Improvement in the strength of friction-stir-welded ZK60 alloys via post-weld compression and aging treatment

Although the microstructure of Mg alloys can be significantly refined after friction stir welding (FSW), the joint strength often decreases due to texture redistribution and precipitate dissolution. In this study, cast ZK60 alloy plates were successfully joined by FSW. Then, post-weld compression and aging treatment were applied on the joints, and their effects on microstructure, texture, and mechanical properties were examined. A local basal texture similar to that reported for FSW AZ31 alloy was formed in the stir zone of the ZK60 alloy after FSW, and the grain size was refined to ~3.7µm in the stir zone. Profuse {101¯2} twinning was generated in various regions after 5% post-weld compression. Thus, the yield strength of ZK60 joint increased by 45MPa. In contrast, the yield strength increased by 32MPa after the aging treatment. This indicates that post-weld compression increased the number of precipitates in the ZK60 joint during subsequent aging, because the twins and dislocations generated during the compression provide more sites for precipitation.