Influence of Strip Entry Temperature on Spangle Size of Hot-Dip 55%Al-Zn-Si Coated Steel Sheets

Objectives: We investigate the effect of the strip entry temperature (SET) of steel sheets on the spangle size of hot-dip 55%Al-Zn-Si (Galvalume) coating. Methods: The hot-dip Galvalume coatings with different SETs were prepared by a hot-dip simulator on a 2.0 mm thick steel sheet. The surface of the coating, the morphology of the coating, and the structure of the interfacial alloy layer were analyzed by using an optical microscope (OM) and field emission scanning electron microscope (SEM). Results: The average size of spangles on the coatings decreased from about 3.4 mm (29 pcs per 100 mm) at the SET of 500°C to about 1.9 mm (53 pcs per 100 mm) at the SET of 650°C. The thickness of the intermetallic compound layer in the interface layer increased from about 2.6 μm at the SET of 500°C to about 3.4 μm at the SET of 650°C. Conclusions: The increase in the SET increased the diffusion of iron atoms through the interfacial FeAl 3 /α-AlFeSi phase, and the thickening of the interfacial alloy layer was conducive to the nucleation of the aluminum-rich dendrites, which resulted in the decrease in the spangle size.