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 (λ₂) 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.