三角形铝件微弧氧化膜层不均匀之因探讨

Causes Leading to Inhomogeneity of Micro-Arc Oxidation Coatings on Aluminum Substrates with Regular Triangular Shapes

微弧氧化膜层表面不均匀会对其应用产生影响,过去对其产生的原因研究很少。利用自制的微弧氧化电源在恒压模式下于硅酸盐电解液中对边长为100 mm的正三角形纯铝件进行微弧氧化处理,利用涡流测厚仪、SEM分析以及电化学分析等对三角形顶角区域、边缘中心区域和中心区域的膜层厚度、形貌和性能不均匀性进行了表征。结果表明:微弧氧化层的相组成几乎没有差别,但膜厚分布不均匀,顶角区域膜厚最大,中心区域膜厚最小,两者相差约20%;顶角区域微孔数量较中心区域少,但孔径较大;顶角区域的耐蚀性优于边缘中心,边缘中心优于试样中心,这是试件边角处电场弯曲造成的强烈放电的结果;随着氧化时间的延长,试样不同区域放电程度差别减小,从而导致膜层的不均匀程度减小。

AI substrates with regular triangular shapes(side length of 100 mm) were micro-arc oxidized in silicate electrolyte in constant voltage mode using a home-made micro-arc oxidation(MAO) power supply.The thickness,microstructure and corrosion resistance of the MAO coatings were investigated using a vortex thickness gauge,a scanning electron microscope and an electrochemical test rig.It was found that as-prepared MAO coating had nearly uniform phase composition,but its thickness varied greatly along with varying locations.Namely,the thickness at the corner was the largest,while that at central region was the smallest,showing a difference of about 20%.In the meantime,as compared with the central region,the corner had fewer and larger micro-pores.In terms of the locations,the corrosion resistance of the MAO coating was ranked as corner zone > edge zone > central zone,and this result was attributed to the intensive discharge at the corner zone caused by bending effect of electric field.Besides,with the increase of processing time,the difference of discharge degree at different sites was decreased,leading to deceased inhomogeneity of the MAO coating.