Diffusion behavior and reactions between Al and Ca in Mg alloys by diffusion couples

The diffusion behavior and reactions between Al and Ca in Mg alloys by diffusion couple method were investigated. Results demonstrate that Al₂Ca is the only phase existing in the diffusion reaction layers. The volume fraction of Al₂Ca in diffusion reaction layers increases linearly with temperature. The standard enthalpy of formation for intermetallic compounds was rationalized on the basis of the Miedema model. Al-Ca intermetallic compounds were preferable to form in the Mg-Al-Ca ternary system under the same conditions. Over the range of 350–400 °C, the structure of Al₂Ca is more stable than that of Al₄Ca, Al₁₄Ca₁₃and Al₃Ca₈. The growth constants of the layer I, layer II and entire diffusion reaction layers were determined. The activation energies for the growth of the layer I, layer II and entire diffusion reaction layers were (80.74 ± 3.01) kJ/mol, (93.45 ± 2.12) kJ/mol and (83.52 ± 1.50) kJ/mol, respectively. In layer I and II, Al has higher integrated interdiffusion coefficients ${\stackrel{?}{D}}_i^{Int,layer}$ than Ca. The average effective interdiffusion coefficients ${\stackrel{?}{D}}_{Al}^{eff}$ values are higher than ${\stackrel{?}{D}}_{Ca}^{eff}$in the layer I and II.