Effect of manganese on the microstructure and mechanical properties of magnesium alloys

The influence of Mn on the microstructure and mechanical properties of as-cast and as-solution Mg-Mn alloys was investigated in the present work. X-ray diffraction patterns revealed that the dominant phases of the experimental alloys were the alpha-Mg matrix and Mn precipitates. The average grain sizes of the as-cast Mg-Mn alloys decreased monotonically with increasing Mn content, although Mn addition showed a negative grain refinement effect on the as-cast Mg alloys. Increasing the Mn content enhanced the tensile yield strength of the as-cast alloys from 17.6 to 35.1 MPa. The improved mechanical properties are mainly attributed to precipitation hardening; a large number of Mn precipitates were located within the matrix and along the grain boundaries. Meanwhile, the lower tensile strength and Vickers hardness of the as-solution alloys is explained by the coarsened microstructure and poor solid-solution strengthening behaviour.