Microstructures and properties of rapidly solidified Mg-Zn-Ca alloys

Ternary alloys based on the Mg-Zn-Ca system were produced by twin-roll rapid solidification. The alloys were characterized by OM, SEM, HRTEM, XRD, EDS and Micro-hardness. The results show that the rapidly solidified flakes are of fine dendritic cell structures with the cell size ranging from 1 to 5 mu m. The Mg-6Zn-5Ca alloy in RS and annealing (200 degrees C for 1 h) states are mainly composed of alpha-Mg, Mg2Ca, Ca2Mg6Zn3 and a small quantity of Mg51Zn20, MgZn2 and Mg2Zn3. Micro-hardness increases with the increment of Ca content and age hardening occurs after aging at 200 degrees C in the flakes probably due to the precipitation strengthening of the fine precipitates Mg2Ca and Ca2Mg6Zn3, Some phases at the grain boundary in Mg-6Zn-5Ca alloy are identified by means of HRTEM, which may be beneficial to the improvement in thermal stability of the alloy.