Study On The Corrosion Behaviour Of Zinc-nickel Compound Coatings On Q235 Low Carbon Steel

The basic material used in this experiment is Q235 low carbon steel,which is easily damaged by corrosion.This experiment aims to get zinc nickel coatings and trivalent chromium based conversion coating(CCC)by electrodeposition to improve the corrosion resistance of low carbon steel.It is found that the bath temperature must be lower than 30 degrees in the process of electroplating.In addition,Zinc Oxide,nickel sulfate and current density have significant effects on the content of nickel in zinc nickel alloy layer.We found that the nickel content is gradually decreased with the increase of the concentration of Zinc Oxide;nickel content is gradually increased firstly and finally stable with the increase of the concentration of nickel sulfate;the nickel content is increased,and the change is very fast with the increase of current density.We found that the surface of Zn Ni coatings is smooth and compact by SEM,and the surface is consist of zinc nickel particle;the surface of the trivalent CCC has many microcracks,and the number of micro-cracks will change by the conversion conditions.Polarization curves and salt fog test were used to test the corrosion resistance of the coating.The results showed that the nickel content of Zn Ni alloy coating is about 13% which has the lowest corrosion current density.Salt fog test also indicated that Zn Ni alloy with 13% nickel content has the longest time for red rust,.Salt fog test results show that when the passivation liquid pH is 1.1,the passivation time is 20 s,and the passivation temperature is 25 degrees,the time when it has red rust is the longest,indicating that the passivation layer has good corrosion resistance.We can know the corrosion resistance mechanism of zinc nickel alloy and the trivalent CCC through EIS.We get that zinc nickel coatings can enhance the ability of anticorrosion by processing corrosion products.We also can know that the way of enhancing ability of anticorrosion on the trivalent CCC is processes corrosion products,and the corrosion products can fill the surface cracks.