The role of calcium addition through powder sintering process in microstructure and mechanical behavior of a microalloyed magnesium

Calcium effectively strengthens magnesium through grain refinement when added in small quantities using the ingot metallurgy process. The extremely low solubility of calcium in magnesium restricts its addition using traditional powder metallurgy processes. However, the powder metallurgy process provides advantages like reduced material loss, properties control, and net-shape products. Hence, in this study, a diluted magnesium-calcium alloy was processed using the traditional blend-press-sinter (BPS) powder metallurgy process. Commercially pure magnesium was microalloyed with 0.4 wt% calcium. The sintered magnesium-calcium alloy was subjected to high-temperature extrusion. Microstructural characterization of the microalloyed Mg0.4Ca alloy revealed that the elemental calcium diffused into the magnesium particles during the sintering process and developed a gradient granular microstructure. The added initial calcium nanoparticles also acted as nucleation sites for magnesium during the sintering process. The gradient microstructure recrystallized and grew into equiaxed grains during the subsequent extrusion process. Mechanical properties characterization revealed that the addition of calcium as solute atoms increased the hardness, compressive strength, and ductility of magnesium, which was further enhanced by the extrusion process. The presence of calcium as solute atoms increased the tensile strength of extruded magnesium by a reasonable amount, while ductility remained almost unchanged.