Effect of Calcium on the Rate of Grain Boundary Migration in Pure Magnesium During Annealing

This study investigates the influence of calcium (Ca) on grain boundary migration in pure magnesium (Mg) during annealing. Pure Mg and Mg-0.5Ca alloy samples undergo compression and subsequent annealing at various temperatures to reveal that the presence of Ca impedes grain growth through solute drag effects and Zenner pinning induced by Mg₂Ca particles. The segregation of Ca solute atoms at grain boundaries imposes solute drag, reducing boundary mobility, while Mg₂Ca intermetallic particles also act as barrier to grain boundary migration. The research demonstrates weakened basal texture and smaller grain size in Mg-0.5Ca, attributed to particle-stimulated nucleation (PSN). Twin boundaries (TBs) also influence grain growth kinetics, with dislocation effects limiting grain coarsening at lower annealing temperatures. As annealing temperature increases, dislocation annihilation occurs, enabling freer grain boundary migration. Vickers hardness test was employed which revealed increased hardness in Mg-0.5Ca alloy because of stress accumulations arising from obstacles hindering the movement of dislocations, which are generated by solute elements and second-phase particles. Conversely, the reduction in hardness values as annealing temperature rises in both materials indicates a heightened dislocation annihilation process due to static recovery occurring at elevated temperatures.

Graphical Abstract