Metallurgical structure of A356 aluminum alloy solidified under mechanical vibration: An investigation of alternative semi-solid casting routes

This study investigated the effects of mechanical vibration during solidification on the metallurgical structure of hypoeutectic aluminum-silicon A356. A series of casting trials were conducted. Emphasis was placed on the morphological changes of the primary aluminum phase of the as-cast alloy, which was subjected to different levels of mechanical vibration at various values of pouring temperature and solid fraction. It was found that the average grain size of the primary phase became relatively finer and more globular as the degree of vibration increased. This suggested that during the solidification process, dendrites that formed normally in the liquid alloy were subsequently disturbed and fragmented by the mechanical vibration introduced into the melt. This effect was enhanced when the vibration was introduced into an alloy with a larger solid fraction, as was observed with solidification at lower pouring temperatures. In addition to the macrostructure examination, semi-solid properties were also assessed and reported using the Rheocasting Quality Index. It was shown that the introduction of mechanical vibration into the A356 melt with adequate solid fraction prior to complete solidification successfully resulted in an as-cast structure featuring semi-solid morphology. (C) 2009 Elsevier Ltd. All rights reserved.