目的：通过共生沉积技术将α-Al2 O3微粒引入到铸造Al-Si合金微弧氧化膜中,并研究其对膜层耐蚀性的影响。方法利用SEM和XRD分析α-Al2 O3微粒对微弧氧化膜微观结构及成分的影响。通过极化曲线、交流阻抗谱及中性盐雾试验评价膜层的耐蚀性。结果α-Al2 O3微粒复合改变了微弧氧化膜的组成及结构。微弧氧化膜呈双层结构,表面存在大量微孔,主要组成为γ-Al2 O3；加入α-Al2 O3微粒后,微弧氧化复合膜的表面微孔大幅减少,致密度提高,且膜层中α-Al2 O3相增多。此外,α-Al2 O3微粒复合改善了微弧氧化膜的耐蚀性。微弧氧化膜在质量分数为3.5%的NaCl溶液中的自腐蚀电流密度约为1.476×10-5 A/cm2,多孔层电阻Rp及阻挡层电阻Rb分别为0.259 kΩ·cm2及69.18 kΩ·cm2,耐盐雾试验时间为1200 h。加入α-Al2 O3微粒后,微弧氧化复合膜的自腐蚀电流密度仅为微弧氧化膜层的28%, Rp大幅增加至274.5 kΩ·cm2,且Rb 也上升了一个数量级,耐盐雾试验时间可达1440 h。结论α-Al2 O3微粒的引入可以大幅提高铸造Al-Si合金微弧氧化膜的耐蚀性。
ABSTRACT:Objective To study the effect of α-Al2 O3 microparticles on the corrosion resistance of composite ceramic coatings formed on Al-Si cast alloy by microarc oxidation ( MAO) in electrolyte. Methods SEM and XRD analysis were used to study the effect of α-Al2 O3 particles on the micro structure and composition of coating. Through the polarization curve, ac impedance spec-troscopy and neutral salt spray test, the corrosion resistance of coating was evaluated. Results The results showed that the incorpo-ration of α-Al2O3 microparticles changed the microstructure and phase composition of microarc oxidation (MAO) coating. The MAO coating had double-layer structure and was porous, and the main phase composition wasγ-Al2 O3 . After addingα-Al2 O3 , the composite coating had much fewer micropores and enhanced compactness, with increased α-Al2 O3 phase in the coating layer. In addition,α-Al2 O3 particles also improved the corrosion resistance of the MAO coating. In the 3. 5wt.% NaCl solution, the corro-sion current density of MAO coating was 1. 476×10-5 A/cm2, the resistance of porous layer (Rp) and the resistance of barrier layer (Rb) of MAO coating were 0. 259 kΩ·cm2 and 69. 18 kΩ·cm2, respectively. The salt spray resistant test time was 1200 h. However, the corrosion current density of the composite coating after addition ofα-Al2 O3 microparticles was only 28% of that of the MAO coating. The resistance of porous layer (Rp) of the composite coating was 274. 5 kΩ·cm2, which was much higher than that of MAO coating. In addition, the resistance of barrier layer ( Rb ) of the composite coating was higher than that of the MAO coating by an order of magnitude, and the salt spray resistant test time was 1440 h. Conclusion α-Al2 O3 microparticles could effectively improve the corrosion resistance of MAO coating formed on Al-Si cast alloy.
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