Rheological Behavior Research And Thermo-mechanical Coupled Analysis Of Aluminium Continuous Roll Casting Process

Twin roll casting process is a kind of technology which combines fast solidification and continuous deformation progresses together. In recent years, because of improving roll casting speed and decreasing strip thickness can bring many advantanges such as reducing the energy consumption, raising the work efficiency and obtaining good mechanics performance etc., which aroused the attention of numerous researchers. But with the increase of roll casting speed and the decrease of strip thickness, rheological behavior of the metal in the roll casting zone is strengthened, especially when the thickness is reduced to equal to or less than 2mm, high temperature solid-solid rheology phenomenon stands out, roll casting process rapidly enters mighty force rolling at the liquid-solid critical point. Now research of the rheological constitutive relation of the metal in the roll casting zone is nearly a blank, and its thermodynamics behavior is also difficult to be analysed with traditional laws. In order to abtain accurate understanding of some new phenomena in high speed roll casting and set up optimum technologic system in the production process, it has already been a very urgent need to research the basic law of the rheology behavior of the extremely intensive roll casting course.This paper based on the State Planning and Administration Committee Project of Industrialization Prophase Key Technology and Whole Set Equipment Development "New Technology and Equipment Development of Aluminium and its Alloy Roll Casting" and the subitem "Multiple Coupling Mechanism of Energy Transfer and Microstructure Forming during Transient Solidification and Continuous Deformation Process" of State Key Project of Foundamental Research "FoundamentalResearch about Improvement the Quality of Aluminum"("973" project), to study the rheological behavior in transient solidification and contiuous rolling process, then to carry on thermo-mechanical coupling simulation of such process. The main contents are as following:(1) A set of experimental equipment which in conjunction with Gleeble-1500 Thermal-Mechanical Simulation Tester is developed to carry on physical analogy experiment research of the normal and high speed roll casting, the whole course from transient solidification to continuous deformation is finished within 10~-2-10 seconds. Meanwhile, a series of simulating experiments on the rheological behavior and its influential factors have been studied, and the changes of microstructure of aluminium alloy during such process have been obtained.(2) On the basis of thermodynamics theory, the deformation characteristics and the physical simulating experimental data of continuous roll casting, and the comparing and analysing of existed various kinds of constitutive models for semi-solid and solid state aluminium alloy, relative constitutive models of continuous roll casting were set up; parameters depend on temperature and strain rate in those models were obtained through multivanable linear regression analysis, a set of constitutive equations applicable for roll casting process were built and then applied to the analyse of roll casting course, the analysis results were compared with the experimental ones, which proved that the established constitutive equations can describe its real rheological rules.(3) Based on heat transfer principle and basic finite element theory, heat transfer finite element mathematics models, which combined casting strip and roll shell together, were set up. Then a kind of analysis method to carry on temperature field simulation was put forward. With ANSYS, aset of temperature field analysis software system for continuous roll casting process was set up. Through changing relative parameters according to different work conditions (pouring temperature, rolling speed, etc.), then reexecuting the pre-compiled order flow of ANSYS software, relative temperature field simulation results were obtained, which offers the theoretical foundation for parameter design of roll casting course. Meanwhile, the results can provide temperature field information for thermo-mechanical coupled simulation.(4) A set of thermal-mechanical coupled finite element analysis equations were set up based on rigid visco-plasticity finite element principle and mathematics models of temperature field, the influence of thermal contact conductance between casting roller and strip and some other factors, such as metal flows, hot exchanges and deformation energy changing into heat energy etc. were also synthetically considered. A method to conduct multi-nonlinear thermo-mechanical coupling analysis suitable for aluminum strip roll casting process and is explored by carrying out secondary development of ANSYS finite element analysis software, which solved the problem that direct thermo-mechanical coupling anslysis is unable to be used with ANSYS under the condition of both heat mass transfer and phase change phenomenon. The variational rules of temperature field and stress-strain field are obtained in the rheological forming of continuous roll casting; the influencial laws of pouring temperature, rolling speed, length of roll casting zone, etc. on the solidification and deformation behavior were also studied. Simulation results show the thermo-mechanical coupled analyses method, basic equations and programming system basically reflect the real rule of continuous roll casting process and have certain practical value.(5) A series of experimental tests and analysis of the technologic parameters, such as the pouring temperature, exit temperature of strip, rolling velocity and rolling force on the O1003* 1850mm cast roller of aluminium foil mill of Chengdu and O1030xl 600mm super-thin high speed cast roller of North China Aluminum Company were done, the results of those main technologic parameters were obtained. Meanwhile, Simulating results are compared with experimental ones, both are basically matched, which verified the accuracy of simulation.In sum, this paper combined physical simulation research, heat-conduction, basic theories of rigid visco-plasticity finite element and metal formation, studied the rheology behavior in the course of roll casting. The rheological stress curve and relative regression equations established good foundation for engineering calculation of the deformation behavior and numerical simulation of aluminium roll casting course; a method to conduct multi-nonlinear thermo-mechanical coupled analysis suitable for aluminum strip roll casting process was explored, then a set of software system which combined the thermo-mechanical coupled characteristic of continuous roll casting process was elementarily built, which provided a kind of research method for the development of continous roll casting technology.