Method for preparing metal fine-grain material through multidirectional rotation and alternate backward extrusion

Abstract

The invention provides a multidirectional rotation alternate backward extrusion preparation method for a metal fine-grain material. The method is characterized in that quasi-continuous quantitative controllable loading of a product is realized according to the parting mode (number and proportion), the loading area and direction, the rolling reduction and the acting force of the male die; the loading mode can be divided into a rotary alternating mode, a crossed staggered distance mode, a layer-by-layer progressive mode or an odd-even progressive mode and the like; according to the method, the deformation amount can be regulated and controlled according to the use requirements of materials, and the deformation range of the product is accurately controlled by changing the male die shape, the extrusion pass, the rolling reduction and the acting force of the extrusion die; a refining blind area is removed by changing the loading direction and the rotating angle of the blank, the phenomenon of non-uniform refining is improved, and finally the uniform and deep refining effect of the product is achieved; the method disclosed by the invention is not restricted by initial geometrical shape characteristics of the blank and is wider in applicable size range, the used mold structures are simpler and more convenient and can be repeatedly used, the cost is lower, the production efficiency is high, and the method is easy to popularize and apply in industrial production.

Description

Technical Field

[0001] The invention relates to the field of metal material processing, in particular to a method for preparing metal fine-grained materials by multi-directional rotation and alternating reverse extrusion. Background Art

[0002] Grain refinement is an effective way to improve the mechanical and forming properties of metal materials. Among the many technologies for reducing grain size, violent deformation methods represented by equal channel angular extrusion, high pressure torsion and reciprocating extrusion are most commonly used.

[0003] Equal channel angular extrusion refers to the process of feeding the blank from one channel and extruding it from the other side through a cavity channel with two axes intersecting at a certain angle and equal cross-sectional shape and size, and repeating the process as many times as needed. The equal channel corner part will cause the grains of the flowing material to be refined due to shear deformation. Repeated loading significantly increases the cumulative deformation, which can deeply refine the grain size and improve its roundness and distribution uniformity. It is an effective means to prepare ultrafine grain materials, which is often used in laboratory research. The high-pressure torsion method is to apply pressure to the sample while rotating the pressure head, and use the friction force under high-pressure loading conditions to apply severe torsional shear deformation to the sample. Compared with other severe deformation methods, this method can produce a large shear deformation in a single pass and significantly improve the degree of grain refinement. However, the deformation amount from the center to the edge of the product is different, resulting in uneven refinement in various parts, and only relatively small samples can be prepared; reciprocating extrusion is composed of two cavities, a tightening zone and punches placed in the two cavities. The cross-sectional areas of the cavities are equal and on the same axis, connected by the tightening zone in the middle. During the extrusion process, the sample reaches the tightening zone under the action of the punch, undergoes positive extrusion deformation, and then undergoes upsetting deformation under the action of the punch in another cavity. After reciprocating extrusion and compression, the material produces a large strain to obtain an ultrafine, equiaxed ultrafine grain structure. However, this method is limited by the extrusion ratio and the shape of the billet, and is mostly used for bar processing and cannot be applied to plates; alternating reverse extrusion is mainly composed of a left punch, a right punch, a sleeve and a pad. The billet is placed in an extrusion container with a closed bottom, and the punches separated on both sides are alternately moved downward, and the billet is continuously refined under the action of shear force. This method provides a new SPD idea, but there are still problems of uneven refinement and blind spots that need to be further solved.

[0004] In order to expand the ways of grain refinement and avoid the shortcomings of the above-mentioned prior art, the invention patent with Chinese patent number ZL201610230131.8 and publication date April 10, 2018 discloses a method for preparing fine-grained magnesium alloy by multi-directional repeated forging with a temperature-reducing variable rate, which is performed multiple times and at different temperatures and speeds each time, and the billet is turned over after each forging to achieve multi-directional loading of the billet, wherein the multi-directional loading specifically refers to turning the billet 90° after each deformation, so that the magnesium alloy forging has a uniform and fine grain structure. In order to make the billet multi-directional extrusion efficient and fast, and convenient to take out after extrusion, the invention patent with Chinese patent number ZL201910489530.X and publication date June 6, 2019 discloses a multi-directional extrusion strong deformation die and method thereof, which can obtain a fine and uniformly distributed organizational structure through the coordinated multi-directional extrusion of the billet by the upper die head and the surrounding heads, and significantly improve the comprehensive performance of the material. The arrangement of the pressure heads around the die allows the billet to be extruded in multiple directions without turning it over, which reduces the interference of human factors and is conducive to continuous production.

