• Pericleous, Koulis
• Tonry, Catherine
• Bojarevics, Valdis
• Djambazov, Georgi

Abstract

Uniformity of composition and grain refinement are desirable traits in the direct chill (DC) casting of non-ferrous alloy ingots. Ultrasonic treatment (UST) is a proven method for achieving grain refinement, with uniformity of composition achieved with additional melt stirring. The immersed sonotrode technique has been employed for this purpose to treat alloys both within the launder prior to DC casting, and directly in the sump. In both cases mixing is weak, relying on buoyancy driven flow or in the latter case on acoustic streaming. In this work we consider an alternative electromagnetic (EM) technique used directly in the caster, inducing ultrasonic vibrations coupled to strong melt stirring. This ‘contactless sonotrode’ technique relies on a kilohertz frequency induction coil lowered towards the melt with the frequency tuned to reach acoustic resonance within the melt pool.The technique developed with a combination of numerical models and physical experiments has been successfully used in batch to refine the microstructure and degas aluminum in a crucible. In this work we extend the numerical model, coupling electromagnetics, fluid flow, gas cavitation, heat transfer and solidification to examine the feasibility of use in the DC process. Simulations show that a consistent resonant mode is obtainable within a vigorously mixed melt pool, with high pressure regions at the Blake threshold required for cavitation localized to the liquidus temperature. It is assumed extreme conditions in the mushy zone due to cavitation would promote dendrite fragmentation and that, coupled with strong stirring, would lead to fine equiaxed grains.

Topics

• impedance spectroscopy
• grain
• experiment
• simulation
• melt
• aluminium
• ultrasonic
• casting
• solidification