Deformation behavior of as-rolled Mg-Al-Ca-Mn alloy sheets with Al₂Ca phase and Mg₂Ca phase

In this study, Mg-Al-Ca-Mn alloy sheets containing distinct Laves phases (Al₂Ca phase and Mg₂Ca phase) were fabricated via composition modulation and hot rolling to systematically investigate the influence of Laves phase types on deformation behavior. Despite microstructural similarities, the Mg-5.0Al-2.0Ca-0.4Mn (wt.%) alloy dominated by Al₂Ca phase exhibited balanced mechanical properties with yield strength (YS) ∼ 180 MPa, ultimate tensile strength (UTS) ∼ 290 MPa and elongation to failure (EF) ∼ 23 %, while the Mg-1.0Al-3.0Ca-0.4Mn (wt.%) alloy dominated by Mg₂Ca phase showed inadequate strength and significantly reduced ductility (YS ∼ 196 MPa, UTS ∼ 251 MPa, EF ∼ 11 %), highlighting the mechanical property response that varies with Laves phase types. A set of complementary in-situ characterization techniques over multiple-length scales were utilized to reveal the deformation modes. Synchrotron X-ray diffraction combined with electron backscatter diffraction (EBSD) revealed that basal slip was the dominant deformation mechanism in the initial stage due to weak texture. Simultaneously, the fine grains suppressed twinning and enhanced non-basal dislocation activity. With increased tensile strains, lattice mismatch between Mg/Laves phases induced pronounced interfacial strain gradients under combined matrix plastic flow and Laves phase rigidity. The deformable Al₂Ca phase enhanced strain compatibility and stimulated geometrically necessary dislocation (GND) nucleation, thereby enhancing the ductility and work hardening of the alloy. In contrast, microcracks frequently initiated and propagated within the hardly deformable Mg₂Ca phase, which suppressed dislocation activity in the matrix and promoted early fracture. This work provided a theoretical basis for optimizing the strength-ductility synergy of Mg-Al-Ca-based alloy sheets by Laves phases selection.