A preparation process for large-volume heavy-grained aluminum alloy coil bar

Abstract

The present invention relates to a preparation process of a large coil weight fine grain aluminum alloy coil bar material, which comprises a rapid cooling continuous casting process, a continuous expansion extrusion process, a large reduction cold rolling process and an annealing process performed in sequence. After the aluminum alloy melt undergoes the rapid cooling continuous casting process, an aluminum alloy casting rod material with a fine fiber grain structure can be obtained; then, after the continuous expansion extrusion process, the grain structure of the aluminum alloy rod material is deformed and refined and its processing performance is improved; then, after the large reduction cold rolling process, the grain structure of the rod material is further refined. Compared with the existing semi-continuous ingot extrusion method and the semi-continuous cast rod hot rolling method, the preparation process of the aluminum alloy coil bar material of the present invention has the characteristics of shorter production process, larger rod coil weight, finer grains and more uniform structure, which helps to improve the forming performance of aluminum alloy parts and better meet the raw material requirements of automatic production of parts.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloy processing, and in particular relates to a preparation process of a large-volume heavy-grained aluminum alloy coil bar. Background Art

[0002] With the rapid development of advanced equipment manufacturing industry, the application of lightweight aluminum alloy materials is becoming more and more extensive, and the market prospect is very broad. At the same time, the manufacturing of lightweight parts has entered the era of automation, intelligence, high speed and low cost. The traditional fixed-length aluminum alloy materials will be replaced by large-volume high-performance aluminum alloy materials with excellent comprehensive performance and good uniformity and consistency, and the demand is increasing.

[0003] At present, the production process of aluminum alloy bars is mainly semi-continuous ingot casting-extrusion method (see Figure 2 ) and semi-continuous casting-hot rolling method (see Figure 3 ). The semi-continuous ingot casting-extrusion method is a fixed-length extrusion process, which specifically includes: semi-continuous casting → ingot homogenization → ingot heating → hot extrusion → aluminum alloy bar. Due to the limitation of the weight of the extruded ingot, it is mainly a straight bar or a single roll of jointless light-weight bar products (usually <200Kg, and it is actually difficult to achieve more than 150Kg), and it cannot completely solve the technical problem that the structure and performance of conventional forward extrusion products are very uneven along the length (the uneven metal flow on the surface and inside of the material, the head and the tail during the extrusion process, and the inconsistency and instability of the extrusion temperature, lead to uneven structure and performance in the bar products).

[0004] In order to extend the length of aluminum alloy bars to meet the needs of automated production of parts, the industry has developed a semi-continuous casting-hot rolling method in recent years. After the semi-continuous large-diameter cast bars are homogenized, they are heated and rolled alternately in width and height directions through multiple rack pass types to achieve thermal deformation from large-diameter cast bars to small-diameter bars. Compared with the fixed length of the above-mentioned semi-continuous ingot casting-extrusion method, the semi-continuous casting hot rolling method can use a semi-continuous ingot with a length of about 10m, and then hot-roll it into a bar with a larger coil weight (about 250Kg).

[0005] However, both the semi-continuous ingot casting-extrusion method and the semi-continuous hot rolling method are based on the production process of large-diameter ingots. During the process of aluminum alloy melt casting large-diameter ingots, the ingot grains are coarse (the grains of aluminum alloy semi-continuous casting rods are usually above 200μm) and non-uniform and serious component segregation, and coarse intermetallic compounds are caused by the influence of casting cooling rate and the large temperature difference between the inside and outside of the large diameter. Although this situation is alleviated after ingot homogenization treatment and hot working deformation by extrusion or hot rolling, the grains of the bars of the semi-continuous ingot casting-extrusion method are usually above 50μm, and the grains of the bars of the semi-continuous hot rolling method are usually above 30μm.

