Investigation of the Effect of Rotation Speed and Post-Weld Heat Treatment on Mechanical Properties and Structure of Friction Stir Welding AA6061 Joints

<div>This study aims at examining the effect of tool rotational speed on the microstructural and mechanical properties of friction stir welded joints of AA6061 aluminum alloy, both pre- and post-heat treatment. The quality of the joints was assessed initially through tensile, hardness, and charpy impact tests, as well as microscopic observations. During the second stage, solid solution heat treatments were conducted at 535°C, followed by aging on additional specimens welded at identical speeds. The latter underwent hardness tensile tests and microscopic examinations. A comprehensive assessment of the outcomes from various tests validated the influence of metallurgical phenomena, including recrystallization, precipitation, and structural defects on overall resistance. The results showed an improvement in strength, ductility, and impact energy was observed in the case of welding at high rotation speed (1400 rpm). At the same speed, ductility almost doubled after post-weld heat treatment. However, the treatment leads to a slight increase in strength and a decrease in ductility and impact energy at low speeds.</div>