Microstructure, mechanical properties and corrosion behavior of extruded Mg-Zn-Ca alloys with same Zn/Ca atomic ratio

The influence of Zn and Ca contents with the same Zn/Ca atomic ratio of 0.1 on the microstructure, mechanical properties and corrosion behavior of Mg-xCa-yZn (MCZ) alloy was explored. The results showed that Mg2Ca was unique phase in all of the four alloys and it was distributed in discontinuous strip composed by the irregular particles along the extrusion direction. With increasing the Zn and Ca contents, the volume fraction and the average size of Mg2Ca increased simultaneously. The grain size was reduced from 5.3 mu m in MCZ1 to 2.4 mu m in MCZ5 alloy after extrusion. This contributed to the high yield strength (YS) and ultimate tensile strength (UTS) by grain boundary strengthening and secondary phase strengthening, but deteriorated the ductility of the alloys. In addition, the corrosion rate was accelerated as increasing the alloying contents due to the galvanic corrosion caused by the high volume fraction of Mg2Ca. However, MCZ5 and MCZ3 alloys exhibited more uniform corrosion performance than that of the MCZ2 and MCZ1 alloys. This was mainly attributed to the reduced distance of the Mg2Ca phase, which could assist the fast connection of the corrosion product and avoid the local corrosion.