| Magnesium alloys have been widely used in various industries.AZ80 A magnesium alloy has good plasticity,high strength,good performance,and has a price advantage,has become one of the most popular deformation magnesium alloy.In this paper,the extruded AZ80 A magnesium alloy bars were used as raw materials.The method of preparing semi-solid billet was strain induced melting activation method(SIMA).The effects of holding temperature and holding time on the microstructure evolution of semi-solid AZ80 A magnesium alloy were studied by a series of test characterization methods.Isothermal compression tests were carried out on semi-solid AZ80 A magnesium alloy by Gleeble3800 thermal simulation testing machine under the conditions of 598K-673 K and strain rates from 0.001 to 1s-1.A constitutive model of peak stress was established based on the true stress-true strain curves obtained from the experiments.Finally,the microstructure characteristics of semi-solid billet after hot compression were analyzed.The main conclusions are as follows:(1)Semi-solid AZ80 A magnesium alloy is mainly composed of ?-Mg grains and networked liquid phase eutectic Mg17Al12;(2)The evolution of semi-solid microstructure is mainly divided into three stages: initial grain coalescence and growth,grain spheroidization,separation and final coalescence and coarsing.(3)In the process of billet making,the average grain size and liquid-phase ratio of semi-solid microstructure increased with the increase of holding temperature and holding time,and the shape factor showed a trend of first increasing and then decreasing.Through comprehensive analysis and comparison,the optimal process parameters are obtained as follows: the holding temperature is 550?,the holding time is 45min;(4)Based on the experimental data,the relationship models of the three influencing factors,liquid-phase rate,average grain size and shape factor,with holding time and holding temperature were obtained by fitting.These models have certain guiding significance for the preparation of semi-solid billet of extruded AZ80 A magnesium alloy.(5)The true stress-true strain curves of semi-solid AZ80 A magnesium alloy under given conditions were obtained,and the constitutive equation of peak stress was constructed:(?)=2.1369*1010[sinh(0.0158?)]4.3611exp(-197512.6503/RT)The thermal deformation activation energy(Q)of the semi-solid sample was calculated as 197512.65037J/(mol· K).The calculation results show that the accuracy of the model is high. |
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