Dynamic Recrystallization Behavior Of Rare Earth Magnesium Alloy After Hot Torsion Deformation

As a new type of high-strength and heat-resisting material,rare earth magnesium alloy has broad application prospects in the fields of aerospace and weaponry.At present,studies on the alloys of this type usually use the hot tensile test and the thermal compression test to simulate the changes in the microstructure and properties during the metal thermal deformation process.However,these conventional methods have the defects of plastic instability such as necking and bulging.While the thermal torsion experiment solves this problem,it can realize the uniform deformation process of the material under the shear stress and avoid the surface friction effect between the sample and the contact object.Based on the Gleeble thermal simulation and torsion experiment,the microstructure and rheological behavior of rare earth magnesium alloy under shear stress conditions are studied.The main work contents are as follows:(1)The rheological curves of thermal torsion deformation have distinct dynamic recrystallization characteristics.With the increase of the strain,the stress rapidly rise to the peak and then gradually decreased The analysis of single-factor deformation parameters found that the peak equivalent stress is positively correlated with the strain rate and negatively correlated with the deformation temperature.The constitutive equation with respect to temperature and strain rate was:? = 3.8684 × 1010[sinh(0.020183?)]2.3164exp(-163.45674/RT)]Deformation process was carried out uniformly and energy was utilized efficiently at optimum parameters area which ranged from 450 ??480?,0.001s-1?0.01s-1.While the instability range is 300?-420?.0.5s-1-1s-1 and 300?-330??0.001 s-1-0.01 s-1.Massive LPSO phases precipitated which is not conducive to plastic deformation in this range.(2)Based on the inherent relationship between the work hardening rate and the evolution of the material structure,the critical condition for the occurrence of dynamic recrystallization is explored on the positional relationship of the rheological curve.Quantitative relation model of peak conditions and critical conditions was:?p=3.246129?c,?p=1.20639?c.Through the introduction of Z-parameters,the response of deformation temperature and strain rate to critical strain is characterized,and the critical strain model and dynamic model for dynamic recrystallization are established:?c = 2.86582 ×10-3Z0.06981;z=?exp(163457/RT)XDRX = 1-exp[-0.7010(?-?c/?*)1.00261](3)The dynamic recrystallization process is influenced by the strain rate,deformation temperature and strain amount.When the temperature of thermal torsional deformation rises from 350? to 400?,the grain size of recrystallized grains is negatively correlated with the strain rate.As the temperature rise,the newly DRXed grains grow up,the grain size of recrystallized grains is positively correlated with the strain rate.Block LPSO phase hinders the recrystallization,while short rod and granular promote LPSO occurrence.In combination with EBSD orientation imaging analysis and microstructure evolution,dynamic recrystallization has obvious nucleation and growing process,which presents a typical discontinuous dynamic recrystallization mechanism.The evolution of microstructure and microhardness corresponding to hot torsion rheological behavior,therefore,the effect of temperature increase on grain coarsening and the effect of accelerated strain rate on grain refinement should be considered when we select the deformation parameters.