Papers by Keyword: Initial Transient

Abstract: In the present study, we report on an image analysis procedure, which enables to extract from synchrotron radiographs the long range solute profiles in the whole sample and in both phases (solid and liquid). This image analysis is based on the measurement of local density differences, and is applied to study the directional solidification of Al - 4wt% Cu alloy, from planar to onset of the initial instability. Dedicated experiments were carried out at the European Synchrotron Radiation Facility (ESRF) in Grenoble (France). In order to validate this analysis the value of a key solidification parameter, namely the partition coefficient, was experimentally determined during the planar solidification, and a very good agreement was found with value found usually in the literature. On a further step, the evolution of the microstructure and solute profile during the initial transient of solidification was analysed in detail.

Abstract: Traditional gravity pour down-sprue methods of filling moulds in the making of aluminum castings inherently lead to oxide and air bubble entrainment. The reason for this is found in the high velocities the metal flow experiences during the filling of a mould. The Nemak Windsor Aluminum Plant (WAP) produces cylinder blocks using the low-pressure Cosworth process, which includes low velocity up-hill filling of the sand mould package. This doctrine is followed in all except one part of the process: the runner system. The nature of the resulting defect is generally known as Head Deck Porosity. Runners were cast full in open production runners at three different velocities with the resulting quickly chilled castings analyzed using X-ray radioscopy, and Scanning Electron Microscopy. Results reveal that the subject bubble porosity is indeed the result of air entrained during initial transient flow within the production runner system whose velocity is higher than the critical value of 0.5ms-1. This theoretical value is corroborated by experimental results. In addition, a new "sessile" runner of optimized shape, filled at a velocity slower than the critical value, is proposed and analyzed using Magmasoft mould fill modelling software. The design can potentially replace the existing runner providing a casting free of entrained air.