Multi-scale Simulation And Experiment Research Of Cu/Al Cladding Strip Bonding Interface In Single Facility- Double Flow Cast-rolling Process

Copper resources are severely lacking in China and degree of foreign dependence on copper reaches to 75%, while aluminum resources are relatively rich and electrolytic aluminum production is seriously overcapacity. “Saving copper by aluminium” has become an important means of persisting usage of copper resource and degrading over-capacity of production, so production facilities and forming technology of Cu/Al cladding strip have widely been paid attention. Cu/Al cladding strip has also been a new developing trend of power transmission and heat transmission. Based on traditional twin roll caster, a kind of cast-rolling bonding technology named single facility- double flow is put forward by combining rapid solidification with roll-bonding technology. It is adding auxiliary roller on the side of primary roller. The whole process include mono-metal roll casting and bimetal bond rolling two stages. It has many advantages such as compact process, high-precision on base/composite stip temperature and thickness. In order to reveal the micro-mechanism and conditions of Cu/Al metallurgy bonding, the finite element simulation is combined with molecular dynamics method and device of independent development for strips compressing with unequel temperature to realize multi-scale simulation of Cu/Al bonding and experiment research, which provides theoretical evidence for compound equipment and new technology of the the single facility- double flow technology.On macroscopic scale, a coupled thermo-deformable finite element model of copper strip and aluminum strip mono-metal asymmetrical roll casting is constructed based on MSC.MARC and its secondary development technology. The continuous dynamic process of mono-metal roll casting is implemented by using of element birth and death method. Effects of pouring temperature and roll-casting speed on inlet temperature of bonding region can be acquired. On this basis, the finite element modeling of thermo-mechanical stresses in Cu/Al bond rolling is applied to analysis the temperature and stress distribution on the bonding interface. Numerical simulation on the variable parameters Effects of initial temperature of copper strip and aluminum stripcT andaT, reduction ratio e on contact heat transfer between copper and aluminum and temperature/stress distribution on Cu/Al bonding interface are analyzed. The results show copper strip of high temperature and low-fusing aluminum strip transfer heat under pressure in bond rolling zone and surface of aluminum strip will be melt with right technics parameters because of there is a big difference between copper and aluminum, then solid-liquid bonding effects of Cu/Al will appear.Process conditions of solid-liquid bonding are got in this paper and the results are true for common bond rolling with diferent strip temperature.On microscopic scale, taking macroscopic temperature and pressure as boundary condition, molecular dynamics model of Cu/Al bond rolling with diferent strip temperature is established to study on kinetic and thermodynamic behaviors of atoms at bongding interface under different system temperature and pressure. The results show that the copper atoms diffusion to aluminium side is predominant, the main diffusion mechanism is vacancy diffusion. Rising temperature and increasing pressure can both speed the diffusion behaviors, at the same time systematic structure changes to the formless and disordered state. The rising slope of thickness of diffusion layer with pressure increasing shows a slowdown. The atomic diffusion behaviors are more affected by temperature, when the system temperature is lower, atoms diffusion almost don’t happen, diffusion effect is not obvious even increasing pressure, when the system temperature is higher, atoms diffusion is vigorous without pressure. When the system temperature is above melting point of aluminium, diffusion layer thickness has a sudden increase, it is verified hat the solid-liquid diffusion rate is higher than the solid-solid diffusion rate on the further.In order to further research on Cu/Al boding mechanism, experiments of Cu/Al bonding by hot-pressing processes are done on device of independent development. Microstructure observation and composition analysis of bonding interface are made by means of the metallurgical microscope and the electron microscope. The studies find that the diffusion layer is mainly composed of Cu9Al4(copper side), Cu Al, Cu Al2(aluminum side). It reveals the Cu-Al binary alloy reaction diffusion is the main mechanism of Cu/Al metallurgical bonding when local fusion exists. At the meantime, effects investigation of pressure and temperature on diffusion layer thickness studied by method of molecular dynamics simulation is proved to be qualitatively coincident with the experimental practice.