Effect of heat treatment on the microstructure and corrosion behaviour of Mg-Zn alloys

Microstructure and corrosion behaviour in simulated body fluid of as-cast and heat treated Mg-xZn (x = 3 and 6) alloys for different heat treatment times were studied. The results revealed that as-cast Mg-3Zn alloys consist of Mg12Zn13 phase and alpha-Mg matrix, while Mg-6Zn is composed of Mg51Zn20, Mg12Zn13 compounds and alpha-Mg matrix. After heat treatment of Mg-6Zn alloy at 340 degrees C, the Mg51Zn20 phase decomposed to the matrix and Mg12Zn13 while, the microstructure of Mg-3Zn remained unchanged. The results also indicated that heat treatment at 340 degrees C has little influence on the corrosion behaviour of Mg-3Zn. In contrast, heat treatment improved the corrosion resistance of the Mg-6Zn alloy as the decomposition of the Mg51Zn20 phase decreased micro-galvanic corrosion. The corrosion resistance of both as-cast Mg-3Zn and Mg-6Zn alloys marginally improved with increasing heat treatment times.