NdFeB Permanent Magnet Material
Study on Electroless Plating Ni-Co-P Alloy Protection Deposit of Sintered NdFeB Permanent Magnet Material
In this paper,N45 sintered NdFeB permanent magnet materials were protected by the electroless plating Ni-Co-P to improve its corrosion resistance.In first period,carton steel was used as substrate,in which the pre-treatment technology and electroless plating bath and plating technology parameters were optimized.Based on this basis,the Ni-P/Ni-Co-P alloy deposits were prepared on the NdFeB permanent magnet,in which the deposits combined with the porous magnets substrate closely.And the structures and properties of Ni-Co-P deposits were studied.
The optimization steps of the pre-treatment processes on sintered NdFeB permanent magnet material are:electrolytic degreasingŁ¬weak acid activation and pre-plating alkaline Ni-P alloy,in which the plating temperature is 85ˇćand plating time is 20min.The optimization results of electroless plating bath and plating technology parameters are:the complexing agent is sodium citrate,stabilizer is a trace thiourea,metal ion concentration ratio is within 0.3~0.6,pH value is 9~10 and plating temperature is 85ˇć.The results of Ni-P/Ni-Co-P deposits structure show that,the bonding interface between the deposit and substrate presents the form of interdigitate,the surface of Ni-Co-P deposit is flat and silver-white metallic luster,the porosity of deposit is almost zero,and the Ni-Co-P deposit on the Ni-P deposit is combined closely.As the pH value increases,the Ni-Co-P deposits structure transforms from amorphous to crystalline.The deposit structure are amorphous structure when the metal ion concentration ratio is in the range of 0.2~0.6,but the structure of the Ni-Co-P deposits changes from amorphous structure to microcrystalline as the metal ion concentration ratio increased continuously to 0.8.The Ni-Co-P deposits consist of cellular with different dimensions,and the cellular size of the deposit surface decreases gradually with the metal ion concentration ratio increase.When the metal ion concentration ratio increases up to 0.6,the cellular size of the deposit surface coarsens.EDS analysis shows that with the metal ion concentration ratio increase,the Co content is increasing and the Ni and P content are decreasing in plating.And P elements tend to segregate in the junction of one cell connected with another cell.The experiment results on corrosion resistance of deposits show that the metal ion concentration ratio of 0.3 has the best acid-corrosion resistance,while the metal ion concentration ratio of 0.6 is best on alkali salt corrosion resistance.In the electrochemical environment(corrosive medium of 3.5%NaCl solution),the metal ion concentration ratio of 0.3 has the best corrosion resistance.
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