Cold upset forging joining of ultra-fine-grained aluminium and copper

This paper describes a study investigating joining copper, which is expensive but has excellent electrical properties, with aluminium, which is cheaper but is characterized by much worse mechanical and electrical properties. Metals with ultra-fine-grained structure were studied to understand the process of cold upset joining of hydrostatically extruded materials with a large deformation. Much greater difficulties were expected, based on the combination of conventional metals. The study verified the possibility of bonding such metals with various surface preparation methods and different parameters of the joint. The bond quality was checked by the static tensile test to study their tensile strength. To present the difference in joining conventional materials and ultra-fine-grained materials, was tested joining annealed copper and aluminium, and the results of this test were compared with tests for hydrostatically extruded material. The permanent joints were tested based on the hardness distribution across the joint and by observation of the fracture specimen's joints and EDS examination, which allowed us to determine that the connection mechanism does not rely on the diffusion of copper atoms to aluminium and vice versa.