Effect Of Pre-aging At 300℃ On Dynamic Recrystallization Behavior Of Mg-9Gd-4Y-2Zn-0.5Zr Alloy

Rare earth magnesium alloy has a broad application prospect in aerospace,aviation,weaponry and other fields due to its excellent high temperature and room temperature mechanical properties.And the deformed magnesium alloys with low layer fault energy are prone to dynamic recrystallization,which makes the grain refinement and thus improves the toughness.In order to solve this problem,this article takes the extrusion of Mg-9Gd-4Y-2Zn-0.5Zr（wt.%）alloy as the research object,and studies the effect of different aging（0h,20h,and52h）treatments on dynamic recrystallization behavior using hot compression methods,providing a theoretical basis for developing a plastic deformation process of magnesium alloy with fewer processes and shorter processes.The conclusions are as follows:1.As the aging time increases,the microstructure difference of the alloy lies in the grain needle-likeβphase;Theβphase is observed as a rod shape in the cylindrical direction and as a triangle in the base direction.As the aging time increases,the length ofβphase varies from3.02μm increased to 5.56μm.The proportion increased from 2.23%to 9.52%;The length ofβphase varies from 2.81μm increased to 4.4μm.The proportion increased from 1.99%to 6.91%.2.The compression curves under different deformation conditions show a similar deformation trend during the deformation process:the flow stress increases rapidly at first,then increases slowly to the peak value,and then decreases slowly;The increase of temperature,the decrease of rate and the increase of aging time are beneficial to reduce the peak stress;the hardening rate of the sample:solution-treated alloy（520℃×40h）>aged sample（300℃×20h）>aged alloy（300℃×52h）;theε_c point for DRX:solution-treated sample（520℃×40h）>aged sample（300℃×20h）>aged alloy（300℃×52h）the aging specimens softened first.3.Under the same deformation conditions,the proportion of DRX grains:aged sample（300℃×52h）>aged sample（300℃×20h）>solution-treated sample（520℃×40h）;Average grain size in the whole region:aged sample（300℃×52h）<aged sample（300℃×20h）<solution-treated sample（520℃×40h）;Average size of DRX region:aged sample（300℃×52h）>aged sample（300℃×20h）>solution-treated sample（520℃×40h）;texture strength:aged（300℃×52h）specimens<aged（300℃×20h）specimens<solution（520℃×40h）specimens,the combined effect of these factors leads to a decrease in peak stress with increasing aging time.4.During the deformation process,the dislocation density is the highest in the aging（300℃×52h）specimen,followed by the aging（300℃×20h）specimen and the smallest in the solid solution（520℃×40h）specimen,and the increase in dislocation density is favorable to DRX;the increase in the percentage of DRX grains leads to a decrease in the overall average grain size and weave strength;the DRX nucleation mechanism and deformation mechanism（slip and twinning）lead to a shift from<0001>-<11-20>to<0001>.At the same time,during deformation,blocky LPSO phases promote DRX;the lamellar LPSO phases are densely aligned,DRX is hindered,and the alignment spacing is large,DRX is promoted.5.An increase in temperature or a decrease in rate leads to a decrease in peak stress and stress-strain:at 350°C deformation,dynamic recrystallization accounts for a small percentage,plastic deformation mechanism is mainly controlled by basal slip and twinning,less plastic deformation mechanism,which is not conducive to dislocation release,making the flow stress higher;at 450°C deformation,dynamic recrystallization accounts for a large percentage,plastic deformation mechanism is mainly controlled by basal slip,conical slip,a small amount of twinning and LPSO phase torsion coordinated deformation,reducing the stress concentration and resulting in lower flow stress;At 0.1s^-1,more twins are generated,which is not conducive to slip,and the DRX grains account for a small percentage of the flow stress.