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

• Published in: Surface & coatings technology 2019-11, Vol.377, p.124904, Article 124904
• Main Authors: Zhou, Peng, Liu, Yang, Liu, Lianhe, Yu, Baoxing, Zhang, Tao, Wang, Fuhui
• Format: Article
• Language: English
• Subjects: Alkaline cleaning; Aluminum alloy; Aluminum base alloys; Conversion coating; Corrosion resistance; Pickling; Pretreatment; Protective coatings; Sodium hydroxide; Surface properties; Volta potential; Zirconium
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2019.124904

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 (ΔE); 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 ΔE; the addition of HF will lead to the overactivation of alloy surface since it will decrease ΔE and increase ΔH. An ideal pretreated surface shown exhibit a combination of mediate ΔH and high ΔE. •Height difference (ΔH) and Volta potential difference (ΔE) were investigated.•Alkaline cleaning is necessary to improve the corrosion resistance of ZrCC.•A longer alkaline cleaning time will increase ΔH, while simultaneously decreases ΔE.•The increase of HNO3 concentration will simultaneously increase ΔH and ΔE.•HF is detrimental since it increases ΔH and decrease ΔE.•An expected pretreated alloy surface should exhibit a mediate ΔH and high ΔE.