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 ¼ 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 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 matrix by solute calcium and the retardation of dislocation annihilation attributed to the eutectic intermetallic phase.

Evaluation of Dislocation Density in a Mg-Al-Mn-Ca Alloy Determined by X-ray Diffractometry and Transmission Electron Microscopy

“…AM50 + xCa (x ¼ 0:47, 0.95 and 1.72 mass%) die-cast alloys are superior in high temperature capability to AM50, as reported by Itoh et al 1) Also, the value of the dislocation density of AX52 (AM50 + 1.72Ca) die-cast alloy has been measured with transmission electron microscopy (TEM) techniques. The chemical composition of AX52 is shown in Table 1. 1)…”

“…To discuss the validity of the results obtained in this study and the method employed, values reported previously on the dislocation density of magnesium alloys 1,4) are listed in Table 4, together with the value obtained in this study.…”

“…Itoh et al reported the dislocation density of AX52 diecast alloy, 1) which is the same alloy used in this study. They measured the density with TEM techniques, and their reported value of & is smaller than that of this study.…”

“…It is therefore desirable to develop magnesium alloys with high temperature capability. 1) AM (Mg-Al-Mn) series alloys are commonly used in automobiles because of a good combination of their mechanical properties, corrosion resistance and die-castability. Calcium is a cost-effective, lighter alternative to rare-earth elements for improving the resistance to high temperatures of AM series alloys.…”

Effect of Prior Deformation on Creep Behavior of a Die-Cast Mg-Al-Ca Alloy

“…1(a), by using lever arm creep machines at 423 and 473 K under applied stresses that varied between 60 and 80 MPa. The prior deformation was interrupted at the time corresponding to the end of transient region for each creep condition, 12,13) by using compressed air under load followed by water quenching. The creep specimens with a gage length of 28 mm and a rectangular cross section of 6 Â 3 mm 2 shown in Fig.…”