Extrusion of different aluminium alloys ; experimental work and modelling treatments

The present work reports on modelling of extrusion of both generic and commercial alloys. The uniqueness of the work is the coupling of microstructural based models and FEM-models applied and validated both on laboratory and industrial scales. The extrusion trials were carried out at the laboratory press at SINTEF and at an industrial press at SAPA. Focus in that respect was on the extrusion productivity in terms of ram loads (deformation resistance). Correlations between flow stresses obtained in torsion tests and uniaxial compression tests and the extrudability parameters (breakthrough force and die force) for the same materials and same preheating and processing conditions have been studied. The finite element codes ALMA and FIDAP have been coupled with a microstructural based flow stress model (ALFLOW) and tested on the experimental observations. The constitutive parameters for the different alloys, which is an important input in the ALMA model has been obtained by the ALFLOW model (which has been verified by experimental results in torsion and uniaxial compression). In the case of the ALMA model the predictability of extrusion forces of the investigated alloys are very good. The FIDAP predictions of the industrial extrusion trial are also in reasonable agreement with the experiments. In general, it has been shown that the FEM simulations are very sensitive to the applied constitutive equation and the material constants in this equation

A model for the electrical conductivity of peak-aged and overaged Al-Zn-Mg-Cu alloys

A physically based model for the electrical conductivity of peak-aged and overaged Al-Zn-Mg-Cu (7xxx series) alloys is presented. The model includes calculations of the ?- and the S-phase solvus (using a regular-solution model), taking account of the capillary effect and ? coarsening. It takes account of the conductivity of grains (incorporating dissolved alloying elements, undissolved particles, and precipitates) and solute-depleted areas at the grain boundaries. Data from optical microscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry (EDS), and transmission electron microscopy (TEM) are consistent with the model and its predictions. The model has been successfully used to fit and predict the conductivity data of a set of 7xxx alloys including both Zr-containing alloys and Cr-containing alloys under various aging conditions, achieving an accuracy of about 1 pct in predicting unseen conductivity data from this set of alloys

Analysis of heat affected zone in welded aluminum alloys using inverse and direct modeling

The concept of constructing parameter spaces for process control and the prediction of properties within the heat affected zone (HAZ) of welds using inverse modeling is examined. These parameter spaces can be, in principle, either independent or a function of weld process conditions. The construction of these parameter spaces consists of two procedures. One procedure entails calculation of a parameterized set of temperature histories using inverse heat transfer analysis of the heat deposition occurring during welding. The other procedure entails correlating these temperature histories with either a specific process control parameter or physical property of the weld that is measurable. Two quantitative case study analyses based on inverse modeling are presented. One analysis examines the calculation of temperature histories as a function of process control parameters. For this case, the specific process control parameter adopted as prototypical is the electron beam focal point. Another analysis compares some general characteristics of inverse and direct modeling with respect to the prediction of properties of the HAZ for deep penetration welding of aluminum alloys. For this case, the specific property adopted as prototypical is hardness. This study provides a foundation for an examination of the feasibility of constructing a parameter space for the prediction of weld properties using weld cross-section measurements that are independent of weld process conditions