Effect of nozzle tip shape and solute segregation on surface qualities of Al-3%Si-1%Fe alloy twin-roll cast strips

Aluminum alloy strips fabricated by vertical-type high-speed twin-roll casting have periodic surface patterns consisting of shiny and un-shiny areas, which adversely affect mechanical properties and appearance quality of the strips. The surface patterns are thought to be caused by the movement of molten metal in the gap at the contact point between the nozzle tip and roll surface. In this study, Al-3%Si-1%Fe alloy strips with different surface qualities were obtained by the vertical-type high-speed twin-roll casting with various nozzle tip shapes. Microstructural observation and compositional analysis of these strips were conducted to investigate the effect of nozzle tip shape on the surface qualities of the strips. When a nozzle with the tip facing the center of the roll was used, un-shiny strips over the entire surface without periodic patterns were fabricated. This is thought to be due to an increase in surface roughness caused by the lower molten metal height and insufficient contact between the molten metal and rolls. Furthermore, comparison with Al-3%Si binary alloy strips revealed that Al-Fe-Si intermetallic compound particles have a significant influence on the formation of un-shiny areas.