Analysis on the Influence Mechanism of Hot-dip Galvanized Steel uniaxial deformation on phosphate conversion coating formation

The mechanism of residual internal stress on the growth and corrosion resistance of phosphate conversion coating (PCC) on hot-dip galvanized (HDG) steel sheets was investigated by finite element analysis , electrochemical tests, scanning electron microscopy (SEM), and coating weight experiments. The results indicate that residual compressive stress inhibits the electrochemical activity of HDG steel sheets. The formation of PCC is also restrained. Residual tensile stress can effectively enhance the electrochemical activity of the substrate, and as the residual tensile stress increased, the cathodic reaction rate of the substrate was increased. In particular, when the residual tensile stress value was 221.0 MPa, PCC grew completely on the surface of the substrate and showed excellent corrosion resistance. When the residual tensile stress reached 261.8 MPa, the fast micro-cathode reaction rate led to the formation of a large number of PCC crystal nuclei, which covered the active site of the substrate and inhibited the further occurrence of the coating formation reaction. The corrosion resistance of the PCC also decreased at this time.