A heterogeneous aluminum alloy rod with a network nanostructure and a preparation method thereof

Abstract

The present invention relates to a heterogeneous aluminum alloy bar having a network nanostructure and a method for preparing the same. The method comprises the following steps: Step 1: homogenizing the aluminum alloy bar and then water quenching it; Step 2: performing equal channel angular extrusion (ECAP) processing; Step 3: cold rolling the bar obtained in Step 2 on a twin-roll mill; Step 4: performing recrystallization annealing on the aluminum alloy bar obtained in Step 3 to obtain a heterogeneous aluminum alloy bar; Step 5: processing the sample obtained in Step 4 into a round bar; Step 6: processing the heterogeneous aluminum alloy bar by axial mechanical rolling to obtain a strip-shaped nanocrystalline layer with equal spacing; Step 7: performing circumferential surface mechanical rolling on the bar processed in Step 6 to obtain a heterogeneous aluminum alloy bar having a network nanostructure. The present invention combines ECAP, rolling, and surface nanocrystallization to introduce heterogeneous and network nanostructures into the aluminum alloy, significantly improving the strength of the aluminum alloy bar while retaining its plasticity.

Description

Technical Field

[0001] The present invention belongs to the field of material preparation, and in particular relates to a heterogeneous aluminum alloy rod with a network nanostructure and a preparation method thereof. Background Art

[0002] In the 21st century, we are moving towards a so-called "light alloy civilization" dominated by aluminum alloys. Aluminum alloys offer low density, excellent mechanical properties, and superior electrical conductivity, thermal conductivity, and corrosion resistance. However, the inability of metals to achieve both strength and ductility has significantly limited their widespread application and promotion. This is largely due to the simple composition or structure of traditional alloys, which are insufficient to achieve a combination of superior properties. In recent years, material sintering and multi-level microstructuring have been widely researched and promoted. Based on this concept, the multi-level microstructuring, combining nanostructures with coarse-grained structures, can achieve the effect of strengthening and toughening the composite structure without changing the aluminum alloy's composition, thereby significantly improving the alloy's overall performance.

[0003] Chinese invention patent CN105821180A discloses a method for constructing a grain size gradient on the surface of a metal material. The method comprises: cold-rolling the metal material to obtain a cold-rolled texture or fine-grained structure; then degreasing the cold-rolled sheet or fine-grained sheet, performing surface grinding and polishing, and roughening and blackening the cold-rolled sheet to increase the laser absorption efficiency of the cold-rolled sheet surface; and using a continuous laser to set reasonable parameters to laser heat treat the cold-rolled sheet surface to form a grain size gradient structure on the metal material surface. The gradient structure material obtained by this processing method has the advantages of large surface grain size, small core grain size, and no obvious interface layer. However, the mechanical properties of the gradient structure material prepared by this method are very sensitive to process parameters, and the repeatability and product performance stability are poor.

[0004] Chinese invention patent CN112048687A provides a method for preparing an ultrafine-grained magnesium alloy with a multi-scale microstructure. This method can adjust the gradient rate of the gradient material by changing the characteristic dimensions according to the specific material size and actual needs. The material processing method includes the following steps: first, a round rod-shaped alloy ingot is homogenized at a temperature of 420–460°C for 4–8 hours and then air-cooled; then, 3–6 passes of equal channel angular extrusion are performed. The extruded sample is then rolled using a three-phase asynchronous rolling mill under ultra-low temperature conditions at a rolling mill speed of 950–970 rpm. -1The method uses 2–4 rolling passes. After rolling, the sample is immersed in liquid nitrogen for 10–15 minutes before removal. The final annealing temperature is 330–360°C for 3–30 minutes, followed by air cooling. The advantages of this preparation method are low investment costs for production equipment and a simple and feasible process. However, the disadvantages are that the process can easily cause irregular deformation, and the high proportion of coarse-grained regions in the material results in a less pronounced strengthening effect.

