High-modulus magnesium alloy: Control of microstructure and mechanical properties via in-situ synthesis of the Al2RE phase

Magnesium, being the lightest structural metal, faces limitations in alloy development due to its inherently low elastic modulus. Therefore, this study develops high-performance, high-modulus Mg-15Gd-8Y-xAl-0.3Mn (wt.%) (x = 6, 8, 10) alloys and investigates their microstructure and mechanical properties. The findings indicate that the alloys primarily consist of Al₂RE and α-Mg phases, with both the amount and size of Al₂RE phase increasing as the Al content rises. After extrusion, both the grains and the Al₂RE phase are refined. The increased modulus of the alloys is mainly due to the formation of the high-modulus Al₂RE phase. When the Al content is 6 %, 8 %, and 10 %, the modulus of the alloys is 51.8 GPa, 53.8 GPa, and 56.1 GPa, respectively. Additionally, the Al₂RE and Mg₅RE phases can jointly regulate the microstructure and mechanical properties of the alloys. As the Al content increases, the amount of Al₂RE phase increases, consuming the rare earth elements in the alloy and reducing the nano-precipitated Mg₅RE phase. Consequently, with the increase in Al content, the recrystallization rate increases, and the recrystallized grains become larger. When the Al content is 6 %, the alloy exhibits a bimodal structure with the smallest recrystallized grains, resulting in the highest yield strength of 341 MPa. When the Al content is 8 %, the alloy has a fine, fully recrystallized structure, leading to a relatively high elongation of 9.1 %. These findings provide valuable insights for designing high-modulus magnesium alloys with optimized yield strength and elongation for structural applications.