Diffusion of 65Zn in AZ91 and in QE22 reinforced by Saffil fibers

Effective diffusion coefficients D-eff of radioisotope Zn-65 in Mg-based alloys AZ91 and QE22 with short Saffil fibers were measured by serial sectioning method in the temperature interval 648-728 K. The results were compared with Zn-65 volume diffusion coefficients D-v obtained with the same materials without the reinforcement. This enabled to assess the influence of the interfaces between the matrix and the fibers upon the effective diffusion coefficients and to estimate the diffusion coefficients D-i of Zn in Saffil/matrix interphase boundaries. It was observed that temperature dependence of both D-eff and D-i is significantly concave in the studied temperature interval, which was ascribed to relaxation of thermo-elastic stresses present in the composite as a consequence of considerable differences between the coefficients of thermal expansion (CTE) of both the constituents. D-eff and D-i tend to higher values close to 693 K, where the CTE is in a local minimum - i.e., where the maximum dislocation density by the phase interface can be expected. (C) 2007 Elsevier Ltd. All rights reserved.