Abstract: In order to improve the surface quality of aluminum-silicon plated steel sheet, the microscopic morphology and composition of the point-like defects appeared on the surface of aluminum-silicon plated steel sheet were analyzed by using optical microscope(OM), scanning electron microscope(SEM) and energy spectrum(EDS). The results show that the point defects generated on the surface of the aluminum-silicon plated steel sheet are mainly divided into four categories. The type I point defect components are mainly Al-Si oxide and zinc oxide, which are caused by the adhesion of aluminum dross and zinc dust on the coating surface. The cause of type II point defects is that aluminum slag or foreign matter is pressed into the surface of the coating. The type III point defects are composed of Al-Fe-Si oxides, Al-Si oxides and W-Co-C alloy compounds, which are caused by co-adhesion with the aluminum dross on the surface of the coating. The type IV point defects have the microscopic morphology of middle depression and edge slight bulge, which are caused with surface scratching by foreign objects. In view of the above causes of the defects, some measures are proposed, such as strict controlling of the temperature of the aluminum pot, increasing the frequency of slag fishing, and reducing the oxygen content in the furnace nose.

Key words: hot dip aluminum-silicon plated steel sheet, point defects, cause analysis, improvement measures