Effect of Nozzle Shape on Periodic Surface Patterns of Al-3 mass% Si Alloy Strips Fabricated by Vertical-Type High-Speed Twin-Roll Casting.

Shiny and un-shiny periodic patterns are formed on the cast strip surface of aluminum alloys fabricated by using vertical-type high-speed twin-roll casting. The periodic surface patterns reduce the ductility of the rolled sheets produced from the cast strip, and thus should be suppressed. The surface patterns are caused by the vibration of the molten metal in the gap at the contact point between the nozzle tip and roll surface. In the present study, three types of nozzles (normal, release agent, and bent tip nozzle) were prepared. The effect of the nozzle shape on the surface patterns of Al3 mass% Si alloy containing 1 mass% Fe, 0.5 mass% Mg, and 0.8 mass% Cu cast strips was investigated. The normal nozzle produced a periodic surface pattern and Si segregation in the un-shiny region was observed. Cross-sectional observation showed a difference in cooling rate between the shiny and un-shiny regions caused by the vibration of the molten metal near the nozzle tip. The release agent nozzle suppressed the periodic surface pattern slightly and Si segregation remained. The bent tip nozzle produced a strip surface where the shiny and un-shiny regions were mixed instead of a periodic surface pattern, and Si segregation was not observed. Because the gap near the nozzle tip was small, the vibration of the molten metal was strongly suppressed. [ABSTRACT FROM AUTHOR]