Microstructure and defects of rectangular Cu-Ag wires fabricated by the continuous extrusion forming process

In this work, the microstructural evolution and common defects of Cu-Ag (0.075 wt.%) alloy during continuous extrusion molding (CONFORM) were characterised and analyzed. The microstructures at different positions inside the CONFORM cavity and the exit were comprehensively revealed by combining electron backscatter imaging, electron backscatter diffraction, energy dispersive spectroscopy, and finite element modelling. The results showed that the temperature of the cavity was much higher than the recrystallization temperature of the Cu-Ag alloy. However, both deformation and recrystallization structures were observed in the cavity due to the extremely high extrusion rate. Owing to the different speeds of the extrusion and coining rollers, the friction forces on the upper and lower surfaces of the Cu-Ag bar were different, resulting in shear stress. Such shear stress leads to a slight difference in grain size between the upper and lower layers of the extruded wires. The existence of low-angle boundaries caused by grain fragmentation and dislocation arrangement accelerates the dynamic recrystallization process in the upper layer and the residual strain on the upper surface of the wire was larger than that in the middle and lower layers.