Composition Homogenization Evolution of Twin-Roll Cast 7075 Aluminum Alloy Using Electromagnetic Field

Many microstructural defects such as well-developed dendritic crystal and severe segregation have been found in 7075 aluminum alloy strips by continuous twin-roll casters. Morphology and phase composition of 7075 alloy strips were tested in this paper. Electromagnetic field of 0.13 T was applied during a twin-roll casting (TRC) process to study the difference in solute element distribution compared to conventional process. The most soundest method by which the microstructure of slabs was greatly refined and equiaxed, and segregation bands narrowed down efficiently, was an alternating oscillating process with industrial frequency current and frequency of 386 A and 50 Hz, respectively. In addition, t (AlZnMgCu) phase with high density was formed at (sub) grain boundaries, which was refined and homogenized consecutively in accordance with direct chill (DC) electromagnetic field, half-wave oscillating field and alternating oscillating field; moreover, netlike precipitates completely disappeared at oscillating TRC processes.