Influence of vibration on the solidification behaviour and tensile properties of an Al-18 wt%Si alloy

This paper is concerned with the influence of vibration on the mechanical properties of castings. The main vibration effects include promotion of nucleation and thus reducing as-cast grain size: reduction of shrinkage porosities due to improved metal feeding; and production of a more homogenous metal structure. In this study, mechanical mould vibration was applied to an Al-Si hypereutectic alloy at fixed amplitude and different frequencies. Tensile tests were done on specimens obtained with the different vibrating frequency levels. Experimental results show that mechanical properties were influenced by the level of applied frequency. The tensile strength was improved for low vibration frequencies but decreased for high frequencies, as compared with gravity castings without vibration. A microstructure analysis along with a solidification behavior study was performed in order to understand the mechanism responsible for the previous behavior. A heat-transfer mechanism, that is acceleration dependent, seems to be responsible for the shift in mechanical properties response to the vibration effect. (C) 2008 Elsevier Ltd. All rights reserved.