Study On Process And Properties Of Ni-Cr-Mn Alloy Coating By Pulse Plating

Recently it has been difficult for the Ni-Cr alloy coating to meet the requirements of materials used in harsh environments,because of the low Cr content and the thin thickness.Researches find that the addition of Mn can improve the corrosion resistance of alloy coating.With the purpose of strengthening the corrosion resistance of Q235 steel,Ni-Cr-Mn alloy coating is prepared on the surface of Q235 steel by pulse plating.Effect of bath constitutes,coordination agent,additive,bath temperature,pH,current density,electroplating time,duty cycle and electrodeposition methods on coatings element composition,deposition rate,surface morphology and corrosion resistance was investigated by GDS,SEM,Tafel curve and EIS.The optimal bath composition and process parameters were determined.Molar ratio of NiSO₄·6H₂O,CrCl₃·6H₂O and MnSO₄·H₂O was 3:5:10.Compound coordination agent A was 0.35 mol/L.The optimal process parameters were bath temperature 40℃,p H value 2.6,average current density 13 A/dm2,electroplating time 30 min,duty cycle 20%.Comparing with alloy coating prepared by direct current,single pulse current and pulse reverse current electrodeposition methods,the pulse reverse current with the minimum surface roughness exhibited the best corrosion resistance.Electrodeposition behavior of Ni-Cr-Mn alloy in sulfate-chloride system was studied by means of polarization curves,cyclic voltammetry curves and time current curves.The results showed that the deposition of Ni-Cr-Mn alloy was an irreversible process.And the alloy coating had the best corrosion resistance.