Friction stir welded structural materials: beyond Al-alloys

The friction stir welding (FSW) technique is widely accepted to be one of the most significant welding techniques to emerge in the last 20 years. Friction stir welding of Al-alloys is now commonplace and is covered in several recent reviews, including one in this journal. Consequently, the technique is currently being used for joining of these alloys in various industrial applications. Complementary to these developments has been a dramatic increase in research into joining of other alloys and systems by FSW. This field is very active, but less mature. Thus, the aim of this review article is to build on our understanding of the fundamentals, as applied to Al-alloys that laid out in the previous review in this journal, and to address the current state-of-the-art of FSW developing beyond Al-alloys, including Mg-alloys, Cu-alloys, steels, Ti-alloys and metal matrix composites, focusing particularly on microstructural aspects, including texture formation, and the resulting properties of these joints. Material selection for tooling will also be covered to some extent while modelling studies of material flow during FSW are outside the scope of this paper. Finally, residual stresses are mentioned in a number of places and while these have been measured extensively for Al-alloy systems there are fewer measurements for other systems.