Studies On Preparation And Electrodeposition Behavior Of Pulse Electroplating Ni-Cr-Mo Alloy Coating

In order to improve corrosion resistance of Q235 steel in seawater,Ni-Cr-Mo alloy coating was deposited on the surface of Q235 steel.Effects of bath constitutes,ammonium citrate content,urea content,bath temperature,p H value,average current density,duty cycle and electroplating time on coating element composition,deposition rate,porosity,and corrosion resistance were investigated by glow discharge spectroscopy(GDS),scanning electron microscopy(SEM),filter paper method,Tafel curve and electrochemical impedance spectroscopy(EIS),respectively.Molar ratio of the optimal bath compositions Ni SO4·6H2O,Cr Cl3·6H2O and Na3 Mo O4·2H2O was 10:1:1.The optimal ammonium citrate content was 0.6 mol·L-1.The optimal urea content was 1.0 mol·L-1.And the optimal process parameters were bath temperature 30?,p H value 3.5,average current density 10 A·dm-2,duty cycle 0.2,electroplating time 50 min.Comparing with alloy coatings deposited by direct current and single pulse current,alloy coating deposited by pulse-reverse current with the minimum surface roughness exhibited the best corrosion resistance.Ni-Cr-Mo alloy electrodeposition behavior was studied by polarization curve,cyclic voltammetry(CV),electrochemical impedance spectroscopy(EIS)and chronoamperometry.Ni-Cr-Mo alloy electrodeposition in citrate-urea system was an irreversible process controlled by diffusion.Adsorption to electrode surface of active intermediates and nucleation process existed during electrodeposition process.