[0005] How to further improve the refinement effect of the metal material structure and develop it in the direction of quantitative, precise, controllable and continuous development is a long-term goal in the field of severe plastic deformation research, and it has important strategic significance for improving the quality of metal materials and the manufacturing of high value-added products. Summary of the invention

[0006] In order to solve the problems of uneven refinement, blind spots, small billet size and limited materials that are prone to occur in the process of fine grain preparation by traditional severe plastic deformation methods. The present invention provides a method for preparing metal fine-grained materials in a multi-directional rotating alternating reverse extrusion manner. By continuously changing the loading action mode of the split punch and continuously flipping and changing the orientation of the billet, continuous quantitative controllable loading is achieved in all directions, without blind spots and from multiple perspectives. Continuous severe shear deformation occurs at the interface of the split punch and the deformation accumulates and increases continuously, which is suitable for deep refinement of the grain morphology of metal materials and improvement of the uniformity of the organization. In addition to conventional metal materials, this method is also suitable for low-plasticity and difficult-to-deform metal materials, and is not constrained by the initial geometric shape characteristics of the billet. It has a wider applicable size range and is easy to promote and apply in industrial production. In addition, this method can quantitatively control the stress / strain of different local micro-regions of the billet, so that the grain morphology of different regions of the billet is distributed according to certain regular characteristics, which also provides a new paradigm for the preparation of metal heterogeneous materials.

[0007] The present invention is achieved through the following technical solutions: Step 1, processing the alloy billet into a predetermined billet size; Step 2: Place the extrusion cylinder on the base, and put the cushion block, the blank, the first punch, and the second punch into the extrusion cylinder in sequence; Step 3: Heat the entire device assembly to a predetermined temperature and place it on a press workbench; Step 4: The first punch starts to move downward by a distance of L. The metal on the lower side is deformed by pressure and begins to flow. According to the principle of constant volume, the second punch on the opposite side moves back. Step 5: At this time, the second punch moves downward by a distance L, causing the metal below it to begin to flow. According to the principle of constant volume, the first punch retreats to the initial position, and a loading cycle is completed; Step 6: Take out the blank, rotate it 180° vertically and then 90° horizontally, and move the first punch and the second punch down alternately according to the above working sequence; Step 7: Rotate and reverse-extrude the remaining four faces alternately.

[0008] The present invention adopts the above technical solution, so it has the following beneficial effects: 1. The innovation of the present invention lies in that while the split punches are alternately extruded downward, the loading mode of the split punches can be continuously changed according to actual needs, including the splitting mode (number and proportion) of the punches, the loading area and direction, the pressing amount and the magnitude of the force, so as to realize quasi-continuous quantitative controllable loading of the product in all directions, without blind spots and from multiple perspectives; Second, the punch parting design criteria and loading mode are the key to the present invention. The split punch can be designed into two or more parts according to different requirements. The cross-sectional areas of the split punches are the same or different. The loading mode can be divided into rotating alternating type, cross-staggered type, layer-by-layer progressive type or odd-even progressive type, which is more flexible and diverse. 3. As the punch adopts split structure design and various loading modes, under the action of periodic continuous loading, the blank continuously turns and changes its orientation, and the split punch interface produces continuous and severe shear deformation, achieving the purpose of continuous accumulation and increasing deformation, realizing the deep refinement of the grain morphology of the metal material and the improvement of the comprehensive performance; Fourth, the method of the present invention can realize customization by precisely controlling the loading position and range of the product, the degree of grain refinement, etc., according to the requirements of the degree of grain refinement, through the coordinated optimization design between various process parameters such as the shape and size of the blank, the shape, number and cross-sectional proportion of the split punch, the number of loading passes, the amount of pressing and the magnitude of the force; 5. Compared with the traditional alternating reverse extrusion preparation method, the present invention is not limited by the number of loading passes and can be loaded continuously. And by changing the loading direction and rotation angle of the blank, the uneven refinement caused by the existence of loading blind areas or the large difference in deformation of each part can be eliminated, so that the product can be deeply refined and the uniformity of the structure is also improved simultaneously; Sixth, the present invention can quantitatively control the stress / strain of local micro-regions in different parts of the blank by changing the number of split punches, the cross-sectional size and the mode of action, so that the grain morphology in different parts of the blank is distributed according to certain regular characteristics, providing a new paradigm for the preparation of metal heterogeneous materials; 7. This method can increase the cumulative deformation and can quantitatively control the overall / local micro-region morphology and deformation. Therefore, in addition to conventional metal materials, it is also suitable for the refinement of ultrafine grains or nano-grains of low-plasticity and difficult-to-deform metal materials, and the selection range of materials is wider and universal; 8. Traditional severe plastic deformation methods are all independent "preparation" processes. To obtain ideal products, it is necessary to make blanks and then connect with the subsequent forming process, that is, the "two-step method". The present invention only needs to replace one side of the mold cavity pad with a core mold with holes to achieve the integration of blank making and extrusion forming short process, shortening the production cycle, reducing energy consumption and costs, etc. 9. Compared with other severe plastic deformation technologies that are mostly applicable to the preparation of small-sized billets, the method of the present invention is not restricted by the initial geometric shape characteristics of the billet and has a wider range of applicable sizes. The mold structure used is relatively simple and reusable. The process is easy to implement and has high production efficiency, which is easy to promote and apply in industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a schematic diagram of the two-dimensional plane structure of the extrusion device of the method of the present invention; Figure 2 It is a schematic diagram of a structure with four punch parting modes; Figure 3 It is a schematic diagram of the structure with five punch parting modes; Figure 4 It is a schematic diagram of the cube blank rotation process of the method of the present invention. DETAILED DESCRIPTION

