Effects of Mo addition on anti-corrosion and mechanical properties of Al coating deposited sintered Nd-Fe-B magnets

Due to the poor mechanical properties and insufficient corrosion resistance of Al coating on sintered Nd-Fe-B magnets, the effect of the addition of Mo as well as the ratio of Al and Mo during the co-deposition process are systematically investigated. The Al 75 Mo 25 coating with the amorphous structure exhibits the superior corrosion resistance because of the flatter surface and dense passivation film, which cuts off the rapid propagation channel of the corrosion medium such as Cl - . The corrosion current density of the Al 75 Mo 25 coating reaches 6.1 × 10 -7 A·cm -2 , which is about one-third of the Al coating. Additionally, the coating demonstrates excellent mechanical properties, and the hardness of the coating increased from 0.41 GPa for the Al coating to 6.52 GPa. Furthermore, the amorphous coating does not compromise the magnetic properties of the Nd-Fe-B substrate. The results show that the addition Mo within limits can improve the anti-corrosion and mechanical properties of the Al coating. The work above clearly illustrates the practical value of the Al-Mo amorphous coating in improving the surface protection effect for the magnets. The work provides a promising way for improving the properties of Al coated sintered Nd-Fe-B magnets.