Permanent Rare-Earth Magnets—The Need to Protect Them against Corrosion
- 1 Corrosion and Protection Laboratory, LCP, Institute for Technological Research—IPT, São Paulo, Brazil
- 2 Innovation and Business Officer, DIN, Institute for Technological Research—IPT, São Paulo, Brazil
Abstract
The RE-Fe-B permanent magnets have a complex microstructure and they are susceptible to corrosion process. In this paper, the commercial nickel coatings adhesion was investigated. The microstructure of the RE-Fe-B without coating was analyzed by scanning electronic microscopy and electrochemical techniques. The interface magnet/coating was studied by scanning electron microscopy and the nickel-plated Nd-Fe-B commercial magnets were tested in a salt spray chamber. The ferromagnetic and RE-rich phases were observed. After the anodic polarization curve, a strong intergranular corrosion was observed and the RE-rich phase was preferentially attacked. The interface magnet/Ni coating presented inter-granular corrosion that can affect the nickel coating adherence. This attack had probably occurred during the electrodeposition process. Not all the samples suffered localized corrosion during the salt spray tests and the Ni triple-layer coating presented a few corrosion points. RE-Fe-B alloy magnets need to be protected with appropriate coatings to each environment to which they will be exposed and the protective coating must not be damaged.
- Rocio, M.A.R., da Silva, M.M., de Carvalho, P.S.L. and Cardoso, J.G. da R. (2012) Terrasraras: situação atual e perspectivas [Internet]. BNDES Setorial. https://web.bndes.gov.br/bib/jspui/handle/1408/1527?mode=full&submit_simple=Mostrar+ registro+em+formato+completo
- UNITED STATES GEOLOGICAL SURVEY (2016) Mineral Commodity Summaries Rare Earths. USGS, Reston. http://minerals.usgs.gov/minerals/pubs/commodity/rare_earths/mcs-2016-raree.pdf
- Lima, I.B. and Leal Filho, W., Eds. (2016) Rare Earths Industry Technological, Economic, and Environmental Implications. Elsevier, Amsterdam.
- Brown, D.N. (2016) Fabrication, Processing Technologies, and New Advances for RE-Fe-B Magnets. IEEE Transactions on Magnetics, 52, 1-9. https://doi.org/10.1109/TMAG.2016.2535482
- Dent, P.C. (2012) Rare Earth Elements and Permanent Magnets (Invited). Journal of Applied Physics, 111, 07A721-07A721. ttps://doi.org/10.1063/1.3676616
- Schultz, L., El-Aziz, A.M., Barkleit, G. and Mummert, K. (1999) Corrosion Behaviour of Nd-Fe-B Permanent Magnetic Alloys. Materials Science and Engineering, A267, 307-313. https://doi.org/10.1016/S0921-5093(99)00107-0
- Rodewald, W. (2007) Rare-Earth Transition Metal Magnets. In: Handbook of Magnetism and Advanced Magnetic Materials, Wiley, 1-22. https://doi.org/10.1002/9780470022184.hmm406
- VACUUMSCHMELZE GMBH & CO. KG (Germany) (2013) Coating. http://www.vacuumschmelze.com/index.php?id=1130
- Panossian, Z. (1993) Revestimentos metáLicos. In: Panossian, Z., Ed., Corrosão e proteção contra corrosão em equipamentos e estruturas metálicas, Instituto de Pesquisas Tecnológicas, São Paulo, 590-612.