Corrosion Resistance, Mechanical and Magnetic Properties of Cold-Sprayed Al Coating on Sintered NdFeB Magnet

A protective aluminum coating was deposited by cold spray on the surface of a sintered neodymium substrate (Nd2Fe14B) made from an alloy of neodymium, iron, and boron and used as a permanent magnet. Most of the sprayed aluminum particles softened and deposited onto the substrate, forming a uniform and dense coating with a thickness of about 45 mu m. The bonding strength and Vickers hardness of the coating were 26.0 MPa and 7.02 GPa, respectively. The corrosion current (I-corr) densities of the sintered NdFeB with and without the aluminum coating in 3.5 wt.% NaCl solution were 3.847 x 10(-5) A/cm(2) and 3.866 x 10(-4) A/cm(2), respectively. The sintered NdFeB with the protective aluminum coating survived up to 200 h in the neutral salt spray test (NSS). Its coercivity, remanence, and maximum energy product were 14.813 kOe, 13.994 kGs, and 46.798 MGOe, respectively. They were lower than that of the substrate without coating by 2.94%, 0.03%, and 1.69%.This study showed that the aluminum coating prepared by cold spray could effectively increase the corrosion resistance of the sintered NdFeB magnet with a weak effect on its magnetic properties.