[0010] Specific implementation method 1: Combination Figure 1 , Figure 4This embodiment is described. This embodiment includes: a first punch 1, a second punch 2, an extrusion barrel 3, a blank 4, a cushion block 5, and a base 6. This embodiment is completed by the following steps: 1. Place the extrusion barrel 3 on the base 6; 2. Place the cushion block 5 in the extrusion barrel 2 from above, then put the blank 4 into the extrusion barrel 2 and place it on the upper end of the cushion block, and then place the first punch 1 and the second punch 2 on the upper end of the blank respectively, and heat it to the expected temperature; 3. Place the heated extrusion barrel as a whole on the workbench of the press; 4. The first punch 1 starts to move, and moves downward a distance L. The metal on its lower side is compressed and deformed and begins to flow. According to the principle of constant volume, the second punch on the opposite side produces a retreat. 5. The second punch 2 moves downward by a distance L, causing the metal on its lower side to begin to flow. According to the volume invariance principle, the first punch retreats to the initial position, and a loading cycle is completed; 6. The billet 4 that has undergone one alternating reverse extrusion is taken out, first rotated 180° in the vertical direction and then 90° in the horizontal direction to perform an alternating reverse extrusion; 7. Repeat the rotational alternating reverse extrusion for many times; 8. According to the usage of the material, several rotational cross-alternating reverse extrusion large plastic deformations are completed to finally obtain a uniform and significantly refined grain structure.

[0011] Specific implementation plan 2: Combined Figure 2 , Figure 4 To illustrate this embodiment, the first punch 1, the second punch 2, the third punch 3, and the fourth punch 4 of this embodiment are placed side by side and have the same height. The first punch and the third punch press down by L1, at which time the second punch and the fourth punch retreat by a distance of L1, then the second punch and the fourth punch press down by L1, and the first punch and the third punch retreat to the initial position, and a loading cycle is completed. According to the specific embodiment one, the blank is rotated, and the first punch and the third punch press down by L2, at which time the second punch and the fourth punch retreat by a distance of L2, then the second punch and the fourth punch press down by L2, and the first punch and the third punch retreat to the initial position, completing a rotation alternating reverse extrusion. The other operating steps are the same as those in the specific embodiment one.

[0012] Specific implementation method three: Combination Figure 3 , Figure 4 The first punch 1, the second punch 2, the third punch 3, the fourth punch 4, and the fifth punch 5 are placed side by side and have the same height. The first punch, the third punch, and the fifth punch press down a distance of L1. At this time, the second punch 2 and the third punch 3 retreat a distance of L2. Then, the second punch 2 and the third punch 3 press down a distance of L 2， The first punch, the third punch, and the fifth punch retreat a distance of L1 to complete one alternating reverse extrusion. The other operation steps are the same as those in the first specific implementation.

