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

Abstract The diffusion behavior and reactions between Al and Ca in Mg alloys by diffusion couple method were investigated. Results demonstrate that Al 2 Ca is the only phase existing in the diffusion reaction layers. The volume fraction of Al 2 Ca 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 Al 2 Ca is more stable than that of Al 4 Ca, Al 14 Ca 13 and Al 3 Ca 8 . 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 D ˜ i I n t , l a y e r than Ca. The average effective interdiffusion coefficients D ˜ A l e f f values are higher than D ˜ C a e f f in the layer I and II.