Integrated Approach for Prediction of Hot Tearing

Shrinkage, imposed strain rate, and (lack of) feeding are considered the main factors that determine cavity formation or the formation of hot tears. A hot-tearing model is proposed that will combine a macroscopic description of the casting process and a microscopic model. The micromodel predicts whether porosity will form or a hot tear will develop. Results for an Al-4.5 pct Cu alloy are presented as a function of the constant strain rate and cooling rate. Also, incorporation of the model in a finite element method (FEM) simulation of the direct-chill (DC) casting process is reported. The model shows features well known from literature such as increasing hot-tearing sensitivity with increasing deformation rate, cooling rate, and grain size. Similar trends are found for the porosity formation as well. The model also predicts a beneficial effect of applying a ramping procedure during the start-up phase, which is an improvement in comparison with earlier findings obtained with alternative models. In principle, the model does not contain adjustable parameters, but several parameters are not well known. A full quantitative validation not only requires detailed casting trials but also independent determination of some thermophysical parameters of the semisolid mush.Materials Science and EngineeringMechanical, Maritime and Materials Engineerin

Method of recovering a metal from a mixture

The invention relates to a method of recovering a metal from a mixture comprising more than one metal. According to the invention, the methods comprises the steps of (a) melting the mixture to produce a melt; (b) passing the melt over a cooled surface, causing the metal to be recovered to crystallise out on the cooled surface and a desired metal-depleted melt is discharged from the cooled surfaceMechanical, Maritime and Materials Engineerin

Modification of a thermomechanical model to predict constitutive behavior of Al-Mg-Si alloys

A previously developed constitutive model for quantification of the effect of the condition of Mg and Si in AA6xxx alloys was used for the prediction of the flow stresses measured by plane strain compression (PSC) tests. As an extension of earlier work, two AA6xxx alloys were subjected to different thermal pretreatments and were plane strain compression tested at temperatures and strain rates typical for hot extrusion. Heating rates to the test temperature were varied. Dissolution behavior of the ß precipitates, needed for the quantification, was experimentally validated using differential scanning calorimetry. Significant differences in flow stress during PSC testing were observed as a function of the heating rate to the deformation temperature and of the different conditions that resulted from the different thermal pretreatments. The model was also applied to the combined set of present data and data reported earlier. This combined set of data encompasses a wide range of alloy compositions and thermal histories. It is found that the model gives a fair prediction. Excellent agreement was obtained by assuming that the parameter describing the solution hardening behavior in the model is temperature dependent instead of constant.Aerospace Materials & ManufacturingAerospace Engineerin