12th International Conference on Zinc & Zinc Alloy Coated Steel Sheet - GALVATECH 2021

Recently, the demand for high strength hot-dip galvanized steel sheet is continuously increasing due to light weight and safety of automobiles. However, in the case of hot-dip galvanized steel sheet, it is found to have a problem that LME(Liquid Metal Embrittlement) cracks occur during welding process, therefore it is limited to supply to the automakers. The hot dip galvanized steel sheet having a low melting point of the coating layer has a problem in that the coating layer melts and penetrates along the grain boundaries during welding process. Aluminum coated steel sheets used in HPF do not produce LME due to the formation of Al-Fe intermetallic compounds having a high melting point at the interface of the coating layer and the substrate, but have no sacrificial corrosion resistance such as Zn. To solve these problems, POSCO has developed new product that are free of LME cracks and have excellent sacrificial corrosion resistance. The new product was developed by adding Zn and Mg to ensure corrosion resistance on Al-base coating which does not generate LME cracks. Although Zn and Mg tends to suppress the formation of Al-Fe intermetallic compounds with high melting point, 1162℃, it promoted the formation of Al-Fe intermetallic compounds during the welding process and suppresses penetration of the molten metal. It also improved the anti-galling properties because of hard coating layer and showed no micro cracks in the bending test.ecause of hard coating layer and showed no micro cracks in the bending test.