Microstructure and Mechanical Properties of As-extruded and Heat-treated Mg-6Zn-1Mn-2Sn-0.5Ca

The microstructures and mechanical properties of as-extruded and peak-aged Mg-6Zn-1Mn-2Sn-0.5Ca (ZMT612-0.5Ca) alloy were studied by optical microscopy (OM), X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), hardness tests and uniaxial tensile tests. The results show that the as-cast alloy consists of alpha-Mg, Mn, Mg7Zn3, Ca2Mg6Zn3 and CaMgSn phases. The as-extruded ZMT612-0.5Ca alloy presents a totally recrystallized microstructure. The average grain size of extruded alloy is similar to 2.8 mu m. After heat treatment, the strength increases obviously, and the yield strength and ultimate tensile strength of as-extruded alloy are increased to 320 and 390 MPa, respectively. Strength enhancement is attributed to the grain boundary strengthening, solid solution strengthening and precipitation strengthening.