Abstract:The effect of phosphating temperature on formation, microstructure, and corrosion resistance of the phosphate chemical conversion (PCC) coatings and that on the magnetic property of the sintered Nd-Fe-B permanent magnets were investigated. The results show that the coating mass is increased slightly with increasing the phosphating temperature. The scanning electron microscope observation demonstrates that PCC coatings have blocky structure with the grain size of 5~10 μm. The analyses of energy dispersive spectra and Fourier transform infrared spectrometer spectra reveal that the coatings are mainly composed of neodymium phosphate hydrate, praseodymium phosphate hydrate, and a small amount of iron phosphate hydrate. The oxygen and phosphorous elements in PCC coatings are mainly distributed on the grain surface, while the iron element is mainly concentrated at the grain boundaries. The distribution of neodymium and praseodymium is relatively uniform. The electrochemical analysis and static immersion corrosion test show that PCC coatings prepared at different temperatures can effectively improve the corrosion resistance of the sintered Nd-Fe-B permanent magnets. The coatings prepared at 70 °C exhibit a better corrosion resistance due to the uniform and dense microstructure. Although the magnetic properties of the sintered Nd-Fe-B permanent magnets with PCC coatings are decreased, those with PCC coatings prepared at 70 °C are relatively fine. The optimal phosphating temperature of 70 °C for the sintered Nd-Fe-B permanent magnets is determined.