Influence of Nozzle Shape on Near-Surface Segregation Formation During Twin-Roll Casting of Aluminum Strips

The near-surface segregation is a characteristic defect of twin-roll cast strips. Intergranular intrusions and bleeds rolled into the strip surface deteriorate the mechanical properties and corrosion resistance. The following mechanisms cause these segregations: periodic fluctuation of the melt meniscus and low-pressure zones between the rolls and the solidified aluminum shells. The aim of this study is to identify how strong the influence of the first mechanism is. To adjust the meniscus length, two different nozzles—one conventional with a butt end and one tailored with a pointed end—are utilized. The lab scale twin-roll cast trials for the production of 3 mm strips from the aluminum alloy EN AW-1050 are conducted in the vertical plane. The microsections with a total length of up to 300 mm are analyzed to establish the intensity and regularity of distribution of surface bleeds along the strips. Additionally, their mechanical properties are compared.