LASEK Stanislav VSB-Technical University of Ostrava

Spoluautoři DOBROVODSKÁ Nela, SKOTNICOVÁ Kateřina

Economical and useful NdFeB magnets, produced by powder metallurgy, are sensitive to corrosion, especially in wet or water environments, therefore protective galvanic coatings of metals (Ni, Cu, Zn) are mostly applied on their surface. This contribution deals with verification and comparison of corrosion properties of selected commercial combined Ni/Cu/Ni coating and simple Ni coating (made in laboratory) on NdFeB magnet type in the shape of a ballet and cylinder. Chemical composition of coatings and of basic material was verified by microanalysis and magnetic phase of the type Nd2Fe14B was identified. According to the performed standard salt spray test was found out that corrosion resistance of selected magnets with tested coatings is low. The degradation started from rust points (pits) and stain, through lifting and cracking of coatings to their peeling and then intensive corrosion of the base material under action of galvanic cell. Metallographic analysis after test has confirmed that total thickness of the Ni coating or thickness of each layer in the coating Ni/Cu/Ni would not have a significant effect on the corrosion resistance of the NdFeB magnet. Adhesion and presence of through imperfections in the coating are important, as they influence galvanic corrosion under coating. The influence of hydrogen should be reduced or eliminated at surface pre-treatment and coating application for increasing the effectiveness of protective coatings