Caracterização microestrutural de uma liga Al-Zn-Mg-Si-Cu conformada por spray

Abstract

The 7XXX series aluminum alloys are widely used by the aeronautical and automotive industries due to their lower density and better mechanical performance. Adding alloying elements, such as zinc, magnesium, copper, silicon and others, it improves mechanical properties. Due to the presence of these elements in significant quantities, new forming techniques are required, such as powder metallurgy and spray forming. The latter was used in the conformation of the alloy studied and consists of the atomization of liquid metal in the form of droplets through a high-pressure inert gas, which is responsible for providing high cooling rates, while the droplets are collected by the substrate. The present research aims to analyze the microstructure, according to quadrants and specific regions of a sample of an Al-Zn-Mg-Si-Cu alloy, through an optical microscope and how this affects mechanical resistance, from the values obtained for Vickers micro hardness. The mean micro hardness of the alloy was 144.3 HV0.3, however according to the analysis region higher values were found, such as the maximum value of 167.1 HV0.3. Equiaxial grains with medium diameters between 18.0 to 48.6 μm, Mg2Si phases well distributed in the aluminum matrix, and a phase present between grain contours were observed. Porosity is reported as the main disadvantage of the process and, therefore, it was also analyzed. The mean value of porosity was 3.11%, however according to regions of the sample, a larger and lower pore content was found. In the region in contact with the substrate, there were interstitial pores resulting from gas entrapment, reaching a value of 12.28%, and as the deposition occurs the interstitial pores disappear, leaving in a smaller amount of gaseous porosity in 0.82%. It was concluded that the spray conformation method contributed effectively to increased Al-Zn-Mg-Si-Cu alloy micro hardness, because the presence of smaller equiaxial grains and refined phases due to high cooling rate, provides greater area constituted by its limits, being responsible for preventing mechanisms of plastic deformation. As for the porosity formed, other processing such as lamination, extrusion and hot isostatic pressing is needed to decrease or even eliminate it.