The high-Mg-content Al-Mg-Zn-Si alloy, as a novel aluminum alloy, exhibits excellent strength, toughness, and corrosion resistance, demonstrating significant application potential in lightweight structural components for aerospace, weapon systems, rail transportation, and other fields. In this study, friction stir welding was employed to weld the high-Mg-content Al-Mg-Zn-Si alloy. Subsequent aging treatment was applied to establish the relationship between the mechanical properties and microstructural characteristics of the welded joint, aiming to elucidate the strengthening mechanisms of the new alloy and provide insights for achieving high-quality welds. The results indicate that the microhardness profile of the as-welded joint exhibited a “W” shape, with overall low hardness values and minor differences between zones. After the aging treatment, the microhardness increased significantly in the base material (BM), the thermo-mechanically affected zone (TMAZ), and the stir zone (SZ), whereas the heat-affected zone (HAZ) adjacent to the SZ exhibited only a marginal increase, making it the softest region in the aged joint. The yield strength and ultimate tensile strength of the aged joint increased to 327 MPa and 471 MPa, respectively. The enhancement in microhardness and strength after aging treatment was attributed to the precipitation of numerous nano-sized T-phase particles within grains. Interestingly, the tensile samples of the aged joint fractured in the high-hardness SZ instead of the low-hardness HAZ. This fracture behavior was primarily attributed to continuous grain boundary precipitates, which reduced intergranular cohesion. In contrast, the elongated grain structure in the HAZ more effectively resisted intergranular crack propagation compared to the equiaxed grains in the SZ.

In this study, we investigated the hot deformation behavior and microstructural evolution of a novel high-magnesium-content (high-Mg) aluminum alloy, bridging the disciplines of material processing and physical metallurgy. Uniaxial hot compression tests were performed over the temperature range of 280~400 °C and strain rates of 0.001~10 s⁻¹ to investigate its hot deformation behavior. The flow stress curves were systematically analyzed, and a constitutive model was developed to describe the thermo-mechanical response of the alloy. Microstructural evolution was characterized using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The results indicate that dynamic recovery serves as the dominant softening mechanism at lower deformation temperatures (≤320 °C). As the temperature increased to 400 °C, a significant rise in dynamic recrystallization was observed. Moreover, at 400 °C, higher strain rates led to the formation of abundant, network-like, mushroom-shaped dynamically recrystallized grains.