Microstructural evolution during unsteady-state horizontal solidification of Al-Si-Mg (356) alloy

Abstract

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 (VL), cooling rate (TC) and solidification local time (tSL) on the formation of the macrostructure and on the dendritic microstructure evolution were evaluated. A columnar to equiaxed transition (CET) was found for VL and TC 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 (λ1 and λ2, respectively). Experimental laws of λ1 =f(VL, TC) and λ2 =f(tSL) were proposed. It is observed that the interdendritic region is composed of the following eutectic mixture: α(Al)+Si+π-Al8Mg3FeSi6+θ-Mg2Si.