Theoretical And Experimental Research On Twin-roll Strip Casting Of Copper Alloys

The twin-roll strip casting technology can directly cast and roll high-temperature molten metal,which has the advantages of short cycle,high efficiency and low power consumption.Compared with the traditional process,the thin metal strip rolled by this process has finer grains,more uniform distribution structure,lower element segregation,and better physical properties.The twin-roll strip casting copper alloy technology involves many disciplines and fields such as heat transfer,fluid mechanics,solidification and thermal deformation.Any slight change or instability in the process parameters during continuous casting may lead to serious defects in the finished thin strip.At present,the research on continuous casting copper alloy is not in-depth,and the distribution law of temperature field,flow field and solute field of molten pool under different process parameters and the cracking mechanism of continuous casting copper alloy thin strip need further discussion and research.In this thesis,based on the Φ265×120 twin-roll strip casting mill,the experiment of twin-roll strip casting of T2 copper alloy was carried out.The solidification structure in the molten pool of continuous casting copper alloy was obtained by E-Stop technology,and a series of post-treatment processes such as coarse grinding,fine grinding,polishing and corrosion were adopted,and its texture morphology and crystal evolution were analyzed.Based on the theoretical basis of fluid mechanics,heat transfer,microstructure solidification theory and microscopic nucleation model,a mathematical model of fluidsolid-thermal multi-physical field coupling was established.The temperature field and flow field of molten pool were simulated and analyzed by Pro CAST software,and the CAFE algorithm was used to simulate the solidification microstructure and dendrite distribution of molten pool,which was basically consistent with the solidification microstructure of copper alloy obtained by thin strip continuous casting experiment.The influence of casting temperature,casting speed,molten pool height and roll gap width on the distribution of temperature field,flow field and solute field in thin strip continuous casting was investigated by establishing a high-precision fluid-solid-thermal multi-physical field coupling mathematical model.Based on the simulation analysis of mathematical model,it is found that the change of process parameters will cause the change of physical field of molten pool in thin strip continuous casting process,in which too fast casting speed,too high casting temperature,and too large molten pool height and roll gap width will lead to more solute aggregation in the core area,which will aggravate the tendency of thin strip segregation.In this thesis,the cracking mechanism of casting strip billet is further analyzed.Based on thin strip continuous casting experiment,multi-physical field coupling mathematical model,casting and rolling cracking experiment,as well as the material deformation and cracking theory,the forming mechanism of crack of continuous casting thin strip billet is analyzed.It is found that in the process of thin strip continuous casting,the distribution of Kiss curve is unstable due to the uneven distribution of molten pool temperature field,which leads to the different amount of compression in each area of thin strip blank.The slip band is formed between the regions with large and small amount of pressure,and the stress concentration is generated.The experimental results show that when the shear stress in the slip band exceeds the limit of the material,many micro cracks will appear in the slip band at first.With the increase of deformation potential energy,these tiny cracks expand and connect with each other,thus forming macroscopic cracks.