Numerical Simulation Study On The Heat-fluid Coupling In The Vertical Twin Roll Thin Strip Cast Aluminum Molten Pool

Energy saving,consumption reduction and environmental improvement are becoming more and more necessary conditions for the sustainable development of human life and society.People are looking for a green and harmonious development model.Lightweight is obviously one of the effective development paths,among which aluminum alloy is the preferred metal material for lightweight.The twin-roll continuous casting and rolling process for the production of aluminum alloy thin strip has the advantages of short process,energy saving and good product performance.It is one of the main technologies for the production of aluminum alloy sheet and strip.With the development of the automotive industry,the demand for aluminum alloys has increased and the quality requirements are higher.At present,most domestic production is based on traditional casting machines,which have low casting speeds and few types of alloys.The high-speed twin-roll casting method is widely concerned at home and abroad due to its advantages of high casting speed,wide range of aluminum alloy production,thinner strip thickness and better performance,but it has not been industrialized domestically.The requirements of high-speed casting and rolling technology on process control and casting machine design are different from traditional casting machines.Changes in casting machine parameters and process parameters will affect the flow and heat transfer behavior of aluminum liquid in the molten pool.It is difficult to understand through physical experiments.In this paper,the characteristics of flow field and temperature field in molten pool during vertical high-speed twin roll casting of aluminum alloy strip are studied by numerical simulation method,which has important reference significance for caster design and process parameter control.The main contents and results of this paper are as follows:(1)The mathematical model of heat flow coupling in the molten pool area of 6061aluminum alloy thin strip in vertical twin-roll casting was established,the boundary conditions of the model were determined,and the mathematical model was numerically solved using the Fluent module under the commercial software ANSYS to obtain The flow field and solidification temperature field in the molten pool area are included.(2)In the mathematical model of heat flow coupling in the molten pool of twin-roll thin strip continuous casting,it is difficult to deal with the movement of the solidified shell in the molten pool.Based on the Laplace equation,a solidified billet shell motion model is established,and the solid-phase motion is processed by calculating the pulling speed.Compared with the other two pulling speed processing methods,the flow field and temperature field distribution obtained by calculating the pulling speed are more reasonable.(3)Calculate the flow field characteristics(reflow zone and vortex zone)and temperature field characteristics(upwelling and wedge shape)in the molten pool under high-speed casting and rolling conditions,and analyze the characteristics.The effects of casting roll diameter,molten pool height,thin strip thickness and casting roll speed on the characteristics of the flow and temperature fields were studied.Increasing the casting roll diameter,molten pool height and casting roll speed all exacerbated the changes in the flow and temperature field characteristics.In the flow field,the positions of the vortex zone and the recirculation zone move up,the area increases,and the bulge in the temperature field becomes more obvious;while the increase in the thickness of the thin strip will slow down the characteristic changes.(4)Simplify the distribution system in the existing literature and design 6 types of nozzle structures to study the effect of the distribution method on the flow field and temperature field in the molten pool.The flow field and temperature field of 6 types of nozzles are compared and analyzed.The temperature field distribution of the 6th type of nozzle(Nozzle 9)is more conducive to the forward rolling process.(5)Simulatively studied the temperature field and flow field of the molten pool area under different process parameters(pouring temperature,heat transfer coefficient and casting roll speed),and analyzed the influence of each process parameter on the position of the kiss point.Compared with the pouring temperature and heat transfer coefficient,the roll speed of the casting roll has the greatest influence on the flow field and temperature field.In order to ensure the continuous casting process runs forward(within the distance between the kiss point and the minimum roll gap within 50mm),the flow and temperature fields under different roll speeds are simulated to obtain a reasonable process control range at each roll speed:The pouring temperature is controlled in the range of 20℃～40℃on the liquidus.when the casting roll speed is0.3m/s(18m/min),the heat transfer coefficient is 6000W·m~2/K～7000W·m~2/K;when the casting roll speed is 0.5m/s(30m/min),the heat transfer coefficient is 10000 W·m~2/K～11000 W·m~2/K;when the casting roll speed is 0.7m/s(42m/min),the heat transfer coefficient is 14000 W·m~2/K～16000 W·m~2/K;when the casting roll speed is 1.0m/s(60m/min),the heat transfer coefficient is 22000 W·m~2/K～24000 W·m~2/K.