Numerical Evaluation of Cyclone Application for Impurities Removal from Molten Aluminum

The purification of gaseous and liquid media by means of a cyclone concept is well known and has been successfully applied in different industries. While the impurities removal from molten metal has been an important issue for many years, to the best of our knowledge, the application of a cyclone concept has rarely been considered for molten metal applications. The presence of impurities in cast products is detrimental to their quality. In this article, computer simulations are used to evaluate the possibilities of cyclone application in molten aluminum processing by determining the following: the fluid flow for flow velocities of 0.01, 0.1, and 1 m/s; the particle behavior for discrete particle sizes in the range of 20 to 100 ?m; and the collection efficiency of the cyclone. The geometrical features are discussed. The results show that the cyclone concept can be effectively used as an alternative method to remove the impurities from a stream of molten aluminum in a wide range of flow regimes.Department of Materials Science and EngineeringMechanical, Maritime and Materials Engineerin

Investigation of fracture behavior of high strength aluminum alloys in the as-cast condition

Materials Science & EngineeringMechanical, Maritime and Materials Engineerin

Numerical simulation of residual thermal stresses in AA7050 alloy during DC-casting using ALSIM5

Non-homogenous cooling rates and solidification conditions during DC-casting of high strength aluminum alloys result in the formation and accumulation of residual thermal stresses with different signs and magnitudes in different locations of the billet. Rapid propagation of microcracks in the presence of thermal stresses can lead to catastrophic failure in the solid state, which is called cold cracking. Numerical models can simulate the thermomechanical behavior of an ingot during casting and after solidification and reveal the critical cooling conditions that result in catastrophic failure, provided that the constitutive parameters of the material represent genuine ascast properties. Simulation of residual thermal stresses of an AA7050 alloy during DC-casting by means of ALSIM5 showed that in the steady-state conditions large compressive stresses formed near the surface of the billet in the circumferential direction. Stresses changed sign on moving towards the centre of the billet and became tensile with high magnitudes in radial and transverse directions, which made the alloy prone to hot and cold cracking.Materials Science & EngineeringMechanical, Maritime and Materials Engineerin

Effect of Grain Refinement on Structure Evolution, “Floating” Grains, and Centerline Macrosegregation in Direct-Chill Cast AA2024 Alloy Billets

Direct-chill (DC) cast billets 192 mm in diameter of an Al-Cu-Mg alloy were examined in detail with the aim to reveal the effects of grain refining (GR) and casting speed on structure, “floating” grains, and centerline macrosegregation. Experimental results show that grain size and dendrite arm spacing (DAS) tend to coarsen toward the billet center with a local refinement DAS in the center. In GR billets, grain size does not change much with the cooling rate, casting speed, and grain refiner amount. Coarse-DAS (floating) grains are observed around the billet axis regardless of GR and the amount of Ti, though their amount is significantly higher in GR billets. Macrosegregation profiles show a negligible influence of GR, while the effect of casting speed is large. The concept of solute-depleted floating grains contributing to the centerline macrosegregation is substantiated by microsegregation measurements, which show that, independent of GR, coarse dendrite branches have a depleted concentration plateau in contrast to the fine dendrite arms.Materials Science and EngineeringMechanical, Maritime and Materials Engineerin

On the development of a cold cracking criterion for DC-casting of high strength aluminum alloys

Materials Science & EngineeringMechanical, Maritime and Materials Engineerin

Constitutive parameters, mechanical properties and failure mechanism in DC-cast AA7050 billets

Materials Science & EngineeringMechanical, Maritime and Materials Engineerin

Application of a criterion for cold cracking to casting high strength aluminum alloys

Direct chill (DC) casting of high strength 7xxx series aluminium alloys is difficult mainly due to solidification cracking (hot cracks) and solid state cracking (cold cracks). Poor thermal properties along with extreme brittleness in the as-cast condition make DC-casting of such alloys a challenging process. Therefore, a criterion that can predict the catastrophic failure and cold cracking of the ingots would be highly beneficial to the aluminium industry. The already established criteria are dealing with the maximum principal stress component in the ingot and the plane strain fracture toughness (KIc) of the alloy under discussion. In this research work such a criterion was applied to a typical 7xxx series alloy which is highly prone to cold cracking. The mechanical properties, constitutive parameters, as well as the KIc values of the alloy were determined experimentally in the genuine as-cast condition and used as input data for the finite element package ALSIM5. Thermomechanical simulations were run for billets of various diameters and the state of residual thermal stresses was determined. Following the contour maps of the critical crack size gained from the model, the casting conditions were optimized to produce a crack-free billet.Materials Science & EngineeringMechanical, Maritime and Materials Engineerin