Application of electromagnetic stirring for the homogenization of aluminium billet cast in a semi-continuous machine

摘要

Several billets have been cast at different levels of current induced in the stirrer coil, they have been characterized under the microstructural aspects and their features have been compared with the characteristics of the as-cast billets and of the thermally homogenized ones, because these last ones are used in the typical and traditional technological route. The coupling of the computational simulations - performed by a multiphysic platform - allows us to estimate the flow patterns induced by the different current levels applied in the stirrer coil. The homogenization of the electromagnetically treated billet has certainly taken place implying a finer distribution of the intermetallic phases. The thermal homogenizing is always associated with a softening of the metal alloys whereas the electromagnetically refined structure shows a hardening phenomenon caused by the induced finest grain size. The flow pattern imposed by the electromagnetic stirrer is strongly dependent on the current intensity that is pointed out as the ruling variable conditioning the velocity field of the liquid pool. Thus, an electromagnetic stirring working at low frequency and a correct modulation of current intensity can be useful for improving the technological route finalized to the extrusion of the aluminium alloys, taking into account that such a route involves the use of extrusion machines featured by a higher power level.