Towards High-Performance Heat-Resistant Magnesium Alloys: The Role of Mn in Asymmetric Extruded Mg-Al-Sn-Ca Alloys

This work systematically investigates the influence of Mn content (0.1, 0.3, and 0.5 wt.%) on the microstructure, mechanical properties, and high-temperature stability of asymmetric extruded Mg-4.0Al-0.8Sn-0.3Ca-xMn alloys. The results demonstrate that Mn addition effectively promotes the formation of multi-scale secondary phases. Increasing the Mn content refines the average grain size from ∼2.82 µm to ∼1.89 µm and significantly modulates the recrystallization behavior of the alloy. The ATX4103-05Mn alloy (0.5 wt.% Mn) exhibits an optimal strength–ductility synergy, achieving a yield strength of 281.8 MPa and an elongation of 19.1%. Quantitative analysis reveals that this enhancement is predominantly governed by dispersion strengthening (∆σp∼34.1 MPa), with supplementary contributions from grain boundary and dislocation strengthening. Furthermore, the ATX4103-05Mn alloy shows superior resistance to abnormal grain growth after thermal exposure at 400 °C for 10 h, which is attributed to effective Zener pinning by the uniform distribution of short rod-shaped Al8Mn5 phases along the grain boundaries. This study elucidates the multi-scale strengthening and thermal stabilization mechanisms enabled by Mn microalloying, providing a viable pathway for developing high-performance, thermally stable magnesium alloys.