[0005] Chinese invention patent CN112981290A discloses a method for preparing a copper alloy with a bamboo-jointed nanostructure, comprising the following steps: first, a copper alloy rod is milled by longitudinal surface mechanical milling to obtain a rod with a uniform surface nanocrystalline layer; then, the obtained rod with a uniform surface nanocrystalline layer is subjected to transverse surface mechanical milling to obtain a plurality of annular nanocrystalline layers, i.e., bamboo joints, on the rod surface, each having a thickness of 1.5-3 times the thickness of the surface nanocrystalline layer, and finally a copper alloy with a bamboo-jointed structure is obtained. The advantages of this preparation method are simple technology, low cost, and less damage to the material surface. However, as the diameter of the rod increases, the proportion of the surface nanocrystalline layer obtained becomes smaller and smaller, resulting in a weakening of its strengthening effect. Therefore, simple surface nano-crystalization of the rod is not suitable for strengthening treatment of rods with larger diameters. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing a heterogeneous aluminum alloy rod with a network nanostructure, combining the equal channel angular extrusion process and the surface mechanical rolling process, regularly introducing a nanocrystalline structure into the aluminum alloy rod, and preparing a heterogeneous aluminum alloy with both a network nanocrystalline structure and bimodal isomerism.

[0007] The technical solution to achieve the purpose of the present invention is: a method for preparing a heterogeneous aluminum alloy bar with a network nanostructure, comprising the following steps:

[0008] Step (1): Homogenization: placing the aluminum alloy rod in a heating furnace and performing solid solution treatment at 350–480°C for 16–24 h to obtain an aluminum alloy rod with a uniform coarse-grained structure;

[0009] Step (2): Equal Channel Angular Extrusion: The aluminum alloy bar homogenized in step (1) is subjected to equal channel angular extrusion for 4–8 passes at room temperature;

[0010] Step (3): Cold rolling: The extruded aluminum alloy bar is subjected to multiple cold rolling passes at room temperature, with each rolling pass reducing the thickness by 5%, and ultimately reducing the thickness of the bar by 10–20%;

[0011] Step (4): Recrystallization: placing the rolled aluminum alloy bar in a furnace for recrystallization annealing treatment, so that the aluminum alloy bar is partially recrystallized, and the volume fraction of the coarse grain region is 30–40%, thereby obtaining an aluminum alloy with heterogeneity;

[0012] Step (5): turning: turning the aluminum alloy bar obtained after annealing into a round bar;

[0013] Step (6): Axial surface mechanical rolling: performing local linear rolling on the aluminum alloy round bar by axial surface mechanical rolling to obtain multiple axial strip-shaped nanocrystalline layers on the surface of the bar;

[0014] Step (7): Circumferential surface mechanical rolling: The obtained rod having multiple axial strip-shaped and band-shaped nanocrystalline layers on the surface is subjected to circumferential surface mechanical rolling to obtain multiple annular nanocrystalline layers on the surface of the rod, thereby obtaining an aluminum alloy rod with a network structure.

[0015] Furthermore, the die for equal channel angular extrusion in step (2) is composed of two channels with the same shape and equal cross-sectional area intersecting each other at an angle, the inner die corner where the two channels intersect is Ф, and the die center angle where the channels intersect is Ψ; the extrusion path is the Bc path, that is, before each extrusion, the rod is rotated 90° around the long axis, and the extrusion speed is 0.4–0.6 mm / s.

[0016] Furthermore, the inner mold corner Φ where the channels intersect is 90-120°; and the mold center angle Ψ where the channels intersect is 60-90°.

[0017] Furthermore, the recrystallization annealing temperature in step (4) is 280–320° C., and the holding time is 8–12 min.

