Silicon morphology modification in the eutectic Al-Si alloy using mechanical mold vibration

It is well documented that applying mechanical vibration to the mold during solidification has a profound effect on the microstructure and mechanical properties of castings. However, it is still not well understood how mechanical vibration change the resulting microstructure. Most of the available studies are qualitative and provide little quantitative information that can be used by the casting industry. In this work, mechanical mold vibration is applied to an Al-Si eutectic (Al-12.5% Si) alloy at a frequency of 100Hz and variable amplitudes in the range of 18-199 mum. It is shown that the silicon morphology was strongly influenced by the level of vibration amplitude. Generally, increasing the vibration amplitude tends to reduce the lamellar spacing and change the silicon morphology to become more fibrous. However, exceeding a critical value of vibration amplitude tends to coarsen the silicon. The corresponding changes in mechanical properties are also investigated. It is shown that the maximum elongation is more influenced by vibration than the tensile strength for the range of conditions tested here. (C) 2004 Elsevier B.V. All rights reserved.