直流电沉积锌镍镀层钕铁硼的抗腐蚀性及镀层结合力研究

Corrosion Resistance and Mechanical Properties of ZnNi Coatings Deposited by DC Electrodeposition on NdFeB Surface

为了提高钕铁硼材料在不同使用场景中的抗腐蚀能力和镀层结合力,采用醋酸盐型锌镍合金镀液在钕铁硼磁体表面直流电沉积制备了锌镍合金镀层,使用扫描电镜、能谱仪和X射线衍射仪分析镀层形貌、成分和相结构,采用显微硬度仪和万能材料试验机测试镀层的硬度和膜基结合力。实验结果表明,所制备的镀层均为γ相Ni5Zn21,部分镀层还含有少量的单相Ni。其抗腐蚀能力和结合力随着沉积电流密度和沉积温度的提高先增大后减小,电沉积电流密度为15 mA/cm2、温度50℃时制备的Zn-Ni合金镀层表面致密,其晶粒尺寸最小为39 nm,硬度最高为550 HV,膜基结合力最高为13.1 MPa,通过电极化曲线测得的该镀层自腐蚀电流最低为4 uA/cm2,较基体缩小15倍,其耐蚀性也最佳。适当地提高电流密度和沉积温度能增强阴极极化提高形核率,细化镀层的晶粒尺寸,使镀层更加致密从而使其抗腐蚀性能、硬度和结合力得到提高。与粗糙的基体表面相比,抛光基体有利于镀层与基体间的相互作用和外延生长,使镀层晶粒细致、表面平整,使膜基结合力从7.12 MPa提高到12.52 MPa,自腐蚀电流从最高34 uA/cm2降低到11 uA/cm2,抗腐蚀性能明显提高。

In order to improve the corrosion resistance and coating adhesion of NdFeB material in different circumstances, Zn-Ni alloy coating was prepared by direct current electrodeposition on the surface of NdFeB material using acetate Zn-Ni alloy plating solution. The morphology, composition and phase structure of the coating were analyzed by SEM, EDS and XRD. The hardness and film-based adhesion of the coating were tested by microhardness tester and universal material tester. The results show that the prepared coatings are γ Phase Ni5Zn21, part of the coating also contains a small amount of single-phase Ni. Its corrosion resistance and adhesion first increase and then decrease with the increase of the deposition current density and deposition temperature. The surface of the Zn-Ni alloy coating prepared at 50˚C using an electrodeposition current density of 15 mA/cm2 is compact. It obtained the minimum grain size of 39 nm, the maximum hardness of 550 HV, and the maximum film-based adhesion force of 13.1 MPa. The measured electropolarization curve of this coating showed the minimum self-corrosion current of 4 uA/cm2, which is 15 times smaller than the self-corrosion current of the substrate. Its corrosion resistance is also the best. Proper increase of current density and deposition temperature can enhance the cathodic polarization, improve the nucleation rate, refine the grain size of the coating, make the coating more compact, and improve its corrosion resistance, hardness and adhesion. Compared with the rough substrate surface, the polished substrate is conducive to the interaction and epitaxial growth between the coating and the substrate, making the coating grain fine and the surface smooth, improving the film-base bonding force from 7.12 MPa to 12.52 MPa, and reducing the self-corrosion current from the maximum 34 uA/cm2 to 11 uA/cm2, and significantly improving the corrosion resistance.