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INTRODUCTION

MANYmodem

aluminum alloys have shown significant susceptibility to hydrogen damage and have been the subject of extensive study. I~-6] Relatively pure aluminum has been shown to be comparatively insensitive to gaseous hydrogen environments t7'Sj and only slightly susceptible to other forms of hydrogen degradation,j91 although the subject has not received nearly the same sort of attention as aluminum alloys. The lack of information on the effects of hydrogen on pure aluminum has limited understanding of the hydrogen effects in commercial alloys. One of the few studies on the mechanical effects showed that aluminum (99 pct purity) can be susceptible to intergranular fracture and blister formation when exposed to humid air at 450 ~ I91 When they looked at the interior surfaces of the blisters, they observed that the blisters had formed intergranularly and that little plastic deformation had accompanied their formation. They also reported that the hydrogen exposure did not appreciably affect the tensile properties nor the fracture process, which was microvoid coalescence. Stress corrosion cracking of aluminum alloys has been extensively studied, although in this case as well, the studies have been confined to aluminum alloys. These studies have shown that hydrogen can play a critical role in the SCC of aluminum alloys, though its exact role remains in dispute. [10.m Cathodic charging represents the most severe charging environment and hence the most deleterious effects on properties. Cathodic hydrogen embrittlement in high strength alloys has been studied, in particular with regard to heat treatment, [4'61test temperature, I1'2'4'61and strain rate. I~2'131To the authors' knowledge there exist no studies on the effects of cathodic charging on the mechanical properties of pure aluminum. The present study represents the first effort to determine the effects of cathodically charged hydrogen on the mechanical properties, tensile and microhardness tests, and on the TEM microstructural changes in pure aluminum. J.W. WATSON, formerly Graduate Student, Department of Materials Science and Engineering, Northwestern University, Evanston, IL, is Research Engineer, ARMCO, Inc., Middletown, OH 45043. M. MESHII, Professor, is with the Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208. Y.Z. SHEN, deceased, was a Visiting Scholar, Department of Materials Science and Engineering, Northwestern University, from Shanghai Internal Combustion Engine Research Institute, Shanghai, People's Republic of China. Manuscript submitted October 30, 1987. METALLURGICALTRANSACTIONSA

II.

EXPERIMENTAL

Pure aluminum (99.99 pct) was supplied as cold rolled sheet from Alcoa. The samples were vacuum annealed for 3 hours at 600 ~ prior to cathodic hydrogen charging. This resulted in a grain size between 250 and 500/~m. The cathodic charging was carried out in a solution of 75 pct methanol, 22.4 pct water, 2.6 pct sulfuric acid, and contained 10 mg/l arsenic trioxide, a recombination poison. The sample