Corrosion-resistant Properties of Hot-dip Galvannealed Steel Sheets

Neutral salt spray test(NSST) and electrochemical test of DX56 were performed to study its corrosion properties.The changes of red rust area and weightloss of GI sheet and GA sheet as well as the Tafel polarization curves and electrochemical impedance spectroscopy (EIS) in 2 wt.% NaCl solution were obtained.NSST showed that the red rust on GA sheet occurred much earlier than GI sheet and the weightloss of GA sheet was less than GI sheet obviously.Tafel curves showed that both of GI sheet and GA sheet′s corrosion behaved to be activated dissolution without passivation and that GA sheet′s corrosion potential moved to positive direction in contrast with GI sheet′s.At the same anodic potential,GA sheet′s polarization current density was obviously lower than GI sheet′s.It was obtained from the EIS diagrams and the simulation results of their equivalent circuits that the charge transfer resistance of GA sheet was obviously higher than that of GI sheet.It is shown that GA sheet has better corrosion resistance than GI sheet and using weightloss to judge the corrosion resistance of GA sheet is more accurate than using the time for red rust to occur or the growth rate of red rust area.