Evaluation and Prediction of Microstructure Evolution in Deformed Aluminum Alloys

The understanding of the microstructure evolution during the deformation processes is very important to predict the mechanical properties of the deformed workpiece. In the present work two aluminum alloys from different series were studied in two different deformation processes.;The first part is the surface grain structure evolution in AA6082 hot direct extruded shapes with different ram speeds (0.25, 0.5, 1, 2 mm/sec). The samples were characterized by the light optical microscopy (LOM) and by electron backscatter diffraction (EBSD) to measure the grain size and misorientation angle in the thickest part of the extrudates. Also, numerical simulation process was performed by a finite element package DEFORM(TM) --3D to obtain the state variables such as stress, strain, strain rate, temperature and their distribution in the deformation zone. These state variables were incorporated in a joint dynamic recrystallization model which is developed by Bandar and modified by Depari and Misiolek to predict the surface grain structure and the misorientation angle. The experimental results showed a good agreement with the model predictions.;The second part is focused on the microstructure evolution of asymmetrically rolled AA-5182. Asymmetric Rolling (ASR), where the linear speeds at the surfaces of the upper and lower roll differ in order to impose shear within the workpiece, has been shown to be a promising, economical approach to altering the microstructure of rolled aluminum alloy sheet. The purpose of this process is to produce intense shear deformation throughout the entire sheet thickness, as opposed to superficial shear deformation imposed by conventional rolling. The microstructure response to the ASR process conditions for the aluminum alloy AA5182-O was analyzed using metallographic techniques. The initial sample microstructure and the deformed microstructure after the first and fourth passes were analyzed at three locations in each sample - near the top surface where contact with the upper roll took place, near the mid-plane, and near the bottom surface where contact with the lower roll took place. In each case, the microstructure was examined in the rolling direction (RD) and the normal direction (ND). The results show that the grain size varies within the samples and even more between the samples representing different stages of the ASR process. However, for the reported rolling conditions, the fine grain structure has not been produced.