Development of high-performance Mg–Zn–Ca–Mn alloy via an extrusion process at relatively low temperature

In general, Mg alloys are difficult to process at low temperature (below 200 °C), due to the limited slip systems. High-temperature deformation easily results in the grain growth, which seriously restricts the improvement of mechanical properties. In this study, we report a subsequent low-temperature extrusion technology for ultra-fine grained (UFG) Mg–Zn–Ca–Mn alloys processed through equal channel angular pressing (ECAP), and successfully fabricate the extruded alloy with high yield strength (∼332.8 MPa) and superior ductility (∼17.9%) through grain refinement and texture modification. The initially fine-grained structure in the as-ECAPed alloy is beneficial to improving its low-temperature deformability, because the compatibility stress at grain boundaries can effectively promote the activation of the non-basal slip systems. Although the strength is dramatically increased, the alloy extruded at 100 °C exhibits the poor ductility, which can be ascribed to the dislocation accumulation behavior. With increasing extrusion temperature, the yield strength is remarkably increased at very small expense of ductility, because of the grain refinement, stacking faults, recovery of basal texture and fine secondary phase particles. The dislocations formed during the extrusion can be rapidly annihilated through a dynamic recrystallization process, which contributes to the improved ductility.