Avenues to obtain high joint performance in friction stir welded high performance aerospace alloys

Friction stir welding has grown from a handful of publications in 1998 to approaching 1000/year in the period of 2014-2016. In this period, both technological and scientific aspects have advanced significantly; and in some cases matured as well established technologies. In this overview presentation, an effort has been made to illustrate key scientific developments in the field of friction stir welding of high performance aerospace aluminum alloys. Most widely accepted aerospace applications benefit from high joint efficiency in high strength aluminum alloys. The effect of very long term (>50000 hours) natural aging of 7XXX aluminum alloys in generating ~100% joint efficiency begs the question: What artificial ageing treatment(s) can bring this level of performance? The issue of heat-affected-zone in high strength aluminum is a very important aspect, particularly for thick plates. Consideration of alloy chemistry (Al-Li 2XXX alloys) and process parameters will be highlighted through selective examples. Emerging potential for dissimilar alloys will be emphasized in relationship with the fundamental metallurgical issues and mechanical approaches.