High Temperature Formability Analysis And Deformation Process Optimization Of AZ80 Magnesium Alloy

Magnesium alloy plastic processed products have the advantages of compact structure and high mechanical properties,and have wide application prospects in the fields of aviation,aerospace,automotive,military and other fields.However,the hexagonal closed-packed crystal structure of magnesium alloys results in poor room temperature deformability.Therefore,it is of great significance in engineering practice to study the high temperature deformation behavior of magnesium alloy and optimize its processing process.In this paper,the high temperature forming performance of as-cast AZ80 magnesium alloy was systematically studied,and the deformation process of Equal Channel Angular pressing(ECAP)was optimized.First,The Gleeble thermal compression test of as-cast AZ80 magnesium alloy was carried out in the range of deformation temperature 250～400℃ and strain rate 0.001～1s-1.Based on the data of thermal compression test,three constitutive models of AZ80 magnesium alloy were established,including phenomenological model,physically-based model and BP neural network model.Subsequently,the hot working diagram of AZ80 magnesium alloy based on Prasad instability criterion was established,and the plastic processable zone and rheological instability zone of the alloy were determined.Finally,the temperature-deformation-microstructure coupling multi-physical field finite element model of AZ80 magnesium alloy was established.The specific contents are as follows:(1)For the as-cast AZ80 magnesium alloy,using the linear regression method to establish the four kinds of phenomenological model(strain-compensated Arrhenius model,DRV+DRX two-stage model,original and modified Johnson-Cook.original and modified Fields-Backofen model)),two kinds of constitutive model based on physical concept(dynamic recrystallization model,the modified Zerillii-Armstrong model),and adopts the statistical method to establish a BP neural network model.And on this basis,an optimized Johnson-Cook and Zerillii-Armstrong models are proposed.Through mathematical statistics,three statistical indicators of correlation coefficient(R),average absolute relative error(AARE)and relative error(RE)are used to compare the prediction accuracy of different models,and the BP neural network model has the highest prediction accuracy,Followed by optimized ZA model,dynamic recrystallization model and strain-compensated Arrhenius model,and systematically analyzed the advantages and disadvantages and applicability of each model.(2)Based on the dynamic material model and the Prasad instability criterion,the processing diagram of as-cast AZ80 magnesium alloy with strain rate of 0.5 was established.Combining with the processing diagram and the metallographic analysis of the corresponding region,it was concluded that the instability region with strain rate of 0.5 was within the temperature range of 250～290℃,strain rate of 0.2371～1s-1,and temperature 397-400℃,strain rate of 0.398～1s-1,respectively.However,the processing safety zone was within the temperature range of 250～280℃,strain rate of 0.009-0.1334s-1,and temperature 317～400℃,and strain rate 0.001～0.0237s-1,respectively.(3)A multi-physical fields finite element model of temperature-deformation-microstructure coupling of as-cast AZ80 magnesium alloy was established,and the finite element model was applied to optimize the deformation process of ECAP.In view of the cylindrical sample of Gleeble thermal compression test,the finite element model was established,the Arrhenius constitutive model and dynamic recrystallization model obtained above were coupled to the Deform software to establish the multi-physical fields model of Gleeble hot compression test of cylindrical specimen.For the specific deformation conditions of 573K/0.1s-1,the model analyzes the distribution characteristics of the stress field,strain field and microstructure field of the cylindrical specimen during compression,and was compared with the experiment,shows that the established model is reliable.Then the model established was used to optimize the ECAP deformation process.The range of optimization was the range of the processing zone obtained in the processing diagram:temperature 317～400℃,strain rate 0.001～0.0237s-1,and the optimal deformation process was obtained as follows:Deformation temperature 400℃,pressing speed 0.15mm/s.