The Structure and Corrosion Process Characterization of Galvannealed and Galvanized Steel Sheets

Abstract

The dissolution process of galvannealed (GA) and galvanized (GI) coating was examined by correlating a chemical stripping test in 1MNaCl+0.01MH2SO4solution. The key time of dissolution process of coating was found via measuring the variation of free corrosion potential. Through coating metallographic observations at the key point, the dissolution process of coating can be clear. There are four Fe-Zn intermetallic phases in GA coating, namely gamma-1,gamma,delta and zeta phases, from the substrate. The compressed part of GA and GI coatings was the initial of corrosion process. The net crack will be emerging on the delta phase, which width graduallyincreasing until stripping. Pitting corrosion occurred on the GI coating in the solution containing Cl-ion, the area and depth of pit gradually increasing until stripping. The corrosion potential of Fe2Al5Znxinhibition layer is about-0.8VSCE.