Tailoring microstructure and mechanical properties in a high Ca containing Mg-Al-Ca-Mn alloy: A combined experimental and CPFEM study

To improve the strength-ductility synergy of high Ca containing Mg-Al alloys, this study investigated the influence of pre-extrusion heat treatments—solution treatment (ST), T6 aging, and pre-deformation followed by aging (RT)—on the microstructure and mechanical behavior of an as-extruded Mg-9Al-2.5Ca-0.4Mn alloy. The results show that the T6 sample exhibited the highest yield strength of 325.6 MPa, while the RT sample achieved the best strength-ductility synergy with a yield strength of 302.6 MPa and an elongation of 6.5 %. Microstructural analysis revealed that the high Ca content (2.5 wt%) played a critical dual role: the thermally stable Al₂Ca network hindered recrystallization and promoted dislocation accumulation, but simultaneously consumed Al solute atoms. This "solute depletion" effect weakened the precipitation strengthening potential, resulting in the RT sample being slightly weaker than the T6 sample. Quantitative analysis using crystal plasticity finite element modeling (CPFEM) revealed that the T6 treatment provided the highest strengthening effect on basal slip, with a fitted critical resolved shear stress (CRSS) of 95 MPa, consistent with the highest value calculated from each strengthening mechanism. Furthermore, CPFEM unveiled the origin of the ductility difference: the poor ductility of the ST sample is linked to an unfavorable reliance on hard pyramidal slip among non-basal modes. In contrast, the RT sample effectively suppressed activity and promoted compatible prismatic slip, thereby mitigating fracture initiation despite the existence of strain localization.