Influence of Ga Content and Pre-Treatment on the Mechanical Properties of High-Mg-Content Al-Mg-Zn-Ga Alloys

Al-Mg-Zn crossover alloys are promising lightweight structural materials. This study systematically investigates the effects of Ga content (0–0.8 wt.%) and pre-treated aging (PA) on the mechanical properties and microstructure in high-Mg-content Al-Mg-Zn crossover alloys. The results show that, under two-step aging (90 °C/24 h + 140 °C/24 h), increasing the Ga content from 0 to 0.8 wt.% leads to a significant enhancement in mechanical strength. The hardness, ultimate tensile strength (UTS) and yield strength (YS) increased from 102.8 HV to 169.2 HV, from 457.7 MPa to 592.0 MPa, and from 288.0 MPa to 505.7 MPa, respectively, while maintaining an elongation (EL) of 15.8%. This enhancement is attributed to increased Ga content, which promotes precipitation refinement and a morphology transition from rod-like to fine spherical precipitates. Furthermore, in the alloy containing 0.4 wt.% Ga, the application of PA treatment enhanced the UTS and YS from 527.3 MPa to 569.3 MPa, and from 413.7 MPa to 483.7 MPa, respectively. This work demonstrates that the appropriate addition of Ga and PA treatment effectively enhances the precipitation behavior and tensile properties of Al-Mg-Zn alloys, providing valuable guidance for the development of high-performance, lightweight structural materials.