1994 Volume 43 Issue 3 Pages 139-146
Anodic polarization behavior of Al-4.5Mg-0.3Cu alloy was studied in 0.008, 0.04 and 0.2g/l NH4F solutions and compared with that of pure aluminum at room temperature. It was found that fluoride ions stimulate the anodic dissolution of the aluminum alloy and pure aluminum and that the anodic dissolution is controlled by fluoride ion transport process. The higher the NH4F concentration, the larger the dissolution current density. The pitting potential increases as the concentration of NH4F increses, and at the same time the density of pits increases. It seems that the pits initiate at the precipitates of intermetallic compounds (Al3(Fe, Cu), Al6(Fe, Cu)) under the anodic polarization and that the amount of the compounds exposed on the alloy surface increases in highly concentrated NH4F solution. Higher pore density at higher F- concentrations can be explained in terms of the exposure of intermetallic compounds.