Análise da adição de 2%Ni na liga ternária Al-7%Si-1%Mg solidificada direcionalmente

Abstract

Alloys of the Al-Si-Mg system are applied in the aeronautical and automobile industries and also as structural castings, due to characteristics such as good mechanical resistance and ductility at room temperature, good fluidity and low number of defects arising from the solidification process, in addition to being the basis of chemical composition for alloys of the 3xx.x series of foundry. However, these alloys show a significant reduction in mechanical strength at high temperatures (T> 0.4TF). It is at this point that nickel becomes a promising alloy element, because when added in Al-based alloys it promotes an increase and stability of the mechanical strength. In this context, the present study aims to analyze the influence of 2%Ni (by weight) on the thermal parameters, microstructure and hardness of the directionally solidified ternary Al-7wt.%Si-1wt.%Mg alloy in a transient heat flow regime. The experimental methodology includes the use of a water-cooled solidification device and in the upward vertical direction to obtain the samples; determination of the thermal parameters of solidification as growth rate (VL) and cooling rate (ṪL); microstructural characterization techniques such as optical microscopy (MO), scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray fluorescence (XRD); application of the measurement methods, the triangle and the intercept to measure the primary (λ1), secondary (λ2) and tertiary (λ3) dendrite arm spacings, respectively; and Vickers hardness test. The microstructure of the Al-7wt.%Si-1wt.%Mg alloy is constituted by an essentially dendritic Al-rich (α-Al) matrix surrounded by the ternary eutectic Si + Mg2Si + π-AlMgFeSi. In the case of the Al-7wt.%Si-1wt.%Mg-2wt.%Ni alloy, the Ni3Al intermetallic is also present in the eutectic regions. The addition of Ni promoted a slight refinement of the dendritic arrangement in the ternary Al-Fe-Mg alloy, mainly for secondary branches (λ2). The hardness increased slightly with the addition of Ni.