Effect of Friction Stir Processing on Microstructure and Mechanical Properties of TIG Welded Joint of AA6061 and AA7075

In tungsten inert gas welding (TIG), micro-cracks, porosity, coarse grain structure and high residual stress distribution were found due to persisting thermal conditions. The TIG welded joint is processed using friction stir processing with input process parameters to avoid these defects. In present work, the experimental investigation was conducted to examine the influence of friction stir processing (FSP) on microstructure and mechanical properties of TIG welded joint of AA6061 and AA7075. Tensile test, Vickers hardness test, x-ray diffraction, microscopy and energy-dispersive x-ray test were performed for concluding the optimum set of parameters. The tensile test results shows that the hybrid TIG + FSP welded joint had higher tensile strength than TIG welded joint with filler ER4043, whereas the increment in the micro-hardness of TIG + FSP welded joint was observed. The grain size also decreases when tool pin rotates on TIG welding with different processing parameters. It was found that the maximum tensile stress, % elongation and micro-hardness at nugget zone for TIG + FSP welded joint are 255 MPa, 29.2, and 105 HV respectively. The present investigation demonstrates that the tool rotational speed and traverse speed are the dominating parameters to improve the mechanical properties of TIG welded joint.