Microstructure Evolution of Copper Strip during Continuous Extrusion and Rolling Forming

Abstract

During the continuous extrusion and rolling forming process, the microstructure evolution of copper strip was investigated by the optical microscope and transmission electron microscope. The results indicated that the grains in the centre of as-cast rod billet were squashed in the clamping zone and were elongated in the rigid mobile zone. The fibrous structure formed in the upsetting zone. In the adhesion zone, the dynamic recrystallization occurred and the shear band was found. In the right-angle bending zone, the fibrous structure, recrystallized grains and shear bands existed together. The full dynamic recrystallization occurred in the extending extrusion zone. After continuous extrusion forming, the size of the grains of copper strip was larger than that in the extending extrusion zone. After rolling, the grains in copper strip were evidently stretched along the rolling direction, which resulted in the formation of stable direction. With the increase of rolling reduction, the grains were squashed gradually. When the rolling reduction increased from 2 to 6 mm, the tensile strength increased from 250 to 400 MPa, and the elongation decreased from 48% to 13%.