Constitutive Modeling And Evolution Of Hot Extrusion Microstructure Of Mg-6Gd-5Y-0.3Zr Magnesium Alloy

As the lightest metal in common structural materials,magnesium alloys are also abundant on the earth.Magnesium alloys have great application prospects in automotive,aerospace and 3C industries.However,the engineering application of magnesium alloys is still very limited.It is mainly due to its mechanical properties of low strength,poor plastic forming performance,poor creep resistance,poor corrosion resistance.Rare earth-rich magnesium alloys not only have relatively good comprehensive properties,but also have good application potential.In this paper,Mg-6Gd-5Y-0.3Zr rare earth magnesium alloy was used as the main research material.The evolution of its structure and properties during heat treatment was studied.The stress-strain curves of magnesium alloys under different deformation conditions were analyzed by Gleeble-1500D thermal simulation machine.Based on dislocation theory,a unified viscoplastic constitutive model coupled with multiple internal variables of microstructures is established.ABAQUS was used to simulate the extrusion process of magnesium alloy at different temperatures.The results show that as-cast Mg-6Gd-5Y-0.3Zr rare earth magnesium alloy mainly consists of?-Mg matrix,Mg₅?Gd,Y?phase and phase rich in rare earth.In the solution process,the eutectic phase of Mg₅?Gd,Y?is dissolved into the Mg matrix continuously,and the rare earth atoms are gathered together to form small second phase particles.After solution treatment,the room temperature tensile strength and high temperature tensile strength of magnesium alloys are slightly increased,and the elongation at room temperature and high temperature is nearly double that of as-cast magnesium alloys.In the process of hot compression test,both strain rate and temperature have effects on the flow stress of materials.With the increase of deformation temperature and the decrease of strain rate,the flow stress decreases gradually,the recrystallization integral increases and the average grain size decreases.When the deformation temperature and strain rate are constant,the recrystallization integral increases and the average grain size decreases with the increase of strain.The constitutive model can describe the evolution of dislocation density,recrystallization and average grain size of Mg-6Gd-5Y-0.3Zr rare earth magnesium alloy during hot deformation well.The linear correlation coefficient between predicted and experimental values of flow stress is 0.9844,and the average relative error is 7.27%.It can accurately express the viscoplastic flow and microstructure evolution of Mg-6Gd-5Y-0.3Zr rare earth magnesium alloy during unidirectional compression.ABAQUS was used to simulate the microstructure distribution of materials during hot extrusion at different temperatures,which was in good agreement with the experimental results.The model can simulate the microstructure evolution of materials during hot extrusion well.