[0006] It can be seen from this that the grain size of bars produced by the continuous ingot casting-extrusion method and the semi-continuous casting and hot rolling method still needs to be further refined, and the uniformity of the structure also needs to be further improved. Summary of the invention

[0007] 1. Technical issues to be resolved

[0008] In view of the problems of the prior art, this field still needs to develop a production process for high-performance aluminum alloy coils with heavier coil weights (single coil weight ≥ 400Kg, more preferably ≥ 500Kg), finer grains, and higher organizational uniformity, so as to improve the forming performance of aluminum alloy parts and better meet the raw material requirements for automated production of parts.

[0009] (II) Technical solution

[0010] Research shows that rapid cooling can improve the nucleation rate and refine the casting grain structure due to high supercooling, and large plastic deformation can also effectively refine the grain structure. Based on the above research conclusions, the technical solution of the present invention includes: a preparation process for large-volume heavy fine-grained aluminum alloy coil bar, which includes a rapid cooling continuous casting process, a continuous expansion extrusion process, a large reduction cold rolling process and an annealing process.

[0011] After the aluminum alloy melt undergoes a rapid cooling and continuous casting process, an aluminum alloy casting bar with a fine fiber grain structure can be obtained; after a continuous expansion and extrusion process, the grain structure of the aluminum alloy bar is deformed and refined and its processing performance is improved; and then a large reduction cold rolling process is performed to further refine the grain structure of the bar. Compared with the existing semi-continuous ingot casting-extrusion method and semi-continuous casting and hot rolling method, the preparation process of the aluminum alloy coil of the present invention has the characteristics of a shorter production process, a larger bar coil weight, finer grains and a more uniform structure.

[0012] According to a preferred embodiment of the present invention, the rapid cooling continuous casting process is horizontal continuous casting or upward continuous casting.

[0013] According to a preferred embodiment of the present invention, a steel sheet with a diameter of D is obtained by a rapid cooling continuous casting process. 0 Aluminum alloy casting bars, including D 0 =10-20mm.

[0014] According to a preferred embodiment of the present invention, the cooling rate in the rapid cooling continuous casting process is greater than 200°C / s, preferably 200°C / s-300°C / s, more preferably 240-260°C / s, and more preferably 240°C / s. The cooling rate of the rapid cooling continuous casting determines the fineness and morphology of the grains in the aluminum alloy casting bar. When the cooling rate is too low (such as below 200°C, or even below 160°C), the grains in the aluminum alloy casting bar are larger. When the cooling rate is too fast (such as greater than 320°C), it causes too fast solidification and breaks. By controlling the cooling rate of the rapid cooling continuous casting (200°C / s-300°C / s), the fine fiber grain structure of the aluminum alloy casting bar can be achieved.

[0015] According to a preferred embodiment of the present invention, the speed of rapid cooling continuous casting is 750-880 mm / min, more preferably 800-850 mm / min. After the crystallizer length is reasonably designed and determined, the casting speed of rapid cooling continuous casting is related to the aluminum alloy casting bar xxxx. When the casting speed is too low (such as less than 750 mm / min, or even less than 700 mm / min), the cooling speed is too fast, resulting in breaking. When the casting speed is too fast (such as greater than 950 mm / min), the cooling speed is too low, the grains in the aluminum alloy casting bar are relatively coarse and the component segregation is obvious.

[0016] Preferably, the casting temperature of the rapid cooling continuous casting can be set mainly according to the type of aluminum alloy; for example, the casting temperature of 2024 aluminum alloy can be set to 690-700°C; the casting temperature of 6013 aluminum alloy can be set to 700-710°C; the casting temperature of 7075 aluminum alloy can be set to 680-690°C.

[0017] According to a preferred embodiment of the present invention, the continuous expansion extrusion process is: 0 The aluminum alloy casting bar is extruded into a diameter of D 1 The aluminum alloy bar has an extended extrusion ratio of 6-12. Under the extended extrusion ratio, D 1 Approximately (2-5) × D 0 .

[0018] According to a preferred embodiment of the present invention, in the large reduction cold rolling process, the total reduction is ≥ 70%; specifically, the large reduction cold rolling is used to 1 The aluminum alloy bar is rolled into a round bar or square bar with an equivalent diameter of D. Among them, D is close to the diameter of the target bar product, which is about 1.05-1.20 times the diameter of the target bar product. After the subsequent fine drawing process and annealing process, the product with precise size and performance that meets the preset indicators is obtained. The temperature during cold rolling is generally controlled at room temperature or slightly above room temperature (for example, it can be heated to 250°C) to ensure that the material will not undergo recrystallization and softening due to excessive temperature, which is not conducive to grain refinement.

