Performance and Anti-Corrosive Mechanism of Electroplated Zn-Ni Alloy Coating

The corrosion resistance,phospha-ting performance,hull-painting performance,and welding behavior of the steel plates coated with high-speed electroplated Zn-Ni alloy coating were investigated making use of X-ray diffraction a-nalysis,salt water immersion test,salt-spray test,and measurement of the polarization curves.The anti-corrosion mechanisms of the coatings were primarily explored.It was found that the Zn-Ni alloy coating showed better corrosion resistance than the galva-nized coating in the aqueous solution of 5%NaCl.Namely,no red rust was observed on the Zn-Ni alloy coating immersed in the salt water unless the immersion time rose to 2.5-4.0 times of that of the galvanized coating in the same salt water,and the alloy coating with 13%Ni(mass fraction) showed the best corrosion resistance.Moreover,the steel plates coated with the Zn-Ni alloy coating had better adaptability to phosphating than the cold-rolled counterparts,and the former had satisfactory hull-painting performance and welding behavior as well.With respect to the anti-corrosion mechanisms,the passivation of the electroplated Zn-Ni alloy coating during the corrosion process was not attributed to the enrichment of Ni but to the isolating action of the corrosive products.