烧结钕铁硼磁体表面Zn-Co合金镀层制备工艺与耐蚀性能

Technology and corrosion resistance of electrodeposited Zn-Co alloy coatings on sintered NdFeB magnets

采用氯化物镀液体系在钕铁硼磁体表面制备Zn-Co合金镀层,优化了Zn-Co合金镀层制备过程中的电镀工艺参数(镀液pH值、镀液温度、电流密度以及添加剂浓度),通过中性盐雾试验(NSS)、扫描电子显微镜(SEM)和动电位极化曲线,系统研究了Zn-Co合金镀层的显微组织及耐蚀性能。结果表明:烧结钕铁硼电镀Zn-Co合金镀层的最佳电镀工艺参数为:添加剂浓度为15 mL/L,pH值为4,电镀温度为25℃,电流密度为1 A/dm^2。在最佳工艺条件下制备的Zn-Co合金镀层经钝化后其耐中性盐雾时间可达120 h。合金镀层结构致密,有效填补了钕铁硼磁体的固有缺陷,为后期钝化形成致密钝化膜提供了材料基底基础。钝化后的Zn-Co合金镀层表面平整光亮,动电位极化曲线测试表明,相比Zn镀层,钝化后的Zn-Co合金镀层的自腐蚀电流密度下降了一个数量级,表明Zn-Co合金镀层钝化后具有更加优异的耐腐蚀性能。

Zinc-Cobalt(Zn-Co)alloy coating was deposited on sintered NdFeB magnet by eletroplating method in the chloride eletrolyte,and the electroplating parameters were optimized.The microstructure,corrosion resistance and mechanical properties of the samples were studied by neutral salt spray test(NSS)and scanning electron microscopy(SEM),potentiodynamic polarization curves and adhesion test.The results showed that the optimum parameters for preparing Zn-Co alloy coated NdFeB magnets were additive agent concentration of 15 mL/L,pH value of 4,electroplating temperature of 25℃and current density of 1 A·dm-2.The NSS time of passivated Zn-Co coated NdFeB magnets could reach 120 h.The alloy coating had dense structure,and could fill the inherent defects of NdFeB magnets effectively,resulting in a good foundation for the formation of dense passivation film.Surface of the passivated Zn-Co alloy coating was smooth and bright,and the corrosion current density was one order of magnitude lower than that of pure Zn coating,which meant the better corrosion resistance of the Zn-Co alloy coating.