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A full 3D transient model of direct chill casting is developed to predict the thermal stress during the startup phase for AA5182. Simulations show that tensile stress starts to develop at ingot surface and gradually migrates to ingot center. By varying the position of wiper below the mold, the maximum residual stress in the ingot center is reduced by up to 35% compared to that without the use of a wiper. The closer the wiper is inserted below the mold, the larger is the stress reduction effect, but at a greater risk of remelting surfaces below the wiper. In order to prevent this, forced-convection air cooling is recommended on ingot surface below the wiper. The current study recommends application of a moving wiper, from a lower to the bottom of the sump, to combine the benefit of reducing thermal stress and centerline segregation without surface bleeding-out. [ABSTRACT FROM AUTHOR]

A fully transient model of the direct chill casting process is used to examine the influence of implementing a wiper to divert the free falling water from the ingot surface on transport phenomena and segregation profiles for aluminium alloy 7050. The ingot diameter and casting velocity are varied to determine the proper wiper placement as determined by the predicted composition, temperature, and fraction solid fields. The segregation level was evaluated by comparing steady state radial composition profiles. The wiper alters the dominant radial heat transfer mechanism, causing the surface of the ingot to heat up below the wiper. Placing the wiper too close to the mould causes the surface temperature to increase above the solidus, making the ingot susceptible to bleed outs. The optimal wiper location was found to be near the bottom of the sump for all process conditions examined. [ABSTRACT FROM PUBLISHER]

Numerical simulations can provide insight into physical phenomena during alloy solidification processes that cannot be observed experimentally. These model predictions depend on the material, process and numerical parameters which contain inherit uncertainties due to their origin in experimental measurements or model assumptions. As a step towards understanding the effect of uncertain inputs on solidification process modelling, uncertainty quantification and sensitivity analysis are performed on a transient model of transport phenomena during the solidification of grain refined Al-4.5 wt.% Cu in a rectangular cavity. The effect of microstructural model parameters, thermal boundary conditions and material property input uncertainties are examined for their effect on macrosegregation levels and solidification time. Predictions of the macrosegregation level are most sensitive to the dendrite arm spacing of the rigid mushy zone. [ABSTRACT FROM AUTHOR]

A fully transient model of the direct-chill casting process is used to predict the macrosegregation development of aluminum alloy 7050. The ingot diameter, casting speed, superheat, secondary cooling, and thickness of pure Al at startup are varied. Predicted radial composition distributions are fit to Weibull probability density functions at each axial location, and the normalized standard deviation describes the macrosegregation level and the time when the process reaches steady state. The sump depth, steady-state height, and macrosegregation level were most affected by changes in casting speed and ingot diameter. The pure Al dilutes the alloy and delays compositional steady state. [ABSTRACT FROM AUTHOR]

An analytical model was developed to predict the infiltration of a non-wetting liquid into a sharp-cornered channel with rough walls. The distance from the liquid meniscus to the corner and the liquid radius of curvature predicted by the model are a function of contact angle, corner angle, head height and surface roughness. Measurements of these lengths were made in a model experiment as a function of liquid head height. The results of the experiments suggest that the analytical model accurately predicts the wetting limit of corner sharpness. [ABSTRACT FROM PUBLISHER]