Interdiffusion in Ternary Magnesium Solid Solutions of Aluminum and Zinc

Al and Zn are two of the most common alloying elements in commercial Mg alloys, which can improve the physical properties through solid solution strengthening and precipitation hardening. Diffusion plays a key role in the kinetics of these and other microstructural design relevant to Mg-alloy development. However, there is a lack of multicomponent diffusion data available for Mg alloys. Through solid-to-solid diffusion couples, diffusional interactions of Al and Zn in ternary Mg solid-solution at 400° and 450 °C were examined by an extension of the Boltzmann-Matano analysis based on Onsager’s formalism. Concentration profiles of Mg-Al-Zn ternary alloys were determined by electron probe microanalysis, and analyzed to determine the ternary interdiffusion coefficients as a function of composition. The magnitude of $$\tilde{D}_ZnZn^Mg$$ ternary interdiffusion coefficients was greater than that of $$\tilde{D}_AlAl^Mg ,$$ the magnitude of $$\tilde{D}_ZnZn^Al$$ ternary interdiffusion coefficients was greater than that of $$\tilde{D}_MgMg^Al$$ , and the magnitude of $$\tilde{D}_MgMg^Zn$$ was greater than that of $$\tilde{D}_AlAl^Zn$$ . Appreciable diffusional interactions among Mg, Al, and Zn were observed by variations in sign and magnitude of cross interdiffusion coefficients. In particular, Zn was found to significantly influence the interdiffusion of Mg and Al significantly: the $$\tilde{D}_MgZn^Al$$ and $$\tilde{D}_AlZn^Mg$$ ternary cross interdiffusion coefficients were both negative, and large in magnitude, in comparison to $$\tilde{D}_MgMg^Al$$ and $$\tilde{D}_AlAl^Mg$$ , respectively. Al and Mg were observed influence the interdiffusion of Mg and Al, respectively, with positive $$\tilde{D}_MgAl^Zn$$ and $$\tilde{D}_AlMg^Zn$$ interdiffusion coefficients, but their influence on the Zn interdiffusion was negligible.