针对钕铁硼器件现有Ni/Cu/Ni镀层防护体系存在的磁性能衰减问题,用碱性HEDP络合剂镀液在钕铁硼磁体表面直接电沉积铜层,并在其上电镀镍,构成Cu/Ni镀层防护体系代替通常的Ni/Cu/Ni镀层体系.通过电化学测试研究镀铜液中HEDP络合剂浓度对铜沉积过程的影响;应用SEM,XRD,TEM对铜层微观形貌进行了表征;分别用热震实验和热减磁实验对铜层结合力和钕铁硼器件的热减磁性能进行测试.结果表明: 镀铜溶液中HEDP对铜离子沉积过电位影响较大,铜晶粒在钕铁硼晶界处优先沉积,并以(111)晶面取向为主;钕铁硼磁体上镀铜层结构致密,与钕铁硼的结合力良好,满足SJ 1282-1977的要求;Cu/Ni镀层体系的钕铁硼热减磁衰减率相比于Ni/Cu/Ni镀层显著减小.
To decrease the impact of the regular Ni/Cu/Ni coating on the magnetic performance of sintered NdFeB device, alkaline system of HEDP complexing agent was applied to directly electro-deposit copper layer on NdFeB matrix, then nickel layer was electrodeposited on the copper layer and Cu/Ni coating was finally obtained to replace the regular Ni/Cu/Ni coating.The influence of concentration of HEDP complexing agent on deposition course was tested by electrochemical testing;morphology of copper layer was characterized by SEM, XRD and TEM;the binding force of copper layer and the thermal reduction of magnetic of NdFeB caused by electrodeposited coating were respectively explored through the thermal cycle test and thermal demagnetization test.The results show that the concentration of HEDP has great impact on the deposition overpotential of copper.In the initial electrodepositing stage, copper particles precipitate at the grain boundaries of NdFeB magnets with a preferred (111) orientation.The copper layer is compact and has enough binding force with the NdFeB matrix to meet the requirements in SJ 1282-1977.Furthermore, the thermal demagnetization loss rate of the sintered NdFeB with the protection of Cu/Ni coating is significantly less than that with the protection of Ni/Cu/Ni coating.
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