Numerical Simulation And Experimental Study Of Stirring Friction Modification Of LA103Z Magnesium-lithium Alloy

With a series of advantages such as low density,high specific strength and good low temperature impact resistance,magnesium-lithium alloy is one of the lightest metallic structural materials for engineering applications.However,the deficiencies of magnesium-lithium alloy such as low strength and poor plastic deformation ability at room temperature make it very limited in commercial applications.It is of great theoretical and engineering significance to expand the engineering applications of magnesium-lithium alloy by carrying out the study of stirring friction modification of magnesium-lithium alloy to realize the improvement and optimization of its organization and mechanical properties.In this study,the stirring friction modification of LA103Z magnesium-lithium alloy is studied by a combination of numerical simulation,experimental study and theoretical analysis.The plastic deformation law of LA103Z magnesium-lithium alloy during stir friction modification was investigated systematically.The main research works and conclusions are as follows.(1)Thermal simulation experiments of LA103Z magnesium-lithium alloy were designed and conducted to systematically investigate its thermal deformation behavior in the range of deformation temperature of 250?-500? and strain rate of 0.01 s'1-1s'1.Based on the Arrhenius equation,the ontological model of LA103Z magnesium-lithium alloy was established,which can describe its plastic flow behavior under different deformation conditions more accurately and provide the basic data for numerical simulation.(2)The numerical modeling approach of the stirring friction modification process is studied,and the numerical model of the stirring friction modification process of LA103Z magnesium-lithium alloy is established.The effects of processing speed and stirring head speed on the distribution and evolution of temperature,stress-strain and velocity fields are investigated,and the mechanisms of the processing parameters on the physical constants are discussed.Combined with the analysis of the simulation results,the strain uniformity at the back side of the stirring head was optimized for the process parameters using the response surface method.(3)By comparing the microstructure of the material before and after stir friction machining,the effect of machining speed and stirring head speed on the microstructure was investigated,and the mechanism of the influence of the machining parameters on the evolution of the microstructure in the stirring zone was investigated.In addition,with the increase of stirring head speed and processing speed,the grains in the stirring zone showed a gradient change along the plate thickness direction.(4)The tensile test of LA103Z magnesium-lithium alloy sheet was conducted to investigate the influence of processing speed and stirring head speed on the mechanical and deformation properties of the material by comparing the tensile stress-strain relationship,elongation after fracture and fracture morphology of the specimens under different parameters.The experimental results showed that the tensile strength of the material was increased from 160 MPa to 203 MPa(26.9%increase)after the stirring friction processing,and the plasticity decreased to different degrees.When the stirring head speed is 800 r/min and the processing speed is 100 mm/min,the tensile strength of the material increases compared with the original specimen,while the plasticity decreases less,so that a good comprehensive modification effect can be obtained.