The effect of Ca addition on microstructures and mechanical properties of Mg-RE based alloys

AM-SC1 (Advanced Magnesium-Sand Casting Alloy 1) is a heat-resisting Mg-RE based alloy which has been widely applied in engine block. It would be an effective way to decrease the cost of the alloy by replacing Nd with Ca as addition. The effects of Ca addition on the microstructure and mechanical properties of the alloy were investigated by means of Brinell hardness measurement, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction and tensile tests at room and elevated temperatures. As the addition of Ca is 1.5%, the alloy shows the finest grain size of 16 μm which also contributes to the highest hardness and strength of 62.1 HB and 148 MPa, respectively. After T6 treatment (solid solution treatment at 500 °C for 7 h and aging treatment at 200 °C for 20 h), the morphologies of the phases in the Ca-containing alloys change from net-like to fine short-block and particle-like shapes, and its strengths at RT, 175 °C and 200 °C are correspondingly improved to 186 MPa, 166 MPa and 140 MPa, respectively.

► Calcium can be used to refine α-Mg grains in the Mg-RE based magnesium alloy.
► Calcium causes some thermally stable intermetallic compound phases.
► Those stable phases can effectively improve the mechanical property.
► Unknown four elementary phases are formed at the grain boundary.