Effect of grain boundary segregation on microstructure and mechanical properties of ultra-fine grained Mg–Al–Ca–Mn alloy wires

An extraordinary high-strength dilute Mg-0.8Al-0.1Ca-0.6Mn (wt. %) alloy wire was successfully developed by hot drawing, which exhibits high tensile yield strength of 394 MPa, ultimate tensile strength of 431 MPa and moderate elongation to failure of 6.0%. The high strength was mainly attributed to the ultra-fine dynamically recrystallized (DRXed) grains, coarse elongated unrecrystallized grains with dense dislocations as well as nano-sized Al2Ca and Al–Mn precipitates dispersed in the as-drawn alloy wire. The microstructure observation by transmission electron microscopy reveals that Al and Ca remarkably co-segregated to the DRXed grain boundaries while Al rather than Ca segregated at the low-angle grain boundaries in the unrecrystallized grains. The solute segregations not only exerted strong solute drag effect on the grain boundaries to restrict the dynamic recrystallization and DRXed grain growth, but also contributed to the high strength of the alloy wire by pinning the dislocations. The findings from this work provide a new insight into the development of strong low-cost and light-weight Mg alloy wires.