

3rd International Conference on Mechanical, Automotive and Materials Engineering (ICMAME'2013) April 29-30, 2013 Singapore

128

V. MACRO & MICRO STRUCTURE ANALYSIS Sample I.D: 3

Fig. 1 Macro analysis

Fig. 2 Macro photo graph of weld + HAZ

Fig. 1 Represents complete cross section of the friction

welded rods of AA6061. The top and bottom zone has defects like discontinuity/lack of fusion. The centre zone shows heat marks concentrated.

Fig. 2 Represents enlarged view of the friction welded area. The fusion zone and the TMT zones were measured with “Erma” scale.The values are as follows. Fusion Zone width: 25divisions of the scale.3.906 m.m.TMT Zone left/right: 5 divisions/0.781 m.m. / 3 divisions/0.468 m.m. Total length of TMT Zone + fusion Zone: 4.155 m.m. Friction welded sample No: 3 (microstructures of different zones.)

Fig. 4 Micro structure

Fig. 4 represents the microstructure of AA 6061 parent

metal that has been solution treated and precipitation hardened. The microstructure consists of uniformly precipitated particles of Mg2Si in aluminum solid solution. Some un dissolved particles of (FeMn) Al6 are also present.

Fig. 5 Micro structure

Fig. 5 represents the TMT zone of the material where the grains oriented towards the circular path. The particles of Mg2Si are bigger due to heat.

Sample I.D:8

Fig.8Macrostructure

Fig. 9 Macro structure

Fig. 8 Represents complete cross section of the friction

welded rods of AA6061. The top zone has discontinuity. The centre zone shows heat marks concentrated.

Fig. 9 Represents enlarged view of the friction welded area. The fusion zone and the TMT zones are measured with “Erma” scale. The values are as follows.Fusion Zone width: 25divisions of the scale/3.906 m.m. TMT Zone left/right: 7divisions/1.094.m./6divisions/0.937 m.m. Total length of TMT Zone + fusion Zone: 5.937 m.m. Friction welded sample No: 8

Fig. 11 Micro structure

3rd International Conference on Mechanical, Automotive and Materials Engineering (ICMAME'2013) April 29-30, 2013 Singapore

129

Fig. 12 Micro Structure

Fig. 11 represents the microstructure of AA 6061 parent

metal that has been solution treated and precipitation hardened. The microstructure consists of uniformly precipitated particles of Mg2Si in aluminium solid solution. Some un dissolved particles of (FeMn) Al6 are also present.

Fig. 12 Represents the TMT zone of the material where the grains oriented towards the circular path. The particles of Mg2Si are bigger due to heat. Table 6 given below shows variation of tensile strength and HAZ with the friction welding parameters

TABLE V Variation of tensile strength and HAZ with the friction

welding parameters S No HAZ Width

(mm) Tensile Strength (MPa)

1 3.1 219.6 2 2.6 214.17 3 3.9 149.6 4 3.6 230.6 5 1.4 222.52 6 2.7 238.17 7 2.8 234.27 8 1.7 238.56

The result of tensile testing on the weld made using various

combination of process parameters are listed in table 6. For a given process parameter combinations, variation in ultimate tensile strength (UTS) were observed. However significant differences, ranging from 149.6 Mpa to 238.56, were observed in UTS among the various weld, indicating that the welding parameters have a direct effect on the quality of the joints. Among the eight welded samples ID3 and ID8 showed the lowest (149.6MPa) and highest (238.56Mpa) UTS value respectively.

TABLE VI VARIATION OF WELD TIME AND SHRINKAGE FOR VARIOUS PARAMETERS

S No Weld Time (Seconds)

Shrinkage (mm)

1 15.28 2.24 2 13.02 2.12 3 15.69 2.79 4 13.63 3.10 5 15.5 3.35 6 13.59 3.22 7 15.68 4.63 8 13.69 4.42

It is seen that weld time is more or less the same for all parameters. It varies between 13 to 15 seconds. In the case of dissimilar metal welding, it has been seen that weld time varies significantly with the friction welding parameters. As far as shrinkage is concerned, it is low in the first 2 cases where all the friction welding parameters are on the lower side. Parameters 3 and 4 have higher burn-off lengths and this has resulted in an increase in the shrinkage. Parameters 5 and 6 have a higher upset pressure and hence shrinkage is a little more than parameters 3 and 4...Parameters 7 and 8 have both higher burn-off length and higher upset pressure. Hence, we see that shrinkage increases even more.

