Friction welding of Aluminium Alloy 6063 with copper

Friction welding process is a forging welding process in which work piece are joined due to heat produced by friction between two joining surfaces and upset pressure is applied by non-rotating work piece. Joining of aluminum alloy with dissimilar material is important research area to focus on as maximum aircraft structures havexx Aluminum alloy frame and aerospace designers familiar with Aluminum alloy and its design considerations. After comparison of mechanical properties and application of light weight alloys aluminum alloys, tungsten, stainless steel and copper, copper selected as dissimilar material to join with Aluminum alloy AA6063. AA 6063 also known as architectural alloy selected based upon its properties. This dissimilar joint of AA6063 and Copper has application in electrical conductors as copper is good electrical conductivity and used in maximum electrical conductors. In this research work AA6063 joined with Copper successfully using Rotary Friction Welding process. Through process study effective process parameters like Friction Pressure, Upset Pressure, Spindle Speed, and Friction Time identified and their effect on weld joint strength were studied.Testing for measuring UTS of friction welded joint conducted. Using DOE tool optimized set process parameters for friction welding identified and their effect on weld joint strength studied experimentally. Maximum UTS of 222.787 MPa for Friction welded joint achieved, bend test also performed on friction welded samples.


Introduction
Rotary friction welding is used for joining of round parts like engine valves, steering rod, shafts and other parts in aerospace application. Bimetallic valves are produced using RFW process.
RFW process is solid state joining approach hence limitation of fusion welding of joining different material of different melting point overcome using Friction Welding. In this friction welding process despite of different melting point both AA 6063 and Copper joined which was not feasible earlier by fusion welding process. Aerospace Industry use Aluminum alloy as primary material for structure and frame due to its light weight and mechnaical properties hence Aluminium alloy selected as one material for this research work [1]. Also in aerospace, automobile, marine, defense equipment appliances for joining various copper electrical parts to Aluminum Alloy alloy frame. Mainly in aerospace structures frames made up of Aluminum Alloy and various other metals parts to be joined to Aluminum Alloy frame using friction welding.

Literature Review
Various Researchers aimed at achieving maximum UTS for friction welded joint through parametric optimization of friction welding process. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] While doing parametric optimization following parameters are considered by researchers, Friction Time (FT), Friction Pressure (FP), Spindle Speed (SS), Burn of length (BOL) [1][2][3][4][5][6][7][8][9]. Further sub branching of friction welding parameters can be done in form of upset time, upset pressure, breaking time [1][2][3][4][5][6][7]. Researchers focused on study of microstructure of friction weld joint under electron microscope and micro structural characterization done for friction welded dissimilar metal joints. Researchers also stated interested observations by microstructure study of joints in regards to new layer formation and grain structure at welded joint. Mumin Sachin et al found Friction Time, Friction Pressure have direct effect on tensile strength of joint [5]. C. Meengam et al joined semi solidAA7077 using RFWprocess [2]. L.Zhou et al in their research work considered Rotational Speed as dominant parameter and studied its effect on mechanical properties, on microstructure of Ti-6Al-4V. They have observed along   Trail run taken with two sets of process parameters. In first run Aluminium Alloy 6063 not welded with copper and this runs become void run. Following process parameters used for first trail run and it is observed that selected values of Friction Pressure needs to be increased for successful weld joint between Aluminium Alloy 6063 and Copper.Aluminium Alloy 6063 not welded with copper and this runs become void run. Following process parameters used for first trail run and it is observed that selected values of Friction Pressure needs to be increased for successful weld joint between Aluminium Alloy 6063 and Copper.

Second and third trail run Experiments
With second set of parameters four runs were conducted under second and third trail run. From Parameter set 2 sound friction welded joints produced. But after welding final length received was less hence more losses observed. To reduce losses with same set further trail taken.
In third trial four more trail run with same set of parameters used in second trail run performed. Here actual measured loss was less than second trail run. Final length received after weld also was more than previous trail run which reduces the losses and saving material.
Second and third trial run total eight experiments performed with following set of parameters given in Table No. 3.0  AA6063 successfully welded with copper using friction pressure of 48 Kg/mm 2 and upset pressure of 97 kg/mm 2 at Friction time of 1 sec and upset time 3 sec. and spindle rotation speed SS 1800 RPM.

Ultimate Tensile Strength (UTS) Testing
Friction welded joints obtained from process parameters set 2 and set 3 are tested for measuring its UTS. For measuring UTS testing specimen prepared as per ASM standards specimen diameter set to 12.5mm and testing performed on friction welded joint.

Effect of Process Parameters
Weld joint strength Increases with increase in Friction Time and Upset Pressure up to certain limit. Insufficient weld time results in weak friction welded joint. For first trail run Friction Time (FT) 0.5 Seconds failed to join Al6063 with Copper, increase in Friction Time will form adequate Friction Welded joint. This is proved from later two set of experimentations.
Upset pressure directly proportional to UTS of weld joint up to certain limit as shown in Fig. 8 and Fig.9