Corrosion Behavior of Friction Stir Welded Al-Mg-(Zn) Alloys

The corrosion behavior of friction stir welded Zn-modified Al-Mg alloys was investigated as well as the effects of pre-weld temper conditions on the corrosion behavior of the friction stir welded alloys. Results indicate that both maximum corrosion depth and dominating corrosion mode in different weld regions after post welding heat treatment show obvious variations with an increase in the Zn content. With Zn additions the dominating corrosion mode changes from intergranular corrosion to pitting corrosion, and the severe galvanic corrosion tendency obviously occurs in the precipitation hardened alloys compared to that of the strain hardened alloy. This would be greatly related to the formation of discontinuously distributed grain boundary precipitates as well as abundant intragranular precipitates (mainly T-AlZnMgCu phase) in the precipitation hardened Al-Mg-Zn alloys while it is associated with the continuously distributed β-AlMg phase along grain boundary in the Zn-free Al-Mg alloys.