烧结NdFeB表面等离子喷涂Al防护涂层制备工艺及性能研究

Preparation Technology and Properties of Al Protective Coatings on the Surface of Sintered NdFeB Magnet Via Plasma Spray

目的 采用大气等离子喷涂工艺在烧结NdFeB磁体表面制备Al防护涂层,实现NdFeB磁体防护强化。方法 通过不同喷涂工艺制备Al涂层,采用扫描电子显微镜观测涂层表面、截面形貌和堆积厚度,利用垂直拉拔法测试最佳工艺下涂层的结合强度。喷涂不同厚度Al防护涂层,采用电化学工作站和中性盐雾腐蚀试验研究涂层的耐腐蚀性能,利用脉冲磁场磁强计对比分析喷涂Al涂层厚度对磁体磁性能的影响。结果 喷涂电流从400 A提高至600 A,当喷涂电流为500 A时,涂层表面致密,无明显溅射堆垛和未熔颗粒;喷涂30次,涂层厚度达到40μm,结合强度达15.5MPa。等离子喷涂Al防护涂层对NdFeB基体构成牺牲阳极保护,不同厚度涂层的自腐蚀电位无明显差异,约为–1.1V,自腐蚀电流密度相对NdFeB基体降低了2个数量级。随着涂层厚度的增加,Al防护涂层的耐腐蚀性能逐步提高,喷涂厚度的70μm的Al防护涂层耐中性盐雾腐蚀时间最高可达300 h以上。随着Al涂层厚度从0μm增加至70μm,磁体矫顽力略有提升,剩磁降低为原始样的2.0%~4.26%。结论 等离子喷涂技术可极大改善NdFeB磁体的耐腐蚀性能,为NdFeB防护的工业应用提供了新思路。

The air plasma spraying process is a novel surface protective technology on sintered NdFeB,which have a quantity of advantage on preparation process,corrosion resistance and other properties.There are some researches had been reported about cold spraying and part of hot spraying technology applied on surface protective.Although the air plasma spraying have been mentioned seldom,it can greatly improve the corrosion resistance of NdFeB magnets and can provide new ideas for industrial applications in NdFeB protection.The work aims to prepare Al protective coatings on the surface of sintered NdFeB magnets by atmospheric plasma spraying technology,so as to strengthen the protection of NdFeB magnets by plasma spraying technology.In this work,sintered NdFeB magnets with dimensions of 30 mm×20 mm×4 mm were degreased,dried in air,and then grit-blasted prior to deposition.All specimens were in the state of demagnetization.Pure aluminum powders(>99.9%)were divided into 20-40μm,and then were applied to spray onto the NdFeB substrate.As a result,with the spraying current increased from 400 A to 600 A,through observing the surface and cross-section morphology with SEM(SIGMA500),the best spraying current was 500 A,under which the surface of coating was dense without obvious sputtering stacking and unmelted particles.Finally the sprayed current was 500 A,the carrier gas flow rate was 1800 L/h,the powder feed rate was 0.1 r/min,the distance was 150 mm.Under this process parameter,with the spraying number increased from 20 to 50 times,the thickness of coating had increased;when the spraying number reached to 30 times,the average thickness was up to 40μm and the adhesive strength was over 15.5 MPa.Then,the corrosion resistance of coatings with different thickness were tested through electrochemical workstation(Ivivum)and salt spray test(YWX-750),and magnetic properties were tested with impulse magnetic field magnetometer(Metis Instruments).The Al coating was a sacrificial anode to protect the substrate and the self-corrosion voltage was about–1.1 V vs saturated calomel electrode,which had no apparently influence in thickness of Al coating.The self-corrosion current was smaller two orders of magnitude after deposition of Al coating on the NdFeB matrix,which decreased from 1.18×10–4 A/cm^(2) to 5.12×10–6–6.77×10–6 A/cm^(2);as the thickness of Al coatings increased,the corrosion resistance of Al coatings was increased,and that of coatings as thick as 70μm was over 300 h.With the thickness of coating increased from 0 to 70μm,the coercivity of the magnet was slightly increased and the residual magnetism was decreased from 2.0%to 4.26%of the original sample.Plasma spraying coating with excellent performance in adhesion,corrosion resistance and preparation process were used to prepare Al protective coatings and achieve the great protection to NdFeB magnet.The sprayed Al coating is a sacrificial anode to protect the substrate and have almost no damage to magnet properties.