Effect of Post-FSW FSP Pass on Tensile Mechanical Characteristics and Hardness of Welded Samples of AA6061 Aluminum Alloy

Abstract

Friction stir welding (FSW) is a solid-state joining process in which a rotating tool is inserted into the interface of two independent parts and the joint is established with friction and intensive plastic deformation. Most important factors contributing to the performance of FSW include welding tool geometry, joint geometry, tool rotation speed, tool compressive load bearing capacity, plunge depth, and tool traverse speed. In this research, effect of post-FSW friction stir processing (FSP) on mechanical characteristics and hardness of stir-welded samples of AA6061 aluminum alloy was investigated. To this end, thirteen series of experimental tests were performed to come up with a comprehensive analysis of different situations that may occur following the FSP pass and investigate the effects the FSP parameters on the weld quality. Results showed that the post-FSW FSP pass can significantly improve the ultimate weld strength and percent elongation in all samples. However, the highest strength improvement (10%) was achieved when the traverse direction in the FSP pass was opposite to that of the FSW pass while the rotation was set to be in the same direction as that of the welding pass. Moreover, most of the samples exhibited increased ultimate strength and percent elongation with increasing the tool traverse speed. Finally, performing the post-FSW FSP pass enhanced the weld hardness, especially when the tool traverse motion in the FSP pass was in the opposite direction to that in the welding pass while the tool rotation direction was the same in the FSW and FSP passes.