Effects of heat treatment on the microstructural stability, mechanical properties and degradability of as-cast Mg–1Y and Mg–1Ca alloys: A comparative study

Y and Ca are two alloying elements which are being extensively used to enhance different properties and address the challenges of biodegradable Mg alloys. In this study, the efficiency of Y and Ca for improving microstructure stability during high-temperature solution treatment was assessed and compared by studying the microstructure as well as the mechanical and degradation properties of Mg–1wt%Y and Mg–1wt%Ca alloys. X-ray diffraction and field emission scanning electron microscopy studies demonstrated presence of Mg24Y5 and Mg2Ca particles in Mg–1Y and Mg–1Ca alloys, respectively. In addition, the Mg–1Y alloy witnessed a significantly higher level of grain growth in comparison with Mg–1Ca alloy. The results of shear punch test and hardness experiments demonstrated greater mechanical strength perseverance of Ca-incorporated alloy as the result of the presence of Mg2Ca phase as well as the finer microstructure. Accordingly, it can be pointed out that Ca is a more suitable element for stabilizing the microstructure of Mg-based alloys at high temperatures in comparison with Y. On the other hand, the hydrogen evolution test in phosphate-buffer saline (PBS) solution showed that Y-incorporated alloy possessed higher corrosion resistance. Also, reducing the micro-galvanic corrosion effects by long-term annealing in high temperatures can be an effective approach to enhance the degradability of both alloys, where the best corrosion resistance was observed in annealed Mg–1Y alloy.