A post-friction stir welding heat treatment procedure was developed that reduces abnormal grain growth and restores optimum material properties in heat-treatable aluminum alloys. The innovation is a thermal processing methodology for retaining the fine-grained structure in aluminum alloys subjected to solid-state welding and subsequent forming processes.
Heat treatment of the deformed welds is desirable in order to restore the properties of the alloy negatively affected in the weld region. In these alloys, abnormal grain growth frequently occurs in friction stir welds during solution heat treatment and is known to degrade key materials properties such as strength, ductility, and toughness.
The innovation of inserting an intermediate annealing step reduces abnormal grain growth during post-welding heat treatment, thereby allowing optimum mechanical properties. This is important where Al-Li alloys (and other heat-treatable alloys) are friction stir welded followed by deformation processing. It is especially applicable for high-performance, high-reliability structural components required for aerospace vehicles.