Influence of microstructure on mechanical properties of hypereutectic Al-Si alloys

Conventional mechanical properties and toughness of Al/25Si/5Cu and Al/25Si/5Cu/2Mg MMCs formed to near-net shape using a combination of spray-forming, extrusion and thixoforming have been analysed. Microstructural parameters and principally local distribution and clustering of Si particles play a very important role in MMCs mechanical behaviour. Fracture starts at particle clusters growing rapidly through CuAl2 eutectic and the matrix. Due to the different Si primary particle distribution, the Al/25Si/5Cu/2Mg MMC shows better tensile behaviour for the tested temperature range with a little loss of strength. On the contrary, the performed fatigue precracked toughness tests indicate that the Al/25Si/5Cu alloy has a much better toughness.