Corrosion Behavior of 1 000 MPa Grade Ultra-High Strength Hot-Dip Galvanized Steel Sheets

The corrosion accelerated test for 1 000 MPa grade ultra-high strength hot-dip galvanized steel sheets was carried out in marine atmospheric environment simulated by neutral salt-spray. The corrosion resistance of galvanized steel sheets after salt-spray corrosion for different periods of time was studied by means of laser confocal microscopy, scanning electron microscopy and electrochemical test. The results show that the galvanized steel sheets corroded as pitting. The pit diameters were 15-25 μm, and there was no obvious increase trend. Subsequently, the corrosion form of the galvanized steel sheets gradually developed toward uniform corrosion. Corrosion products were initial looser needle-like, and subsequently developed into denser ribbons and clusters. After the substrate was exposed, the corrosion products were dominated by loose gully. The primary products of zinc layer corrosion were mainly Zn(OH)₂ and ZnO. Chloride ion combined with zinc oxide to form ZnCl and Zn₅(OH)₈Cl₂·H₂O, and destroyed the oxide layer and accelerated the dissolution of corrosion products. Zn₅(CO₃)₂(OH)₆ was generated after salt-spray test for a long time, and the main corrosion products of matrix were Fe₂O₃. When the salt-spray test was conducted for 48 h, the corrosion products were dense, and the corrosion rate of 0.195 g/(m²·h) and corrosion current density of 3.83 μA/cm² were both at a low level. The relatively dense corrosion products could obviously inhibit the overall corrosion of galvanized steel sheets.