[0018] Furthermore, the axial surface mechanical rolling described in step (6) is specifically as follows: using a pressure head with a ball to roll the surface of the aluminum alloy rod, the rod is fixed vertically, and the force direction of the pressure head for surface mechanical rolling is perpendicular to the axial direction of the rod, forming a plastic deformation zone on the surface of the rod, and then moving back and forth along the axial direction of the rod at a rate of v1, while slowly rotating the rod back and forth at a rate of v2 within a certain range with the axial direction of the rod as the rotation axis, so that the ball at the top of the pressure head rolls on the surface of the rod, thereby generating a strip-shaped nanocrystalline layer with uniform thickness on the surface of the rod; lifting the pressure head away from the surface of the rod, rotating the rod around the axis 20-45°, and pressing the pressure head down again to perform axial surface mechanical rolling on the surface of the rod; repeating the above steps until several strip-shaped nanocrystalline layers are evenly distributed on the surface of the rod.

[0019] Furthermore, the rate v1 is 0.5–2 m / s, the rate v2 is 0.01–0.1 RPM, and the rod rotates back and forth around the axis at the rate v2 within the range of 2–10°.

[0020] Furthermore, the circumferential surface mechanical rolling described in step (7) is specifically as follows: the indenter applies a constant pressure to the surface of the rod, the rod rotates at a speed v3, and the indenter moves back and forth at a speed v4 within a certain range along the axial direction of the rod to produce an annular nanocrystalline layer with uniform thickness; the indenter is lifted off the surface of the rod, moved a certain distance along the axial direction, and the circumferential surface mechanical rolling is performed again; the above steps are repeated until several annular nanocrystalline layers are evenly distributed on the surface of the rod.

[0021] Furthermore, the speed v3 is 1–10 RPM, the rate v4 is 0.1–1 m / s, and the indenter moves at a rate v4 within a range of 1–5 mm along the axial direction of the rod; each time the indenter is lifted, it moves 5–20 mm along the axial direction and then presses down; the above steps are repeated until the annular nanocrystalline layer is evenly distributed on the surface of the rod, and finally a network nanostructure is formed on the surface of the rod.

[0022] A heterogeneous aluminum alloy rod with a network nanostructure is prepared by the above method.

[0023] Furthermore, the size of the surface nanocrystals is 30-50 nm, which is 1 / 6-1 / 4 of the size of the ultrafine crystals in the core of the material.

[0024] Compared with the prior art, the present invention has the following significant advantages:

[0025] (1) The present invention combines multiple material strengthening methods. First, the grains are refined to submicron ultrafine grains by equal channel angular extrusion. Second, the ultrafine grains are further refined by 1 / 3 by rolling. Then, local recrystallization is carried out by annealing to introduce a coarse grain structure. The volume fraction of the coarse grain region is about 30–40%, thereby preparing a heterogeneous aluminum alloy with both coarse grains and ultrafine grains. Finally, a uniformly distributed network nanocrystalline structure is prepared on the surface of the material by surface mechanical rolling. The size of the surface nanocrystalline is about 30-50nm, which is about 1 / 5 of the size of the ultrafine grains in the core of the material. The design of the core heterogeneous and surface network nanocrystalline structure can significantly improve the strength of the aluminum alloy while retaining its plasticity as much as possible.

[0026] (2) All process parameters in the present invention can be controlled to adjust the spacing and number of strip-shaped nanocrystal layers and ring-shaped nanocrystal layers;

[0027] (3) The processing techniques involved in the present invention (equal channel angular extrusion, rolling and surface mechanical rolling) are all mature industrial technologies, without any technical difficulties, simple equipment, low cost, high safety factor and strong operability;

[0028] (4) The present invention can flexibly select other alloys according to needs, including: steel, magnesium alloy, copper alloy and titanium alloy;

[0029] (5) Compared with other material preparation processes, the deformation amount during the material processing process in the present invention is small, the process is relatively simple, the process flow is short, and it consumes less time. It has practical significance and can be directly applied to large-scale batch production in factories. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the process flow of the preparation method of the present invention.

[0031] Figure 2 Schematic diagram of the grains of the cross section perpendicular to the axial direction of the rod of the present invention; Figure (a) is a schematic diagram of the AA cross section, and Figure (b) is a schematic diagram of the BB cross section.

