Effect of Casting Speed on Internal Macro-segregation Behavior of Aluminum AA 6016 Alloys and Effect Lanthanum on High Mg Al-Mg Strips Fabricated by Twin-roll Casting

Abstract

Aluminum alloys have unique characteristics, such as high specific strength and lightweight that make them attractive for structural applications in automotive, aerospace and number of other general engineering fields. Aluminum alloys wrought products are highly useful due to their specific properties such as high Ultimate Tensile Strength (UTS) and Yield Strength (YS). Twin-roll casting (TRC) is a proven technology for the economical production of thin aluminum sheets manufactured directly from the melt. The advantages of this casting technique are numerous: -reduced capital costs, energy consumption, operating costs and scrap rate compared with a conventional Direct Chill (DC) casting route. Basically, molten metal is delivered via a refractory feeder tip directly into the gap between two internally water-cooled rolls, where it solidifies and undergoes hot deformation, before emerging as a solid strip or sheet. TRC is a complex process containing solidification followed by hot deformation, which makes it necessary to control numerous parameters, such as the initial melt temperature, melt feeding rate, casting speed, nozzle shape, roll gap, amount of coolant and so on, in a narrow solidification region from the nozzle tip to the roll nip (or kissing point). It is also important to understand the mutual interaction between these parameters. The quality of the final strips is closely related to the interactions of numerous working parameters, and the casting speed is one of the most important factors that reflect the interplay of those parameters. Few papers, however, have discussed stress or mechanical responses of the strips during TRC. When the solidification of melt is incomplete during contact with the cooled rolls, the casting speed is high. This increases the possibility of failure of the TRC process by spilling the melt from the strips. The quality of the strips degrades due to insufficient solidification. On the other hand, if the solidification is complete far enough away from the roll nip, the casting speed is too low. This causes the rolls to get stuck in the nozzle, and the possibility of cracks in the formation of the strip increases. The exit of the nozzle is also stopped and operation is affected. Overall, control of the casting speed is important in successful fabrication of strips.