Modification of Al - Si Alloy ( LM 28 ) By MnO 2 Addition

Modification of primary silicon was studied in Al-Si hypereutectic alloys with 17 Wt % silicon content. The alloys modified through non-conventional method using oxide addition. The effect of oxide on the morphology and size of Si phases in the hypereutectic Al-Si alloys investigated. The results show that the addition of MnO2 to the hypereutectic Al-Si alloys can modify the primary Si phases. In this, the primary Si phase is refine and the shape of the eutectic Si changed from long needle-like to short rod-like. The modified Al-17Si alloys have microstructures consisting of uniformly distributed α-Al phase, eutectic Al–silicon and fine primary Si particles in the inter-dendrite region. The evaluation of microstructure showed that the fraction of primary silicon decreased with increasing the oxide content. The improved properties are dependent on uniform distribution of fine fibrous eutectic Al–silicon and fine primary Siparticles. The finest microstructure could be observed respectively when 2.5 wt % and 5 wt% MnO2 were added. In this case, hardness, tensile strength and % elongation increased than without added casting. Keywords—Hardness, Hypereutectic Al-Si alloy, Microstructural Refinement, Modification, Tensile strength.