Comparison of the Weldability of AA6061-T6 Joint under Different Friction Stir Welding Conditions
2021
In this work, similar butt joints of AA6061-T6 alloy prepared by underwater friction stir welding (UWFSW) and friction stir vibration welding (FSVW) processes were examined. The characteristics of joints were compared with the joints obtained by conventional friction stir welding (CFSW). The different kinds of microstructural modifications that occurred during CFSW, FSVW, and UWFSW processes were analyzed. The results are employed to analyze the different behaviors in strength, ductility, weldability, and hardness of the joints in different processes at different traverse speeds, rotational speeds, and vibration frequency. It was found that mechanical vibration decreases the grain size in the weld zone and hinders the coalescence and regrowth of the precipitates during FSVW. On the other hand, water significantly decreased the joint temperature during UWFSW and led to a refined microstructure in the stir zone, which substantially improved the mechanical properties of the welded joint. The synergetic effect of refined grains and lower dissolution of β″ precipitates (higher evolution of β″ to β′ and β-Mg2Si) due to fast cooling rate (intensified local deformation) led to higher hardness in UWFSW (FSVW) joint compared to CFSW joint. The small size with the uniform distribution of dimples indicated the combination of strength and ductility in FSVW-ed and UWFSW-ed joints. The simple and highly effective welding procedure, FSVW, can be readily scaled up for industrial welding applications.
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