The effects of different homogenization parameters on microstructure and hardness for 6063 and 6005 aluminum alloys

Aluminum alloys are widely used in various industrial fields today. With their light weight, high corrosion resistance, and good mechanical properties, they are an important material group used in sectors such as automotive, construction, and aerospace. Aluminum alloys are highly suitable for the extrusion process, and their use in this method plays an important role in industrial production. In the extrusion process, the raw material, known as billet, is heated to a specific temperature and passed through a die to produce profiles with the desired geometries. The chemical composition and microstructure characteristics of the billets directly affect the mechanical properties and surface quality of the produced profiles. After the aluminum billets are cast, heat treatment is applied to improve the morphology of the phases and to make the homogeneous distribution in the microstructure. This heat treatment, known as homogenization, consists of three steps: heating, soaking, and cooling. The parameters chosen during this process affect not only the final properties of the product but also effects the extrusion efficiency. In this study, heat treatments were applied to 6005 and 6063 aluminum alloys, which were taken without any heat treatment after DC casting. Different combinations of heating rates, temperature, soaking time, and cooling rate parameters were used in the heat treatment process. After these treatments, microstructure examinations were performed on the samples with using optical microscopy and SEM, hardness measurements were taken, and the effects of the parameters on the material microstructure and mechanical properties were investigated. It was observed that the temperature and soaking times had a direct impact on the homogenization transformation rate in the microstructure, with the transformation rates increasing as the temperature and soaking time increased. The transformation rates after casting were 50% for 6005 alloy and 60% for 6063 alloy, while after the applied homogenization treatments, these rates increased to 80-90%. The cooling rate after homogenization affects the size of Mg2Si phases. For high mechanical properties in extrusion, these phases should not be coarse forms after homogenization. The precipitation behavior of these phases in the structure was examined under rapid and slow cooling treatments, and it was observed that the Mg2Si phases coarsened significantly under slow cooling treatments. In parallel, a decrease of about 50% in the hardness values of both alloys was observed. In the next step of the study, the effects of the heterogenization step, which can be applied to increase the production speed in extrusion, on the microstructure were evaluated. The heterogenization treatment applied with the determined parameters caused Mg2Si phases to precipitate in certain sizes in the structure, which led to a decrease in material hardness and deformation resistance. In the final part of the study, the effects of the billet heating step that applied during the extrusion process on the raw material's microstructure were examined by determining heating rate, temperature, three different soaking times, and cooling rates. The selected soaking times were chosen to observe any changes that can be occur during an unexpected production stoppage. It was evaluated that a soaking time of more than 10 minutes at billet heating temperatures could cause excessive precipitation of strengthening phases in the microstructure, which could negatively effect the mechanical properties of the final product.