부산대학교 도서관

There is a direct relationship between grain size obtained from macrostructure characterisation and the globule size and shape factor, obtained from the microstructure characterisation: the smaller the grain size, the smaller the globule size and shape factor. Due to this relationship a Rheocast Quality Index (RQI=globule size/grain size * Shape Factor) was used to evaluate the morphological evolution of the A356 alloy produced by electromagnetic stirring during the partial remelting heat treatment. The structure that presents the smallest grain size, the smallest shape factor, and the most homogeneous and globular size of the primary phase, has the best behaviour in the semi-solid forming. Three different as-rheocast initial structures and one as-cast (dendrite), were partially melted at 580 °C at holding times of 0, 30, 90, 210, and 600 s. Both, macro and microstructure were characterised by a Clemex Image Analysis System. The morphological evolution was studied to determine an optimum holding time for thixo-forming processing. [Copyright &y& Elsevier]