Analyse On The Heat Transfer Behavior And Microstructure Of Aluminum Strip During High Speed Cast-Rolling With Copper Roller Covers

Aluminum alloy sheet and strip market demand is large,and the application is wide.China is a big consuming country of aluminum sheet and strip,accounting for 50% of the total consumption of aluminum sheet and strip in the world.Twin-Roll Casting,as a new short process with high efficiency,green and low cost,has been widely used in the field of aluminum strip industrial production.At present,the maximum production speed of steel roll casting and rolling in industrial production is only 1.5m/min,which is difficult to match with the production capacity of downstream mills and seriously restricts the production efficiency of plates.How to improve the casting and rolling speed has become an urgent problem in the metallurgical industry.The cooling capacity of twin-roll casting sets determines the solidification rate of aluminum liquid.Under the premise that the development of steel roller sleeve and internal cooling system is bottlenecked,in order to improve the casting and rolling speed,this paper combines finite element analysis and casti0 ng and rolling experiments to study the influence of copper roller sleeve and steel roller sleeve on the heat transfer behavior of aluminum strip casting and rolling interface and ultimate casting and rolling capacity,respectively.Based on the one-dimensional heat transfer principle,the copper-aluminum and steelaluminum heat transfer coefficients were tested respectively,and the corresponding copper and steel rods were prepared.The heat transfer surface was immersed in aluminum liquid,and the temperature rise curves of the internal temperature measurement points of the copper and steel rods were read by using Labview software.Using Commercial finite element software Deform,the heat transfer coefficients between the copper and steel rods and the aluminum liquid were inverse solved based on the principle of least squares,and the quantitative equations of copper-aluminum heat transfer coefficient and steel-aluminum heat transfer coefficient versus temperature were obtained,which provided the basic data support for the next finite element simulation analysis of the temperature field.We designed a roll system with both copper and steel rolls,the left half of the cast roll is a copper roll sleeve and the right half is a steel roll sleeve.This can largely exclude the influence of other uncontrollable factors,and better compare the casting and rolling temperature field,microstructure and mechanical properties of the finished strip with those of copper and steel rolls.Based on the commercial finite element software Fluent,the two-dimensional and three-dimensional heat flow coupling models of twin-roll casting and rolling were established respectively.First of all,through finite element simulation,the ultimate casting and rolling speeds of copper roll sleeve and steel rod sleeve are 11m/min and 6m/min respectively.Then,the relationship models between Kiss height and casting speed were proposed for copper and steel roller sleeves respectively.Finally,the effects of the copper and steel roller sleeves on the temperature and flow fields of the melt pool are compared visually by the three-dimensional heat-flow coupling model.In order to verify the accuracy of the finite element simulation results,pure aluminum casting and rolling experiments were conducted.When the casting temperature is 680?,the ultimate speed of steel roll casting and rolling is derived,and the effect of the increase of casting and rolling speed on the microstructure and mechanical properties of the strip is analyzed.Then,the influence of the ultimate speed of copper roll casting and rolling on the microstructure and mechanical properties of the strip under the same external conditions was investigated.Finally,a simultaneous copper/steel roll casting and rolling experiment is carried out to compare more clearly and visually the effects of copper rolls on the casting and rolling temperature field,microstructure and mechanical properties of the sheet under the same conditions.The conclusions of the paper can provide some guidance for the industrial production of high-speed casting and rolling of copper rolls.