Research progress on the microstructure and mechanical properties of friction stir welded Al-Li alloy joints

Aluminum-lithium (Al-Li) alloys have attracted attention in the fields of aerospace and military owing to their low density, high elastic modulus, high specific strength, good fatigue and corrosion resistance. To grasp the research status of the global Al-Li alloy welding, the academic papers on Al-Li alloys welding indexed in the Web of Science database from 1998 to 2020 were analyzed through bibliometrics. The results show that friction stir welding (FSW) is the major welding method for Al-Li alloys. Subsequently, the process characterization, microstructure evolution of Al-Li alloys FSW were reviewed in detail. The influence of process parameters such as pin shape, shoulder shape, rotation speed, welding speed and heat input on the microstructure and mechanical properties of the friction stir welded joints were analyzed and summarized. Finally, the key research directions of Al-Li alloy FSW are suggested, mainly including post-weld heat treatment, Al-Li alloys and dissimilar materials joining, FSW of thick Al-Li alloys plates, etc.