[0032] Figure 3 Schematic diagram of the grains in the axial cross section of the rod of the present invention; wherein Figure (a) is a schematic diagram of the CC cross section, and Figure (b) is a schematic diagram of the DD cross section. DETAILED DESCRIPTION

[0033] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process. However, the protection scope of the present invention is not limited to the following embodiment.

[0034] like Figure 1 As shown, the following embodiment involves a seven-step process including: homogenization, equal channel angular extrusion, cold rolling, temperature-controlled recrystallization to obtain a heterogeneous aluminum alloy, axial surface mechanical rolling to obtain a uniformly distributed strip-shaped nanocrystalline layer, and circumferential surface mechanical rolling to obtain a uniformly distributed ring-shaped nanocrystalline layer, ultimately obtaining an aluminum alloy bar with a surface network nanostructure and a heterogeneous core. The specific implementation steps are as follows:

[0035] (1) Samples of 11 mm × 11 mm × 100 mm were cut, and the surface and edges were polished before homogenization annealing at 450 °C for 20 h to prepare coarse-grained aluminum alloy bars with more uniform grain size. (2) The aluminum alloy bars were extruded through the Bc route using the equal channel angular extrusion process for 8 passes to obtain aluminum alloy bars with ultrafine grain structure. The extrusion speed was 0.4 mm / s, the extrusion temperature was room temperature (25 °C), the extrusion path was the Bc path, and the inner die corner φ of the channel intersection was 9 0°, the die center angle where the channels intersect is Ψ, which is 90°; (3) the extruded aluminum alloy bar is subjected to multiple cold rolling passes at room temperature, with each rolling pass reducing the thickness by 5%, and ultimately reducing the thickness of the bar by 20%; (4) the rolled aluminum alloy bar is placed in a furnace for recrystallization annealing treatment, and annealed at 300°C for 10 minutes to obtain a heterogeneous aluminum alloy; (5) the annealed bar is turned into a round bar with a diameter of about 8 mm; (6) the aluminum alloy bar is subjected to local nano-crystallization treatment by axial surface mechanical rolling. The force direction of the indenter during surface mechanical rolling is perpendicular to the axial direction of the rod, forming a plastic deformation zone on the surface of the rod. The indenter then moves back and forth along the axial direction of the rod at a rate of v1 (v1≈0.5m / s), and at the same time, within a range (5°), the rod is rotated back and forth slowly at a rate of v2 (v2≈0.01RPM) with the axial direction of the rod as the rotation axis, so that the ball at the top of the indenter rolls on the surface of the rod, thereby generating a strip-shaped nanocrystalline layer of about 100μm on the surface of the rod; the indenter is lifted, the rod is rotated 20° with the axial direction as the rotation axis, and then pressed down again; the above axis is repeated. (7) Mechanically rolling the rod in the circumferential direction, with the rod rotating at a speed of v3 (v3≈5RPM), keeping the pressure of the indenter constant, and moving the indenter back and forth at a speed of v4 (v4≈0.1m / s) within a range of 1mm along the axial direction of the rod, to produce an annular nanocrystalline layer with a thickness of about 100μm; the indenter is lifted, moved about 10mm along the axial direction, and pressed down again, repeating the above circumferential surface mechanical rolling steps until several annular nanocrystalline layers are evenly distributed on the surface of the rod.

