| At present, the aluminum foil used for preparing the high voltage electronic components (hereafter referred to as the high voltage electronic aluminum foil) is mainly produced by the raw materials made from three layer electrolysis in domestic plants. As the result, the energy consumption is large, and the cost is high. In the present paper, in order to lower the cost and to provide an alternative way, based on the project of "the production-study-research combination" type supported by Xinjiang Joinworld Corporation and Northeastern University, the evolution of microstructure and texture as well as the effect of trace impurities on the etching behavior of the aluminum foils during preparing the high voltage electronic aluminum foils by the aluminum ingots produced by segregation method were systematically studied. The obtained main results are as following:(1) It is found through the contrastive study on the microstructural transformations during hot-rolling the aluminum ingots produced by segregation method and three layer method (Hereafter referred to as segregation ingot and three layer ingot) that:as compared to the microstructure of the plates obtained through hot-rolling the three layer ingot, the obvious inhomogeneity in the microstructure of the plates obtained through hot-rolling segregation ingot exists in the cross and longitudinal section; i.e., the recrystallization on the surface layer occurred while the grains were elongated and coarse in the center layer.(2) As the rolling reduction increasing during the cold rolling of the plate obtained through hot-rolling the segregation ingot, the cold-rolled banded microstructure becomes closer gradually. After intermediate annealing, both of the cold-rolled plates obtained from two types of ingots fully recrystallized. However, as compared to the three layer aluminum foil, the grain sizes in the segregation foil are more inhomogeneous and ranges from several micrometers to -80 micrometers after intermediate annealing. Since the rolling reduction during the final cold rolling is smaller, the fully recrystallized microstructures are elongated slightly. After the final annealing, the full secondary recrystallization occurs and the grains grow to -240 micrometers.(3) The texture evolution of the aluminum foils during their preparation processes respectively with the segregation ingot and the three layer ingot was studied. It was found that the texture after hot rolled shows a significant difference between the plates made from the segregation ingot or made from the three layer ingot. The distributions of the component, the orientation density, the spreading width and the volume fraction of the texture in the hot-rolled plate made from the segregation ingot are more inhomogeneous than those in the hot-rolled plate made from the three layer ingot along the cross and the normal direction. In the surface and subsurface layer, the{001}<110> texture component is relatively strong. And strong Brass texture appears in the center part of the plate. Because the{001}<110> component is a type of shear texture, the above results indicate that there is an inhomogeneous plastic flow during hot rolling which is not favorable for the formation of strong S component. Brass component is a stable texture, and is transformed into R component during the annealing of high voltage foils, become into a competitive relation with the formation of cubic texture.(4) The small amount of Zn in the high voltage electronic aluminum foils could be enriched on the surface of aluminum foils, which makes the pit density increase, the distribution of pits on the surface homogeneous, the pit size decrease slightly and the excessive surface dissolution decrease. As the result, the specific surface area of the aluminum foil is increased. The small amount of Zn has no influence on the formation of cubic texture and could increase the bending strength. The compositive effect is to increase the specific capacitance of the aluminum foils.(5) The segregation of the small amount Mn in the high voltage electronic aluminum foils on the surface of the foil is not significant. Increasing the content of Mn could make its concentration increase and its distribution more homogeneous on the surface and along the depth, which make the pitting more homogeneous, the pit density increase, the pit size decrease and the length of tunnels tend to be distributed in a narrow range during electrochemical etching. As the result, the specific surface area of the aluminum foil after etched is enlarged effectively and results in the increase of the specific capacitance of the aluminum foils.(6) A small amount of Ga solid soluted in the high voltage electronic aluminum foils forms with other elements into secondary phase, which make the matrix be purified, the convertation of the rolling texture into the cubic texture be retarded and the content of the cubic texture decrease. When the content of Ga is increased to 11.6×10-6, the grain sizes in the hot rolled aluminum plate decrease, the sizes of the recrystallized grains in the finally annealed foils increase and the specific capacitance is slightly increased. However, when the content of Ga increases to 21.4×10-6, although the microstructure of the foils is almost unchanged, the merged pits on the surface of the chemically treated foils increase, which leads to the decrease of the specific capacitance. |
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