| Due to its advantages of high specific stiffness and strength,low density,good ductility and excellent shock absorption ability,magnesium alloy can be used in electronic 3C products,military and other fields.Magnesium alloy plate and foil can be used as raw materials for mobile phone shell and sound diaphragm products,and also have good application prospects.Generally speaking,rolling will make the basal texture pile up and strengthen the basal texture.In this thesis,the asynchronous warm rolling process not only effectively avoids the basal texture accumulation,but also realizes the grain refinement,and also successfully processes 0.25 mm ultra-thin Mg-Li alloy plate,which is conducive to the further processing of magnesium alloy plate.In this thesis,finite element modelling,visco plastic self consistent(VPSC)simulation and metallographic electron microscopy observation,electron back scattered diffraction(EBSD)and room temperature tensile test are combined to realize the processing of ultra-thin LZ91 Mg-Li alloy plate with high tensile strength and high elongation with a thickness of 0.25 mm by using asynchronous warm rolling process.Firstly,the original extruded plate with thickness of 1mm is homogenized and annealed,and then it is subjected to multi pass asymmetric warm rolling to obtain0.5mm and 0.25 mm ultra-thin rolled plates respectively.The samples of ultra-thin rolled plates are observed by metallographic electron microscope and EBSD experiment.At the same time,the asymmetric warm rolling process of LZ91 Mg-Li alloy is simulated by finite element modelling,and the changes of output temperature field,equal effect force field and equivalent plastic strain field are analyzed and discussed.Then,VPSC simulation is carried out,and the Voce hardening parameters are continuously adjusted to match the simulated stress-strain curve with the real stress-strain curve obtained from the tensile experiment.Then,combined with the opening law of the slip system and twin system and the evolution law of the twin volume fraction,the plate texture evolution law of LZ91 Mg-Li alloy in the plastic deformation process and its influence on the mechanical properties are analyzed in detail.The EBSD experimental results show that the maximum basal texture strength of1 mm initial plate and 0.25 mm ultra-thin rolled plate are 36.02 mud and 29.19 mud respectively.asymmetric warm rolling process not only reduces the base texture strength,but also significantly refines the grains.The tensile test results show that the tensile strength and yield strength of 0.25 mm ultra-thin rolled plate along the rolling direction have reached 206.8MPa and 138.4MPa respectively,and the anisotropy of yield strength has also been significantly improved.This will have a positive effect on the mechanical properties of subsequent materials.VPSC results show that the base slip is the main factor in Mg-Li alloy asymmetric warm rolling,and a large number of tensile twinning are initiated due to the coordinated deformation of BCC phase.In this case,the micro deformation is assisted by tensile deformation,which is conducive to improving the plastic deformation capacity of Mg-Li alloy.In order to explore how the weak basal texture of 0.25 mm ultra-thin plate is formed,this thesis compares the finite element modelling and VPSC simulation with the experimental results,obtains the stress-strain results on the macro scale and the evolution law of microstructure and texture during the rolling process,and describes the plastic deformation behavior and microstructure change of the Mg-Li alloy plate during the rolling process in detail,providing reference and basis for the plastic processing of ultra-thin Mg-Li alloy. |
PDF Full Text Request