Achieving superior combination of yield strength and ductility in Mg–Mn–Al alloys via ultrafine grain structure

Abstract

Ternary magnesium-based alloys with an aluminum content of 0.5 wt.% and a varying manganese content of x = 1, 2, and 3 wt.% (Mg-xMn-0.5Al) were prepared and characterized. The study focused on the effect of Mn addition on the formation of ultrafine grains (UFGs, average grain size <1 μm) and the mechanical properties of the alloys. After extrusion at a relatively low temperature of 250 °C, the average grain sizes of Mg-2Mn-0.5Al and Mg-3Mn-0.5Al samples were successfully refined to values of 0.9 ± 0.39 μm and 0.8 ± 0.34 μm, respectively, of submicron scale. The Mg-3Mn-0.5Al sample simultaneously demonstrated superior yield stress (YS, 274 MPa) and fracture elongation (FE, 48.9%). The high YS was associated with the UFG structure, residual dislocations, and nanosized precipitates, while the high FE was attributed to the low dislocation storage rate and UFGs with random orientations. The formation of UFGs is mainly caused by a recrystallization process promoted by particle-stimulated nucleation. The grain growth is suppressed by dynamic precipitated α-Mn particles.