Effect of Alloy 2 Composition on the Microstructure of Al-Si Alloy Prepared by Controlled Diffusion Solidification with Simultaneous Mixing

Abstract

Taking pure Al as Alloy 1, the effect of Si content in Al-Si alloy (Alloy 2) on microstructures of Al-Si alloy castings prepared by controlled diffusion solidification with simultaneous mixing was investigated mainly by using theoretical simulation and calculation. The results indicate that at a given superheat, the Si content in the Al-Si alloy essentially affects the liquidus temperature, and thus, its mixing temperature and the temperature difference with pure Al melt, causing the variation of temperature field of the resulted mixture besides the solute field. As a result, both the supercooling degree and width of supercooling zone in the pure Al pockets are altered, and consequently the nucleation rate and the size and morphology of primary α-Al grains are varied. At the same liquidus and mixing temperatures (also the same temperature difference with the pure Al melt), the nucleation rates at using hypoeutectic Al-Si alloys are higher than those at using hypereutecitc ones due to the larger supercooling degree and width of supercooling zone of the former condition than the latter condition. Subsequent experiment results on microstructure observation of the CDS castings verify these results, and further confirm that an ideal nondendritic microstructure can be achieved only when the nucleation rate is up to a critical value (corresponding to 30% of solidified mesh number in the simulation).