球墨铸铁微弧氧化陶瓷层扩散退火前后的组织状态

Microstructure of Micro-Arc Oxidation Ceramic Coatings on Ductile Iron before and after Diffusion Annealing

过去,对铸铁件热浸镀铝再微弧氧化仅有少量的研究,且还存在残留铝影响氧化层性能的问题。为此,对球墨铸铁先热浸镀铝后再微弧氧化形成陶瓷层,采用扫描电镜、能谱分析和X射线衍射分析了陶瓷层的相组成及形貌,并探讨了对陶瓷层进行扩散退火处理的可行性。结果表明:球墨铸铁浸镀铝后微弧氧化获得的陶瓷层主要由α-Al2O3相和γ-Al2O3相组成;600℃扩散退火时,因陶瓷层与纯铝层之间热膨胀系数不匹配会导致界面处产生热应力,造成陶瓷层与纯铝层的界面处出现明显孔洞;球墨铸件微弧氧化形成的陶瓷层不适合扩散退火处理;对微弧氧化后,热浸镀铝层剩下多少为佳及处理的问题,应进一步研究。

Ceramic coating was prepared on the surface of ductile iron by hot-dip aluminizing in association with micro-arc oxidation.The phase composition and morphology of the ceramic coating were analyzed by means of scanning electron microscopy,energy-dispersive spectrometry and X-ray diffraction.Moreover,the feasibility to conduct diffusion annealing of the ceramic coat-ing was discussed.Results show that the ceramic coating formed on ductile iron after hot-dip aluminizing and micro-arc oxidation is mainly composed of α-Al2O3 and γ-Al2O3.After being diffu-sion annealed at 600℃,thermal stress and pores were generated at the interface of the hot-dip aluminizing layer and micro-arc ox-idation ceramic layer because of mismatched thermal expansion coefficient.This means that the micro-arc oxidation ceramic coat-ing grown on hot-dip aluminizing layer can not be diffusion an-nealed,otherwise its microstructure and performances will be de-structed.