The grain size control of A356 aluminum alloy by horizontal electromagnetic stirring for rheology forging

In this paper, the morphology of the change of primary Al phase in A356 alloy by a self-designed horizontal electromagnetic stirrer was used to determine the rheological behavior of A356 aluminum alloy. Electromagnetic stirring has been recognized as the most efficient way to produce globulitic structured pre-material for forming. The globularity of the structure is the key to the low apparent viscosity and also to good rheological properties. The stirring promotes the coarsening of primary particles by the formation and melting of grain boundaries produced either by deformation or by sintering of the primary particles. The initial dendritic structure is fragmented by the stirring of the partially solidified alloy, so that the melting of the grain boundaries is the predominant mechanism during the initial stage of stirring. The effects of the stirring current, the stirring time, the pouring temperature and the holding time were determined. The greater stirring current and longer stirring time were to get the finer Al phase. However, over a certain stirring current and stirring time, the primary-Al was merged together and was increased. The optimum conditions of horizontal electromagnetic stirrer have been investigated for rheology forging with controlled solid fraction.