Exploring low-alloyed as-extruded Mg alloy with high strength and high corrosion resistance

The tradeoff between strength and corrosion resistance restricts the development of low-alloyed magnesium (Mg) alloys. In this work, a low-alloyed Mg-1Sm-0.8Mn-0.5Ca-0.4 Zn alloy was prepared through a simple process of conventional casting followed by proper hot-extrusion. The as-extruded alloy exhibits a very high yield strength of 402 MPa, an acceptable elongation of 5%, and a low corrosion rate of 0.56 mm y^-1 which is close to that of high-purity Mg, and such comprehensive properties are superior to most reported Mg alloys, whether high alloying or low alloying. The special fine microstructure is responsible for high strength, including fine dynamic recrystallized (DRXed) grains, strong textured un-DRXed grains, dislocations and uniformly dispersed nano-spaced α-Mn nano-precipitates. An important finding of this study is that the corrosion film microstructure has amorphous characteristics, and this inevitably contributes to the high film protectiveness, and finally improves the corrosion resistance of the as-extruded alloy with relatively strong micro-galvanic corrosion tendency. In addition, the influence of micro/submicron-sized Mg₂Ca with anodic nature and nano-sized cathode α-Mn precipitates with strong strengthening effect on the corrosion film is also discussed. This study suggests that the strength-corrosion tradeoff can be evaded by regulating the microstructure of alloy substrate and corrosion film in the low-alloyed Mg alloy.