Heat treatment effect on the corrosion behaviour of black passivated ZnNi alloys

Electrochemical corrosion behaviour of ZnNi and black passivated ZnNi alloys in aerated and partially deaerated 5% NaCl solution was studied using dc and ac techniques. The heat treatment (24 h, 120 °C) effect on black CCC properties was analyzed. No changes in the Rp values were observed, but differences in the potentiodynamic curves and in EIS diagrams suggested a change in the corrosion mechanism. Comparative studies by AFM and electrochemical techniques showed that these changes in the corrosion behaviour could be explained by taking into account the different effect of heat treatment on the inner and outer layers of the CCC.