Análise da microestrutura, formação de fases e variação de dureza de ligas al-cu-li nas condições consolidada por fricção e tratada termicamente por envelhecimento

Abstract

Solid state materials processing is a technique that combines severe plastic deformation with heat generation in order to produce a material with advanced mechanical properties, such as Al-Cu-Li alloys for aeronautical applications, at a low energy cost. One of these processes is friction consolidation, which consists of producing consolidated disks of metal powder or chips, which serve as raw material for other techniques, such as friction extrusion or friction surfacing. In the process, a die is pressed against a rotating container containing metal powder, generating heat due to friction, and severe plastic deformation occurs due to the rotation. In this regard, this work aimed to study Al6CuXLi alloy disks, with X = 2, 4 and 6 wt% of lithium, consolidated via friction consolidation with different process times: 20 s, 40 s and 60 s. First, a microstructural analysis was carried out via optical microscopy of three samples of an Al6Cu2Li alloy, varying the process time between 20 s, 40 s and 60 s. Subsequently, the process time was fixed at 60 s, but the lithium content of the alloys was varied by three levels: 2%, 4% and 6%, and the microstructures of the resulting samples were analyzed, also via optical microscopy. It was observed that the six samples produced had a heterogeneous microstructure, showing a consolidated part, a partially consolidated part and a part that was only compacted, indicating variations in the temperature gradient and plastic deformation with the height of the sample. All samples were then subjected to Vickers microhardness tests, resulting in six different maps, which showed that the hardness followed the same trend as the microstructure, where the fully consolidated parts of the disk had higher hardness values, showing heterogeneity in the mechanical properties. This was due to the greater influence of precipitation hardening and grain refining mechanisms in the regions with greater consolidation. Subsequently, a heat treatment was carried out on one of the samples, in order to study the aging profile and determine the approximate aging time corresponding to the microhardness peak. Finally, an X-ray diffraction analysis was carried out to verify the presence of hardening precipitates in the three alloys, indicating the formation of δ' and T1 precipitates in all three.