Room and high temperature ECAP processing of Al-10%Si alloy

An Al-10%Si metal matrix composite has been processed by severe plastic deformation over a range of temperatures in order to refine microstructure and improve mechanical behaviour. Material in the as-cast state is too brittle to process significantly at room temperature and requires higher temperatures for processing, while material given a previous globularising heat treatment or previously hot extruded is more ductile and can be processed at relatively low temperatures. All processing treatments lead to refinements of matrix grain and Si particles, with corresponding improvements in both strength and ductility. Microstructures are not refined as much as expected, based on previous studies of Al-7%Si, which is explained by the inability to accumulate high densities of geometrically-necessary dislocations and construct the refining grain boundaries. The strengthening found is due to a combination of grain boundary hardening, matrix and particle hardening, and dislocation hardening, with this latter term being the most important for low processing temperatures but negligible when processing at high temperatures.