Interdiffusion and impurity diffusion in polycrystalline Mg solid solution with Al or Zn

Highlights: • Interdiffusion coefficients within Mg(Al) and Mg(Zn) solid solutions. • Impurity diffusion of Al and Zn in Mg. • Interdiffusion coefficient in Mg(Zn) was higher than that of Mg(Al). • Zn impurity diffusion coefficient was higher than that of Al in Mg. - Abstract: Interdiffusion and impurity diffusion in Mg binary solid solutions, Mg(Al) and Mg(Zn) were investigated at temperatures ranging from 623 to 723 K. Interdiffusion coefficients were determined via the Boltzmann–Matano Method using solid-to-solid diffusion couples assembled with polycrystalline Mg and Mg(Al) or Mg(Zn) solid solutions. In addition, the Hall method was employed to extrapolate the impurity diffusion coefficients of Al and Zn in pure polycrystalline Mg. For all diffusion couples, electron microprobe analysis was utilized for the measurement of concentration profiles. The interdiffusion coefficient in Mg(Zn) was higher than that of Mg(Al) by an order of magnitude. Additionally, the interdiffusion coefficient increased significantly as a function of Al content in Mg(Al) solid solution, but very little with Zn content in Mg(Zn) solid solution. The activation energy and pre-exponential factor for the average effective interdiffusion coefficient in Mg(Al) solid solution were determined to be 186.8 (±0.9) kJ/mol and 7.69 × 10⁻¹ (±1.80 × 10⁻¹) m²/s, respectively, while those determined for Mg(Zn) solid solution were 139.5 (±4.0) kJ/mol and 1.48 × 10⁻³ (±1.13 × 10⁻³) m²/s. In Mg, the Zn impurity diffusion coefficient was an order of magnitude higher than the Al impurity diffusion coefficient. The activation energy and pre-exponential factor for diffusion of Al impurity in Mg were determined to be 139.3 (±14.8) kJ/mol and 6.25 × 10⁻⁵ (±5.37 × 10⁻⁴) m²/s, respectively, while those for diffusion of Zn impurity in Mg were determined to be 118.6 (±6.3) kJ/mol and 2.90 × 10⁻⁵ (±4.41 × 10⁻⁵) m²/s