Effects of Mn addition on the microstructure and mechanical properties of Mg–Zn–Sn alloys

Abstract The effects of Mn addition on the microstructure and mechanical properties of Mg–Zn–Sn alloys have been investigated by optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and uniaxial tensile tests. The results show that the addition of Mn can significantly improve the mechanical properties of the as-extruded and aged Mg–Zn–Sn alloys, which is mainly due to the grain refinement and precipitation strengthening. For the as-extruded alloys, the Mn element mainly exists in the form of α-Mn particle phase, which is dispersed in the matrix and play the role of fine grain strengthening and dispersion strengthening. For the single-aged and double-aged alloys, the dispersed α-Mn particle phases can also serve as the heterogeneous nucleation cores of rod-like β 1 ' precipitates during the ageing treatment, which is beneficial to the nucleation rate of the precipitates. The crystallographic characteristics research shows that the directional relationship between α-Mg, β 1 ' and α-Mn is [ 2 1 ¯ 1 ¯ 0 ] α ∕ ∕ [ 0001 ] β 1 ’ ∕ ∕ [ 012 ] Mn , i.e., the β 1 ' phase can form a coherent interface on the α-Mn phase.