Efeito dos parâmetros térmicos na microestrurura e microdureza da liga Al7Si0.3Mg (0.15Fe) via solidificação horizontal transiente

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−7wt%Si−0.3wt%Mg (0.15wt%Fe) (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 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 secondary and tertiary dendrite arm spacings (1, 2 and 3, respectively). Experimental laws of 123 = f (VL, TC) and 2 =f (tSL) were proposed. Microstructural characterization by optical microscopy, SEM/EDS elemental mapping and microanalysis of the punctual EDS compositions allowed to observe the presence of an Al-rich dendritic phase (Al()) with interdendritic phases second composed of an eutectic mixture: Al(-eutectic) + Si +Al8Mg3FeSi6() + Mg2Si(). Microhardness test has been performed in the center of the dendrite (Al-rich phase) and the interdendritic region. Higher HV values were observed within the eutectic mixture. A comparative analysis with works from literature for binary and ternary alloys of the series Al-7%Si-(0.3% Mg) (mass fraction) has been elaborated.