Compression-torsion Deformation Behavior And Microstructure Evolution Of Rare Earth Magnesium Alloy

Rare earth magnesium alloy shell components with various inner rings and high ribs are the key load-bearing components of major national defense equipment,and are an inevitable choice in the context of lightweight.Mg-Gd-Y-Zn-Zr alloy is a kind of important high-strength heat-resistant rare-earth magnesium alloy,especially because it contains LPSO phase and has excellent mechanical properties at room temperature and high temperature.It is suitable for parts and components that work for a long time at 200-300?.It has a broad application prospect in aerospace,transportation,weapons and other fields.However,the castings of this alloy have poor mechanical properties and poor plasticity,which cannot meet the service conditions.In addition,the traditional deformation method can not achieve the overall plastic forming of such components.North University of China proposed to use rotary extrusion method to form a large shell with inner ring ribs,which can form a complex shape while strengthening and toughening the material.Because the deformation mechanism of mg-13gd-4y-2zn-0.5zr alloy is very complicated in the process of rotary extrusion,this paper USES Gleeble 3500 thermal simulation torsional unit to study the metal rheological characteristics and microstructure evolution of mg-13gd-4y-2zn-0.5zr alloy under different deformation temperatures and strain rates,which lays a theoretical foundation for rotary extrusion.The results show that:The macroscopic morphology of the sample after compression and torsion deformation can be obtained:under the same deformation conditions,the formability of the Mg-13Gd-4Y-2Zn-0.5Zr alloy under compression and torsion is better than that of pure torsion deformation.The compressive and torsional deformation characteristics of mg-13gd-4y-2zn-0.5zr alloy were obtained by the experiment.After the compressive and torsional deformation,the rheological behavior of mg-13gd-4y-2zn-0.5zr alloy underwent the competitive process of process hardening and rheological softening,and the stress-strain curve showed typical recrystallization characteristics.The stress-strain curves in different states of compression torsion and pure torsion are similar,but the peak stress of torsional deformation under the same conditions is higher than that under compression and torsion deformation.The former critical strain value of dynamic recrystallization is smaller than the latter.The constitutive equation of the alloy with temperature compensation factor is obtained as follows:?=103.63ln{(Z/2.19×1017)1/4.8517+[(Z/2.19×1017)2/4.8517+1]1/2}The thermal working diagram shows that the optimum working range of the alloy under compression and torsion conditions is temperature T=420??480?,strain rate=0.025s-1?0.001s-1.It provides a theoretical basis for the formulation of engineering application parameters of the alloy.The research shows that the dynamic recrystallization mechanism of the alloy under compression and torsion gradually changes from continuous dynamic recrystallization at low temperature to discontinuous dynamic recrystallization at high temperature;With the increase of strain rate at the same temperature,the recrystallization mechanism changes from continuous dynamic recrystallization to discontinuous dynamic recrystallization.Increasing the temperature and decreasing the strain rate will increase the dynamic recrystallization rate,and the recrystallization position will gradually develop from the grain boundary to the inside of the original grain as the temperature increases.The size of recrystallized grains increases with increasing temperature and decreasing strain rate,but it is mainly affected by temperature.The morphology evolution of the LPSO phase in the alloy is significantly affected by the deformation parameters during compression and torsion:when the temperature is low and the strain rate is large,the LPSO phase will deform and twist to coordinate the deformation due to the effect of stress concentration;The degree of deformation is negatively correlated with quantity and temperature,and positively correlated with strain rate and strain.The bulk LPSO phase breaks after the temperature rises,and the degree of breakage increases as the strain rate decreasesThe deformation texture is significantly affected by the strain rate and temperature under compression and torsion:as the strain rate decreases and the temperature increases,the degree of texture weakening increases,and the texture component will develop from a single base texture to a non-base Texture.The intensity change of the pole density from the inside to the outside in the radial direction is not obvious,and the angle of the position of the strongest pole density deviating from the compression direction increasesThe mechanical properties of mg-13gd-4y-2zn-0.5zr alloy can be improved by compression and torsion deformation.The microhardness increases from the inside out along the radius direction.The increase of temperature and the decrease of strain rate will result in the decrease of mechanical properties of the alloy.