[0013] Specific implementation plan 4: Combination Figure 3 , Figure 4 The first punch 1, the second punch 2, the third punch 3, the fourth punch 4, and the fifth punch 5 are placed side by side and have the same height. The third punch is pressed down by L1, and the second punch and the fourth punch are fixed. At this time, the first punch and the fifth punch retreat by a distance of L2, and then the first punch and the fifth punch are pressed down by a distance of L 2， The second punch and the fourth punch are fixed, and the first punch, the third punch, and the fifth punch retreat a distance of L1 to complete an alternating reverse extrusion. According to the specific implementation method, the blank is rotated, the second punch and the fourth punch press down a distance of L1, and the third punch is fixed. At this time, the first punch and the fifth punch retreat a distance of L1, and then the first punch and the fifth punch press down a distance of L 2， The third punch is fixed, the second punch and the fourth punch are moved back by a distance of L1, and one alternating reverse extrusion is completed. The other operation steps are the same as those in the first embodiment.

Claims

1. A method for preparing fine-grained metal materials by multi-directional rotation and alternating reverse extrusion, characterized in that The device comprises a first punch 1, a second punch 2, an extrusion cylinder 3, a blank 4, a cushion block 5, and a base 6; wherein the extrusion cylinder 3 is placed above the base 6, the cushion block 5 is placed in the extrusion cylinder and located at the bottom thereof, the blank 4 is placed in the extrusion cylinder and placed on the upper end of the cushion block, and the first punch 1 and the second punch 2 are placed on the upper end of the blank.

2. The method for preparing fine-grained metal materials by multi-directional rotation alternating reverse extrusion according to claim 1, characterized in that The first punch 1 and the second punch 2 are arranged side by side and have the same height, and the cross-sectional area is rectangular.

3. The rotating alternating reverse extrusion device structure according to claim 2 is characterized in that The first punch 1 and the second punch 2 are evenly divided into four punches with rectangular cross-sectional areas and equal to each other.

4. The rotating alternating reverse extrusion device structure according to claim 2 is characterized in that The first punch 1 and the second punch 2 are evenly divided into five punches with rectangular cross-sectional areas and equal to each other.

5. The method for preparing fine-grained metal materials by multi-directional rotating alternating reverse extrusion according to claim 1, characterized in that The method comprises the following steps:

1. placing the heated extrusion barrel as a whole on the workbench of the press machine; 2. the first punch starts to move, moves downward by a distance of L, the metal on the lower side thereof is deformed under pressure and starts to flow, and according to the volume invariance principle, the second punch on the opposite side moves back by a distance of L; 3. the second punch moves downward by a distance of L, causing the metal on the lower side thereof to start to flow, and the first punch moves back to the initial position, and a loading cycle is completed; 4. Take out the billet that has undergone one alternating reverse extrusion, rotate it 180° in the vertical direction and then 90° in the horizontal direction, and then perform another alternating reverse extrusion; 5. Repeat steps 2, 3, and 4 for many times; 6. Complete N times of rotational alternating reverse extrusion according to the usage of the material, and finally obtain a uniform and significantly refined grain structure.

6. The method for preparing fine-grained metal materials by multi-directional rotation alternating reverse extrusion according to claim 1, characterized in that The repeated directional extrusion of the billet is to take out the billet that has undergone one round of alternating reverse extrusion, rotate it 180° vertically and then 90° horizontally, and then perform another round of alternating reverse extrusion.

7. The method for preparing fine-grained metal materials by multi-directional rotation alternating reverse extrusion according to claim 1, characterized in that The number of punch types M (M≥2) can be set according to the different detailed requirements of the material.

8. The method for preparing fine-grained metal materials by multi-directional rotation alternating reverse extrusion according to claim 5, characterized in that The pressing amount L and the number of cycles N loaded by the punch can be adjusted according to the different usage of the material. By appropriately increasing or decreasing the pressing amount L and the number of cycles N, better mechanical properties can be obtained and further costs can be saved.

9. The billet repeated directional extrusion according to claim 6, characterized in that The extrusion direction can be customized according to the difference between the billet and the mold to achieve multi-directional rotational alternating reverse extrusion. For the cubic billet, the billet is first divided into three sides, A, B, and C. First, the A side is subjected to rotational alternating reverse extrusion, and then the C and B sides are subjected to rotational alternating reverse extrusion in turn. Repeat the multi-directional rotational alternating reverse extrusion N times until the required grain size is reached.

Images