Weld Formation Investigations of FSW of Al 6061-T6 Lapped Workpieces Using Dual Shoulders Tool

In present paper, dual shoulders friction stir welding (FSW) tools were used for lapped Al 6061-T6 workpieces (152 mm X 102 mm X 3 mm) in open air-cooling conditions and different tool rotational speeds and tool feeds. Total 17 experiments were performed using seven differently designed dual shoulders tools, two different fixtures and two different vertical milling machines to investigate effect of tool parameters on weld formations with different processing parameters window. Some of the tools generated less effective material flow due to less amount of frictional heat generation and insufficient tool stirring action to push material towards horizontal interface of workpieces and intermixing of workpieces material at the horizontal interface of lapped workpieces. Based on investigations of weld formations, dual shoulders tools were redesigned and resulted in improved frictional heat generation, enhanced plasticized material flow and material intermixing at weld interface and generated good weldments. Series of experiments performed by applying updated and modified dual shoulders tools, finally generated the weldments from the unwelded to good welded, although with very few hole/porosity defects at the advanced side of the weld nugget zone. Investigations lead towards the redesigns of dual shoulders tool for defect free welding of lapped workpieces.