汽车发动机缸盖用铝合金的稀土转化工艺与膜层的腐蚀行为研究

Process and Corrosion Behavior of Rare Earth Conversion Coatings on Aluminum Alloy for Automobile Engine Cylinder Head

为了促进稀土转化膜在汽车发动机缸盖用LY12铝合金领域的应用,通过条件试验在LY12铝合金表面优选稀土Ce盐转化工艺,通过电化学腐蚀、扫描电镜、能谱分析等方法研究了最优稀土转化膜的耐腐蚀性和微观形貌。结果表明:LY12铝合金经过固溶+时效处理后,析出的第二相可作为稀土转化膜成膜的阴极相,有利于稀土转化膜的形成,提高了稀土转化膜的成膜速率。短时的碱洗活化有利于稀土转化膜的形成,考虑到快速成膜的要求,优先选择CeCl3溶液进行成膜。同时针对CeCl3成膜体系下膜层的龟裂问题,提出了双层稀土转化膜工艺,有效地解决了快速成膜过程中出现的膜层龟裂问题。电化学分析表明,经过双层转化膜加CeCl3+C6H5COONa+磷酸盐封闭处理的LY12铝合金具有最佳的耐腐蚀性能。

In this paper,the application of rare earth conversion coating process on LY12 aluminum alloy for automobile engine cylinder head was studied through experiments.The corrosion resistance and microscopic morphology of rare earth conversion coatings were studied by electrochemical corrosion,scanning electron microscopy and energy spectrum analysis.Results showed that after the solid solution and aging treatment of LY12 aluminum alloy,the precipitated second phase could be used as the cathode phase of the rare earth conversion coating film,which was beneficial to the formation of rare earth conversion coating and the improvement of the film formation rate.Moreover,short-time alkaline washing activation was beneficial to the formation of rare earth conversion coating.Considering the requirements of rapid film formation,CeCl3 solution was preferred for film formation.At the same time,in order to solve the cracking problem of the lower layer of CeCl3 film-forming system,a double-layer rare earth conversion film process was proposed.Electrochemical analysis showed that the LY12 aluminum alloy after the application of double-layered conversion film plus CeCl3+C6H5COONa+phosphate sealing treatment had the best corrosion resistance.