Study On Hot Processing Map And Microstructure Of Mg-16Al Magnesium Alloy

In this paper,the extruded Mg-16Al magnesium alloy bars were studied by gleeble-2000D thermal simulation machine.The hot compression deformation behavior of Mg-16Al magnesium alloy bar was studied.The corresponding constitutive equation was established.The critical condition of dynamic recrystallization was determined.The hot working diagram was drawn and the evolution law of microstructure was analyzed.The temperature range was 523 K～673 K,and the strain rate was 0.0001 s^-1～0.1 s^-1.The main results are as follows:（1）The as extruded microstructure of Mg-16Al magnesium alloy bar is mainly composed ofα-Mg grain and Mg₁₇Al₁₂ phase.The Mg₁₇Al₁₂ phases are divided into bulk Mg₁₇Al₁₂ phase with discontinuous network distribution near the grain boundary ofα-Mg grain and cellular Mg₁₇Al₁₂ phase inα-Mg grain boundary.After solid solution treatment,the original discontinuous network distribution of bulk Mg₁₇Al₁₂ phase is partially dissolved,while cellular Mg₁₇Al₁₂ phase is completely dissolved intoα-Mg matrix.（2）The Mg-16Al solid solution alloy exhibits obvious work hardening and continuous flow softening immediately after strain rate≥0.01 s^-1.However,when the strain rate is less than 0.01 s^-1,a significantly different rheological behavior is observed:when the temperature of the alloy is≥623 K,the initial work hardening composition decreases and only the initial work hardening occurs in the strain range of 0～0.01,and the flow softens It shows steady state flow;and when the temperature is less than 623K,the work hardening degree is stronger at higher temperature,followed by light flow softening.（3）Mg-16Al solid solution alloy shows obvious work hardening characteristics at the initial stage of hot compression deformation.With the progress of plastic deformation,the alloy recovers and recrystallizes,and the peak stress appears in the deformation rheological curve of the alloy.The average deformation activation energy Q value of the alloy is 144 KJ/mol.The average value of hardening index n is 3,and the hot deformation mechanism of the alloy is mainly the solute drag mechanism controlled by dislocation slip.（4）The critical dynamic recrystallization stressσ_c range of Mg-16Al solid solution alloy under different deformation conditions is 8.5MPa～198 MPa,which is less than that of AZ series common commercial grade magnesium alloy（38 MPa～255MPa）.The main reason is that Mg₁₇Al₁₂ phase in the alloy provides driving force for recrystallization ofα-Mg grains,thus promoting the dynamic recrystallization ofα-Mg grains nucleation.（5）The hot working maps of Mg-16Al magnesium alloy bar can be divided into three different regions:workability region,chang-over region and instability region.During the hot working process,the diffusion and migration of Al atoms and the coordinated interaction of dislocation motion reduce the steady deformation range.The suitable range of hot working parameters for Mg-16Al magnesium alloy bar is small:temperature range is 633 K～673 K,strain rate range is 0.001 s^-1～0.1 s^-1.At low strain rate,the alloy is prone to flow instability:under 673 K and 0.0001 s^-1 deformation,the dissolution of Mg₁₇Al₁₂ phase in the alloy will lead to the initiation of local microcracks;at 523 K and 0.0001 s^-1 deformation conditions,the cellular Mg₁₇Al₁₂ phase precipitates in a certain degree,which results in microcracks.