Research on Microstructure and Properties of Pure Copper Tube during Rolling Process

Abstract

The pure copper tube with strong axial orientation columnar grain and equiaxed grain respectively were rolled using a three-roller precision tube mill. Optical microscope, hardness testing machine and universal testing machine were used to investigate the microstructure and mechanical properties of the pure copper tube rolled with different deformation degrees. The results show that the pure copper tube with two kinds of microstructure can be directly rolled from the dimension of Φ68.5mm×57.9mm to Φ34.7×30.4mm by 8 passes with accumulated deformation degree nearly 80% and without intermediate annealing. With the increasing deformation degree, the primary columnar grain boundaries of the pure copper tube with columnar grain blurred gradually until completely disappeared. However, the microstructures of pure copper tube with equiaxed grain completely transformed into fibrous microstructures when the deformation degree reaches to 79.11%. The columnar grain is without transverse grain boundaries but with small-angle boundary, which is conducive to axial deformation. It is also found that with the increasing deformation degree, the tensile strength of pure copper tube increased steadily, while the elongation decreased gradually. The elongation of pure copper tube with columnar grains is higher and the microhardness is lower than that of equiaxed grains, indicating that the cold deformation properties of pure copper tube with columnar grain was more excellent.