Abstract:The alloy AZ91 containing calcium was prepared under protection of a mixed gas atmosphere of SF↓6 (1%, volume fraction) and CO₂. The added calcium mainly dissolves into the Mg₁₇Al₁₂ phase in the alloy and increases its melting point and the thermal stability. The empirical electron theory (EET) of solid and molecules was used to calculate the valence electron structures (VES) of Mg₁₇Al₁₂ phase with different amounts of calcium additions. The theoretical calculations indicate that calcium dissolved in Mg₁₇Al₁₂ phase increases the strengths of atomic bonds that control the thermal stability of Mg₁₇Al₁₂ phase, and also makes the distribution of valence electrons on the dominant bond network as well as in the whole unit cell of Mg₁₇Al₁₂ more uniform, which are consistent with the experimental results.

Key words:   magnesium alloy; Mg₁₇Al₁₂; calcium; valence electron structure