| A dense and adhesive aluminum coating was successfully electrodeposited on NdFeB rare earth alloy by using THF organic solvent electrolyte. Properties of Al coating were systematically investigated. It was found that aluminum coating could offer NdFeB rare earth alloy excellent protection, and better deposits could be obtained through controlling the electroplating variables, such as electrolyte compositon, current density and time. Effects of heat treatment on Al coating were also studied in this paper.Cathode current efficiencies were almost above 90% in all electrodeposition experiment. No side reations were observed on the cathode surface. Current distribution on cathode was great, and uniform deposits could be electrodeposited on more complicated substrate. Energy consumption was acceptable in the electrolyte composion selected in this study when current density was below 4A/dm~2.Structural analysis of the deposits showed that it was pure aluminum. Morphological analysis of Al coating were investigated. Better surface with even Al particles appeared when molar ration of AlCl3 and LiAlH4 was 3:1 and current density and electroplating time was in range of 2-4A/dm~2 and 30-60min respectively, and it did contributed to excellent properties of Al coatings.Properties of Al coating, such as thickness, hardness, adhesion and corrosion protection were tested in detail. The results showed the thickness of Al coating was in the range of 9-42μm. Thickness of Al coating (Electroplating rate) was propotional to the product of current density and current efficiencies. Microhardness increased slightly in the range of 45-80HV with the increaing of current density and electroplating time. Adhesion force of Al coating to the substrate was all above 40N, and there was a maximum in the curve of adhesion force to current density and electroplating time in range of current density 2-4A/dm~2 and electroplating time 30-60min respectively. Al coating improved the performance of NdFeB magnets in high temperature. Weight increase was much less than the increase of NdFeB magnets in the same situation. When current density and electroplating time was 2-4A/dm~2 and 30-60min respectively, Al coating had less weight increase. Also, maximum of R_p values of Al coating in neutral 3.5%NaCl occurred with current density and electroplating time among 2-4A/dm~2 and 30-60min respectively. R_p values of Al coating were all above 2.5×10~4Ω·cm~2. Al coating offered a great corrosion protection for NdFeB magnetsAfter long time heat trement in high temperature, element diffusion occurred at the interface of Al layer and NdFeB rare earth alloy. The morphologies changed obviously, and little boundaries disappeared, but little cracks between big particles were kept down. The adhesion force decreased because the expanding of Al deposits disagreed with NdFeB rare earth alloy during heating. Corrosion resistance of Al coating didn't improve after heat treatment. |
PDF Full Text Request