镁合金稀土转化膜技术是近年来发展起来的一种环保型镁合金表面处理新技术.通过正交试验对压铸镁合金AZ91D稀土镧化学转化处理工艺进行了研究.利用扫描电子显微镜(SEM)、能量色散谱(EDS)和X射线光电子能谱(XPS)研究了膜层的表面形貌及其组成,并通过容量法对膜层在5%NaCl(pH=6.8～7.0)溶液中的耐腐蚀性能进行了研究.结果表明:La转化处理工艺能够在压铸镁合金AZ91D表面形成均匀、完整的转化膜;膜层主要由La2O3和MgO以及少量的A2O3组成;La转化膜在浸泡初期的10 h内耐腐蚀性能与铬酸盐转化膜相当.
Rare earth conversion coatings on magnesium alloys have been developed as an environmental-friendly surface treatment technology for magnesium alloys. The process of rare earth lanthanum conversion coating for magnesium alloy AZ91D was studied by using orthogonal test. The surface morphology and composition of lanthanum conversion coating were studied by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of magnesium alloy in 5% NaCl solutions with pH 6.8～7.0 was analyzed by evolving hydrogen gas measurement. The results showed that uniform coating by the process of lanthanum conversion was obtained on Mg alloy. The lanthanum conversion coating was mainly composed of MgO, La2O3 and a little amount of Al2O3. During immersion in 5% NaCl solution for 10 h, the corrosion resistance of lanthanum conversion coating was comparable with that of chromate conversion coating.
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