A process model for on-line quenching of aluminium extrusions

A complete process model for the cooling of aluminium extrusions is presented. It is capable of predicting both thermally induced distortions and possible strength reductions. The model consists of three parts: a thermal part, a metallurgical part, and a mechanical part. The thermal part includes heat-transfer and heat-conduction models and generates the temperature history needed as input to the other two parts. The metallurgical part consists of a kinematic model for the precipitation of nonhardening particles during cooling, and it predicts the resulting strength after subsequent aging. Finally, the mechanical part comprises the usual compatibility and consistency equations, as well as a unified material model that is very accurate both for rate-dependent material behavior at high temperatures and for the virtually rate-independent behavior at low temperatures. Water-cooling experiments have been performed, and finite element simulations were executed using the process model. The heat-transfer coefficient for water quenching is shown to be extremely sensitive to geometry and other cooling conditions. In addition, the cooling characteristics and the material model are factors of equal importance in the prediction of distortions.