@masterthesis{Michev, type = {Bachelor Thesis}, author = {Michev, Dimitar}, title = {Recrystallisation Behaviour of Extruded 3000-series Aluminium after Minor Deformation}, school = {Hochschule Rhein-Waal}, abstract = {A large part of the tube elements of a conventional tube/fin heat exchanger, designated in industry under the names multi-port extrusion (MPE) or micro-multiport (MMP) tubes, are produced from aluminum of the 3XXX series. The production of that tubing commonly consists of direct chill (DC) casting of the raw material, homogenization of the billet, extrusion, coating, coiling and final dimensioning. Additionally, to being straightened and cut to the final length, those tubes undergo height and width calibration through cold forming, to meet the customer tolerances. Consequently, this critical amount of cold work done to the material leads to recrystallization followed by the growth of very coarse grains during the brazing process. This coarsening of the microstructure reduced the strength, hardness and corrosion resistance of the material. In this paper, a characterization of the behavior of the microstructure in relation to the level of deformation is done by examining multiple samples. Three different coils each having different cross-sectional profiles, two made from the same alloy AlMn0.5 and the third made from AlMn0.2Cu0.4 were examined. From each coil samples were produced and calibrated to different changes in height and width: none (Δh=Δb=0), medium (Δh=Δb=0.05) and high (Δh=Δb=0.1). The specimens were exposed to diverse temperatures and dwell times, simulating brazing conditions. Temperatures chosen, varied from 510°C to 590°C and holding times were between 3 and 10 minutes. Optical microscopy was used to inspect and quantify the fraction recrystallized microstructure of the samples in metallographically prepared cross-sections. The data gathered from the microscopic investigation was analyzed using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model. The resulting graphs showed the effects of other parameters on the recrystallized fraction/dwelling time function. An approximation of the model was used to show the percent recrystallized microstructure and temperature dependency. This allowed the determination of the temperature at which nearly 100\% of the microstructure has recrystallized, hence the process is completed.}, language = {en} }