<p>To address the scarcity and high cost of rare-earth elements, as well as the inadequate high-temperature performance of conventional magnesium alloys, this study developed a novel low-cost, high-strength heat-resistant magnesium alloy based on the Mg-4Al-0.4Mn system. This was achieved through the combined addition of Sn and Sr in a fixed ratio (Sn: Sr = 2:1). The as-cast alloys were subjected to solution treatment and subsequent hot extrusion. A systematic investigation was conducted on the microstructure, mechanical properties, and texture evolution of the as-extruded Mg-4Al-0.4Mn-xSn-ySr alloys (<i>x</i> = 0, 0.4, 0.8, 1.2, 1.6; <i>y</i> = 0, 0.2, 0.4, 0.6, and 0.8 wt.%). The results indicate that the addition of Sn and Sr preferentially forms high-melting-point Mg₂Sn and Al₄Sr phases, which enhance the thermal stability of the alloys. During extrusion, these secondary phases are fragmented and refined, effectively inhibiting grain growth. Both room-temperature and high-temperature mechanical properties initially increase and then decrease with increasing Sn and Sr content, with the Mg-4Al-0.4Mn-1.2Sn-0.6Sr alloy exhibiting the optimal performance. EBSD analysis reveals that Sn and Sr play a dual role in regulating dynamic recrystallization (DRX): at low concentrations, solute atoms inhibit DRX, whereas at higher concentrations, secondary phases promote DRX via the particle-stimulated nucleation (PSN) mechanism. Appropriate additions of Sn and Sr effectively weaken the {0001} basal texture, increasing the proportion of grains with basal slip systems oriented favorably for activation. This facilitates basal slip and consequently improves the ductility of the alloys.</p>