| Sintered Nd-Fe-B is widely used due to its excellent magnetic properties.However,due to the potential difference between the main phase and the intergranular yttrium phase,the sintered Nd Fe B is prone to intergranular corrosion,and the corrosion resistance of sintered Nd Fe B is improved by surface protection treatment.It is a hot spot in the industry.In this thesis,the surface of sintered Nd Fe B is firstly treated with organic phosphating,and then the copper-graphene composite coating is electrodeposited by ultrasonic assist in the non-cyanide copper plating solution to improve the protective properties of sintered Nd Fe B.The effects of organic phosphating on the surface of sintered Nd Fe B,the effect of ultrasonic assisted frequency on copper electrodeposition and the performance of copper-graphene composite coating were discussed.For surface phosphating,phytic acid phosphating is best compared to other phosphating agents.The surface of Nd-Fe-B is treated by phytic acid phosphating.The maximum magnetic energy product and residual magnetic properties are improved below 150°C.The magnetic properties above 150°C are the same as those of untreated.For the surface phosphating of Nd-Fe-B,The formation of the phosphating film is accompanied by the mild corrosion of the magnet,and the phosphating also has the function of de-corroding layer,which can be used for rust removal of the surface of the Nd-Fe-B,and the surface treated by the phytic acid is relatively flat,and the layer can be dehumidified gently.Moreover,the magnetic loss is small,and the phosphating solution with a small phytic acid phosphating solution concentration of 0.5 mol/L is selected and a suitable phosphating time is controlled to obtain a better phosphating conversion film at the grain boundary.In the ultrasound-assisted study,under the condition of no ultrasound,the microscopic surface of the copper deposit layer is loose and porous,and as the ultrasonic frequency is increased to 40 k Hz,the crystal becomes fine and the surface becomes more and more flat and dense,and the hardness of the deposited layer increases with the ultrasound.The enlargement,the combination of the deposited layer and the substrate is getting better and better,and the deep plating ability is improved,which satisfies the requirement of deep plating and rapid deposition in the high-activity porous sintered Nd-Fe-B hole to reduce the corrosion of the substrate by the plating solution.As the ultrasound is enhanced to 40 k Hz,the overpotential decreases and the polarization decreases when the copper deposits.The electromorphic morphology changes from lamellar polymorphism to pyramidal crystal,and the crystal orientation of the(111)crystal plane increases.Large,(111)and(200)lower index crystal plane orientations are enhanced,while(220)and(311)higher index crystal plane orientations are reduced,crystal grains with smaller grain size are increased,grain refinement,and crystallization is accelerated.The quality of the coating is improved.As the ultrasonic is enhanced to 40 k Hz,the current efficiency increases when copper is deposited,and the current density distribution range when a good deposited layer is obtained increases,which satisfies the requirement for instantaneous plating of large current density of sintered Nd-Fe-B.As the ultrasonic intensity is increased to 40 k Hz,the corrosion resistance of the copper deposit layer,thereby improving the surface anti-corrosion of the sintered Nd-Fe-B.And ultrasound has no significant negative impact on magnetic properties.For the copper-graphene composite film,as the graphene concentration in the bath increases from 0g/L to 0.9g/L,the surface of the composite material is refined,the surface morphology tends to be flatter,and the cross-sectional morphology tends to be smoother.The strength of the composite material is improved;however,the surface of the composite has a high and low undulation as the graphene content increases,and the water contact angle gradually increases and the hydrophobicity increases.The graphene sheets are stacked in a copper matrix in a card slot.As the content of graphene in the composite increases,it may increase the amount of alkane or naphthenic desulfurization groups that enter the composite material,and may also cause electrohydrogenation of graphene to graphane,sp~2C in graphene.The hybridization intensity is slowly enhanced,while the sp~3C hybridization is obviously weakened.At the same time,the oxygen content is reduced,and the copper in the composite material has a tendency to change from a high oxidation state to a low oxidation state or a reduced state;and plating of 0.3 g/L graphene is performed.The composite material prepared in the liquid has the best copper crystallizing property.In addition,the composite film prepared in the plating solution of 0.3 g/L graphene,that is,the composite material having a graphene atomic ratio of about 10%,has the best electrochemical stability,and the weakest corrosion of the primary battery.It can be seen that for different sintered Nd-Fe-B,the phosphating solution with lower phytic acid concentration(such as 0.5mol/L)is used for preliminary pretreatment phosphating protection,and then the copper plating layer and the proportion of graphene atoms are deposited under ultrasonication.10%copper-graphene composite coating can greatly improve the surface protection performance of sintered Nd-Fe-B. |
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