Effect of deep cryogenic treatment on plastic deformation mechanisms of aging-treated AXM alloy: An in-situ tensile and digital image correlation analysis

Sequential heat treatment strategies offer considerable potential for augmenting mechanical properties to fulfill the rigorous specifications of advanced applications. Nevertheless, their application remains limited, particularly for Mg alloys, due to the inherent challenges posed by their hexagonal close-packed crystal structure and the complexities involved in optimizing multi-stage thermal processing. Therefore, A fundamental understanding of process interactions and synergistic effects is essential for developing cost-effective, high-performance Mg alloys. To bridge this knowledge gap, the present study incorporates deep cryogenic treatment (DCT) into the standard T6 aging pathway for Mg-Al-Ca-Mn alloy sheets. The investigation utilized an integrated, real-time characterization strategy, combining in-situ tensile testing with electron backscatter diffraction (EBSD), scanning electron microscopy-based digital image correlation (SEM-DIC), and transmission electron microscopy (TEM) to accurately elucidate DCT's influence on deformation mechanisms, enabling a comprehensive assessment of microstructural evolution, mechanical responses, and strain development dynamics during deformation. Comparative analysis with conventional T6 samples demonstrated that DCT significantly enhanced both strength and ductility, achieving an ultimate tensile strength of 346 MPa with Improved elongation reaching 27.5%. Microstructural analysis revealed that this superior performance originates from synergistic mechanisms, where strength was enhanced through refinement of precipitates (30 nm), increased dislocation density, and nanoscale sub-grain formation. Simultaneously, ductility gains stem from weakening basal texture, the activation of twinning and non-basal slip, and suppression of microcrack propagation. These findings demonstrate that DCT-integrated sequential heat treatment is a viable strategy for overcoming the strength-ductility trade-off in Mg alloys, providing a valuable framework for designing high-performance Mg components.