Research On The Integration Of Shape And Control Properties Of AZ31B Magnesium Alloy Plastic Processing

In order to obtain high-performance wrought magnesium alloy products with good forming quality,this paper studies the microstructure evolution and plastic workability of pre-extruded AZ31B magnesium alloy during plastic processing by numerical calculation,theoretical analysis and experimental research,and the relationship between the two and the deformation mechanism.Firstly,Gleeble thermo-mechanical simulation experiments of magnesium alloy were carried out in the deformation temperature of 200?-350? and the strain rate of 0.001 s-1-1 s-1,and the flow stress curve was obtained.Then,using the quantitative metallographic analysis method,the microstructure evolution model for the dynamic recrystallization process of magnesium alloy was established,and the model was coupled with finite element to simulate and predict the microstructure evolution of cylindrical sample free upsetting and gear forging.Then,based on the experimental data of the flow stress curve,the processing map of magnesium alloy was established,and the finite element model coupled with processing map was constructed.The response surface method was used to determine the workability domain of the spur gear,and the processing path was optimized.Finally,the deformation mechanism of magnesium alloy during thermal deformation was analyzed by experimental data such as stress exponent,deformation activation energy.The relationship between deformation mechanism,microstructure evolution and plastic workability was investigated in order to provide theoretical basis and analysis basis for further improving the performance control and shape control level for integrated manufacturing of wrought magnesium alloy products.The main conclusions obtained in this paper are as follows:(1)In the process of cylindrical upsetting and gear forging,deformation and microstructure are nonuniformly distributed.The deformation and microstructure inhomogeneity are closely related to the friction between the billet and the mold and the flow stress curve of the AZ31B magnesium alloy.Decreasing the deformation temperature or increasing the strain rate facilitates the acquisition of fine-grained structures,but at the same time increases the deformation and microstructure non-uniformity.(2)The flow instability during gear forging process is related to the deformation temperature,the punch velocity and the billet reduction.In the low temperature range of 250?-300?,flow instability such as cracking,mainly occurs in the early stage of gear forming,while in the high temperature range of 350?-400?,flow instability mainly occurs in the late stage of tooth filling.This is closely related to the deformation mechanism and dynamic recrystallization behavior of magnesium alloys at different temperatures and deformations.In addition,increasing the punch velocity will weaken the extreme formability of the gear.(3)There are complex interactions between microstructure evolution,plastic workability and deformation mechanism.At the temperature of 250?,the stress exponent and activation energy are relatively low,which indicates that prismatic slip and pyramidal slip can not initiate,resulting in the poor plastic workability of AZ31B magnesium alloy at 250?.At the temperature range of 300?-350?,the value of stress exponent and activation energy are higher than that at 250?,the cross-slip of dislocations can initiate and promotes the dynamic recrystallization of the magnesium alloy,which the main reason for the improvement of the plastic workability of the magnesium alloy.At the temperature of 400?,although non-basal slip and cross-slip can initiate,grain coarsening weakens the plastic workability of the magnesium alloy due to higher temperature.