Investigation on Properties of Electroless Ni-P-W/Al<sub>2</sub>O<sub>3</sub> Composite Coatings Deposited on Sintered NdFeB Permanent Magnet

The Ni-P-W/Al 2 O 3 composite coatings were deposited on the surface of sintered NdFeB permanent magnet by electroless plating method. The morphology and the phases of Ni-P-W/Al 2 O 3 composite coatings were investigated using scanning electron microscopy and X-ray diffraction respectively. The hardness and the corrosion resistance of the composite coatings were also tested. The results indicated that the composite coatings morphology appears closely nodules morphology, and the microhardness increases linearly with increasing incorporation of Al 2 O 3 ratio. Compared with NdFeB magnet and Ni-P-W amorphous alloy coating, the corrosion resistance of the composite coatings was superior to that of the NdFeB magnet and the amorphous alloy coating obviously. However, for the corrosion resistance of Ni-P-W/Al 2 O 3 composite coatings with different Al 2 O 3 concentration, there is not a linear increase with the Al 2 O 3 concentration increasing. The self-corrosion potential of Ni-P-W/Al 2 O 3 composite coatings reaches the highest value while increasing incorporation of Al 2 O 3 ratio up to 10 g/L.