Effect of Al in the Coating Layer of Zn-coated Steel Sheet on Zn Oxidation during Hot-stamping Heating

During hot stamping, Zn oxidation occurs on the surfaces of Zn-coated steel sheets such as galvanized iron and galvannealed sheets. In order to elucidate the effect of Al in the Zn coating layer on the Zn oxidation, the present study investigated the amount of ZnO formed on the Zn-coated steel sheets with and without Al addition to the coating layer. The amount of ZnO was found to decrease upon Al addition. The microstructural analysis of the Zn-coated steel sheets with Al addition revealed that the added Al became the ZnAl2O4 layer at the interface between the ZnO layer and Zn coating layer after hot stamping. As a result, Zn oxidation is considered to be suppressed by the presence of the ZnAl2O4 layer.