A strategy to regulate the microstructure and properties of Mg-2.0Zn-1.5Mn magnesium alloy by tracing the existence of Mn element

Abstract

The role of Mn existence types on microstructure and mechanical properties of extruded Mg-2.0Zn-1.5Mn magnesium alloy is investigated. Four different Mn existence types in Mg-2.0Zn-1.5Mn magnesium alloy are obtained by different heat treatment. The four types include: (1) solid solution Mn atoms, (2) nanoscale α-Mn phase, (3) solid solution atoms + micron scale α-Mn phase, (4) micron scale α-Mn phase + nanoscale α-Mn phase, respectively. The result shows pre-existed nanoscale α-Mn particles present good pinning effect for refining grains. The micron scale α-Mn phase activates the particle stimulated nucleation (PSN) mechanism. The combination of micron scale α-Mn phase + nanoscale α-Mn phase state presents the best grain refining effect with an average grain size of 1.3 µm. The mechanical properties are significantly enhanced, the tensile yield strength, tensile strength and fracture elongation are 267 MPa, 305 MPa, 28.6%, respectively. Based on the results, four basic rules for preparing fine grained Mn-containing Mg alloys are proposed and an ideal pre-extrusion state of Mn-containing alloy is obtained: namely, direct extrusion in the as-cast-aging state. Besides has great potential for grain refinement, this state also can be regulated by the coordination of PSN effect and pinning effect in Mn-containing Mg alloy.