The influence of alumina-silica sol addition on microstructure and protective properties of electrodeposited zinc coatings on NdFeB magnet

Alumina-silica embedded zinc coatings with an enhanced protective performance for sintered NdFeB magnet were prepared using electro-deposition method from a mixture of alumina-silica sol (ASS) and zinc plating solution. The zinc-ASS coatings have been fabricated with various ASS concentrations in sol contained plating baths (SCPB). According to electrochemical results, the positively charged ASS particles adsorbed on cathode and deposited with the electro-deposition of zinc coatings. The influence of the ASS concentration in SCPBs on the deposited coating structure, composition and growth mechanism were investigated.With the increase of ASS concentration, more ASS particles got adsorbed on cathode surface during the deposition process, which affected the crystal structure and composition of the deposited zinc coatings. Among the prepared samples, ASS embedded zinc coating exhibited relatively good wetting behavior, adhesive and wear properties, which should be attributed to the adsorption and incorporation of ASS particles. The corrosion current density of 10%-SCPB prepared zinc coating was more than an order ofmagnitude lower than the sol free zinc coating. This kind of approach was helpful to fabricate zinc-ASS coatings with enhanced mechanical and anti-corrosion properties for NdFeB magnets.