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

Abstract

a b s t r a c tInterdiffusion 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 Â 10 À1 (±1.80 Â 10 À1 ) m 2 /s, respectively, while those determined for Mg(Zn) solid solution were 139.5 (±4.0) kJ/mol and 1.48 Â 10 À3 (±1.13 Â 10 À3 ) m 2 /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 Â 10 À5 (±5.37 Â 10 À4 ) m 2 /s, respectively, while those for diffusion of Zn impurity in Mg were determined to be 118.6 (±6.3) kJ/mol and 2.90 Â 10 À5 (±4.41 Â 10 À5 ) m 2 /s.

Self-learning kinetic Monte Carlo simulations of Al diffusion in Mg

“…In SLKMC simulation, the anisotropy of an HCP lattice is naturally included as well as all the possible vacancy-Mg and vacancy-Al exchange processes. In comparison to those obtained by Kammerer et al [36], the activation energy for the total diffusion is within the error bars and the effective prefactor has the same order of magnitude, but the effective prefactor has a very large error bar. On the other Table 4.…”

“…[37] To obtain Al atom diffusivities, Das et al [34], extrapolated interdiffusion coefficients in hcp Mg-Al solid solution to 0% Al concentration using Wagner's approach. [44] While Kammerer et al [36] (∼ 100 − 500 µm grain size) and Brennan et al [38] (∼ 30 − 60 µm grain size) extrapolated interdiffusion coefficients obtained using the Boltzmann-Matano method [45] to less than 1at.% Al concentration of Mg-Al solid solution using the Hall method [47]. Brennan et al [37] used depth profiling with secondary ion mass spectrometry (SIMS) and, utilized the thin film method and the diffusion equation for the thin film solution to extract the Al atom diffusivities.…”

“…1. Table. 2 shows a comparison of effective activation energies and effective diffusion prefactors for an Al atom diffusion (within and perpendicular to the basal plane, and total diffusion) in Mg matrix obtained from SLKMC simulations, 8-frequency model [32,33], diffusion couple experiment using single crystal Mg [34], solid-to-solid diffusion couple of polycrystalline Mg and Mg-Al solid solution [36,38] and via depth profiling of Al penetration in polycrystalline Mg (∼ 10 µm grain size). [37] To obtain Al atom diffusivities, Das et al [34], extrapolated interdiffusion coefficients in hcp Mg-Al solid solution to 0% Al concentration using Wagner's approach.…”

Exact Model of Vacancy-Mediated Solute Transport in Magnesium

“…Magnesium alloys may substitute for aluminum and steel in aerospace and automotive industries with their higher specific strengths [9][10][11]. The growing interest in magnesium has driven experimental [12][13][14][15][16][17][18][19] and computational [20][21][22][23] studies of transport coefficients of the common Al and Zn solutes that improve strength and rare earth elements that improve ductility. Transport coefficients are fundamental inputs for models at the length and time scales of microstructure evolution.…”

Comparison of the Sauer-Freise and Hall Methods for Obtaining Interdiffusion Coefficients in Binary Alloys

“…While the SF and BM techniques usually agree with each other, the results of the HM analysis can be quite different. [26][27][28][29] In the present paper, using numerically simulated interdiffusion profiles we will test the validity of these three methods at the dilute ends and along the bulk of the composition profiles.…”