ABSTRACT
Hot-dip galvanized steel sheet (GI) has been more and more used in household electric,autombile construction,with its excellent corrosion resistance and pressing.The most important problems of hot dip galvanized steel in the processing of the deformation process is a large number of coating zinc dust drop off,that is,coating flaking problem.The flaking of the coating will not only affect the processing of deformation capacity, but also deteriorated the corrosion resistance of the coating, and easily lead to surface defects.Therefore, the difficulty of the research and development is to meet the corrosion resistance,good formability of the coating.
In this paper,chosing the low-carbon aluminum killed steel as experimental materials, continuous hot-dip galvanizing processing. Use of the the drawbead tensile test method and the flat-panel sliding method, flaking resistance of different aluminum contents of the coatings were studied,and using OM, SEM,XRD and EPMA experimental methods to analyze the changes in the structure of the organization in different aluminum content in the coatings,which has an effect in flaking resistance .
The results show that the amount of flaking and friction coefficient with the increase in coating aluminum content was broken line shape changes, that is. first dropped to a certain value, after another slight rise. The greater the friction coefficient,the greater the amount of coating flaking. When coating aluminum content of of 0.30 wt.% and greater than 1.07wt.%,the coating flaking resistance is best. The aluminum content in the coating will affect the coating and steel substrate binding and the formation of 8 phase in the coating, C,phase and phase. The aluminum content in the coating will affect the coating and steel substrate binding and the formation of 8 phase in the coating,〔 phase and r| phase. With increasing aluminum contents in the coatings, the coatings of Fe-Al inhibition layer became thicker and the interface is relatively flat, the aluminum content in the coating increased to 1.07wt%, the coating of plastic 5 phase , r| phase. In addition, coating contain a strong diffraction peak (002) r phase. C phase (101), and 5-phase (100) and Fe (112). the C phase (101) diffraction peak the higher the coating formed in the Fe-Zn alloy phase of ‘ phase in the more adverse to the resistance of the coating faking. When the coating of aluminum content of 0.36 wt% near and 1.07wt%,the flaking resistance of the coating is best.a small amount of ( phase in the coating containing strong (002) diffraction peak of Zn,Zn (101) and Fe (100),which Zn (101) and Fe (100) peak the higher the coating processing deformation resistance is better. Deformation of the coating presents the characteristics of the furrows, and along a certain direction. From A1 element in the coating of steel substrate gradually increased and reached the maximum inhibition layer, the subsequent sharp decline; Zn from the steel substrate to the coating surface gradually increased; Fe contents gradually reducted.
The coating and steel substrate form Fe-Al inhibition layer, which content Al-rich poor Zn, has play a role in adhesion and prevent the Fe-Zn alloy reaction between the coating and steel substrate, and the thiner Fe-Zn alloy layer, the better deformation properties of the coating , which means the better flaking resistance. At the same time the formation of Fe-Al inhibition layer between coating and steel substrate,the formation of a large amount of plasticity 5 phase and r phase, and less fragmentation of brittle ; phase,the better of the flaking resistance.The formation of the alumium metal compounds in coatings make the coating uneven and induce the faking resistance of the coating get worse.
Key words: GI; coating organization; flaking resistance;Al content
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