Effect of Calcium Additions on Creep Properties of a Die-Cast AM50 Magnesium Alloy

Abstract

Tensile creep tests have been carried out for the die-cast AM50 + xCa (x=0.47, 0.95 and 1.72 mass pct) alloys in the temperatures between 423 and 523 K to elucidate the effect of calcium additions on creep properties for the AM50 alloy. The creep curve for the AM50 + xCa alloys is characterized by a minimum in the creep rate followed by an extended accelerating stage, and the decrease in creep rate during transient stage becomes pronounced with calcium concentration. The creep strengthening by calcium addition is emphasized at lower stresses and lower temperatures, resulting in the positive dependence of creep parameters, n and Q_c, against calcium concentration. It is found that the eutectic intermetallic phase covering the primary α grains detected in the AM50 + xCa alloys prevents the dislocation annihilation at grain boundaries. The creep strengthening by the addition of calcium results from both the solid solution strengthening of the α matrix by solute calcium and the retardation of dislocation annihilation attributed to the eutectic intermetallic phase.