Quantitative Investigation Of Microstructural And Texture Evolution During Cold Rolling Aa3104 And Aa1050 Aluminum Alloys

This thesis reports a quantitative investigation of microstructural and texture evolution of two typical industrial aluminum alloys AA3104 and AA1050 during cold rolling from low to high strains using electron channeling contrast (ECC), electron backscattered diffraction (EBSD) and transmission electron microscope (TEM) techniques.The investigation of the deformation microstructure evolution during cold rolling has yielded the following results: (1) Several reconstruction methods for enhancing the EBSD map contrast has been analyzed and discussed, and a general software package Texture 5.0 has been developed in order to improve the EBSD map contrast of deformed metals alloys. (2) The dislocation boundary structure evolution and its correlation with grain orientation have been quantitatively investigated during cold rolling these two alloys from low to medium strains. It is found that most grains are subdivided into extended planar dislocation boundaries (Geometrically Necessary Boundaries, GNBs) with an angle of 30°~40°to rolling plane. According to the observed subdivision pattern, the microstructures can be classified into three types as follows: Type A grains, containing two sets of GNBs (with orientations near Copper, Brass and Goss orientations); Type B grains, containing one set of GNBs (with orientation near S); and Type C grains, composed of nearly equiaxial cells (with orientations near Cube orientation). Most GNBs are nearly parallel with the traces of {111} slip planes identified by Schmid factor analysis. (3) The microstructure and texture evolution of two alloys cold rolled to high strains has been analyzed. It is found that the deformation microstructure evolves into a typical lamellar boundaries (LBs) structure within which most of LBs are approximately parallel to rolling direction (RD). The grain orientation dependence of the deformation microstructure is still observed even at high strains. The texture at high strains is composed of strong rolling texture components Brass, S and Copper. (4) The effect of second-phase particles on the deformed microstructure evolution has been studied. Different second-phase particles present in the microstructure of AA3104 alloy have different effects on the deformation microstructure. Fine dispersoids have no clear effect on the grain orientation dependence of the dislocation boundary structure formed in the strain range examined, and the microstructure is similar to that of pure Al and AA1050. In contrast, large scale structural heterogeneities are formed, and significant orientation gradients are observed near the coarse constituent particles. The lattice rotations around the coarse particles are close to TD-rotations with an alternating pattern of"+ - + -"rotations. (5) Structural parameters during cold rolling have been quantitatively characterized. With increasing strain, the average boundary spacings of GNBs and IDBs for AA3104 alloy decrease with power exponents of -0.52 and -0.27 respectively, while the average boundary misorientations increase with power exponents of +0.69 and +0.29. In contrast, the boundary spacings of AA1050 decrease with power exponent of -0.45 and -0.28, while the boundary misorientations increase with power exponent of +0.5 and +0.28. The flow stress and ultimate tensile stress of these two alloys increase with increasing strain, and no saturation in each is reached. Based on the experimentally determined structure parameters, the predicted flow stress, with contributions from grain boundary strengthening related to GNBs and from dislocation strengthening related to IDBs, is in good agreement with experimentally measured values.