The Structure and Corrosion Process Characterization of Galvannealed and Galvanized Steels

摘要

The dissolution process of galvannealed(GA) and galvanized(GI) coating were examined by correlating a chemical stripping test in 1MNaCl+0.01MH_2SO_4 solution. 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 have been cleared. There were 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 would be emerging on the delta phase, which width gradually increasing 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 Fe_2Al_5Zn_x inhibition layer was about -0.8V_(SCE).