[0019] It should be noted that the finishing process is not necessary. If the diameter D of the bar processed by the large reduction cold rolling process is consistent with the target bar product diameter, the finishing process is no longer required. If the diameter D of the bar processed by the large reduction cold rolling process is inconsistent with the target bar product diameter, the finishing process is adjusted to the precise diameter of the target product. In the present application, the finishing drawing uses a disc drawing machine (for example, a 1200-type inverted disc drawing machine) to draw the aluminum alloy coil processed by large reduction cold rolling into a product with a target diameter.

[0020] According to a preferred embodiment of the present invention, the annealing conditions of the coiled rod are generally an annealing temperature of 315°C-500°C, which is specifically determined according to the alloy composition; for example, the annealing conditions of 2024, 6013, and 7075 aluminum alloy coils are 415°C for 2h, furnace cooling to 260°C, and air cooling.

[0021] After testing, according to the preparation process of the present invention, the final aluminum alloy coil product has a grain size of less than 5μm and high uniformity (i.e., the grain size is uniform and evenly distributed). This organizational feature also provides a basic guarantee for downstream parts production and improving the mechanical properties and fatigue resistance of parts. The process of the present invention uses rapid cooling and continuous casting to obtain a small-diameter billet (diameter not greater than 20mm), so its theoretical length is not limited. The length of a single jointless coil can be from more than ten meters to several thousand meters, preferably more than 500m, and the unit weight can reach 400Kg, preferably 500Kg-1000Kg.

[0022] (III) Beneficial effects

[0023] The present invention aims at the technical problems that the current semi-continuous ingot casting-extrusion method and semi-continuous hot rolling method for aluminum alloy bars both use large diameter ingots. The large diameter ingots are affected by the cooling speed of the casting process, the large internal and external temperature difference, etc., and the grains are coarse and uneven, the segregation is serious, the intermetallic compounds are coarse, even after the ingot homogenization treatment and the hot processing deformation of extrusion or hot rolling, the grain size and grain structure uniformity are still not ideal, and it is difficult to produce ultra-large coil weight aluminum alloy coil bars due to the weight limit of the ingot. The production process of the present invention can obtain aluminum alloy casting bars with fine fiber grain structure through rapid cold continuous casting; then the grain structure of the aluminum alloy bar is refined and its processing performance is improved through continuous expansion extrusion deformation; and then the grain structure of the bar is further refined through large reduction cold rolling treatment. Compared with the existing semi-continuous ingot casting-extrusion method and semi-continuous hot rolling method for casting bars, the present invention has the advantages of short production process, larger single coil weight of products, finer grains, and more uniform grain size and distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a flow chart of the preparation process of large coil heavy fine-grained aluminum alloy coil bar.

[0025] Figure 2 The present invention is a flow chart of the existing semi-continuous ingot casting-extrusion method for preparing aluminum alloy coils and bars.

[0026] Figure 3 The present invention is a flow chart of the existing semi-continuous hot rolling method for preparing aluminum alloy coils and bars.

[0027] Figure 4 These are the grain size analysis results of the heavy-weight 2024 aluminum alloy coil bar prepared in Example 1.

[0028] Figure 5 These are the grain size analysis results of the heavy-weight 6013 aluminum alloy coil bar prepared in Example 2.

