Phytic acid pretreatment activate hot-dip galvanized steel to enhance the corrosion resistance of silane film

Abstract

In this work, hot-dip galvanized steel were pretreated with different concentrations of phytic acid(C6H8O24P6，PA) solution to obtain more hydroxyl groups, which act as an activated site on the surface of zinc layer. Then, 3-Glycidoxypropyl methyldiethoxysilane (GPTMS) / tetraethylorthosilicate (TEOS) hybrid silane film was prepared. The structure and morphology of film were tested by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM-EDS). The results indicated that phytic acid treatment at a concentration of 5 ml/L improved the denseness and uniformity of the silane film while increasing its thickness. The results of electrochemical impedance spectroscopy (EIS) showed that the corrosion impedance of silane films under PA pretreatment was greatly improved. Furthermore, there were less rusts after 120h salt spray test.