EBSD Study of 55 Wt.% Al-Zn Coating and Corrosion Behavior Effected by Austenitization Heat Treatment

Abstract

Reduction of CO2 emission and enhancement of fuel efficiency are an important environmental issue and the design trend of vehicle structures. Hot stamping process has been employed to for advanced high-strength steel (AHSS) parts for the automobile components. Several coating systems, such Al-Si, Zn, and Zn-Al, on the AHSS for the hot stamping process have been reported. The microstructural evolution during austenitization differs in the type of the coating, which is mainly characterized using the SEM and TEM, as well as the EDS. Electron back-scattering diffraction (EBSD) is a kind of the crystal identification technologies. Due to the difference in the crystal orientation of phases, the phase mapping is power for detailing large-scale microstructural evolution. In this study, the EBSD was employed to identify the phase evolution of a 55 wt.% Al-Zn coated steel during different heat treatments. The result showed that the Fe2Al5 was the major phase formed at 800℃ for 5 min and no Fe-Zn IMCs was found in the coating. As the temperature of the heat treatment was increased to 900℃, the FeAl phase formed on the top of the coating and gradually became the major constituent of the coating. Moreover, the Zn did not react with the FeAl phase and gathered on the top of the coating to form the Zn-oxide. The result of pole figure indicates that the texture orientation of the FeAl phase had changed; however, the orientation change of the Fe2Al5 phase was not obvious and showed preferred orientation. Finally, the chemical stripping results show that the potential of the coating was active than the steel substrate and the potential gap between the coating and steel substrate was approximately 500 mV, which is closed to the result of Zn-coated steel without heat treatment.Key words: 55 wt.%Al-Zn coating, EBSD, austenitization heat treatment, Fe-Al IMCs, chemical stripping Figure 1