Tailoring Al2Y Reinforcement in Mg–Al–Ca–Mn Composites via a Master Alloy Approach: Microstructure Evolution and Strength–Ductility Synergy

Balancing strength and ductility remains a central challenge in low-alloy Mg–Al–Ca–Mn alloys. In this study, a Mg–12Al2Y master alloy was added to Mg–1.2Al–0.8Ca–0.4Mn to obtain nominal Al2Y contents of 0, 1, 3, and 5 wt.%. The composites were prepared by stir casting and hot extrusion. In the as-cast condition, Al2Y particles occurred both within α-Mg grains and in interdendritic regions; the 3 wt.% Al2Y composite had the finest structure. Extrusion produced a bimodal microstructure of fine dynamically recrystallized (DRXed) grains and coarse unrecrystallized regions, and fragmented Al2Y and Al2Ca particles formed stringers along the extrusion direction. The 1 wt.% Al2Y composite showed the highest tensile yield strength (346 MPa) and ultimate tensile strength (361 MPa), with an elongation of 5.8%. At 3 wt.%, the yield strength, ultimate tensile strength, and elongation were 316 MPa, 332 MPa, and 11.8%, respectively, representing the best strength–ductility balance among the compositions examined. Increasing the Al2Y content to 5 wt.% raised the elongation to 12.6% but reduced the strength because of particle agglomeration and microstructural coarsening. The variation in mechanical response is discussed in relation to recrystallized grain size, retained deformation, texture, and particle distribution. Within the processing window examined here, master-alloy addition offers a practical route for controlling Al2Y reinforcement in Mg–Al–Ca–Mn composites.