【作者】 刘文生；

【导师】 胡树兵；

【作者基本信息】 华中科技大学 ， 材料学， 2007， 硕士

【摘要】 NdFeB永磁体是20世纪80年代从日本最先发展起来的新材料,具有优异的磁性能。由于永磁材料资源丰富、价格低廉,在短短的几十年内就在电子工业、通迅信息、交通、国防、医药卫生、环保及石油等领域得到迅猛广泛的应用,在国民经济发展中发挥了显著作用。但是NdFeB永磁体材料的化学活性极强,耐腐蚀差,且易于被氧化。在潮湿环境中,在其磁体表面形成微电池,加速其腐蚀速度,导致其磁性能降低,严重影响其应用范围。为了提高NdFeB永磁体的耐腐蚀性能,人们进行了许多的尝试,这其中包括:(1)提高磁体本身的耐蚀性,即添加各种合金元素;(2)采用有效的保护涂层。在保护镀层中,以Ni-P非晶态合金材料,具有比相应的晶态材料更优异的力学性能、磁学性能和耐腐蚀性能,可以作为NdFeB永磁体等基体材料的一种优质的防护镀层。本文就在总结了近年来NdFeB永磁材料腐蚀机理和防护处理主要研究进展的基础上,采用化学镀的方法,在磁体表面镀覆镍基合金,以提高磁体的耐腐蚀性能。烧结NdFeB永磁体表面疏松、多孔,且其中Nd元素具有很强的活性(E=-2.4eV),非常活泼,无论在酸性或碱性化学镀液中,都会给施镀带来困难,因而对其前处理工艺和施镀工艺要求更高。减轻前处理和施镀过程中对磁体的腐蚀,是获得理想镀层的关键。经过优化确定的烧结NdFeB磁体的前处理工艺,主要包括打磨、封孔、除油、酸洗活化及预镀铜等工艺。采用超声波碱性除油,可以为后序施镀打下良好基础;而采用硝酸(质量分数为65%)30～40mL/L,硫脲0.5g/L,氨水调其pH值在4～5范围内,必须严格控制室温下酸洗时间20～30秒。实验研究发现不能在NdFeB磁体表面直接进行酸性配方施镀,否则磁体基体发生腐蚀,无法施镀上去,宜采用碱性或中性镀液施镀。先预镀铜,再中性化学镀液中施镀一层Ni-P合金,然后再在超声波碱性化学镀液中施镀,所获得的复合镀层同直接在超声波碱性镀液中所获得的镀层相比具有孔隙率小,耐腐蚀性效果好等特点。而采用超声波预镀铜工艺,可明显提高镀层结合强度,有效降低镀层的孔隙率,提高耐腐蚀性。从镀层与基体的结合力实验及断面形貌和表面镀层(SEM)分析表明,Ni-P化学镀层表面是由大小相当的胞状颗粒组成,镀层致密,没有裂纹,具有良好的表面,镀层与基体的结合力良好。复合络合剂的镀液比添加单一络合剂的镀液更稳定,镀速也较高,因此得到的镀层致密性较好、孔隙率也较低。实验研究表明碱性化学镀液中施加40kHz的辅助超声场,和没有超声场中的化学镀Ni-P镀层相比,镀层组织颗粒更加细小、更加紧密、合金的耐腐蚀性能得到增强。更多还原

【Abstract】 NdFeB type magnet, which possesses excellent magnetic properties, is a new type of permanent magnet material, which is discovered by Japan in 1983. Permanent magnetic material is rapidly widely used in the electronics industry, communication, information, defense, medicine and health, environmental protection and oil fields etc. in a short period of several decades because of its rich source and low price. But the strong chemical activity, poor anticorrosion and easy being oxidized of NdFeB magnets material seriously affect its scope of application.To improve the corrosion resistances of NdFeB type magnets, lots of attempts have been done, such as enhancing the intrinsic corrosion property of material by the addition of elements and applying various protective coating on the surface of the magnets. Among all surface coatings amorphous Ni-P coating, which possesses more mechanical, magnetic and anti-corrosion performance over the crystal materials, may be one of the most excellent. In this thesis, reports on corrosion mechanism and anticorrosion process of NdFeB permanent magnet are reviewed. On this basis, electroless deposition of Ni-based alloy was employed to NdFeB magnet to enhance its corrosion resistance.Surface loose, lots hole and Nd element very active(E=-2.4eV) and vivacity of the sintered NdFeB permanent magnet, the pretreatment processes and apply plating process which is difficult to apply plating whether in acidic or alkali electroless plating bath, it is the key to get ideal coating that alleviate corrupt. The optimized pretreatment processes include burnish process, plug process, oil removing process, picking and activation process, and precoppered process. Oil-removed by supersonic, and acidwashing must be carried in 30-40mL/L of nitric acid (65%) with the addition 0.5g/L of thiourea, in pH adjusted to 4–5 by ammonia liquor, in limited time of 20-30s.Experiments find that we can’t direct plat with acidic solution in the sintered NdFeB magnets’surface, otherwise magnet corrosion. In this paper, the composite deposit coating include first pre-copperplating coating, second litmusless plating coating and last alkaline plating coating. The composite deposit coating has a better corrosion resistance and little porosity than ultrasonic electroless plating. The pre-copperplating can improve coating adhesion strength and corrosion resistance, effectively reduce the porosity of the coating. Microstructure analysis performed by means of SEM, the results show that the coating and magnet surface has a stronger adhesion, and the same size of cellular particles composite of the coating.The results have shown that the composite complexing agnet has more stability solution than single complexing agnet, and has a higher deposit rate. So the composite coating has a more compactability and fewer porosity.The experiment indicate that the alkaline electrolessly plating Ni-P deposit ,which were prepared for the sintered NdFeB magnets under 40 kHz frequency ultrasonic field, has better fine microstructure and adhesion force than the Ni-P deposit without ultrasound field.更多还原