A Study On The Homogenization And Hot Deformation Behavior Of As-cast AZ80A Magnesium Alloy

As the lightest structural material in engineering applications,magnesium alloys have been gradually used in various industries.AZ80 A magnesium alloy has good plasticity,high strength,excellent performance,relatively cheap price,and broad industrial application prospects,and is increasingly favored by scholars at home and abroad.In this paper,the optical microscopy（OM）,X-ray diffractometer（XRD）,scanning electron microscope（SEM）,and energy spectrometer（EDS）were used to study the microstructure and element distribution of as-cast AZ80 A magnesium alloy before and after homogenization heat treatment.The effects of homogenization temperature and holding time on the microstructure of as-cast AZ80 A magnesium alloy were analyzed.The effects of homogenization on the tensile strength,elongation and hardness of the alloy were analyzed using an electronic universal testing machine and a Brinell hardness tester.The tensile fracture morphology of the alloy before and after homogenization was analyzed by SEM.Gleeble-3800 thermal simulation tester was used to conduct isothermal hot compression test on the homogenized alloy to obtain the flow stress-strain curve of the alloy at different temperatures,different strain rates and different deformations.Based on the stress-strain curve,the material constitutive model,dynamic recrystallization（DRX）kinetic model,DRX grain size model,and DRX volume fraction model were established,and the strain rate sensitivity index（SRS）distribution maps under different strains were drawn.OM and electron backscatter diffraction（EBSD）were used to analyze the microstructure evolution,DRX behavior and texture changes of the alloy during hot compression.Concluded as follow:（1）The as-cast AZ80 A magnesium alloy is mainly composed of an α-Mg matrix and a brittle and hard β-Mg17Al12 phase.The best homogenization process is 683 K + 20 h.After homogenization,the comprehensive mechanical properties of the alloy are improved.Among them,the tensile strength increased by 40.64%,and the elongation increased by 152.44%.But the hardness decreased by 8.36%.（2）The room-temperature tensile fracture morphology of as-cast AZ80 A magnesium alloy is characterized by brittle fracture along grains.After homogenization,the tensile fracture morphology of the alloy appears as a penetrating fracture with higher energy.（3）A constitutive model of AZ80 A magnesium alloy after homogenization is constructed:Hyperbolic sine constitutive model:（?）Constitutive model considering strain effects:（?）This model can accurately calculate the rheological behavior of AZ80 A magnesium alloy during thermoplastic deformation after homogenization.（4）The dynamic softening region of the homogenized AZ80 A magnesium alloy is a temperature of 680K⁷23K and a strain rate of 0.001s^-10.01s^-1.（5）By performing linear regression analysis on the true stress-strain curve obtained from the isothermal hot compression test,the DRX critical condition,DRX dynamic model and DRX grain size model of AZ80 A magnesium alloy were obtained.（?）（6）The increase of deformation temperature and the decrease of strain rate are conducive to the occurrence and development of DRX.As the amount of deformation increases,the low-angle grain boundaries（between 5° and 75° in 20% deformation）gradually transform into large-angle grain boundaries（between 50° and 90° in 60% deformation）,and DRX becomes more and more sufficient.（7）At the beginning of the deformation,the deformation is mainly based on the {0001} base slip,and there is a small amount of {1 0-1 0} cylinder slip,and there are two different textures parallel to the compression direction.With increase in deformation,the deformation is mainly dominated by {1 0-1 0} cylinder slip.The texture is gradually transformed from a base texture parallel to the direction of compression to a texture perpendicular to the direction of compression,and in this process,twinning is the main deformation mechanism.