Study Of Additive And Corrosion Resistance Of Zn-Fe Alloy On Sintered NdFeB Substrate

The as-sintered NdFeB permanent magnetic material, which has the best magnetisem,is widely applied in industry. However, the poor corrosion resistance limits its furtherdevelopment. The excellent properties of Zn-Fe alloy coatings have been consideredto an alternative for traditional electroplating Zn and Ni coatings, which can providebetter protection. In this paper, the suitable electroplating Zn-Fe alloy additive forNdFeB substrate and the role of additive in electroplating process has been researchedby combining Hull cell test with constant temperature uniform mixing test and cyclicvoltammetry method. Meanwhile, the morphology and corrosion performance ofZn-Fe alloy coatings and passivated film on NdFeB substrate have been studiedthrough SEM、three dimensional (3D) white-light interfering surface analysis、XRDand electrochemical method.The best contents of Zn-Fe alloy electroplating brightener for sintered NdFeBmagnet are the main brightener benzylidene acetone0.2g/L, the carrier brightenerTKZ-803g/L, auxiliary brightener sodium benzoate2g/L、high concentration ofdispersant NNO1.6g/L and dodecyl benzene sulfonic acid sodium0.06g/L. Then thebest contents of Zn-Fe alloy electroplating stabilizer are ascorbic acid1g/L, tartaricacid1g/L, sodium gluconate12g/L, sodium potassium tartrate4g/L.The Zn-Fe alloy coatings with high corrosion resistance were prepared onsintered NdFeB magnet substrate from a light acid chloride solutions. The Zn-Fe alloycoating contain0.9wt%Fe has more density coating to acquire compact passivationfilm. Finally, the trivalent chromium passivated Zn-Fe alloy coating could provideboth better anodic protection and physical barrier function reducing the total corrosionrate comparing with pure Zn system. Therefore it showed excellent corrosionprotection properties for the NdFeB substrates.The iron element in Zn-Fe alloy coatings which contain0.7-0.9wt%Fe is onepart inη-phase and the other part in pure Fe. The corrosion resistance of Zn-Fe alloyare improved with the increasing of coating Fe contain. The trivalent chromiumpassivated film of Zn-Fe alloy which contain0.7-0.9wt%Fe in coating was integral and smooth. However, the passivated film was rough and easily damaged after the Fecontent exceeding1%. Therefore, the prepared Zn-Fe alloy coating has the bestcorrosion resistance when Fe content is0.7-0.9wt%.