针对热镀锌板三价铬钝化膜发白的问题,通过色差仪和中性盐雾试验检测了钝化膜的耐污渍性和耐蚀性,采用光学显微镜、扫描电镜及能谱仪分析了钝化膜的微观形貌和元素成分.结果表明:与正常试样相比,发白试样的耐污渍性和耐蚀性较差,钝化发白主要缘于涂覆辊磨削纹引起的膜层不均匀和固化温度偏低导致的疏松多孔结构.通过提高辊面研磨精度,优化辊涂工艺,提高固化温度等措施,因钝化发白造成的不合格率由1.2%降低至0.1%以下.
To solve the whitish defect of trivalent chromium passivation film on hot-dip galvanized steel sheet, the stain and corrosion resistance of passivation film were examined by color difference measurement and neutral salt spray testing. The microscopic morphology and elemental composition of passivation film were analyzed using optical microscope (OM), scanning electron microscope (SEM), and energy-dispersive spectrometer (EDS). The results showed that the stain and corrosion resistance of the whitish samples was worse than that of the normal ones. The whitish defect was mainly resulted from the nonuniform film formation due to the grinding texture of coating roller and the porous structure caused by curing at insufficiently high temperature. The failure rate related to whitish defect was decreased from 1.2% to less than 0.1% by taking the following measures: improving the grinding accuracy of coating roller, optimizing the grinding process, and increasing the curing temperature.