Study On Process And Properties Of AZ91D Magnesium Alloy Electroplated Nickel-cobalt Alloy

Magnesium alloys are widely used in commercial and living fields such as computer communication,automobile manufacturing,weapon manufacturing,aerospace,etc.due to their unique characteristics,such as low density,light weight and high specific stiffness.However,its chemical nature is lively and corrosive.Therefore,improving the corrosion resistance of magnesium alloys is beneficial to the application and promotion of magnesium alloys.The quality of magnesium alloy pretreatment directly affects the performance of magnesium alloy electroplated nickel-cobalt alloy.The experiments on the magnesium alloy pretreatment process for alkali washing,pickling,activation,primary zinc immersion and secondary zinc immersion have been studied,and water film is used.The pretreatment results were evaluated by the method of electrochemical analysis,surface roughness and weight loss.The results showed that the surface oxide film of the magnesium alloy after pickling was removed,which increased the roughness of the magnesium alloy matrix to some extent.After the potassium process is activated,the surface of the magnesium alloy is flattened;after one zinc immersion,the surface of the magnesium alloy is covered by the zinc immersion layer,and the zinc immersion layer is relatively flat.After the second immersion zinc,the substrate is completely covered by the zinc immersion layer,and the immersion is performed.The zinc layer is flatter than the zinc immersion once;the addition of 2.0 g/L Fe³⁺and 2.0 g/L Ni²⁺to the zinc immersion solution can promote the coverage of the zinc immersion layer,and the obtained zinc immersion layer is better.The optimized experimental formula is:35 g/L ZnSO₄·7H₂O,125 g/L K₄P₂O₇·3H₂O,5 g/L NaF,5 g/L Na₂CO₃,2.0 g/L NiSO₄,2.0 g/L FeCl₃,zinc immersion temperature 65°C,immersion time 15 min,pH=11.For the magnesium alloy electroplating nickel-cobalt alloy process,this experiment used single factor analysis to study the influence of the main components in the electroplating bath on the nickel-cobalt alloy coating.The laser confocal microscope,X-ray diffractometer and scanning electron microscope were used to rough the coating.The degree,composition and microstructure were analyzed.The corrosion resistance of the coating was tested by drop test,salt spray test and electrochemical test technique.The electroplated nickel-cobalt alloy process was optimized.The experimental results show that NiSO₄ and CoSO₄.The amount of NH₄HF₂ has an effect on the corrosion resistance of the coating.With the increase of the dosage,the corrosion resistance of the coating decreases.The temperature,current density and pH affect the roughness of the coating.The larger the parameter value,the rougher the surface of the coating.The optimized electroplated nickel-cobalt alloy process is:110 g/L NiSO₄,30 g/L CoSO₄,105 g/L NH₄HF₂,3 g/L sodium saccharin,0.1 g/L sodium lauryl sulfate,temperature65°C,pH It has a current density of 1.0².5 A/dm² and a plating time of 20 min.Under this process,a complete and dense spherical crystal coating can be obtained.The corrosion resistance of the coating is excellent,and the self-corrosion current density is at least 8.184×10^-7 A/dm²,3%CuSO₄ drip test time is 58s,and the salt spray test can reach 2.5h.