A STUDY OF HYDROGEN PERMEATION IN ALUMINUM-ALLOY TREATED BY VARIOUS OXIDATION PROCESSES

A set of oxide coatings was formed on the surface of an Al alloy (wt%: Fe, 0.24; Si, 1.16; Cu, 0.05-0.2; Zn, 0.1; Al, residual) by means of various oxidation processes. The hydrogen permeability through the alu minum alloy and its coating materials was determined by a vapor phase permeation technique at temperatures ranging from 400 to 500 degrees C using high-purity H-2 (99.9999%) gas with an upstream hydrogen pressu re of 10(4)-10(5) Pa. The experimental results show that the hydrogen permeability through aluminum oxide coating is 100-2000 times lower th an that through the aluminum alloy substrate. This means that the alum inum oxide is a significant hydrogen permeation barrier. A high hydrog en permeation resistance was observed in an oxide layer prefilmed in 2 00 degrees C water, while an anodized aluminum oxide film had a less o bstructive effect, possibly caused by the porous structure of the anod ic oxide. The hydrogen permeability through films of aluminum oxide wa s not a simple function of the aluminum-oxide phase configuration. (C) 1997 Elsevier Science B.V.