| Due to the characteristics of low density,high strength and high specific rigidity,plastic processing products of magnesium alloys have broad application prospects in transportation,aerospace,3C and other fields.However,due to the close-packed hexagonal structure of magnesium alloys,the room temperature slip system is too few,resulting in poor plastic deformation ability,which limits the large-scale use of magnesium alloys.Studying the plastic deformation behavior of magnesium alloys has certain engineering guiding significance.This paper takes the as-cast AZ80 magnesium alloy as the research object,studies its plastic deformation behavior,and optimizes the deformation process in combination with the forward extrusion experiment.First,an isothermal compression experiment is carried out,and the deformation condition is temperature(523-673K)and strain rate(0.001-1s-1).Based on the experimental data,the original and improved Johnson-Cook(J-C)models were established to predict the high-temperature flow behavior of materials,and on this basis,an optimized J-C model was proposed.Then the dynamic recrystallization behavior of the material was an alyzed based on the predicted data of the J-C constitutive model;the dynamic recrystallization kinetic model and the recrystallization grain size evolution model were established based on the Zener-Hollomon parameters,and the effect of the Z parameter on the recrystallization rate and recrystallization was analyzed.The influence of percentage and recrystallized grain size.Finally,using the stress and strain data predicted by the constitutive model,the thermal processing diagrams of two instability criteria are established;combined with the dynamic recrystallization model and microstructure,the processing diagrams are compared and analyzed,and the suitable processing interval is optimized.Finally,a forward extrusion experiment was carried out to test and analyze the mechanical properties of the material after extrusion under different process conditions,and to verify the suitable processing area.The conclusions are as follows:(1)The peak flow stress of as-cast AZ80 magnesium alloy decreases with the increase of temperature;it increases with the increase of strain rate.The original JC model cannot predict the high temperature softening behavior of the material well;the improved J-C model can predict the flow softening of AZ80,but it cannot reflect the flow behavior of the material in the work hardening-dynamic recovery stage;this is because the two do not consider the effect of strain and strain rate and temperature on flow stress,the optimized J-C model makes up for the shortcomings.It can predict material flow stress well in the full range(strain 0 to 0.69),and the prediction accuracy is better than the original J-C model and the improved J-C model.The optimized J-C model correlation coefficient(r)value is 0.9829,and the average relative error(AARE)is 5.60%.(2)The activation energy of hot deformation of as-cast AZ80 magnesium alloy is calculated based on the Arrhenius equation.Combining the comparison of microstructures,it is found that the second phase of the network will segregate and precipitate around the matrix phase,which will increase the thermal deformation activation energy of the material.A dynamic recrystallization model was established based on Zener-Hollomon parameters.The higher the temperature and the lower the strain rate,the lower the Z value.The Z value has an important influence on the dynamic recrystallization kinetics.The lower Z value reduces the critical strain,and the easier dynamic recrystallization occurs,and the more complete the recrystallization.Microstructure observations show that when the true strain reaches=0.69,the recrystallization percentage of all samples has reached more than 50%.Under three sets of conditions(T=673K,?=0.001s-1,T=673K,?=0.01s-1,T=623K,?=0.0001s-1)completely recrystallized,choosing to recrystallize is easier and more recrystallized It is better to perform thermal deformation in a complete process interval.In addition,the smaller the Z value,the larger the recrystallized grain size.(3)In the full strain range(0 to 0.69),based on the Prasad instability criterion and Murty instability criterion,the hot working diagrams of the as-cast AZ80 magnesium alloy were established respectively.The comparison shows that the thermal processing map based on Murty criterion is more accurate.When the strain amount is less than 0.4,the processing map changes greatly with the increase of strain;affected by the dynamic recrystallization softening effect,when the strain is greater than 0.4,the processable zone and the instability zone change little,and the instability zone has a low temperature and high strain rate area.The trend of contraction.Through the verification of the thermal deformation experiment of forward extrusion,the optimal deformation process interval is determined as the temperature T=623K?673K,?=0.0001 s-1?0.01s-1 and T=660K?673K,?=0.01s-1?0.1s-1.The room temperature tensile mechanical properties of the material are measured under this process condition,the tensile strength is above 300MPa,and the elongation can reach 0.15... |
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