In the whole manufacturing chain of aluminium products, hot rolling significantly impacts the obtaining of favourable microstructures and desired mechanical properties of final products. The ...determination of crucial differences between the reverse hot rolling on a single-stand mill and the tandem hot rolling on a tandem-stand mill presented a major challenge. Besides the grain-size distribution in the microstructure’s cross-section, the crystallographic textures of hot-rolled strips were also determined and compared. The alternating band areas of a coarse-grained microstructure and fine-grained microstructure due to reverse hot rolling and, especially, the appearance of extremely fine grains on the surfaces present limitations compared to the tandem hot rolling. For subsequently cold-rolled foils, classical mechanical properties were measured. Besides, the usefulness of EN AW-8021B foils with a thickness of 60 µm for pharmaceutical-packaging applications was tested with a burst test. A minor but important difference of 1 % in the elongation is shown for the convex height increased by 1 mm.
The changeover to cast Al strip for foil production has been defined by the management of Impol as the key part of its strategy for the plant's development and the restructuring of roll-casting ...technology. In comparison with hot-rolled strip, continuous cast strip is a cost-effective raw material for foil production, but different in terms of microstructure, phase composition, formability and other technological characteristics. Due to the very rapid solidification of molten metal in continuous thin strip, the microstructure consists of a strongly supersaturated aluminium solid solution and an increased fraction of fine particles of intermetallic phases, precipitated in Al crystal grains. This has a negative effect on cast-strip formability, and moreover, the cast strip's surface is oxidized and contaminated with graphite. For the purpose of producing strip from technical aluminium (group AA 1xxx) and alloys of the Al-Fe type (group AA8xxx) it was necessary to change the casting parameters as well as the parameters for further strip processing, which differ from conventional roll-casting procedures. Continuous cast strip is primarily intended for insulation, converter and household foils of different widths. The principal foil characteristics, prescribed by EN standards, are the mechanical characteristics, surface quality, porosity and the thermostability. The research work was focused on achieving the listed characteristics by changing the alloy composition and the conditions of transformation of continuous cast strip into foil. A suitable thermomechanical treatment changes the distribution of alloy elements in the existing microstructural phases and thereby also their effect on static recrystallisation, thereby affecting the surface quality and the mechanical characteristics of the foil. In this study the optimum composition and the process parameters of continuous casting that make it possible to use the strip as raw material for producing sheets and insulation, converter and household foils of standard quality are presented.
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