| HUA Tian-shun,SONG Ren-guo,ZONG Yu,CAI Si-wei.Corrosion Behavior of 7050 Aluminum Alloy after Micro-arc Oxidation under Constant Load in NaCl Solution with Different pH Values[J],49(5):269-278 |
| Corrosion Behavior of 7050 Aluminum Alloy after Micro-arc Oxidation under Constant Load in NaCl Solution with Different pH Values |
| Received:May 13, 2019 Revised:May 20, 2020 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2020.05.032 |
| KeyWord:AA7050 aluminum alloy stress corrosion MAO EIS constant load |
| Author | Institution |
| HUA Tian-shun |
a.School of Materials Science and Engineering, b.Jiangsu Key Laboratory of Materials Surface Science and Technology, Changzhou University, Changzhou , China |
| SONG Ren-guo |
a.School of Materials Science and Engineering, b.Jiangsu Key Laboratory of Materials Surface Science and Technology, Changzhou University, Changzhou , China |
| ZONG Yu |
a.School of Materials Science and Engineering, b.Jiangsu Key Laboratory of Materials Surface Science and Technology, Changzhou University, Changzhou , China |
| CAI Si-wei |
a.School of Materials Science and Engineering, b.Jiangsu Key Laboratory of Materials Surface Science and Technology, Changzhou University, Changzhou , China |
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| Abstract: |
| The paper aims to study the effect of pH value on corrosion behavior and corrosion resistance of aluminum alloy after micro-arc oxidation under constant load. The stress corrosion behavior of 7050 aluminum alloy (AA7050) after micro-arc oxidation in 3.5wt% NaCl solution with different pH was studied with a constant load stress ring. The potentiodynamic polarization curve and in-situ electrochemical impedance spectroscopy (EIS) were used to evaluate the effect of pH value on corrosion resistance of aluminum alloy after micro-arc oxidation under constant load and the corrosion process of coating in 3.5wt% NaCl solution with different pH. The corresponding equivalent circuit model was established. After the constant load tests, the coating on the surface of the specimen in the solution at pH 7 was almost complete, and it was covered with a layer of corrosion products. The coating on the surface of the specimen in the solution at pH 3 was corroded. The coating on the surface of the specimen in the solution at pH 13 was completely fallen off. At the initial stage of corrosion, the low frequency impedance modes of MAO specimens in solution at pH 3, 7 and 13 were 35 000, 90 000, 500 Ω•cm2, respectively. Their corrosion potential and corrosion current were –1.41, –1.43, –1.46 V and 2.85×10–5, 9.17×10–6, 1.75×10–4 A/cm2, respectively. After constant load test, the elongation of MAO specimens in solution with pH 3, 7 and 13 were 3.41%, 3.98%, 1.63%, respectively. The pH value of solution had a significant effect on the corrosion resistance and plasticity of aluminum alloy after MAO under constant load. The corrosion resistance and plasticity of AA7050 after MAO was the best in solution pH 7, intermediate in solution pH 3 and least in solution pH 13. According the corrosion behavior of EIS, the whole corrosion stage was divided into three stages: initial stage, middle stage and later stage. At the initial stage of corrosion, the corrosion resistance of the MAO specimens decreased at first and then increased. In the middle stage of corrosion, the corrosion resistance decreased at first and then stabilized, while the coating of the MAO specimen in solution at pH 13 was completely exfoliated during the middle stage of corrosion. At the later stage of corrosion, the corrosion resistance of MAO specimens in solution with different pH decreased again. |
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