Corrosion of Zn-Ni Alloy Films Electroplated on Iron

The corrosion behavior of inhomogeneous Zn-Ni alloy films electroplated on iron substrates specimens has been studied. Zn-Ni alloy was electroplated in a Hull cell, and immersion tests were carried out in 3% NaCl solutions and in pH6 buffer solutions. In both solutions corrosion took place heterogenously and caused grooves. In the 3% NaCl solutions, both red rust and white rust were formed, the red rust appearing only in a thick layer region, while in the buffer solutions, rust formation was not observed. Corrosion potential and pH at various positions on the specimen were measured. In the 3% NaCl solutions, pH changed markedly depending on position, while in the buffer solutions, the corrosion potential changed. This indicates that a macroscopic corrosion cell is formed along the specimen, and that the buffer capacity of the solutions affects the corrosion behavior.