Microstructure evolution and mechanical properties of the Mg–5Al–1Mn-0.5Zn-xCa alloys prepared by regular extrusion

Abstract

High strength-ductility synergy Mg–5Al–1Mn-0.5Zn-xCa (x = 0.5, 1 and 2, in wt.%) alloys without rare earth elements were prepared by conventional extrusion at 360 °C with an extrusion ratio of 25:1. The microstructure evolution and mechanical properties of Mg–5Al–1Mn-0.5Zn-xCa alloys were investigated by OM, XRD, SEM, EBSD, TEM and tensile tests. The as-extruded alloys are almost fine equiaxed grains with dispersed particles (Al2Ca, Al8Mn5, Mg2Ca and nanoscale (Al, Mn)-rich precipitates). With the increase of Ca addition, the average grain size decreases, the fine particles increase and basal textures become stronger, which result that the strength of the extruded alloy increases gradually while the elongation decrease. As-extruded Mg–5Al–1Mn-0.5Zn–2Ca exhibits excellent comprehensive mechanical properties of the ultimate tensile stress (UTS) of 340 MPa and fracture elongation (FE) of 12.8% with fine grains (2.42 μm), strong basal texture, high density of precipitates and dislocations. The TEM results show that Ca and Zn are segregated at the grain boundaries and a large amount of dispersed second-phase particles existed in the Mg–5Al–1Mn-0.5Zn–2Ca alloy, which is beneficial to grain refinement. Besides, the activated nonbasal slips are beneficial to the ductility which result from the restriction of twinning in fine grains and high Schmid factor (SF) of nonbasal slips.