[0029] Figure 6 These are the grain size analysis results of the heavy-weight 7075 aluminum alloy coil bar prepared in Example 3. DETAILED DESCRIPTION

[0030] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0031] In order to improve the mechanical properties and fatigue resistance after zero-additive forming, the grains of the material should be as fine and evenly distributed as possible. In order to meet the needs of automated parts production equipment, a single jointless coil bar with a long length or a large coil weight must be provided as the production blank for the parts. However, the aluminum alloy bars produced by the existing aluminum alloy bar semi-continuous ingot casting-extrusion method and the semi-continuous casting and hot rolling method have coarse and uneven grains, severe segregation, and coarse intermetallic compounds. Even after ingot homogenization treatment and extrusion or hot rolling thermal processing deformation, the grain size and grain structure uniformity are still not ideal, and it is difficult to produce ultra-large coil weight aluminum alloy coils. The present invention proposes the following technical solutions: See Figure 1 The process shown in the figure is a process for preparing a large coil of heavy fine-grained aluminum alloy coil bar, which includes four steps, namely, a rapid cooling continuous casting step, a continuous expansion extrusion step, a large reduction cold rolling step, and an annealing step. The rapid cooling continuous casting step is a horizontal continuous casting step or an upward continuous casting step, so that the aluminum alloy melt is made into a diameter D 0 (D 0 =10-20mm) aluminum alloy casting bar, and then 0 The aluminum alloy casting bar is extruded into a diameter of D 1 The aluminum alloy bar material with an expansion extrusion ratio of 6-12 is then cold rolled with a large reduction to form a diameter of D 1The aluminum alloy bar is rolled into a round bar or square bar with an equivalent diameter of D, and the total reduction is controlled to be ≥70%. Among them, D is close to the target bar product diameter, which is about 1.05-1.20 times the diameter of the target bar product. After subsequent processing only through the fine drawing process and the annealing process, a product with precise size and performance that meets the preset indicators is obtained. After testing, according to the preparation process of the present invention, the final aluminum alloy coil bar product has a grain size of less than 5μm and high uniformity (that is, the grain size is uniform and uniformly distributed), and the unit weight can reach 400Kg, preferably more than 500Kg. Compared with the prior art, the present invention has the advantages of short production process, larger single coil weight of the product, finer grains, and more consistent and uniform grain size distribution. The following is an example of illustration in conjunction with the embodiment. By Figure 1 and Figure 2-3 By comparison, it can be seen that the preparation process of the large-volume heavy-grained aluminum alloy coil bar of the present invention is significantly simplified in terms of process steps.

[0032] Example 1

[0033] This embodiment provides a preparation process of a large coil weight fine grain 2024 aluminum alloy coil bar, the target product diameter is 15mm, the single coil weight is greater than 500Kg, and the product is used as a production blank for fasteners. The preparation process of the large coil weight fine grain 2024 aluminum alloy coil bar is as follows:

[0034] (1) Rapid cooling continuous casting: 99.7% aluminum ingots, magnesium ingots, and Al-5Mn and Al-10Cu master alloys were used. The weight ratio of each alloy was calculated according to the chemical composition range of 2024 aluminum alloy. The materials were mixed according to this ratio. After melting, refining, heat preservation and online filtration in a double 1000 kg gas melting furnace, samples were taken for alloy chemical composition testing, as shown in Table 1.

[0035] Horizontal continuous casting is used to continuously cast 2024 aluminum alloy small-diameter disc round rod billets with a diameter of 12 mm and a weight of 552 kg. The continuous casting temperature is controlled at 690-700°C, the casting speed is set at 800 mm / min, and the cooling rate is about 250°C / s.

[0036] (2) Aluminum alloy coils with a diameter of 12 mm were extruded into aluminum alloy coils with a diameter of 30 mm using continuous expansion extrusion on a 350 type continuous extruder, and the expansion extrusion ratio was 6.25.

[0037] (3) Aluminum alloy coils with an extrusion diameter of 30 mm were rolled into round bars with a diameter of 16 mm on a twelve-stand cold rolling mill, with a total reduction of 71.6%.

[0038] (4) A round bar with a diameter of 16 mm is drawn on a 1200 type inverted disc drawing machine into a finished product size of 15 mm in diameter.

[0039] (5) The drawn product with a diameter of 15 mm is annealed in a box-type annealing furnace. The annealing process is to keep the temperature at 415°C for 2 hours, cool the furnace to 260°C, and then air cool it out of the furnace.

