Solid-state additively manufactured Mg-Al-Zn-Mn alloys: Effects of Al content on microstructures and mechanical properties

Additive friction stir deposition (AFSD), as an advanced solid-state additive manufacturing technique, offers significant potential for fabricating large-scale engineering structural components. In this study, Mg-xAl-1Zn-0.5Mn (x = 3, 6, and 9 wt. %) alloys were fabricated via AFSD. And the effect of Al content on the microstructural evolution, mechanical properties, and fracture behavior was systematically investigated. The results reveal that all AFSD AZ series Mg alloys exhibit refined equiaxed grains and a typical basal texture, with the (0002) axis parallel to the build direction (BD). However, increasing Al content results in a gradual decrease in both average grain size and basal texture intensity. Alloy with low content of Al (≤ 6 wt. %) exhibits uniform grain size and precipitate distribution, whereas alloy with high content of Al (e.g., 9 wt. %) displays a bimodal structure composed of fine grain bands decorated by β-Mg₁₇Al₁₂ phase near grain boundaries and coarse grain bands. For this, a clear strength-ductility trade-off is observed: with increasing Al content, the yield strength rises from 152.8 ± 17.9 MPa to 215.5 ± 17.7 MPa, accompanied by a reduction in fracture elongation from 15.9 ± 0.6% to 12.3 ± 0.6%. These findings can offer theoretical insight and practical guidance for the AFSD AZ series (Mg-Al-Zn-Mn) alloys with synergistic strength and ductility.