Micro Hardness Variation Studies for Dissimilar Friction Stir Welding of AA7075-T651 and AA6061-T651 Related to Tool Pin Profiles

This research presents the microhardness variations studies related to tool pin profiles on dissimilar joints of AA7075-T651 and AA6061-T651 aluminium alloys. The weld consolidation and quality was evaluated through observations of macro and micro structure. The microhardness variations were determined in the cross-section of the weld for different rotational and welding speeds. In all the specimens where the hardness distribution was measured, the AA7075 alloy was located at the Retreating side (RS) and the AA6061 alloy was in the Advancing side (AS). The Friction stir welded materials were joined under three different tool rotational speeds (800, 900 and 1,000 rpm) and three welding speeds (90, 100 and 110 mm/min), which are the two prime joining parameters in Friction stir welding (FSW). The axial load and the tilt angle parameters are kept constant at 12kN & 0°. Three different pin profiles (Taper cylindrical threaded, Taper square threaded and Square) tools were used to consolidate the weld in which the taper cylindrical threaded tool yields higher hardness of about 114.2 HV in the stirred zone with good mixing of these two alloys.