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

Abstract

In present paper, dual shoulders friction stir welding (DSFSW) tools were used for friction stir welding of lapped Al 6061-T6 workpieces (152 mm X 102 mm X 3 mm) in open air-cooling conditions using different tool rotational speeds and tool feeds. A total of 17 experiments were performed using seven differently designed DSFSW tools, two different fixtures, and two different vertical milling machines to investigate the effect of tool parameters on weld formations with different processing parameters window. Some of the initial tools produced ineffective material flow due to insufficient amount of frictional heat generation and inadequate stirring action, which hindered the material movement towards the horizontal interface of lapped workpieces and reduced intermixing of workpieces material at there. Based on investigations of weld formations, a series of experiments was subsequently performed using the redesigned and modified DSFSW tools with optimized combinations of tool rotational speed and feed rate which was finally resulted in improved frictional heat generation, enhanced plasticized material flow, and sufficient material intermixing at weld interface, thereby producing improved weldments. These experiments demonstrated a progressive improvement in weld quality, ranging from unwelded joints to sound weldments, although a few hole/porosity defects were observed on the advancing side of the weld nugget zone. The investigation led to the successful development of practical DSFSW tool designs capable of producing sound friction stir welds in lapped Al 6061-T6 workpieces.