汽车制动卡钳酸性镀锌及锌镍合金的性能

Properties of environmentally friendly acid zinc and zinc–nickel alloy electroplating for automobile brake caliper

通过扫描电镜观察了汽车制动卡钳在前处理、酸性镀锌和锌镍合金、三价铬钝化以及封闭后的表面形貌,采用金相显微镜测量了镀层厚度,以中性盐雾试验和湿热试验考察了电镀后制动卡钳的耐蚀性。结果表明,钝化后锌和锌镍合金镀层的外观、厚度、附着力、耐湿热性和六价铬含量均满足要求,酸性镀锌可满足耐热冲击腐蚀试验(即150°C保温2 h后再做中性盐雾试验)144 h白锈≤5%、480 h无红锈的要求,酸性镀锌镍合金可满足耐热冲击腐蚀试验240 h白锈≤5%、720 h无红锈的要求。酸性锌镍合金镀层比酸性锌镀层更致密,防腐蚀性能明显更优。

The surface morphology of automobile brake caliper after pretreatment, acid Zn and Zn-Ni alloy electroplating, trivalent chromium passivation and sealing was observed by scanning electron microscopy （SEM）. The coating thickness was measured by metallograph. The corrosion resistance of electroplated brake caliper was examined by neutral salt spray test and damp heat test. The results showed that the appearance, thickness, adhesion strength, damp heat resistance and hexavalent chromium content of the passivated Zn and Zn-Ni alloy coatings meet the requirements. Acid zinc electroplating can achieve white rust area 〈5% for 144 h and no red rust for 480 h in neutral salt spray test after baking at 150℃ for 2 h, while acid Zn-Ni alloy electroplating can achieve white rust area 〈5% for 240 h and no red rust for 720 h. The Zn-Ni alloy coating is more compact and has better anticorrosion performance than the Zn coating.