[0040] Finally, samples were taken from the head and tail of the annealed 2024 aluminum alloy coil product for scanning electron microscopy backscattered electron (EBSD) grain size analysis. The results are as follows: Figure 4 As shown in the figure, the grain size is fine, about 2.4μm, and has good uniformity. The grains are arranged in a paving stone shape, and the grain sizes in different parts are highly consistent.

[0041] Example 2

[0042] This embodiment provides a preparation process of a large coil, heavy and fine-grained 6013 aluminum alloy coil bar. The target product is a 8.5mm×10.5mm square bar with a single coil weight of >500Kg. The product is used as a production blank for 3C product parts. The preparation process of a large coil, heavy and fine-grained 6013 aluminum alloy coil bar is as follows:

[0043] (1) Rapid cooling continuous casting: 99.7% aluminum ingot, quick-dissolving Si, magnesium ingot, and Al-5Mn and Al-10Cu master alloys were used. The weight ratio of each alloy was calculated according to the chemical composition range of 6013 aluminum alloy. The materials were mixed according to this ratio. After melting, refining, heat preservation and online filtration in a double 1000 kg gas smelting furnace, samples were taken for alloy chemical composition detection, as shown in Table 1.

[0044] Horizontal continuous casting is used to continuously cast 6013 aluminum alloy small-diameter disc round rod billets with a diameter of 10 mm and a weight of 612 kg. The continuous casting temperature is controlled at 700-710°C, the casting speed is set at 850 mm / min, and the cooling rate is about 260°C / s.

[0045] (2) Aluminum alloy coils with a diameter of 10 mm were extruded into aluminum alloy coils with a diameter of 30 mm using continuous expansion extrusion on a 315 type continuous extruder, and the expansion extrusion ratio was 9.

[0046] (3) The aluminum alloy coil bar with an extrusion diameter of 30 mm is rolled into a square bar of 8.5 mm × 10.5 mm on a 12-stand cold rolling mill, with a total reduction of 87.4%. At this point, the square bar has reached the target size and no further fine drawing is required.

[0047] (4) The 8.5 mm × 10.5 mm square bar was annealed in a box-type annealing furnace. The annealing process was 415 ° C for 2 h, the furnace was cooled to 260 ° C, and then air-cooled.

[0048] Finally, samples were taken from the head and tail of the annealed 6013 aluminum alloy square bar coil product for scanning electron microscope backscattered electron (EBSD) grain size analysis. The results are as follows: Figure 5 As shown in the figure, the grain size is fine, about 4.7μm, and has good uniformity, and the grain size consistency in different parts is high.

[0049] Example 3

[0050] This embodiment provides a preparation process of a large coil weight fine grain 7075 aluminum alloy coil bar, the target product diameter is 15.5mm, the single coil weight is greater than 500Kg, and the product is used as a production blank for high-strength aluminum alloy fasteners. The large coil weight fine grain 7075 aluminum alloy coil preparation process is as follows:

[0051] (1) Rapid cooling continuous casting: 99.7% aluminum ingot, zinc ingot, magnesium ingot and Al-5Mn, Al-5Cr, Al-10Cu master alloys were used. The weight ratio of each alloy was calculated according to the chemical composition range of 7075 aluminum alloy. The ingredients were mixed according to this ratio. After melting, refining, heat preservation and online filtration in a double 1000Kg gas melting furnace, samples were taken for alloy chemical composition detection, as shown in Table 1. 7075 aluminum alloy small diameter disc round rod billets with a diameter of 12mm and a weight of 568Kg were continuously cast by horizontal continuous casting. The continuous casting temperature was controlled at 680-690℃, the casting speed was set at 800mm / min, and the cooling rate was about 250℃ / s.

[0052] (2) Aluminum alloy coils with a diameter of 12 mm were extruded into aluminum alloy coils with a diameter of 30 mm using continuous expansion extrusion on a 350 type continuous extruder, and the expansion extrusion ratio was 6.25.

[0053] (3) Aluminum alloy coils with an extrusion diameter of 30 mm were heated to 200° C. and rolled into round bars with a diameter of 16 mm on a twelve-stand cold rolling mill, with a total reduction of 71.6%.

