Impurity Diffusion Coefficients of Al and Zn in Mg Determined from Solid‐to‐Solid Diffusion Couples

Abstract

Increasing use and development of lightweight Mgalloys have led to the desire for more fundamental research in and understanding of Mg-based systems. As property enhancing components, Al and Zn are two of the most important and common alloying elements for Mg-alloys. We have investigated the concentration dependent interdiffusion of Al and Zn in Mg using diffusion couples of pure polycrystalline Mg mated to Mg solid solutions containing either <9 at.% Al or <3 at.% Zn. Concentration profiles were determined by electron micro-probe microanalysis of the diffusion zone. The interdiffusion coefficients were determined by the classical Boltzmann-Matano method within the Mg solid solution. As the concentration of Al or Zn approaches the dilute ends, we employ an analytical approach based on the Hall method to estimate the impurity diffusion coefficients. Results of Al and Zn impurity diffusion in Mg are reported and compared to published impurity diffusion coefficients typically determined by thin film techniques.

A diffusion mobility database for magnesium alloy development

“…For Sn, a single dataset for diffusion in single crystal Mg exists and was optimized [22]. Ag [19,22], Al [23][24][25][26][27][28][29], and Zn [19,26,30,31] solutes, which have thermodynamic descriptions in the current ThermoCalc database and multiple datasets in the literature, were also optimized. Sb [22], In [19,22], and Cd [22] solute mobilities in HCP-Mg were not optimized because single crystal values are reported and the elements are not assessed in the current TCMG2 thermodynamic database [32].…”

“…While there are several experiments for the diffusion of Al into Mg, none of them include tracer diffusion results, as the 26 Al isotope is very expensive and not readily available. Brennan [24,25] deposited Al thin films onto Mg and measured the compositional profile after diffusion using secondary ion mass spectrometry.…”

“…Kammerer [26] and Kulkarni [27]. Relative errors in the reported diffusion coefficients were obtained from each respective paper when available or from comparison to similar experimental methodologies.…”

“…Cermak [31] diffused the radioactive 65 Zn isotope into polycrystalline Mg samples and measured the depth profile using standard serial sectioning and residual activity methods. Kammerer [26] fabricated diffusion couples between polycrystalline Mg and Mg-6wt%Zn alloys to study the diffusion of Zn between 623 and 723°C. The composition profiles obtained from EPMA were used to extract the interdiffusion and impurity diffusion coefficients.…”

“…(A) Diffusion in the dilute limit, (B) Concentration dependent Zn diffusion. Data taken from Lal '66[19], Cermak '06[31], and Kammerer '13[26].…”