Role of Grain Boundary Segregation and Nanoprecipitation on the Tensile Properties and Thermal Stability of Dilute Mg–0.7Al–0.3Ca (wt%) Alloy

A dilute Mg–0.7Al–0.3Ca (AX0703, wt%) alloy with high strength is developed via conventional low-temperature extrusion, with tensile yield strength of 376 MPa and elongation of 5.3%. As-extruded AX0703 sample exhibits the bimodal grain structures consisting of dynamically recrystallized (DRXed) ultrafine grains and coarse non-DRXed grains with strong basal texture, which contributes to the strength. The numerous nano-Al₂Ca phases were developed in non-DRXed grains during extrusion, which not only generates the remarkable precipitation hardening effect, but also favors the improved thermal stability by retarding recrystallization process. Also, it is found that co-segregations of Al–Ca solutes at DRXed grain boundaries hinder grain growth during heat treatment at 300 °C, contributing to the thermal stability of as-extruded AX0703 alloy. This work provides valuable insights into the development of high-strength and low-alloyed Mg extrusions with high thermostability.