| Copper/aluminum composite material with advantages of high electrical conductivity, high thermal conductivity, low cost and light weight, has promising prospects in terms of power cables, electronic devices, etc. The manufacture of copper/aluminum composite material has great significance for the use of excess aluminum metal and the saving of precious copper metal. In this paper, Cu/Al bi-metal plates were produced by symmetrical and asymmetrical cold rolling, effects of thickness reduction on the components deformation rules, bond strength and the development of bonding surface as well as interfacial bonding mechanism and mechanical behavior were evaluated, at the same time, this thesis also focused the influence of annealing on diffusion layers development of asymmetrical cold roll bonded Cu/Al bi-metal plates, aiming to provide guidance for rolling and annealing process. The main results are as follows:(1) Research about the impact of thickness reduction and initial thickness ratio on the component deformation of symmetrical and asymmetrical Cu/Al bi-metal plates, found that the deformation of the aluminum is greater than copper. As the thickness reduction increases, the difference between the two deformation decreases. Compared with symmetrical rolling, asymmetrical rolling which resulting larger difference in component deformation. When the initial thickness is smaller, the deformation difference gets small, which contributes to obtain relatively good plate shape.(2) By studying the development of bond strength and interface of symmetrical and asymmetrical Cu/Al bi-metal plates with different thickness reduction, we find that, at the same thickness reduction, bond strength of asymmetrical Cu/Al bi-metal plates is greater than symmetrical plates, and the strength curve of which is more stable. During the rolling process, fresh aluminum and copper is extruded through the brittle cracks of surface, copper nails into aluminum substrate, aluminum is spreaded to the copper substrate surface, which forming a good bonding of bi-metal plates. The bonding process of copper/aluminum plates can be divided into three stages:1) physical contact.2) mechanical combination.3) metallurgical bonding. There is flow velocity difference between two metal particles that causes friction at the interface, and the friction of asymmetrical rolling is more complex and sever than symmetrical rolling. (3) With the increasing of annealing temperature or time, diffusion thickness of the asymmetrical rolling copper/aluminum increases. Compared to annealing time, diffusion thickness is greatly affected by annealing temperature. In this research, the relation between annealing temperature Tand diffusion layer thickness w is derived as the following equation:ln w=-2.35/T+7.99The variations of annealing time t and diffusion layer thickness w can be presented by the equation as below: ln w=0.501nt-1.52.(4) Annealing at low temperature, the diffusion layers are mainly composed of solid solution of Cu and solid solution of Al. Annealing temperature between350℃to500℃, intermetallic compounds begin to appear, three intermetallics:Al2Cu, AlCu and Al4Cu9can be detected in diffusion layer. Increasing the annealing temperature and/or time, the first reaction product is Al2Cu and Al4Cu9, then the next product is CuAl. Using the modified effective heat of formation (MEHF) to predict the first phase of formation in Al-Cu binary system, Al2Cu is expected to form first at the diffusion zone, the next phase to appear is AlCu, followed by Al3Cu4and Al4Cu9. After the annealing process, three main reasons:1. decreasing of the work hardening degree;2.formation of brittle intermetallic compounds Al2Cu and AlCu;3. development of a porous structure of diffusion layer, that weaken the bond strength of Cu/Al bi-metal plates. The selection of annealing temperature below350℃will favor the Cu/Al plates to maintain a relatively high bonding strength while obtain a certain formability. |
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