Structural Change in Hot-Stamped GA Coating and Influence on Corrosion Resistance by Tempering

Hot-stamped galvannealed steel sheets (GA) are widely applied to produce automobile components that require high strength. The hot-stamped components tempered for the control of strength improve the collision property. This study investigated the structural changes in the hot-stamped GA coating and the influence on corrosion resistance by tempering. It has been revealed that by tempering between 500-600 degrees Celsius, the Fe-Zn solid-solution phase in the hot-stamped GA coating changed into two phases: the Γ phase and the Fe-Zn solid-solution phase with less Zn, and these changes in the coating structure improved the corrosion resistance. The phase decomposition is considered to result from discontinuous precipitation of the Fe-Zn supersaturated-solid-solution.