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

Jiahong Dai¹，Hong Xiao¹，Bin Jiang^2,3，Hongmei Xie¹，Cheng Peng¹，Zhongtao Jiang⁴，Qin Zou²，Qingshan Yang⁵，Fusheng Pan^2,3

1. College of Mechanical and Electrical Engineering, Yangtze Normal University2. State Key Laboratory of Mechanical Transmissions, College of Materials Science and Engineering, Chongqing University3. Chongqing Academy of Science and Technology4. Research Institute for New Materials Technology, Chongqing University of Arts and Sciences5. School of Metallurgy and Materials Engineering, Chongqing University of Science and Technology

摘 要：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, Al₁₄Ca₁₃ and 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） k J/mol,（93.45 ± 2.12） k J/mol and（83.52 ± 1.50） k J/mol, respectively.In layer Ⅰ and Ⅱ, Al has higher integrated interdiffusion coefficients D^{Int, layer}ithan Ca. The average effective interdiffusion coefficients D_Al^eff values are higher than D_Ca^eff in the layer Ⅰ and Ⅱ.

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