Diffusion research in HCP Mg–Al–Sn ternary alloys

Diffusion behavior in the HCP Mg–Al–Sn ternary alloys was experimentally investigated at 673 K and 723 K by analyzing solid-state diffusion couples. From the composition profiles analytically represented by error function expansion, the inter- and impurity diffusion coefficients were extracted by the Whittle-Green and generalized Hall methods respectively, which enable to establish the diffusion properties of the HCP Mg–Al–Sn alloys. The present results, together with the binary diffusion data of Mg–Al and Mg–Sn binaries, reveal that the average value of the main interdiffusion coefficient D˜_SnSn ^Mg over the investigated compositions is 1.39 times larger than D˜_AlAl ^Mg at 673 K and 1.36 times at 723 K, respectively, implying Sn diffuses comparably faster than Al in the HCP Mg–Al–Sn alloys. The main interdiffusion coefficients D˜_AlAl ^Mg and D˜_SnSn ^Mg and the impurity diffusion coefficient D_Sn(Mg−Al) ^* increases with increasing the content of diffusing element, either Al or Sn, however, D_Al(Mg−Sn) ^* increases first and then decreases as the Sn composition increases. The cross interdiffusion coefficients are scattering, their composition dependences are not very conclusive, however, a trend that D˜_AlSn ^Mg and D˜_SnAl ^Mg become negligibly small or even negative was evidenced as the content of Al or Sn approaches 0.