The Microstructure and Mechanical Properties of Die-Cast Mg-6Al-2Sm-xCu Alloys

In the present study, the effect of Cu content on the microstructure and mechanical properties of die-cast Mg-6Al-2Sm-xCu (x = 1, 3, 5) alloys has been investigated. The microstructure and components of the alloys were observed and identified by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS), respectively. The phases of the alloys were analyzed via X-ray diffractometer (XRD). The mechanical properties at different temperatures were studied by tensile tests. The experimental results show that all die-cast Mg-6Al-2Sm-xCu alloys consist of α-Mg, β-Mg17Al12, Al4Cu9, Al3Sm, and Mg2Cu6Al5 phases. These components, i.e., Al3Sm and Al4Cu9 phases, have high thermal stability and can prohibit dislocation movement and grain boundary sliding. TEM analysis shows that the Al3Sm phase possesses a tetragonal structure. With the increase in Cu content, the microstructure is refined firstly and then becomes coarsened. Moreover, the tensile strength increases firstly and then decreases as Cu content increases at room temperature and an elevated temperature. All fractures of the alloys at room temperature show a complex mode of brittle and ductile fracture. However, at an elevated testing temperature, the fractures of the alloys exhibit more ductile fractures.