Investigation of enhanced strength anisotropy in an extruded Mg-Al-Ca-Mn alloy at cryogenic temperature

This study systematically compared the microstructural evolution and mechanical behavior of the extruded AXM10304 alloy during tensile deformation along both the extrusion direction (ED) and transverse direction (TD) at cryogenic temperature (CT) and room temperature (RT). The results indicate that the variations in work hardening mechanisms contribute to the observed strength anisotropy in both the ED and TD samples. The yield strength discrepancy between different orientations is similar to 88 MPa at RT and similar to 179 MPa at CT. It is evident that the alloy exhibits more pronounced strength anisotropy during cryogenic deformation. It is noteworthy that in the CT-ED samples, the ratio of the critical resolved shear stress (CRSS) for pyramidal I and II to that of basal dislocations is relatively minimal, facilitating the activation of more pyramidal dislocations. Cross-slip in CT-ED provides a relatively facile path for dislocation slip, resulting in material softening during straining. The CT-TD sample exhibits the highest work hardening capacity and a consistent dislocation storage rate. Twinning significantly contributes to the hardening observed in the TD samples. This study also illustrates that tailoring twinning morphology to a refined needle-like shape through temperature manipulation can further enhance the work hardening of Mg alloys.