Refill Friction Stir Spot Welding of an Al-Li Alloy: The Effects of Rotating Speed and Welding Time on Joint Microstructure and Mechanical Properties

In this work, 2060 Al-Li alloy was joined by refill friction stir spot welding (RFSSW). The effects of the tool’s rotating speed and welding time on the microstructure and mechanical properties of the welded joints were studied. The results showed that joints without defects can be obtained within a wide range of welding parameters. Tiny voids were formed when using a low rotating speed of 1600 rpm, and incomplete refilling was obtained when using a short welding time of 1 s. Increasing the rotating speed from 1600 to 2000 rpm increased the grain size of the stir zone (SZ). When using a short welding time of 1 s, the grains of the SZ were not completely broken with high orientation differences in the grains. Higher hardness was obtained in the SZ when using a lower rotating speed and shorter welding time. Increasing the rotating speed increased the joint strength, while short and long welding times decreased the joint strength.