| XIE Zhi-hui.An Environmentally-friendly Process of Direct Electroless Nickel Plating on AZ91D Magnesium Alloy[J],44(2):24-28,47 |
| An Environmentally-friendly Process of Direct Electroless Nickel Plating on AZ91D Magnesium Alloy |
| Received:October 06, 2014 Revised:February 20, 2015 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2015.02.005 |
| KeyWord:magnesium alloy electroless plating pretreatment stability |
| Author | Institution |
| XIE Zhi-hui |
Chemical Synthesis and Pollution Control Key Laboratory of Sichuan Province,China West Normal University, Nanchong , China |
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| Abstract: |
| Objective To develop a chromium-free and stable direct electroless nickel plating (ENP) technology for magnesium alloy. Methods SEM, EDX, immersion test, polarization curves, scribe and grid test as well as the stability factor and deposition rate were used to compare the effects of the new and traditional processes on the characteristics of the performance of Ni-P coating and plating bath. Results The stability of the base solution with nickel sulfate as the main salt could be obviously improved when 0. 5 mg/ L of thiourea was added. A good corrosion morphology structure of the AZ91D magnesium alloy was achieved after pickling in a mixture of nitric acid and phosphoric acid. This specific surface structure could improve the mechanical adhesion between the substrate and the coating. The coating prepared using the new technology belonged to high-P coating, with a P content of about 11% . Compared to the bare magnesium alloy, the potentiodynamic polarization test in NaCl solution showed that the corrosion potential and the corrosion current density of the new coating increased positively from -1. 5 V to -0. 5 V and decreased by three orders of magnitude, respectively. Conclusion The corrosion resistance of coating obtained from a plating bath using nickel sulfate as the main salt was better than that from a plating bath using basic nickel carbonate as the main salt. The optimal pH and temperature of the ENP processes were 5 and 82 ℃ , respectively. |
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