| Aluminum and aluminum alloys have been widely used in the fields of electronic communication equipment,transportation,aerospace and other engineering fields due to their light weight,high specific strength,good electrical and thermal conductivity,and excellent machining performance.However,the active chemical properties,low hardness and poor corrosion resistance of aluminum alloy,seriously restricts its application range.Since the electroless nickel plating technology can effectively improve the hardness and corrosion resistance of aluminum alloy,and the coating has a certain flexibility,its application range can be further extended to the related fields of electric conduction and deformation.As aluminum is relatively active,the surface is easily formed into an oxide film,which results in poor surface catalytic activity in the electroless nickel plating process.Meanwhile,aluminum would be replaced by nickel ions to form impurity ions,which affects the stability of the plating solution,so nickel plating technology and its pre-treatment process are essential for protecting aluminum alloy and related components.As single complexing agent is not enough to take into account the deposition rate,quality and stability of the plating solution,the secondary zinc immersion pretreatment process is used in this paper to study the effect of ternary complexing agent nickel plating solution composed of different concentrations of succinic acid,citric acid and lactic acid on the structure and properties of the coating.In addition,for the secondary zinc immersion process,the zinc layer formed in the subsequent nickel plating process dissolves and contaminates the plating solution,and the ultrasonic cavitation would affect the nickel immersion pretreatment process.So based on the Taguchi method,the effect of nickel immersion pretreatment and ultrasonic nickel immersion pretreatment on the nickel immersion of aluminum alloy is studied.The coating deposition rate,hardness,microstructure and corrosion resistance are also evaluated based on Taguchi analysis.Based on the above research,the main conclusions are as follows:1.The type and content of the complexing agent have a significant effect on the plating speed and the micro-morphology of the coating.The citric acid and lactic acid content in the plating solution have a great influence on the deposition rate and corrosion resistance of the coating.The succinic acid content has little effect on the deposition rate and corrosion resistance of the coating.A highly corrosion resistant coating with a deposition rate of about 13.4?m/h can be obtained by using a plating solution containing 5 g/L succinic acid,5 g/L citric acid and 25 ml/L lactic acid.2.The concentration of trisodium citrate in the nickel immersion pretreatment process has the greatest influence on the deposition rate,hardness and corrosion resistance of the nickel plating layer.When the concentration of trisodium citrate is0.03mol/L,sodium potassium tartrate is 0.01mol/L,pH value is 9,and the temperature is 55?,the deposition rate of nickel plating after nickel immersion pretreatment is12.46um/h;When the concentration of trisodium citrate is 0.15mol/L,sodium potassium tartrate is 0.01mol/L,pH value is 12,and the temperature is 55?,the relative biggest hardness of the nickel plating layer after nickel immersion pretreatment is411.58 HV;When the concentration of trisodium citrate is 0.03mol/L,sodium potassium tartrate is 0.13mol/L,pH value is 11 and the temperature is 55?,the nickel plating layer has the best corrosion resistance,with a nickel-plated layer charge transfer resistance value of 3.64×105 and a constant phase angle element of 6.03×10-6.Compared with the secondary zinc immersion pretreatment,the charge transfer resistance of the nickel plating layer of this method increases from 7.84×104 to 3.64×105,and the constant phase angle element reduces from 2.38×10-5 to 6.03×10-6.3.Ultrasonic power in the ultrasonic nickel immersion pretreatment process has a great influence on the deposition rate,hardness and corrosion resistance of the nickel plating layer.When the ultrasonic power is 80 W,pH value is 10,and the temperature is 25?,the deposition rate of nickel plating after ultrasonic nickel immersion pretreatment is 11.82 um/h;When the ultrasonic power is 60 W,pH value is 10,and temperature is 55?,the nickel plating layer after ultrasonic nickel immersion pretreatment has the relative biggest microhardness of 427.82 HV.When the ultrasonic power is 40 W,Ph value is 12,and temperature is 25?,the nickel plating layer has the best corrosion resistance,with a nickel-plated layer charge transfer resistance value of 4.90×105 and a constant phase angle element of 5.67×10-6.Compared with the nickel immersion pretreatment,the quality of the nickel plating layer after ultrasonic immersion nickel pretreatment improves,and the immersion nickel temperature also reduces accordingly. |
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