铝合金表面稀土转化膜性能与耐蚀机理研究

Study on Performance and Corrosion Resistance Mechanism of Rare Earth Metal Conversion Coating on Al Alloy Surface

摘要:

在全面分析国内外稀土转化膜的研究成果和存在问题的基础上，结合前期稀土对铝合金缓蚀机理、成膜机理研究成果，对含氧化促进剂的化学方法形成的稀土铈转化膜进行了研究。采用扫描电子显微镜（SEM）、X射线散射能谱分析（EDS）和X射线衍射（XRD）分析、X射线光电子能谱（XPS）的Survey谱图分析转化膜的主要成分和铈的价态。结果表明：铝合金表面稀土转化膜主要由非晶态的四价Ce氧化物/氢氧化物和铝氧化物的混合物组成；在整个转化膜中Ce元素总体分布均匀；转化膜致密均匀，局部镶嵌一些富含Ce沉积物。电化学研究证明，在NaCl溶液中含氧化促进剂H2O2形成致密的非晶态的铈转化膜能够阻止水和Cl离子在转化膜中的渗透，同时抑制了铝合金表面发生电化学腐蚀的阴极过程和阳极过程，稀土转化膜产生点蚀后还具有一定的自修复能力。

Abstract:

Based on an overall review of the research achievements and the problems of rare earth metal conversion coatings for aluminum alloys at home and abroad and combined with our early study of aluminum alloy’s inhibition mechanism and coating formation mechanism, this paper studied the chemically formed cerium conversion coatings on aluminum alloys with the aid of oxidation accelerator. The morphology and the structure and the composition of rare earth metal conversion coating were investigated by scanning electron microscope (SEM) and X-ray energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that rare metal conversion coating on B95 surface formed by Ce(III) is mainly composed of Al and the Ce oxides, the Ce oxides are mainly made up of Ce(IV)(CeO2 and Ce(OH)4 compounds. During the whole process, Ce is distributed evenly; the conversion coating is compact and even. Some deposits rich in Ce stay locally. The conversion coating is non-crystal structure. The mechanism of the corrosion resistance of the coating was studied by electrochemical methods together with scanning electron microscope (SEM) and X-ray diffraction (XRD). The results indicate that H2O2 helps to make the conversion coating on the B95 surface becoming more compact and non-crystal structure , it is able to prevent water and Cl+ from permeating the conversion coating, it will inhibit simultaneously both the cathodic and anodic reactions of corrosion on the alloy surface. The rare earth conversion coating still retains the self-rehabilitation ability after pitting.