High-Shear Deformation Processing on Aluminum Alloy for Sheet Production

Abstract

Aluminum alloy sheets are typically manufactured from cast slabs by multi-step rolling and annealing process. This process is very energy intensive, especially in the homogenization process after casting, which usually is conducted at 480 to 580 ℃ for up to 48 h. To reduce the processing steps and energy, a shear-based single-step deformation process, large strain extrusion machining (LSEM), was used to create strips from AA6013-T6 with and without preheating of the workpiece. Continuous strips were obtained from this alloy with low workability. Flow patterns through the thickness of the strips exhibited primary shear with grains inclined steeply to the faces of the strips, modified to varying degrees by secondary shear from friction with the tools at the surfaces. Through control of the deformation parameters (strain, strain rate and temperature), a wide range of microstructure could be achieved. In high-temperature LSEM, dynamic recrystallization occurs at lower temperatures than in commercial hot rolling processes. LSEM was performed directly on the as-cast AA6013 without homogenization. By appropriate combination of strain and strain rate, continuous strips were obtained in a single step without preheating directly from the as-cast workpiece. The highly deformed LSEM strip has enhanced workability. It can be cold rolled with at least 73% reduction in a single step without cracking. The strips were characterized by strong shear texture with partial {111} and fibers. After annealing, a mixed texture containing simple shear texture and other texture develops. The annealed strips are expected to have better formability than commercial ones made by rolling.In comparison, multi-step warm-rolling and cold rolling were performed on the as-cast AA6013. The as-cast material was preheated to 300 ℃ and rolled with 12% reduction per pass till the same effective strain as the LSEM. The warm-rolled strips were then cold-rolled with the same reductions as those on LSEM strips. The results showed that during warm rolling process, cracking occurs on the strips before reaching the same effective strain and the warm-rolled strips can only be further cold rolled with reduction less than 26% before cracking, compared with 73% reduction without cracking for LSEM strips.Based on the simple shear LSEM process, a novel way to produce aluminum strip/sheet material is introduced. The alloys are cast into disk-shape workpiece and then transferred to the LSEM line. In this line, continuous strips/sheets are obtained in a single step at room temperature. The materials are then coiled if needed and cold rolled to the final gauge. Finally, the strips/sheets are solution treated for further deformation processing. In this method, the conventional homogenization and hot rolling, including reversing and multi-stand hot rolling, are replaced by a single-step LSEM process at room temperature.