Study On The Preparation Process And Properties Of Ni-P-Al₂O₃ Composite Coating By Pulse-assisted Jet Electrodeposition

With the continuous progress of modern manufacturing,China’s economy has achieved significant development.At the same time,mechanical components are also facing challenges brought about by corrosion and wear.The significant losses and scrapping caused by corrosion and wear greatly reduce resource utilization,while also bringing great pollution and damage to the natural environment.Compared to traditional surface protection technologies such as single metal coating and alloy coating,nano-composite deposited layer has unique advantages in surface protection.The Ni-P-Al₂O₃ composite deposited layer exhibits excellent performance in terms of hardness,wear resistance,and corrosion resistance due to the addition of Al₂O₃ nanoparticles.However,the surface effect of the nanoparticles makes them prone to agglomeration during the deposition process.The addition of agglomerating particles increased sedimentary layer defects and reduced sedimentary layer performance.In recent years,jet electrochemical deposition has emerged as a new electrochemical processing technology that can improve the deposition quality of metal-based coatings compared to traditional electrochemical deposition techniques through strong solution stirring,high mass transfer rates,and lower cathodic concentration polarization.In addition,pulse electroplating has the advantages of reducing diffusion layer thickness,increasing nanoparticle uniformity,and increasing ion content compared to direct current electroplating.Based on jet electrochemical deposition,this paper introduces pulse-assisted technology and conducts experimental research on Ni-P-Al₂O₃ preparation using a built pulse jet electrochemical deposition experimental platform.The main research work and results are as follows:（1）Ni-P deposited layer was prepared using pulsed jet electroplating technique.Orthogonal experimental design and control variable method were used to optimize the process parameters for the preparation of Ni-P-Al₂O₃ composite deposition layer.The average current density,pulse frequency,and pulse duty cycle were used as independent variables,and the thickness and hardness of the deposited layer were used as evaluation indicators using the comprehensive balance method to preliminarily determine the process parameters.The pulse frequency had a greater impact on the hardness value of the deposited layer.Further investigation was conducted using single-factor exploration,and the optimal process parameters were determined to be an average current density of 30A/dm²,a pulse duty cycle of 60%,and a pulse frequency of 1500 Hz.The Ni-P deposited layer prepared under these conditions had a hardness of 670HV,a corrosion potential of-0.33V,a depth of indentation of 1682nm,and an elastic recovery ratio of h_e/h_max of 0.34.（2）On the basis of pulsed jet electroplating Ni-P deposition layer,nano-sol Al₂O₃ dispersion was added to prepare Ni-P-Al₂O₃ composite deposition.By comparing with the Ni-P deposition layer prepared under pulse conditions and the Ni-P-Al₂O₃ composite deposition and Ni-P deposited layer prepared under DC conditions,it was found that pulse technology and nano Al₂O₃ particles can effectively improve the surface defects of the deposition layer and enhance the overall quality.（3）The process parameters of pulsed jet electroplating Ni-P-Al₂O₃ composite deposition layer were deeply optimized to further improve the quality of the nano-composite deposition layer.The pulse duty cycle,as an important influencing parameter in the process,was used to prepare the Ni-P-Al₂O₃ composite deposition layer by changing the pulse duty cycle while keeping other process parameters constant.The relevant performance was evaluated to explore the influence of pulse duty cycle on the composite deposited layer.The experimental results showed that the overall quality of the deposited layer first improved and then decreased as the pulse duty cycle increased.The optimal pulse duty cycle was 60%,which can obtain a high hardness,good toughness,and strong corrosion resistance Ni-P-Al₂O₃ composite deposition layer while ensuring the deposition rate.Under this condition,the hardness of the composite deposition layer was817.4HV,the corrosion potential was-0.24,the Young’s modulus was 180.87GPa,and the elastic recovery ratio(h_e/h_max)was 0.36.By using pulse-assisted jet electrodeposition technique and parameter optimization,Ni-P-Al₂O₃ composite deposition was successfully prepared.Through comparing the relevant performance of the deposited layer under different process conditions,the positive role of pulse technology and nano particles in improving the quality of the deposited layer was fully affirmed.Moreover,the comprehensive performance of Ni-P-Al₂O₃ composite deposited layer was effectively improved while ensuring the deposition rate.