Corrosion of Aluminum in Deionized Water at Elevated Temperatures. (On the Factors Affecting Intergranular Corrosion of Pure Aluminum, 1st Report)

Abstract

By the static autoclave tests at the temperatures up to 200°C, the effect of several factors affecting intergranular attacks of pure Al was studied. The results were: (1) Purity of Al: By the short time tests of 99, 99.9 and 99.99%Al, it is ovserved that the higher the purity of Al, the lower is the corrosion resistance in addition,the severer is the preference of intergranular attack. Particularly, 99%Al is resistant because of its uniform oxide formation. (2) Crystal grain size: In the case of 99.99%Al, a fine-grained specimen is less resistant than a coarse-grained, for the individual boundaries of both specimens are penetrated to the same extent. (3) Atomosphere: Intergranular corrosion is almost suppressed under oxygen atomosphere, while under hydrogen atmosphere, it is promoted. (4) pH of water: The total amount of corrosion is minimized when pH of water is lowered down to 3 and intergranular attacks do not occur under such condition. (5) Cold working: The distribution of slip defects formed by plastic deformation alters corrosion interfaces so that higher rolling reduction causes disappearance of intergranular attack but promotes break-down of oxide. These examinations are extended to the interactions between such defects and atomospheric gases. From the all over results, the corrosion mechanisms are discussed in relation to hydrogen hypothesis.