分析了锌酸盐镀锌彩钝层所出现的类似于铵盐镀锌彩钝层的变色现象.其直接原因是钝化层中夹杂的有机物造成存放期间六价铬盐转化为紫色的三价铬盐.锌酸盐镀锌彩钝层的变色受添加剂种类及其在镀液中的含量,工艺采用的阴极电流密度,镀后出光及钝化质量等因素的影响.将工件置于压力锅中蒸煮,可提前判定是否会变色.
The tarnishing of iridescent passivation coating on zinc by zincate zinc plating, which is similar to that by ammonium salt zinc plating, was analyzed. The immediate cause is the conversion of hexavalent chromium to purple trivalent chromium during the storage due to the incorporation of organic impurities. The tarnishing of iridescent passivation coating on zincate zinc plated coating is affected by the type and dosage of additives in plating bath, cathodic current density applied, and quality of bright dipping and passivation. The tarnishing can be predicted by boiling workpiece in pressure cooker.
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