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PREPARATION, STRUCTURE AND CORROSION RESISTANCE OF CHROME-FREE PHOSPHATE FILM FOR MAGNESIUM ALLOY AZ31 |
CUI Xuejun1,2,3, ZHOU Jixue3, WANG Xiuchun3 |
1. Materials Corrosion and Protection Key Laboratory of Sichuan Province, Zigong 643000
2. College of Materials and Chemical Engineering, Sichuan University of Science and Engineering, Zigong 643000
3. New Materials Institute of Shandong Academy of Sciences, Ji'nan 250014 |
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Abstract An environment-friendly phosphate film was obtained on the AZ31 magnesium alloy surface via chemical deposition methods. The morphology, compositions and phase compositions of the film were examined using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD). The results show that a dense, uniform and crack-free phosphate film can be prepared using the solution with free of chromate, fluorides and nitrite. The phosphate films are mainly composed of MnHPO4•2.25H2O, The film thickness is between 12 μm and 15 μm and the compositions consist of O, Mg, P, Mn and Al. the film hardly appears corrosion phenomenon for 72 h in the neutral salt spray test (NSS), and the time could arrive 204 h after the plus paint. The test results indicate that the phosphate film is of good corrosion resistance. Potentiodynamic polarization curves prove that the Ecorr with the film is shifted positively 111 mV (vs. SCE); the Icorr is decreased at least by three orders compared with that of the bare substrate AZ31 respectively. The results show also that the existence of the film has a great inhibitive action on anodic dissolution and restraint action on the cathodic hydrogen evolution, which will effectively improve the corrosion resistance for magnesium alloy AZ31.
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Received: 19 October 2010
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Corresponding Authors:
CUI Xuejun
E-mail: cxj_2046@163.com
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