ANODIC-DISSOLUTION CHARACTERISTICS OF AL- GA ALLOYS IN NACL CONTAINING DILUTE NAOH SOLUTION

The effect of Ga content on the characteristics of anodic dissolution behavior of Al-Ga alloys in a NaCl containing dilute NaOH solution was investigated by means of an electrochemical measurement of the polari zation curves, immersed corrosion tests and scanning electron microsco pic observations of the corroded surfaces for the alloys. The main res ults obtained are summarized as follows: (1) The anodic polarization c urves of Al-Ga alloys in the dilute NaOH solution show a typical activ e-passive transition, and the limiting anodic current density increase s with an increase in the concentration of NaOH and solution temperatu re. However, there is no effect of Ga content in the alloys on the lim iting anodic current of the alloys in the dilute NaOH solution. The ap pearent activation energy for anodic dissolution of the alloys is abou t 25.84 kJ/mol, and the dissolution rates of alloys are controled by t he mass-transport of OH ions through the boundary layer between the so lid and the liquid interface. The corrosion of the alloys is uniform. However, the selective dissolution of Al species from the grain bounda ry layer of Ga containing specimens is observed. (2) The pitting poten tials of Al-Ga alloys in the NaCl containing dilute NaOH solution depe nd upon the concentration of NaCl and the Ga content in the specimens. When the NaCl concentration and the Ga content in the alloys are incr eased, the pitting potentials are shifted to a more basic potential an d the pitting resistance of the alloys is decreased. The pitting corro sion rates also increase with increasing Ga content in the alloys in t he NaCl containing dilute NaOH solution.