Microstructural Characterisation and Hot-Deformation Behaviour of AA6082 Al Alloy Produced by Low-Frequency Electromagnetic Casting

The present paper outlines the main differences observed in the microstructure and hot workability of AA6082 alloys prepared via low-frequency electromagnetic casting (LFEC) and direct-chill casting, i.e. with and without the application of an electromagnetic stirrer to an innovative casting mould. The hot workability was evaluated through hot-compression tests in the temperature range 450-550 C and at three different strain rates (0.001, 0.1, and 1 s21). Metallographic analysis revealed a grain-size refinement due to the electromagnetic stirring, accompanied by a change in the extent and type of intermetallic compounds between the dendritic arms. A globular microstructure was observed only in the central part of the LFEC billet, where b intermetallic precipitates were observed. The shape of the true-stress versus true-strain curves indicated the occurrence of a dynamic recovery phenomenon. Although the values of the maximum stress were similar for all the samples, analysis of the hot-compression behaviour through a constitutive model revealed differences in the hot-deformation activation energy QHW, with the lowest value belonging to the sample cut from the centre of the LFEC billet, where the effect of stirring was most pronounced.