Análise da microestrutura, segregação e dureza da liga Al-1,5%Fe-1%Zn aplicada a componentes metálicos para o setor petrolífero

Abstract

The oil and gas industry is one of the largest consumers of metallic alloys in their applications. Pipes produced in High Resistance and Low Alloy steel (HSLA) have been used due to their high mechanical resistance, which enables the transport of material under high pressure. However, in offshore oil production in deep waters, such steels presented themselves as their high specific weight, low toughness and limited texture resistance in marine environments. In this sense, alloys based on aluminum (Al) appear as interesting alternatives, since they are resistant to aggressive environments, as well as low specific weight, ahead of the ferrous alloys used. Thus, this work aims to study the effect of adding 1% Zn (by weight) on the microstructure, transformation temperatures, macrosegregation and hardness of a hypoeutectic Al-1.5wt.%Fe alloy solidified directly out of equilibrium. Microstructural characterization techniques such as X-Ray Diffraction (XRD), Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) were used, in addition to Vickers microhardness tests. Thermodynamic calculations were performed via Thermo-calc simulation software with the intuition to evaluate the effect of Zn on phase transformation kinetics and final microstructure. The macrostructure exhibits a columnar-equiaxial transition at 5 mm from the metal/mold interface, with equiaxed grains predominating along the length of the Al-Fe-Zn casting. The simulations displayed a slight reduction in the liquidus temperatures and a moderate increase in the final fraction of the Al3Fe intermetallic with the addition of Zn in the Al-1.5wt.%Fe alloy. Cellular growth prevailed along the length the Al-Fe-Zn casting, with a microstructure formed by Al-rich cells (𝛼-Al) surrounded by a eutectic mixture 𝛼-Al + Al3Fe. Zn was consumed in solid solution in the Al matrix. Vickers microhardness levels remained between 21 and 25 HV for the Al-Fe-Zn casting. The addition of Zn reduced the Vickers microhardness of the binary Al-1.5wt.%Fe alloy.