The Simulation Study On Temperature Field And Stress Behavior Of Twin-roll Casting 7000 Series Aluminum Alloy

There are many advantages for 7000 series aluminum alloys, such as high strength and hardness, well welding performance, hot-workability, corrosion resistance and good ductility etc. Thus it has been widely used to in aircraft, aerospace and military fields. The twin-roll casting(TRC) has combined the casting and rolling together, which not only shortens the process, but also reduces production cost. Meanwhile, the continuous and efficient production can be obtained by using TRC. The surface of sheet billet of 7000 series aluminum alloys, manufactured by TRC technology, will cause the cracks and lead to low production yield.Fluid flow model in the molten pool of aluminum alloy coupling stress behavior simulation model was established in this work by using finite element method. The simulation parameters included the temperature field of solidification process of twinroll casting 7000 aluminum alloy slab, thermal stress field and stress field in the deformation area under rolling force, and the stress field of roll-casting plate under air cooling condition. The temperature field of the 7050 aluminum alloy under vertical and horizontal twin-roll casting, aluminum liquid during solidification with different rolling parameters, and the suitable process parameters were analyzed as well. Firstly, characteristics of vertical and horizontal roll-casting process was compared. Then, the temperature field at different composition in solidification process was compared. Thirdly, forming mechanism of cracks in roll-casting process for 7050 aluminum alloy sheet was discussed. Finally, tendency of surface crack for 7050 aluminum alloy cast-rolling plate at different roll-casting speed was discussed. The outlet temperature of cast-rolling was tested. The results proved that the model in this paper is effective compares to the test results.Results showed that the influence law of rolling parameters on the temperature field in cast-rolling area during vertical and horizontal roll casting was consistent. With the increasing of pouring temperature, the speed of roll, and roll gap width, the outlet temperature was increased in cast-rolling area, and the position of completely freezing point for liquid aluminum was deeper. For the300 mm roll diameter of 7050 during vertical twin-roll casting, the best pouring temperature was 963 K, roll-casting speed was 12 r/min(11.304 m/min),roll gap width was 1.8 mm. Structure in castrolling area of vertical roll-casting was more uniform than that of horizontal rollcasting, but the rolling continuity and stability of horizontal roll-casting were better than that of vertical roll-casting. In the optimum processing conditions, the outlet temperature of 7050 aluminum alloy during cast-rolling was lower than 7075 aluminum alloy, so the setting temperature range, heat transfer rate, and heat were smaller, it was easier to form the good performance of the slab using roll casting alloy. The middle of cast-rolling area was under compressive stress, and surface was under tensile stress. In cast-rolling area, the conditions of crack initiation formed by surface tensile stress, and then tensile stress increased during air cooling process, crack was extended to the surface cracking. The cracking tendency of cast-rolling plate not only can be decreased by appropriately improving the cast-rolling speed, but also it can result in more formation of small grains. However, rapid cast-rolling speed could cause the raising of the temperature of the alloy, so it can’t be formed.