Acta Phys. -Chim. Sin. ›› 2008, Vol. 24 ›› Issue (08): 1465-1470.doi: 10.3866/PKU.WHXB20080823

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Preparation and Electrochemical Properties of Trivalent Chromium Coating on 6063 Aluminium Alloy

YU Hui-Cheng; CHEN Bai-Zhen; SHI Xi-Chang; LI Bing; WU Hai-Ying   

  1. School of Metallurgical Science and Engineering, Central South University, Changsha 410083, P. R. China; Center of Modern Testing and Analysis, Central South University, Changsha 410083, P. R. China; Guangzhou Non-Ferrous Metal Research Institute, Guangzhou 510651, P. R. China
  • Received:2008-02-29 Revised:2008-04-22 Published:2008-08-06
  • Contact: YU Hui-Cheng

Abstract: Chromium (Cr3+) conversion coating was prepared on 6063 aluminium alloy using chromic potassium sulfate and phosphoric acid. Tafel polarization curves and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical properties of the coating formed under different conditions. The optimum conditions were obtained as following: temperature was 30-40 ℃, deposition time 9 min, the pH was adjusted to 2.0-3.0, the KCr(SO4)2 and H3PO4 concentrations were controlled within 15-25 g·L-1 and 10-20 g·L-1, respectively. The polarization result showed that the coating had more positive corrosion potential (Ecorr) and pitting corrosion potential (Epit), and lower corrosion current density (icorr), indicating that the coating formed under the optimum conditions had better corrosion resistance. To explain the electrochemical properties of the coating, a simple equivalent circuit was designed. Electrochemical parameters of EIS, such as the resistance (Rcoat) and capacitance (Ccoat), the charge transfer resistance (Rct) and double layer capacitance (Cdl), were obtained by fitting the EIS plots. The results of EIS were in good agreement with those of Tafel polarization curves.

Key words: Conversion coating, Aluminumalloy, Trivalent chromium, Electrochemistry, Corrosion resistance


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