Effect of grain refinement treatment on the microstructure of cast Al-7Si-SiCp composites

An addition of Ti or Ti/B is an accepted technique to produce cast aluminum alloys having fine grain size and superior mechanical properties. Present investigation focuses on the role of grain refinement treatment on the SiC particle distribution in Al-7 wt.% Si-10 vol.% SiCp cast composites and also on the degree of refinement of matrix microstructure. Composites manufactured by vortex method were treated with three different commercial grain refiners namely; K2TiF6 salt, Al-6Ti and Al-5Ti-1B master alloys. Microstructural characteristics including nature of distribution of SiCp in the matrix, grain size and dendritic arm spacing have been studied. It was found that complete dewetting of the SiCp and consequently their rejection from the melt takes place when the composite was treated with K2TiF6 salt. Improved distribution of SiCp in the matrix of composites was observed when the melt was treated with either Al-6Ti or Al-5Ti-1B master alloy. Composite melt treated with Al-5Ti-1B master alloy show excellent combination of matrix grain refinement and uniform SiCp distribution. (C) 2004 Published by Elsevier B.V.