純アルミニウムの耐食性に及ぼすガリウムの影響

Abstract

The degradation of the corrosion resistance was investigated by measurements of polarization curves and potentiostatic or immersed corrosion testes of pure aluminum containing a small amount of Ga as an impurity. The surfaces were observed by SEM and corrosion products were analyzed by EADX of pits of the specimens corroded in the solution of dilute H2SO4 and H2SO4–NaCl at 303 K. The anodic current density of Al–X mass%Ga alloys (X=0 to 0.2 mass%) in a dilute H2SO4 solution under a potentiostatic condition increases with increasing Ga content in the alloys, resulting in the degradation of the uniform corrosion resistance. The pitting potential Epit of the Al–X mass%Ga alloys in the mixed solution of H2SO4–NaCl shifts to a more basic potential with increasing NaCl concentration and Ga content in the alloys. The apparent pitting dissolution rates increase with increasing Ga content in the alloys. The pitting corrosion resistance is thus reduced also. The eflfect of Ga content on the degradation of resistance to the uniform and pitting corrosion is, however, rather small while the Ga content is below 0.02 mass%. The Ga content should be kept less than 0.02 mass% in the pure aluminum.