The Mechanisms And Techniques For Strengthening Cube Texture In High Purity Aluminum Foils

The processing of aluminum foil for the anode of high voltage electrolytic capacitors is very difficult, and a lot of high-techniques for the processing have to be mastered skillfully, which will be applied to the aluminum processing, such as casting, rolling, and heat-treatment. More than 95% cube texture in volume will be necessary for enlarging surface of the anode by etching. The foil products can have been produced only in Japan, France, Germany before, and a commercial production has come true in China in the last few years as well. The formation and evolution of cube texture in FCC materials is a very important subject for the scientists and engineers in metallic materials, on which there are many complicated factors that have strong influence on the formation and evolution of cube texture. Ever since the orientation distribution function (ODF) was advanced, although the research of crystallographic texture has made great achievements, including some valuable theories and models, there are still some uncertainties in this field. For the formation mechanism for recrystallization texture, for example, there are still some different kinds of point of view. Howerver, there are no ideas about the details of recrystallization texture formation. What can be done about is no prediction but explanation. Especially in the commercial production of aluminum foil, this problem will become even more complicated.The impurities, especially Fe, have strong influence on the formation and development of the cube texture in high purity aluminum. The energy transformation model for the effects of impurities is suggested and implemented with the Monte Carlo method. With establishment of the limit solubilities of Fe in Al at different temperatures, the solid solution and precipitation heat treatment are proposed for strengthening cube texture.The results calculated by the crystal plasticity model showed that the cube oriented grains have the smallest Taylor factor. The mechanism for strain induced oriented nucleation of the cube texture based on this result is proposed. The techniques for strengthening cube texture by strainanneal treatment is established, which is based on the mechanism of the strain induced cube crystallite nucleation at low temperature and the oriented growth at high temperature. It is showed that the formation and development of the cube texture are strongly influenced by not only the thermodynamics parameters but also the deformation microstructures. For example, stronger initial cube texture, cube-oriented transition band and the cube-oriented fragmented grains in deformation shear bands are beneficial to the cube texture. The techniques for strengthening cube texture are applied to the industrial production, e.g. high temperature hot rolling and pre-annealing, inhomogeneous shear deformation which are proposed in this thesis.The experimental results revealed that the cube orientation crystallites have higher nucleation rate at low temperature and higher growth rate at high temperature than the others. Both the oriented nucleation at low temperature and the oriented growth at high temperature are suggested and a kinematical model for the oriented nucleation of the cube texture at low temperature is also suggested together with the techniques of strengthening cube texture by two-stage annealing.The deformation microstructure and texture are strongly controlled by the cold rolling lubrication conditions, by which the cube texture in high purity aluminum foil is also greatly influenced. It is demonstrated that kerosene-lubricated rolling leads to the shear texture component {001}<110>, Cu component {112}<111> and shear deformation band, which are induced by the higher friction coefficient. And all of the above textures and microstructure will favor the formation of cube texture.Some techniques for strengthening cube texture have been applied to the commercial production of high purity aluminum foil with the volume fraction of 95% of cube texture for high voltage capacitors in one of the famous aluminum fabrication plants in China.