| The “21st Century Green Engineering Materials” magnesium alloy has good application prospects in many industries by virtue of its superior performance;the extrusion process is widely used in the field of magnesium alloy plastic forming,but it is limited by the close-packed hexagonal crystal structure,and the magnesium alloy is extruded During the process,the grains are prone to preferential orientation and form texture.The texture makes the extruded product anisotropic in mechanical properties and affects the secondary processing forming ability.The decisive factor affecting the texture configuration is the change of strain state and strain path during extrusion;therefore,14 kinds of bar and plate extrusion dies were designed in this subject to investigate the influence of the mold cavity structure on the extrusion deformation behavior.The finite element model was established using the finite element simulation software DEFORM,focusing on the distribution law of temperature field,flow velocity field and strain field in the process of extrusion deformation,and initially established the two-dimensional and three-dimensional characterization methods of the strain path change of the material point in the extrusion process,which provides a reference for the actual extrusion process;the main conclusions of this article are as follows:(1)The influence of the taper angle of the axisymmetric bar extrusion die on the extrusion process was studied.It was found that the larger the taper angle,the higher the peak extrusion temperature(354° at 30° and 363° at 90°).The greater the equivalent strain difference between the edges of the core(30° is 0.4 and 90° is 3.6),the poorer the material flow uniformity is,the more the main strain direction changes are concentrated at the extrusion outlet,and the side rotation angle is greater;Compared with the cone die,the equivalent strain of the edge of the streamline die increases by 3,the material flow is more uniform,the direction of the maximum principal strain of the edge rotates more uniformly with the extrusion process,and the extrusion temperature of the raised die is higher than that of the cone die.At 6?,the equivalent strain at the edge is increased by 4.5,and the flow uniformity is significantly deteriorated.The angle between the maximum principal strain direction of the edge and the ED direction fluctuates significantly,which is significantly different from other axisymmetric molds.(2)The influence of the structure of the asymmetric cone angle die on the extrusion process was studied.The results showed that the bars of the three asymmetric cone angle dies were bent due to the uneven flow velocity of the extrusion outlet.The flow rate difference of the 45-60 cone die reached 3.4mm/ s,the greater the cone angle on the right side of the symmetry plane,the higher the peak extrusion temperature(30° is 320°C,90° is 330°C),the greater the overall equivalent strain value(30° is 4.4,90° is 6.5),the rod The greater the deviation angle of the maximum principal strain direction of the core part from the ED direction in the symmetry plane,the greater the rotation angle of the maximum principal strain direction of the side part;the spiral extrusion die makes the bar material produce a total of 45° torsional deformation during extrusion.The lowest extrusion temperature of all bar extrusion dies is 315?,the lowest flow rate is 6.5mm/s,and the highest equivalent strain value is 8.3.(3)The influence of the diversion channel structure on the sheet extrusion process was studied,and it was found that the peak extrusion temperature of the single-cone angle die was 317?,and the maximum equivalent strain value was 7.2,which was lower than the 352? and 8.0 of the non-cone angle die and the doublecone angle die.At the same time,there is a flow velocity difference between the upper and lower surfaces of the plate and a strain gradient is generated along the plate thickness ND.In the ED-TD plane,the change of the maximum principal strain direction of the plate is mainly located at the edge of the plate.The existence of the cone angle in the ED-ND plane makes the maximum main strain value increase,and the direction of the maximum principal strain direction of the plate surface rotates more completely. |
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