| Due to the superior comprehensive mechanical properties and great development potential,magnesium alloy materials have been widely used in the automotive,aerospace,military and 3C electronics industries,and are known as "the green engineering materials of the 21 st century".However,due to its dense hexagonal structure,the number of slip systems that can be started at room temperature is small,resulting in its poor deformation capacity.In addition,the poor formability and strong basal texture of the traditional extruded or rolled magnesium alloy plates limit the development and application of magnesium alloy.Therefore,strengthening the control of the microstructure and properties of magnesium alloy plates has important theoretical and practical significance for the optimization of the preparation process,large-scale mass production and in-depth research on the deformation mechanism of magnesium alloy.In this paper,two kinds of extrusion deformation experiments are carried out with different AZ31 magnesium alloys as as-received materials.The first part is Shunt Turning Angular Extrusion,STAE,the forward extrusion technology and equal channel angle extrusion technology is combined with the use of CAD and UG,the microstructure and mechanical properties of AZ31 magnesium alloy extruded plates with 2.5mm thick at different temperatures(300?,350?,400?)were studied,in addition,DEFORM-3D finite element numerical simulation software is used to study the changes of the equivalent stress,equivalent strain and velocity of the billet during the extrusion process.The second part is embedded co-extrusion.The as-cast MB15 magnesium alloy is embedded into as-cast AZ31 magnesium alloy extruded at 400?,and the diameter of extruded bar is 10 mm.The microstructure and mechanical properties of the two magnesium alloys under the conditions of separate extrusion and co-extrusion are studied through comparative experiments.The main conclusions are as follows:(1)According to the finite element simulation of the process of Shunt Turning Angular Extrusion,it is found that when the extrusion speed is constant,the velocity of billet increases with the number of extrusion steps.The phenomenon of surge of equivalent strain rate and equivalent stress occurs whenthe blank fills the cavity,turns into plate and flows through the corner,which is related to the deformation resistance and the shear of the corner.The equivalent strain gradually increases with the extrusion steps,and finally stabilizes between8 and 9.The theoretical value of the total strain is 8.354.The calculated result is consistent with the simulation result,which indicates that the finite element simulation of Shunt Turning Angular Extrusion is effective.(2)Fully dynamic recrystallization occurred in all the extruded plates at different temperatures of Shunt Turning Angular Extrusion,and the grain refinement and microstructure uniformity increased significantly with the decrease of temperature.The grain sizes of the extruded plates at 400?,350?and 300? were 18.70?m,7.95?m and 6.40?m respectively.The extruded plates at each temperature all have(0002)extrusion texture,and the temperature has little influence on the texture strength.The angle between the texture pole and ND direction is about 25°.The average Schmid Factor value of the base plane<a> slip of the extruded plate is about 0.31,which is relatively large,indicating that the base plane <a> slip is easy to start,that is beneficial to the plastic deformation of the plate.(3)In the direction of ED,the elongation of the extruded plates at different temperatures was higher than that of the as-received materials,and it was similar to that of the as-received materials in the direction of TD.The tensile strength and yield strength in the direction of ED and TD is increasing with the decrease of temperature.The comprehensive mechanical properties of the extruded plates at 300? are the best,with yield strength of 135MPa(ED)and 225MPa(TD),tensile strength of 360MPa(ED)and 347MPa(TD),elongation of 27.4% and 15.5%.(4)Compared with single extrusion,the dynamic recrystallization of AZ31 magnesium alloy can be improved by co-extrusion.The grain size is refined from 14.7?m to 12.1?m.The dynamic recrystallization degree of MB15 magnesium alloy after extrusion in two ways was similar,and the grain size was10.3?m and 10.0?m respectively.MB15 and AZ31 magnesium alloy after the two extrusions were formed typical(0002)extrusion texture,(0002)extrusion texture intensity of AZ31 magnesium alloy after the co-extrusion significantly higher than that of single extrusion,this is related to the combined effect of the extrusion pressure of MB15 magnesium alloy and the inner wall of the die andthe shear force at the bimetal interface,However,the extrusion method has little effect on the(0002)texture strength of MB15 magnesium alloy.(5)Embedded co-extrusion doesn't change the plastic deformation mechanism of MB15 and AZ31 magnesium alloy,the mechanical properties of co-extrusion bar is related to the volume ratio of its composition alloy.Compression test showed that the yield strength and compression strength of co-extrusion bar increase with the increase of volume of MB15 magnesium alloy,However,the change of the volume ratio of composition alloy has little effect on the compression elongation of co-extruded bar.The pre-compression experiment of 3% in the ED direction of different extruded magnesium alloys showed that under the combined action of grain size and texture strength,AZ31 magnesium alloy is easier to promote the initiation of {10-12} tensile twins than MB15 magnesium alloy,which shows that the number of {10-12} tensile twins in AZ31 magnesium alloy is significantly higher than that of MB15 magnesium alloy. |
PDF Full Text Request