The diffusion of H in Al-0.2at%Mg at 625 to 773K was measured by using a gas permeation technique in which the permeation run for a given sample was repeated many times at high temperatures. Because the Mg trapped H, the permeation rate in the alloy was lower than that in pure Al during the early permeation runs. After many repeated runs, however, the Mg had migrated to the sample surface on the H-reservoir side and was no longer present in the alloy; except on the surface. The permeation rate then suddenly increased. The H diffusivity in the alloy after many permeation runs was found to be described by an activation energy of 0.25eV.

Hydrogen Permeation through an Al-0.2at%Mg Alloy. A.Takasaki, Y.Furuya, T.Kino: Materials Science Forum, 2000, 331-337, 1607-12