Influence of grain refinement and modification on microstructure and mechanical properties of Al–7Si and Al–7Si–2.5Cu cast alloys

The microstructures and mechanical properties (impact toughness, tensile and hardness) of Al–7Si and Al–7Si–2.5Cu cast alloys were studied after various melt treatments like grain refinement and modification. Results indicate that combined grain refined and modified Al–7Si–2.5Cu alloys have microstructures consisting of uniformly distributed α-Al grains, interdendritic network of fine eutectic silicon and fine CuAl2 particles in the interdendritic region. These alloys exhibited improved mechanical properties in as cast condition when compared to those treated by individual addition of grain refiner or modifier. The improved mechanical properties of Al–7Si–2.5Cu alloys are related to breakage of the large aluminum grains and uniform distribution of eutectic silicon and fine CuAl2 particles in the interdendritic region resulting from combined refinement and modification. This paper attempts to investigate the influence of the microstructural changes in the Al–7Si and Al–7Si–2.5Cu cast alloys by grain refinement, modification and combined action of both on the mechanical properties (impact, tensile and hardness).