Study of the inhibition layer formed in a ga bath on a trip mn-al steel

International audienceThe nature of the inhibition layer formed on an industrially galvanized TRIP Mn-Al substrate was investigated. The Zn bath contained low Al content (0.122 wt.%) as generally used before GalvAnnealing (GA) treatment. Prior to hot-dipping, the steel was recrystallized in a gas atmosphere with different oxygen potentials (Dew Point-DP),-40 and-5°C. The morphology and the nature of selective oxides at the steel surface changed from Al-Mn-O film in low DP annealing conditions to MnO nodules in high DP. In-depth characterization of the inhibition layer revealed that it is biphasic, namely Fe2Al5Znx and δ, regardless the DP of annealing atmosphere. The Fe2Al5Znx layer is discontinuous with δ on top. The selective oxides formed during recrystallization annealing were found to be embedded in the inhibition layer. A mechanism accounting for the formation of the inhibition layer in GA bath in presence of selective oxides is proposed in this paper. It will also be highlighted that the nature of the inhibition layer does not depend on the substrate