VI. RESULT AND DISCUSSION Comparison of the mechanical characterization and the

metallurgical evaluations of the macro and micro indicate that the parameters used in sample No: 8 has produced maximum mechanical strength. The uniform hardness along the fusion zone is evident from the higher fusion length. The hardness variation between the parent metal zone and the fusion zone is less. The parameters used in sample No: 6 is closed to No: 8 but the elongation is lower for 6 than 8. The corresponding yield stress is also lower for 8 which have higher in % elongation. The burn-off length of sample 8 is higher producing more heat of fusion compared to sample 6 The measurements of the TMT shows higher values for 8 which is in confirmation with the burn off length and the RPM used. The macro image analysis clearly indicates the uniform thickness of the fusion zone along the diameter with ho severe heat marks. It is evident that uniform heat input is involved in the mechanical process. Comparison with sample No:6 which has the presence of marginal discontinuity at the diameter, the sample No:8 is completely free from any defect. Good flow of grains at the TMT zone indicates the uniform stress and heat input. Comparison with sample-6 the microstructure of sample-8 is free from discontinuity, more homogenous grains of the eutectic particles of Mg2Si particles with uniform grains size observed. The scanning of the fusion zone and the TMT zone of sampl-8 indicates the complete absence of any eutectic grain boundary melting along the longitudinal directions. The solution and precipitation treated aluminum alloy generally loses hardness on subjecting to heat process. A similar phenomenon had taken place invariably in all the parameters. It is inferred that the use of higher pressure with burn off length effected higher mechanical properties with defect free fusion. Though sample No: 4 has defect free fusion zone, the fusion depth is lower compared to sample: 8. This might be due lower upset pressure which had not developed sufficient frictional heat for fusion.

VI. CONCLUSION

6061 Aluminum alloy has been successfully welded with a maximum joint efficiency of around 70%. All specimens failed in the weld region while some specimens exhibited welding defects. HAZ was found to be more for the defective weld pieces. Shrinkage of the specimen increased with increase in burn-off length and increase in upset pressure. The cumulative effect of both the above parameters affected shrinkage more. Weld times for all parameters varied from 13

3rd International Conference on Mechanical, Automotive and Materials Engineering (ICMAME'2013) April 29-30, 2013 Singapore

130

to 15 seconds. Chemical composition of the aluminum used for welding, play an important role in deciding the properties of the weld. Major conclusions of microstructure evaluation of the friction welded joints revealed three distinct zones namely, base metal aluminum plastically deformed welded zone and parent metal aluminum. Hardness variations can be explained by dissolution and recrystallization phenomenon.

ACKNOWLEDGMENT

The authors thanks to Met Mech lab Mr.Parthasaradi, Chennai for the experimental work and Mr.Rangan, I.I.T Chennai for friction welding. They also thank the Management, Sathyabama University and St.Josephs College of Engineering, Chennai.

REFERENCES [1] Mumim Sahin, Materials and Design 30 (2009) 135–144 [2] H. Khalid Rafi , G.D. Janaki Ram, G. Phanikumar, K. Prasad Rao,

Materials and Design 31 (2010) 2375–2380 [3] Mumim Sahin, Int J Adv Manuf Technol (2010) 49:527–534 [4] Jiahu Ouyang, Eswar Yarrapareddy, Radovan Kovacevic, Journal of

Materials Processing Technology 172 (2006) 110–122 [5] G. Liu, L.E. Murr, C-S. Niou, J.C. McClure, and F.R. Vega, Scripta

Materialia, Vol. 37, No. 3, pp. 355-361, 1997 [6] M.N. Ahmad Fauzi *, M.B. Uday, H. Zuhailawati, A.B. Ismail,

Materials and Design 31 (2010) 670–676 [7] Emel Taban, Jerry E. Gould, John C. Lippold, Materials and Design 31

(2010) 2305–2311. [8] Takeshi.S, Hoshinu.K, Yamashita.R (1994) Effect of friction

welding parameters on Mechanical properties of cast iron joints. Q J Japanweld Soc 12(3):328-334.

[9] OzdemirN .investigation of the mechanical Properties of friction welding joint between AISI304L, AISI steel as function rotational Speed.matter Lett 2005:59:25041.

[10] Ozdemir.N, Sarsilmaz.F, Hascalik.A. Effect of Rotational speed on the interface Properties of friction welded AISI 304L to 4340 to Steel material des 2007,28:301

3rd International Conference on Mechanical, Automotive and Materials Engineering (ICMAME'2013) April 29-30, 2013 Singapore

131