[0054] (4) The cold rolled round bar with a diameter of 16 mm is drawn on a 1200 type inverted disc drawing machine to a finished product size of 15.5 mm in diameter.

[0055] (5) The drawn product with a diameter of 15.5 mm was annealed in a box-type annealing furnace. The annealing process was 415°C for 2 h, and the furnace was cooled to 260°C and then air-cooled.

[0056] Finally, samples were taken from the head and tail of the annealed 7075 aluminum alloy square bar coil product for scanning electron microscopy backscattered electron (EBSD) grain size analysis. The results are as follows: Figure 6As shown in the figure, the grain size is fine, about 2.6μm, and has good uniformity. The grains are arranged in a paving stone shape, and the grain sizes in different parts are highly consistent.

[0057] Table 1 Main chemical components of the aluminum alloy of the present invention (weight percentage, %)

[0058] alloy Si Fe Cu Mn Mg Cr Zn Ti 2024 0.092 0.112 4.445 0.672 1.564 0.018 0.026 0.056 6013 0.818 0.125 0.822 0.508 1.016 0.012 0.017 0.032 7075 0.086 0.086 1.718 0.152 2.527 0.124 5.759 0.089

[0059] from Figure 4-6 It can be seen that the 2024, 7075 aluminum alloy round coil bars and 6013 aluminum alloy square bars produced by the production process of the present invention have EBSD grain size analysis and their grain sizes are 2.4μm, 4.7μm and 2.6μm, respectively, which are significantly smaller than the grain size of aluminum alloy products produced by the existing semi-continuous ingot casting-extrusion method (usually above 50μm) and semi-continuous casting-hot rolling method (usually above 30μm), and have good uniformity and high consistency of grain size inside the material. In addition, the single coil weights of 2024, 7075 aluminum alloy round coils and 6013 aluminum alloy square rods produced by the production process of the present invention are 552Kg, 568Kg and 612Kg respectively, all of which are ultra-large coil weight aluminum alloy coils, which solves the technical problem that it is difficult to produce ultra-large coil weight aluminum alloy coils by semi-continuous ingot casting-extrusion method or semi-continuous cast rod hot rolling method; in addition, the present invention adopts fast cooling continuous casting of small diameter (10-20mm) disc round rod billets instead of large diameter ingots, which can solve the problem of uneven grain structure of the material caused by large temperature difference between the inside and outside of the material.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for preparing a large coil of heavy fine-grained aluminum alloy coil bar, characterized in that: It includes a rapid cooling continuous casting process, a continuous expansion extrusion process, a large reduction cold rolling process and an annealing process. The cooling rate in the rapid cooling continuous casting process is 200°C / s-300°C / s, the speed of the rapid cooling continuous casting is 750-880mm / min, and the aluminum alloy casting bar with a diameter of D0 is obtained by the rapid cooling continuous casting process, wherein D0=10-12mm; The continuous expansion extrusion process is as follows: extruding an aluminum alloy casting bar with a diameter of D0 into an aluminum alloy bar with a diameter of D1, the expansion extrusion ratio is 6-12, and after the expansion extrusion, D1 is (2-5)×D0; In the large reduction cold rolling process, the total reduction is ≥ 70%; the aluminum alloy bar with a diameter of D1 is rolled into a round bar or square bar with an equivalent diameter of D by large reduction cold rolling; the diameter D is 1.05-1.20 times the diameter of the target bar product; The material grain size of the heavy-weight fine-grained aluminum alloy coil bar is less than 5 μm, each grain is arranged in a paving stone shape, and the single coil weight is ≥ 400 kg; the heavy-weight fine-grained aluminum alloy coil bar is used for the production blanks of 3C product parts or fasteners.

2. The preparation process according to claim 1, characterized in that: The rapid cooling continuous casting process is horizontal continuous casting or upward continuous casting.

3. The preparation process according to claim 1, characterized in that: Between the large reduction cold rolling process and the annealing process, the aluminum alloy coil subjected to the large reduction cold rolling process is subjected to finish drawing to obtain a target product with a precise diameter.

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