On the temperature-dependent diffusion growth of ϕ-Mg5Al2Zn2 ternary intermetallic compound in the Mg–Al–Zn system

Abstract

The study on the temperature-dependent kinetic behavior of intermetallic compounds (IMCs) in Mg–Al–Zn (AZ) series alloy system is important since its close interrelation with the microstructure evolution under various alloying conditions as well as the T-dependent performance. However, there is a very lack of experimental study on the diffusion kinetics of the ternary IMCs in the AZ series alloy systems. The current work combines the diffusion couple technique and numerical inverse method to investigate the T-dependent kinetic coefficients, i.e., the parabolic growth constant (PGC) and interdiffusion coefficients, for ϕ-Mg5Al2Zn2 ternary IMC in the Mg–Al–Zn alloy system. The Arrhenius formula of both PGC and main interdiffusivities is obtained, i.e., $${}_{{}}^{\phi } k_{p} = 5.48 \times 10^{ - 5} \exp \left( {\frac{120010}{{RT}}} \right)$$ m2/s, $${}_{{}}^{\phi } \tilde{D}_{{{\text{MgMg}}}}^{Al} = 3.48 \times 10^{ - 10} \exp \left( {\frac{50420}{{RT}}} \right)$$ m2/s and $${}_{{}}^{\phi } \tilde{D}_{{{\text{ZnZn}}}}^{Al} = 2.87 \times 10^{ - 7} \exp \left( {\frac{91440}{{RT}}} \right)$$ m2/s, based on which a numerical reproduction of the experimentally determined IMC growth is performed for verification. By comparing the current experimental and calculation results, the rate-controlling factor of the temperature-dependent diffusion growth of ϕ ternary IMC in the Mg–Al–Zn system is further discussed.