Effect of Silicon Content on Solidification Parameters and Microhardness of Al-Si Alloys

In the present work, aluminum-silicon (Al-Si) hypoeutectic alloys were studied in order to investigate the effect of solidification parameters due to the addition of Si in the range of 6 wt. % to 9 wt. % on the structure characteristics and the microhardness. The study was made by directional solidification method in a Brigdman-type furnace. Different types of grains (columnar, equiaxed, and with columnar to equiaxed transition, CET) were visually observed. Such CET depended on the critical thermal gradient G(tc). The analyses carried out indicate that the secondary dendritic spacing (lambda(2)) and the grain size increase significantly with the decrease in the cooling rate (V-e). Furthermore, it was observed that the resulting microhardness increases as the solidification parameters (specifically V-e) increase, this is due to a refinement of the macro and microstructural parameters. Also, it was observed that the microhardness increased with the increase of the Si content.