STUDIES OF PULSE TIG WELDING PARAMETERS ON MECHANICAL PROPERTIES OF DISSIMILAR ALUMINUM ALLOYS AA6061 AND AA5083

Abstract

Aluminum is considered as most abundant metal in the earth crust and is third most common element which comprises of 8 % of earth crust. The consumption of aluminum is around 47.7 billion tonnes which is 40% of the total reserves of metal world wide. The global consumption of aluminum is expected to rise 6% in 2018. Due to increasing application of aluminum in industrial world. The demand for its welding not only similar alloys but dissimilar alloys increases. Welding of dissimilar aluminum poses several challenges to the designer and technologists as they are prone to hot cracking and porosity. These problems can be overcome using controlled heat input which is provided by Pulse TIG (Tungsten Inert Gas) welding. Due to pin point control of heat input, it is most commonly used process for welding aluminum alloys. In this study an attempt has been made to weld dissimilar aluminum alloys AA5083 O and AA6061-T651. Weld was carried out on 6.35 mm plates and butt joint was successfully produced between two plates of length 150 mm using pulse TIG welding. A setup was prepared which automatically moves the welding torch and wire feed. The cost associated with the development of setup was very low around 300 USD as compared to the setup available in the market which is 1000 USD. The two special fixtures was designed and fabricated for holding the MIG wire feeder gun and for holding welding plates firmly together during welding. Integrated Analytical Hierarchy process and Technique for order preference by similarity to ideal solution (AHP-TOPSIS) approach was used to select the best possible combination of filler alloy, electrode and shielding gas from available alternates. The Extensive trails runs were conducted to develop the correct welding procedure for obtaining defect- free joints. The process parameters that can be varied and can have an effect on mechanical properties of the weld were identified. The range, within which those process parameters can be varied, were also found. Based on the central composited design, final experimentation was carried out to study the effect of process parameters on mechanical properties. 32 runs were conducted. Radiography was conducted and then samples for mechanical and metallurgical testing were taken out. Tensile test, impact test and micro-hardness were carried out to see the effect of process parameters on weld properties. Metallurgical testing was carried out using microstructural examination, energy dispersive X-ray spectroscopy analysis and corrosion studies. The tensile strength, impact toughness and micro-hardness were all found to have improved over base material properties. The process parameters, particularly welding speed, was found to have significant effect on mechanical properties. Based on microstructural examination, significant grain refinening is noticed in fusion zone which consist of soluble phase of Mg2Si particles. The result of immersion test shows no crack initiation sites developed.