This study summarises research into the effect of low frequency mechanical vibration on the macro and microstructures of LM6 [Al-Si 12.30%] alloy. Vibration at varying frequencies between 15 and 41.7 Hz and amplitudes between 0.125 and 0.5 mm has been applied to both unmodified and metallic sodium modified LM6 alloys during solidification. The effect of low frequency vibration on the grain size, shrinkage pipe and eutectic silicon were analysed using quantitative metallography. The results indicated that (1) The pipe in the ingot was reduced by vibration with increasing frequency and amplitude. (2) Pipe elimination was more effective with increasing time of vibration of the liquid. (3) Vibration with increasing frequency and amplitude produced grain refinement. (4) Vibration caused coarsening in the eutectic silicon in unmodified and sodium modified LM6 alloy, the extent of which increased with increasing vibration time. (5) Primary silicon in LM6 alloys was coarsened by vibration.