Effect of Alumina Sol on Formation and Properties of Electrodeposited Zinc Coatings on NdFeB Magnet

Al2O3-contained zinc coatings with enhanced protective and mechanical performances were prepared on NdFeB magnets by in situ electro-deposition methods from the zinc plating baths containing alumina sol. The positively charged alumina sol particles migrate to the NdFeB cathode and then gel along with zinc on the cathode surface, which changes the electro-deposition process of zinc. As a result, the surface morphology and phase structure of the zinc coating is significantly changed. The incorporation of alumina particles achieves a denser zinc coating with a smaller grain size and the hardness is well improved. By increasing alumina sol concentration in the plating bath, the micro-hardness and wear resistance of the zinc coatings gradually increased. What's more, the alumina sol addition also improved the corrosion resistance of zinc coatings. When 20 wt. % alumina sol is added, the corrosion potential of the zinc coating is positively shifted for 168 mV and the corrosion current was more than one order magnitude lower than the blank one. Therefore, this approach shows great promise to obtain alumina-contained zinc coatings with enhanced anti-corrosion properties and mechanical properties.