This study explores the influence of Al addition on the microstructure, texture and mechanical deformation behavior of Mg-xAl-1Zn-1Ca (x = 1, 2 wt.%) alloy (referred as AZX211 and AZX311, respectively). Tensile tests were performed at room (24 °C, RT) and cryogenic temperature (-150 °C, CT) to probe the dislocation and twinning evolution and its consequent effect on the strength, ductility and hardening characteristics. The results revealed that AZX311 exhibited an outstanding combination of superior strength and excellent ductility at both temperatures. This unique balance of high tensile strength and consistent ductility outperforms previously documented magnesium alloys, positioning AZX311 as an ideal material for applications that demand both robust mechanical properties and reliable ductility, particularly under low-temperature conditions. The exceptional strength at cryogenic temperatures in this alloy is attributed to the synergistic effect of dislocation strengthening and boundary strengthening, where the increased barriers to dislocation movement lead to significant hardening. The presence of nano-stacking faults and greater activation of pyramidal slip, along with their interactions, result in a substantial increase in tensile strength while maintaining ductility at cryogenic temperature making it a suitable fit for cryogenic applications.

This study investigates the influence of CaO (0.5, 1 (wt.%)) alloying on the microstructural evolution, texture development and deformation behavior of AZ61 magnesium alloy. The uniaxial tension tests at room (RT) and cryogenic (CT, -150 ℃) temperature were performed to investigate the twinability and dislocation behavior and its consequent effect on flow stress, ductility and strain hardening rate. The results showed that the AZ61-1CaO exhibited superior strength/ductility synergy at RT with a yield strength (YS) of 223 MPa and a ductility of 23% as compared to AZ61 (178 MPa, 18.5%) and AZ61-0.5CaO (198 MPa, 21%). Similar trend was witnessed for all the samples during CT deformation, where increase in the YS and decrease in ductility were observed. The Mtex tools based in-grain misorientation axis (IGMA) analysis of RT deformed samples revealed the higher activities of prismatic <a> slip in AZ61-CaO, which led to superior ductility. Moreover, subsequent EBSD analysis of CT deformed samples showed the increased fraction of fine {10-12} tension twins and nucleation of multiple {10-12} twin variants caused by higher local stress concentration at the grain boundaries, which imposed the strengthening by twin-twin interaction. Lastly, the detailed investigations on strengthening contributors showed that the dislocation strengthening has the highest contribution towards strength in all samples.

Deformation twinning is profusely activated in the Mg alloys due to lower critical resolved shear stress (CRSS) compared to the non-basal slip systems (prismatic <a> and pyramidal <c + a>) and plays a significant role in texture reorientation, grain refinement and enhancement of mechanical performance. Twinning is a sequential process comprising twin nucleation, twin propagation and twin growth, hence several intrinsic and extrinsic parameters that facilitate or suppress the process have been critically reviewed. The dependence of twinning on the grain size, deformation temperature, favorable grain orientation and shear strain have been thoroughly discussed in the context of published literature and an attempt has been made to provide a benchmark conclusive finding based on the majority of works. Furthermore, the subsequent effect of twinning on the mechanical performance of Mg alloys, including ductility, formability and tension-compression asymmetry has been discussed in detail. Lastly, the stability of twins, including stress and thermal stability, is summarized and critical issues related to pertinent bottlenecks have been addressed.