Processing of primary silicon and mg2si reinforced hybrid functionally graded aluminum composites by centrifugal casting

Abstract

In the present investigation, FGMs of mono-dispersed in-situ primary Si and their hybrids with mg<inf>2</inf>si reinforcements have been fabricated by the centrifugal casting process using 390 commercial Al alloy. Hard primary silicon particles are formed during the solidification of the 390 alloy and mg <inf>2</inf>si reinforcements are formed by the addition of varying amount of magnesium into the A390 aluminium alloy. Owing to the difference in density both primary silicon and mg<inf>2</inf>si gets segregated towards the inner periphery during centrifugal casting. The size of the mg<inf>2</inf>si in-situ reinforcement phase is relatively smaller and is distributed in the edges of primary silicon particles and also individually in the matrix. The in-situ mg<inf>2</inf>si and primary silicon can significantly increase the hardness and strength of the inner periphery of the casting. Higher Mg contents have been observed to introduce significant porosity leading to poor castings. Addition of phosphorous to the melt has led to the modification and refinement of primary Si morphology and also helped in the reduction of shrinkage porosity. Maximum hardness of 167 BHN is observed towards the inner periphery of the 390Al-2.5%Mg added in-situ composite. © (2012) Trans Tech Publications.