| With the leap-forward development of modern science and technology,the previous mechanized warfare has begun to transform into informatization,and the requirements for precise guidance of weapons and equipment are getting higher and higher.As a result,higher performance requirements have been put forward for military materials.7075 aluminum alloy in 7xxx series aluminum alloys,as a structural material,has better specific strength and processing properties than steel,and is widely used in military equipment and aerospace fields.In this study,extruded 7075 aluminum alloy rods were used as raw materials,and the metal flow law of hollow cup-shaped parts under different deformation processes was studied using finite element analysis(FEM)software.The grain morphology in the bottom region of the cup-shaped parts was observed by an optical microscope(OM),and electron backscatter diffraction(EBSD)was used to analyze the texture,grain size,and dynamic recrystallization mechanism of the bottom three typical regions: bottom corner,bottom upper part,and bottom lower part.The numerical simulation results show that for traditional backward extrusion,reducing the through-hole size can slightly increase the equivalent strain value of the cup-shaped parts;while in rotary backward extrusion,reducing the through-hole size can significantly increase the equivalent strain value,from 3.83 in the 7mm sample to 6.37 in the 5mm sample,an increase of 66.3 In addition,the rotary backward extrusion process can effectively reduce the load on the convex mold during deformation,for the 7 mm through-hole specimen,the maximum load on the convex mold in the traditional backward extrusion was 15258 N,while in the rotary backward extrusion,the maximum load was reduced to 6806 N,a reduction of about 55 While for the 5mm through-hole specimen,rotary backward extrusion can effectively reduce the lower limit of the load on the convex mold.For traditional backward extrusion of hollow cup-shaped parts,defects are easily formed near the axis after deformation,while in rotary backward extrusion,defects are more likely to appear at the edges of the designed through-hole in advance.Regardless of traditional backward extrusion or rotary backward extrusion,reducing the through-hole size can effectively reduce the likelihood of defects.Compared with traditional backward extrusion,rotary backward extrusion can effectively refine the grain size: In the 7mm through-hole specimen,the average grain size of the bottom upper part,bottom lower part,and bottom corner part were reduced from 96.30 um,50.80 um,and 38.6um in traditional backward extrusion to 5.69 um,7.42 um,and 15.80 um in rotary backward extrusion,respectively,with the most significant refinement effect in the bottom upper part,which was refined by about 94 In the 5mm through-hole specimen,the average grain size of the above three areas was reduced from 46.86 um,36.24 um,and 83.17 um in traditional backward extrusion to 7.48 um,20.87 um,and 45.03 um in rotary backward extrusion,respectively,with the best refinement effect in the bottom upper part.Rotary backward extrusion not only refines the grains but also promotes the occurrence of dynamic recrystallization,producing recrystallized grains with different orientations from the parent grains,making the grain orientation more dispersed and the texture strength reduced.In the 7mm through-hole specimen,the texture strength of the bottom upper part,bottom lower part,and bottom corner part in the traditional backward extrusion samples was 9.016,7.654,and 2.485,respectively,and these values were reduced to 1.542,1.654,and 1.970 in rotary backward extrusion.In the 5mm through-hole specimen,the texture strength of the above three areas changed from 3.150,2.005,and 9.282 in traditional backward extrusion to 1.339,2.263,and 2.599 in rotary backward extrusion,respectively. |
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