The Study Of Zn-Cr Coating

A novel excellent corrosion resistant of Zn-Cr film coating had been fabricated with fine zinc powder,chromate and acrylic acid etc in this study. The preparation technique,composition and phase structure of Zn-Cr coating,bonding force,corrosion resistance as well as oxidation resistance had been systematically studied using optic microscope,scanning electronic microscope,X-ray diffractometer and electrochemical corrosion technique.Result shows that the finer the zinc powder and the more the amount of zinc powder,the better the quality of the coating is. A fine quality of Zn-Cr coating can be synthesized as molar ratio of zinc powder:chromate=0.08-0.2,chromate:acrylic acid=0.8-4,the amount of polyvinyl alcohol in the coating bath reaches 20-40at% . And the content of chromate and polyvinyl alcohol also affect the bonding force between the coating and matrix. The optimum content of Zn-Cr film coating bath have been concluded as follows:1000g/L zinc powder,2wt% chromate,0.2wt% acrylic acid,7vt% polyvinyl alcohol through the quadrature experiment. The analysis of scanning electron microscope and X-ray diffractometer show that the composition of Zn-Cr film coating is composed of Zn,ZnO and Cr2O3,and Cr2O3 is as bonding agent between the zinc powder andmetal matrix. The corrosion resistant of Zn-Cr coating is 7 times as high as zinc plating in the solution of 3.5 %NaCl,and in the solution of 3.5 %NaOH is same as zinc plating with the study of electrochemical technique and weight losing method. The study of high temperature oxidation shows that the oxidation resistant of Zn-Cr coating keeps well under 350,the quality of Zn-Cr coating has not been changed through a long period of heating.