Claims

1. A method for preparing a heterogeneous aluminum alloy rod having a network nanostructure, characterized in that: The steps include: Step (1): Homogenization: placing the aluminum alloy rod in a heating furnace and performing solid solution treatment at 350–480°C for 16–24 h to obtain an aluminum alloy rod with a uniform coarse-grained structure; Step (2): Equal Channel Angular Extrusion: The aluminum alloy bar homogenized in step (1) is subjected to equal channel angular extrusion for 4–8 passes at room temperature; Step (3): Cold rolling: The extruded aluminum alloy bar is subjected to multiple cold rolling passes at room temperature, with each rolling pass reducing the thickness by 5%, and ultimately reducing the thickness of the bar by 10–20%; Step (4): Recrystallization: placing the rolled aluminum alloy bar in a furnace for recrystallization annealing treatment, so that the aluminum alloy bar is partially recrystallized, and the volume fraction of the coarse grain region is 30–40%, thereby obtaining an aluminum alloy with heterogeneity; Step (5): turning: turning the aluminum alloy bar obtained after annealing into a round bar; Step (6): Axial surface mechanical rolling: performing local linear rolling on the aluminum alloy round bar by axial surface mechanical rolling to obtain multiple axial strip-shaped nanocrystalline layers on the surface of the bar; Step (7): Circumferential surface mechanical rolling: the obtained rod having multiple axial strip-shaped nanocrystalline layers on the surface is subjected to circumferential surface mechanical rolling to obtain multiple annular nanocrystalline layers on the surface of the rod, thereby obtaining an aluminum alloy rod having a network structure; The die for equal channel angular extrusion in step (2) is composed of two channels of the same shape and equal cross-sectional area intersecting each other at an angle, the inner die corner where the two channels intersect is Φ, and the die center angle where the channels intersect is Ψ; the extrusion path is the Bc path, that is, before each extrusion, the rod is rotated 90° around the long axis, and the extrusion speed is 0.4–0.6 mm / s; The inner mold corner Ф where the channels intersect is 90–120°; the mold center angle Ψ where the channels intersect is 60–90°; The recrystallization annealing temperature in step (4) is 280–320°C, and the holding time is 8–12 min; The axial surface mechanical rolling described in step (6) is specifically as follows: using a pressure head with a ball to roll the surface of the aluminum alloy rod, fixing the rod vertically, and the force direction of the pressure head for surface mechanical rolling is perpendicular to the axial direction of the rod, forming a plastic deformation zone on the surface of the rod, and then moving back and forth along the axial direction of the rod at a rate of v1, while slowly rotating the rod back and forth at a rate of v2 within a certain range with the axial direction of the rod as the rotation axis, so that the ball at the top of the pressure head rolls on the surface of the rod, thereby generating a strip-shaped nanocrystalline layer with uniform thickness on the surface of the rod; lifting the pressure head away from the surface of the rod, rotating the rod around the axis by 20-45 degrees, and pressing the pressure head again to perform axial surface mechanical rolling on the surface of the rod; repeating the above steps until several strip-shaped nanocrystalline layers are evenly distributed on the surface of the rod; The speed v1 is 0.5–2 m / s, the speed v2 is 0.01–0.1 RPM, and the rod rotates back and forth around the axis at the speed v2 in the range of 2–10°; The circumferential surface mechanical rolling described in step (7) is specifically as follows: the indenter applies a constant pressure to the surface of the rod, the rod rotates at a speed v3, and the indenter moves back and forth at a speed v4 within a certain range along the axial direction of the rod to produce a ring-shaped nanocrystalline layer with uniform thickness; the indenter is lifted off the surface of the rod, moved a certain distance along the axial direction, and the circumferential surface mechanical rolling is performed again; the above steps are repeated until several ring-shaped nanocrystalline layers are evenly distributed on the surface of the rod; The speed v3 is 1–10 RPM, the rate v4 is 0.1–1 m / s, and the indenter moves at a rate of v4 within a range of 1–5 mm along the axial direction of the rod. Each time the indenter is lifted, it moves 5–20 mm axially and then presses down. The above steps are repeated until the annular nanocrystalline layer is evenly distributed on the surface of the rod, and finally a network nanostructure is formed on the surface of the rod.

2. A heterogeneous aluminum alloy rod with a network nanostructure, characterized in that: The nanocrystals are prepared by the method described in claim 1, and the size of the surface nanocrystals is 30-50 nm, which is 1 / 6-1 / 4 of the size of the ultrafine crystals in the core of the material.

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