Influence of solution treatment, Sr-modification and short fibre reinforcement on the eutectic morphology of Al-Si alloys

An experimental study has been conducted on different unmodified and Sr-modified Al-Si alloys and one short fibre reinforced AlSi7 alloy (SFRM) to evaluate the morphological differences of eutectic Si in the as cast condition and after solution treatments. Al-Si alloys, with 7% and higher content of Si, present a percolating Si-network in the as-cast condition. The addition of strontium produces morphological changes in the network from lamellar Si to a fine dispersed coral fibrous like architecture. Spheroidization and coarsening of the eutectic Si architecture is studied after different exposure times at 540 degrees C. It is observed that the integrity of these networks is very sensitive to solution treatment disintegrating into Si particles decreasing the hardness of the alloys. This effect is avoided by the embedding of alumina fibres into an AlSi7 matrix forming an Al2O3-Si-network. The morphology and rigidity of these isolated structures revealed by deep etching and hardness tests are studied after different solution treatment times.