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

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Abstract
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.
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