The Simulation Of 2099 Al-Li Alloy Twin-roll Casting Process

Aluminum-lithium alloy has high strength,low density,good matching between strength and toughness,low anisotropy,good thermal stability,and good corrosion resistance and formability.It is an important aviation material that has been verified by practical application,which is widely used in airplane fuselage skin,floor beam and pillar.At present,Al-Li alloy is produced by conventional casting and hot rolling process,with long process flow,low production efficiency and high energy consumption.Using cast-rolling process to prepare Al-Li alloy plate can shorten the process flow,save the production cost,and improve the performance of Al-Li alloy strip.In this paper,the temperature field and flow field of cast-rolling process of Al-Li alloy strip are simulated by numerical simulation method,and the influence of technological parameters on the solidification process of cast-rolling strip is explored to provide theoretical and technical support for improving the central segregation of cast-rolling strip and improving the quality of cast-rolling strip.The paper reaches the following conclusions:(1)ANSYS finite element simulation software was used to establish a two-dimensional numerical model of the cast-rolling zone.The simulation results showed that with the increase of the cast-rolling speed,the exit temperature of the cast-rolling strip would keep rising,.When cast-rolling strip thickness is 6 mm,pouring temperature at 700℃,cast-rolling speed is greater than 1.15 m·min-1 cause the risk of fail.(2)To study the temperature variation process of 2099 Al-Li alloy cast-rolling area,the study found that the center of cast-rolling area changes with the temperature of the surface have the same process,after the fast slow,slow down,then down and accelerating process,and increase the average heat transfer coefficient and reduce the cast-rolling speed can accelerate the rate of temperature drop.(3)The flow characteristics of melt in the cast-rolling zone were studied when casting temperature was 700℃,cast-rolling speed was 0.85 m·min-1,and heat transfer coefficient was 6500 W·m-2·℃-1.In the flow field,there are two groups of symmetrical distribution of backflow area,and the backflow area at the inlet helps release the internal solidification latent heat and promote the melt flow to the roll surface.The core reflux zone is caused by the large rolling deformation force at the front end of the mushy zone,which extrudes the liquid phase from the mushy zone.With the increase of cast-rolling speed,the recirculation zone of the core gradually disappeared,the depth of sump and the length of mushy zone increase gradually.(4)The cast-rolling experiment was conducted according to the simulation results,and the average interfacial heat transfer coefficient was determined to be 6500 W·m-2·℃-1 according to the measured exit temperature of the cast-rolling strip and the simulation results.The reliability of the model was verified by comparing the distance between the secondary dendrite arms spacing of the cast-rolling strip.It was found that the optimal casting temperature of 2099 Al-Li alloy 6 mm thick cast-rolling strip was 690℃ and the optimal cast-rolling speed was 0.85 m·min-1 in the horizontal cast-rolling machine in the laboratory.At this time,the center reflux zone appeared in the cast-rolling area,and the center layer segregation of the cast-rolled strip was significantly improved.(5)Combined with the results of numerical simulation and experimental research,it was found that the depth of sump Z1 and the length of mushy zone Z2 were directly related to the central segregation,and when the ratio of the depth of sump Z1 and the length of mushy zone Z2 to the length of cast-rolling zone Z exceeded the maximum ratio of the generated central reflux zone,the central segregation developed in a more serious direction.The improvement of the center segregation is attributed to the formation of the core reflux zone in the cast-rolling zone.