Abstract:The increasing demand for reducing vehicle weight in the automotive and aerospace industries has raised the need to develop improved structural aluminum-based alloys. Thus, horizontal solidification experiment with the Al-7%Si-0.3%Mg (mass fraction) alloy was carried out. A water-cooled horizontal directional solidification device was developed and used. Microstructural characterization was carried out using traditional techniques of metallography, optical microscopy and SEM microscopy. The Thermo-Calc software was used to generate the solidification path of the investigated alloy with addition of 0.17% Fe (mass fraction). The effects of the thermal parameters such as the growth rate (V_L), cooling rate (T_C) and solidification local time (t_SL) on the formation of the macrostructure and on the dendritic microstructure evolution were evaluated. A columnar to equiaxed transition (CET) was found for V_L and T_C values from 0.82 to 0.98 mm/s and from 1.71 to 2.55 °C/s, respectively. The microstructure was characterized by the measurement of the primary and secondary dendrite arm spacings (l₁ and l₂, respectively). Experimental laws of l₁ =f(V_L, T_C) and l₂ =f(t_SL) were proposed. It is observed that the interdendritic region is composed of the following eutectic mixture: a(Al)+Si+p-Al₈Mg₃FeSi₆+q-Mg₂Si.

Key words: Al-Si-Mg alloy; microstructural transition; dendrite arm spacing; transient heat flow