Focusing on improving the galvanizability of the third generation automotive steel, the effect of surface ox ide morphologies on the galvanizability was studied. The results show that the surface oxide types of sample...Focusing on improving the galvanizability of the third generation automotive steel, the effect of surface ox ide morphologies on the galvanizability was studied. The results show that the surface oxide types of sample steels by X ray photoelectron spectroscopy （XPS） analysis after annealing in different conditions are the same. Only MnO, MnO2 and Cr2O3 were detected and no complex oxide exists on the surface. Morphologies of surface oxides can greatly influence the galvanizability of the third generation automotive steel. Nodule-like oxide surface can contribute to better wettability and inhibition layer than vitreous film like oxide surface. Galvanized panels of nodule-like oxide surface steels only show pinhole sized bare spots, while panels galvanized from vitreous film-like oxide surface steels reveal larger areas of bare spots and uncoated areas. Inhibition layer observed in galvanized panels of nodule-like oxide surface steels is compact but not homogeneous; some inhibition layer grains are fine, and others are coarse, while the inhibition layer grains of panels galvanized from vitreous film-like oxide surface steels have a non-compact morphology with some particularly fine equiaxed crystals which developed deficiently.展开更多
Improving the galvanizability of high silicon advanced high strength steels （AHSS） is a practical technical challenge. In this study, spot defects on an industrial hot dip galvanized （GI） sheet of an AHSS with 1.5...Improving the galvanizability of high silicon advanced high strength steels （AHSS） is a practical technical challenge. In this study, spot defects on an industrial hot dip galvanized （GI） sheet of an AHSS with 1.5 % Si has been studied in-depth. The surface morphologies of spot defects before and after partial and complete removal of the Zn layer, as well as the interface between the outermost coating layer and the sheet substrate were characterized using optical microscopy （ OM）, scanning electron microscopy （ SEM）, a 3-D optical profiler, energy dispersive spectroscopy（ EDS ） and focused ion beam （FIB） analysis. The most outstanding spot defect on the normally coated area of the steel sheet has a diameter of approximately 500μm, with the following characteristics. In the central region of the spot defect,Zn is barely coated and the sheet substrate is covered by a thin silicon oxide film with dispersed Zn-Fe intermetallics. At the periphery of the spot defect, a burst structure of Zn-Fe intermetallics forms on the sheet substrate. Outside the spot defect where the Zn layer is normally coated, there is a continuous Fe2Al5 inhibition layer between the Zn coating and the sheet substrate. These results indicate that a silicon oxide film forms on the substrate during annealing prior to hot dipping, thus preventing the formation of the Fe2Al5 inhibition layer during hot dipping. This causes spot defects on high Si AHSS sheets.展开更多
文摘Focusing on improving the galvanizability of the third generation automotive steel, the effect of surface ox ide morphologies on the galvanizability was studied. The results show that the surface oxide types of sample steels by X ray photoelectron spectroscopy （XPS） analysis after annealing in different conditions are the same. Only MnO, MnO2 and Cr2O3 were detected and no complex oxide exists on the surface. Morphologies of surface oxides can greatly influence the galvanizability of the third generation automotive steel. Nodule-like oxide surface can contribute to better wettability and inhibition layer than vitreous film like oxide surface. Galvanized panels of nodule-like oxide surface steels only show pinhole sized bare spots, while panels galvanized from vitreous film-like oxide surface steels reveal larger areas of bare spots and uncoated areas. Inhibition layer observed in galvanized panels of nodule-like oxide surface steels is compact but not homogeneous; some inhibition layer grains are fine, and others are coarse, while the inhibition layer grains of panels galvanized from vitreous film-like oxide surface steels have a non-compact morphology with some particularly fine equiaxed crystals which developed deficiently.
文摘Improving the galvanizability of high silicon advanced high strength steels （AHSS） is a practical technical challenge. In this study, spot defects on an industrial hot dip galvanized （GI） sheet of an AHSS with 1.5 % Si has been studied in-depth. The surface morphologies of spot defects before and after partial and complete removal of the Zn layer, as well as the interface between the outermost coating layer and the sheet substrate were characterized using optical microscopy （ OM）, scanning electron microscopy （ SEM）, a 3-D optical profiler, energy dispersive spectroscopy（ EDS ） and focused ion beam （FIB） analysis. The most outstanding spot defect on the normally coated area of the steel sheet has a diameter of approximately 500μm, with the following characteristics. In the central region of the spot defect,Zn is barely coated and the sheet substrate is covered by a thin silicon oxide film with dispersed Zn-Fe intermetallics. At the periphery of the spot defect, a burst structure of Zn-Fe intermetallics forms on the sheet substrate. Outside the spot defect where the Zn layer is normally coated, there is a continuous Fe2Al5 inhibition layer between the Zn coating and the sheet substrate. These results indicate that a silicon oxide film forms on the substrate during annealing prior to hot dipping, thus preventing the formation of the Fe2Al5 inhibition layer during hot dipping. This causes spot defects on high Si AHSS sheets.
