Corrosion Resistance And Mechanical Properties Of Zn-Ni And Ni-Co Alloy Coatings Deposited By DC Electrodeposition Of NdFeB

Nd Fe B permanent magnet materials are widely used in various fields of modern industry with their excellent magnetic properties.However,Nd Fe B permanent magnet materials are prone to form defects such as micropores and voids on the surface during the sintering process,resulting in insufficient inherent corrosion resistance.In order to improve the corrosion resistance and mechanical properties of Nd Fe B materials in different use scenarios,this thesis first selects the acid acetate system plating solution,prepares Zn-Ni alloy coating by direct current deposition method,and develops Ni-Co alloy coating with better corrosion resistance and higher hardness on the basis of Zn-Ni alloy plating process research.Test the topograp Hy and performance of coatings using methods such as SEM,XRD,EDS,and electrochemical workstations.The main research contents and conclusions of the thesis are as follows:（1）Using orthogonal experiments,the corrosion resistance of Zn-Ni alloy coating was studied,and the influence of electrodeposition parameters on corrosion resistance was studied by range analysis as follows:plating temperature>electrodeposition time>current density>plating solution p H.The process parameters for the theoretical best corrosion resistance were as follows:electrodeposition temperature 55℃,electrodeposition time 40 min,current density 15 m A/cm²,electrodeposition solution p H=5.0.（2）The influence of different electrodeposition parameters on the coating performance of Zn-Ni alloy coatings was studied by controlling variable method:（1）The prepared zinc-nickel alloy coating was aγp Hase Ni₅Zn₂₁with good corrosion resistance and grew according to the crystal plane orientation of（600）.（2）With the increase of current density,the adhesion,hardness and corrosion resistance of the coating first increase and then decrease,and the coating performance obtained at 15m A/cm²is the best.（3）With the increase of electrodeposition temperature,the performance of the coating first increases and then decreases,and the densest coating can be obtained at 50℃,with the best adhesion,the highest hardness and the best corrosion resistance.（4）p H is too small to increase hydrogen evolution;When the p H is too high,too much Zn（OH）₂precipitation is generated in the plating solution to make the coating worse,and when the p H is 5.0,the grain of the coating is the finest,the mechanical properties are the best,and the corrosion resistance is the best.（5）If the electrodeposition time is too long or too short,the performance of the coating will be reduced,and the coating grain obtained when the electrodeposition time is 40 min is the finest,and the hardness and corrosion resistance are the best;Due to the long time of the coating being eroded by the acid plating solution,the film base adhesion is damaged for a long time,and the best film base adhesion can be obtained at 30 min.（3）The film base adhesion and other properties of the coating were optimized by changing the roughness of the substrate,and the coating was prepared with 400#,800#,1200#sandpaper for grinding and non-grinding（surface polishing state）.The results show that the coating prepared on the polished matrix is the most uniform and dense,the grain is the finest,the hardness is the largest,and the adhesion and corrosion resistance are the best.Then the coating failure model is used to explain the difference of the bonding force of different coatings,and the components acting on the interface in the model can be decomposed into two modes:drawing and shearing,and the shear force at the interface can promote the"interlocking"between the fracture surfaces through effective friction to improve the bonding force;Then add nano-Ti₃C₂particles with concentrations of 0.1 g/L,0.2 g/L,0.3 g/L,0.4 g/L to the electrodepositation solution to try to prepare nanocomposite coating,through XRD and EDS analysis,it was found that the composition and p Hase structure of Ti₃C₂nanoparticles were not detected in the Zn-Ni coating,which may be because the concentration of nanomaterials is not enough or the dispersion in the sediment solution is poor,and the surface energy is easy to agglomerate and settle the bottom,resulting in nanoparticles not plated into the coating.（4）The Ni-Co alloy coatings prepared by experiments are all Ni-Co alloy coatings with fcc structure formed by cobalt atoms entering the nickel lattice through solution substitution,and all of them grow according to the orientation of the（111）crystal plane,and the factors do not change the p Hase structure of the coating.The co-deposition of nickel-cobalt ions is abnormal co-deposition,and the influence of cobalt content in the coating is decisively played by the concentration ratio of cobalt-nickel ions in the plating bath.The concentration of Co SO₄is mainly through solution strengthening to distort the lattice,refine the grain size,and make the coating more dense,thereby affecting the coating performance.The current density and sodium saccharin concentration mainly affect the performance of the coating by regulating the grain size and internal stress of the coating.The hardness was the highest when the concentration of cobalt sulfate was 60 g/L,the current density was 2 A/cm²,and the concentration of sodium saccharin was 1 g/L,which was 594 HV.When the concentration of cobalt sulfate is 20 g/L and the current density is 1 A/cm²,the binding force is the best,which meets the first-level bonding force in the evaluation standard of the grid method.When the concentration of cobalt sulfate was 50 g/L,the current density was 2 A/cm²,and the concentration of sodium saccharin was 1 g/L,the self-corrosion current was the smallest,and the minimum was 1μA/cm².