Friction Stir Welding of Thick AA2519 Alloy: Defect Elimination, Mechanical and Micro-Structural Characterization

Abstract

Friction stir welding (FSW) of thick aluminium sections will pave way for remarkable new defence applications, provided the accompanying challenges are successfully addressed. These challenges include elimination of tunnel defects, loss of strength in heat-treatable aluminium alloys, tool design and excessive process forces. Accounts of defect elimination, detailed micro-structural and mechanical characterization for thick section FSW are scarce in the published literature. Further, special strategies such as bobbin tool, pre-drilled hole for plunging and inverted double pass are generally deployed to overcome these challenges. This makes the process less productive and complex. In the present work, armor grade aluminum alloy AA2519-T87 plates having a thickness of 15.4 mm have been successfully joined with a joint efficiency of greater than 75% without supplementary strategies. The disparity in the effects of tool rotational speed and welding speed in the formation of a sound weld has been addressed in detail to enhance the understanding of FSW of thick sections. Micro-hardness measurements have been carried out throughout the transverse cross-section of the welds and correlated with different zones and their corresponding microstructures. Scanning electron microscopy and X-ray energy dispersive spectroscopy have been used to characterize the coarse phase particles present in the weld zones.