灰铸铁缸体表面异常锈斑产生原因分析

Analysis on Causes of Abnormal Rusty Spots on Gray Cast Iron Cylinder Block Surface

基于发动机缸体在铸造成形后放置过程中出现异常锈斑且人工打磨后反复出现的问题,对缸体表面产生异常锈斑的原因进行了分析研究。通过对锈斑表面和截面两个方向研磨及显微观察发现,在每一异常锈斑的浅表面均存在着大小不等的夹渣。进一步的扫描电镜观察及能谱分析发现,这些夹渣是Ba、Ca、Al、S等外来元素的富集区。分析认为,二次孕育残存在铸件表面并与外界空气相连的夹渣起到了吸潮的作用,使冷芯砂中水分以及空气中的水分子聚集在夹渣附近,并与基体中的铁碳元素发生电化学反应导致了表面异常锈斑的产生。

Based on the problem that the abnormal rusty spots naturally appeared on the surface of the engine cylinder block after casting process and they were still repetitively formed even aiter being manually polished, analysis and research on the formation causes of the abnormal rusty spots on the surface of cylinder block were conducted. It is found that there lie slags underneath the abnormal rusty spots after grinding along the surface and the section of the rusty spots through microcosmic observing. Further analysis by scanning electron microscope observation and energy dispersive spectrometer reveals that these slags contain a great number of elements such as Ba, Ca, and Al elements. It is believed that the residual slags from post inoculation are exposed to ambient air and can absorb moisture. As a result, water molecules from both cold-core box and the ambient air together would likely to accumulate in the slags＇ neighboring area and lead to the electrical-chemical reaction with the Fe and C elements in the matrix, which causes the formation of abnormal rusty spots on the surface of cylinder block.