Novel low-cost magnesium alloys with high yield strength and plasticity

Developing high yield strength and ductility in low-cost Mg alloys using conventional plastic forming process is a tremendous challenge. Mg-Mn-based alloys have drawn considerable attention owing to their low-cost, high ductility and good corrosion resistance. However, the strength of Mg-Mn binary alloy is not satisfactory for industrial scale applications. In the present study, low content of Al alloying in Mg-1Mn alloy is the aim to obtain high strength and ductility of Mg-Mn-based alloys with low cost. Experimental results revealed that phase composition of the targeted Mg-1Mn-xAl (x = 0.3 wt%, 0.5 wt%, 1.0 wt%) alloys were composed of alpha-Mn + Al8Mn5, Al8Mn5 and Al8Mn5+Al11Mn4 phase, respectively. Al-Mn particles significantly refined the dynamically recrystallized (DRXed) grains. Among them, Al8Mn5 particles exhibited the most effective grain refinement. Therefore, Mg-1Mn-0.5Al alloy containing single-phase Al8Mn5 particles possessed the finest microstructure and exhibited the best mechanical properties. The high performance of the alloy was mainly attributed to the fine DRXed grains according to the Hall-Petch effect and to the large amount of fine Al8Mn5 particles through the dispersion strengthening. Meanwhile, the weak texture of fine grains enhanced the ductility. The fine DRXed grains and numerous Al8Mn5 particles effectively suppressed the extension twining, thus substantially enhanced the compression yield strength, and resulted in improved anisotropy.