缸体铸件表面异常锈斑的产生原因及解决措施

Causes and Solutions of the Abnormal Rusty Spots on 4DA Cylinder Casting Surface

4DA缸体铸件清理抛丸后,曲轴箱内腔面在短时间内出现大量斑点状锈斑。通过对锈斑形貌、化学成分和铸造工艺的分析,认为二次随流孕育过程中,Si-Ba孕育剂未完全熔化,部分残留物富集在铸件的特定表面。残留偏析的Ba与H2O反应生成碱性物质,并在涂料、砂芯、树脂等因素的共同作用下而产生的去极化作用促进了铸铁表面的电化学腐蚀过程,形成以残留Ba为中心、外围为氧化铁的腐蚀锈斑。取消Si-Ba二次孕育或用75Si-Fe代替作为随流孕育剂,可以消除异常锈斑的产生。

In several hours after shot-blasting, a large number of rusty spots emerged on the inner surface of 4DA cylinder casting. By comparing the morphology and chemical composition between the rusty spots and the normal surface, and analyzing the casting process, it is believed that during the post inoculation, Si-Ba inoculant is not completely melted into the melt, and some residues enriched on the casting surface. Ba in the residues reacts with H2O, which generates Ba（OH）2. The alkaline environment, interaction with water based coats and the core resin, causes the depolarization action to promote electrochemical corrosion on the iron surface. It can eliminate abnormal rusty spots to utilize 75Si-Fe metal-stream inoculation as a substitute for Si-Ba.