Optimization Of Ultrasonic And Mechanical Grinding Modification Of Electroless Nickel Plating Pretreatment Based On Taguchi Method

Aluminum alloy has some defects such as low surface hardness and poor corrosion resistance,which limit its practical application.In order to further improve the properties of aluminum alloy,it is necessary to use surface modification technology to strengthen the aluminum alloy matrix.Electroless nickel plating is generally regarded as one of the most effective methods to obtain alloy coatings with excellent corrosion resistance.The electroless nickel plating on the surface of aluminum alloy is more uniform and the pinhole ratio is relatively low.But aluminum is a difficult metal to coat.The oxide film on the surface and its own chemical properties will destroy the stability of the plating solution,resulting in the quality of electroless nickel plating.Therefore,it is of great significance to study the protective pretreatment technology of electroless nickel plating on aluminum alloy.On the basis of Taguchi method,the pretreatment technology of electroless nickel plating was improved.Ultrasonic field and mechanical grinding process were introduced on the basis of aluminum alloy nickel immersion pretreatment,and the influence of ultrasonic cavitation and glass ball impact on the quality of chemical coating was systematically studied.In order to solve the problems of instability of chemical bath and weak corrosion resistance of coating caused by traditional secondary zinc dipping,a secondary nickel dipping process was designed based on the secondary zinc dipping process,and the effects of sodium hypophosphite,ammonium chloride and pretreatment temperature on the nickel dipping effect were studied.Finally,Taguchi method was used to analyze the deposition rate,surface microhardness and signal-to-noise ratio of electroless nickel plating layer,in order to obtain excellent electroless nickel plating layer.The conclusions based on the above research contents are as follows:1.Ultrasonic frequency has the greatest influence on the deposition rate and corrosion resistance of the chemical coatings after the ultrasonic assisted nickel plating pretreatment.Compared with the traditional secondary zinc leaching pretreatment process,the efficiency of electroless nickel plating is improved effectively.2.Mechanical grinding pretreatment compared with ultrasonic pretreatment technology can effectively improve the chemical plating phosphorus content and surface microhardness,glass in the process of grinding ball diameter,the most profound effect on the chemical plating through the pretreatment process can rise to refine the coating growth,and better coating surface state,no obvious defects.3.In the second pre-plating solution,sodium hypophosphate was introduced as a reducing agent and ammonium chloride as a promoter to accelerate Ni²⁺deposition,resulting in better pre-plating quality and uniform surface cell body size,which can improve the deposition rate and phosphorus content of electroless nickel plating.Among them,sodium hypophosphate has the greatest influence on the chemical coating and its content needs to be strictly controlled.