Critical role of pretreatment on the corrosion resistance of Zr conversion coating on 6061 aluminum alloy: The combined effect of surface topography and potential difference between different phases

In this work, different pretreatment condition on AA6061 was investigated by altering the alkaline cleaning time in NaOH, the concentration and composition of acidic pickling solution, respectively. The corrosion resistance of ZrCC was evaluated, and the surface property of the pretreated surface was measured by SKPFM. Results demonstrate that a longer alkaline cleaning time is detrimental to the corrosion resistance of ZrCC since it will decrease the Volta potential difference (Delta E); the acidic pickling in HNO3 improves the corrosion resistance of ZrCC, but an increased concentration will not remarkably further improve the quality of ZrCC, due to the accompanying of increased Delta E; the addition of HF will lead to the overactivation of alloy surface since it will decrease Delta E and increase Delta H. An ideal pretreated surface shown exhibit a combination of mediate Delta H and high Delta E.