Microstructure and mechanical property of a novel heat-resistant Mg-Ca-Mn based alloy

Abstract

In this work, the microstructure and mechanical properties at both room temperature (RT) and 250 °C of an as-extruded Mg-Ca-Mn based alloy have been systematically investigated. When the extrusion temperature is as low as 260 °C (XMNdAZ-260 sample), the solute segregation at the grain boundary (GB) is few, and the ultra-fine dynamic recrystallized (DRXed) grains can be formed, which thus leads to an ultra-high yield strength (YS) of ∼426 MPa, and a limited elongation (EL) of ∼1.8% at RT. With increasing the extrusion temperature to 300 °C (XMNdAZ-300 sample), the DRXed grains have grown to some extent, and the YS is decreased to ∼373 MPa at RT, accompanied with a reasonable EL of ∼8.9%. Interestingly, the XMNdAZ-300 sample exhibits a much higher ultimate tensile strength (UTS) of ∼271 MPa at 250 °C, as compared with XMNdAZ-260 sample having UTS of only ∼224 MPa at 250 °C. The obvious solute segregation along GBs played an important role in enhancing high temperature strength via suppressing GB sliding. With the exposure time increasing, most of the GB segregation evolves to nano-precipitations, which thus leads to the strength loss at 250 °C, UTS of ∼190 MPa in 96 h-aged sample. Nevertheless, heat-resistant properties of present Mg alloys are superior to the commercial counterparts, which provides an important insight into developing novel heat-resistant Mg alloys via constructing solute segregation at GBs.