Hydrogen permeation through an Al-0.2 at% Mg alloy

The diffusion of hydrogen in an Al-0.2 at% Mg alloy at temperatures between 625 K and 773 K has been measured by a gas permeation technique, in which the permeation run for the sample was repeated for many times at high temperatures. Because Mg trapped hydrogen, the permeation rate for the Al-0.2 at% Mg alloy was lowered than that for an pure Al for early permeation runs. After heavily repeated runs, however, Mg was transported to the sample surface at the hydrogen reservoir side and was no loner present in the alloy except on the surface, and the permeation rate abruptly increased. The state of Mg on the surface could be a ternary oxide which consists of Mg, Al and O. The diffusivity of the Al-0.2 at% Mg after heavily repeated permeation runs were also determined and the activation energy of hydrogen diffusion was estimated to be 0.25 eV.