Large-specification 7-series aluminum alloy and casting method thereof

Abstract

The invention relates to the technical field of aluminum alloys, in particular to a large-specification 7-series aluminum alloy and a casting method thereof. The casting method comprises the following steps that electrolytic aluminum water or an aluminum ingot is adopted as a raw material, smelting treatment, semi-continuous casting treatment and homogenizing annealing heat treatment are conducted in sequence, and the large-specification 7-series aluminum alloy is obtained; dry well casting is adopted during the semi-continuous casting treatment. Dry well casting is adopted during semi-continuous casting treatment, cooling stress is prevented from being generated, and cracks are restrained; and homogenizing annealing heat treatment is carried out after semi-continuous casting treatment, casting stress can be eliminated, cast ingot cracking is further avoided, and semi-continuous casting of the large-specification 7-series aluminum alloy is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloys, and in particular to a large-size 7 series aluminum alloy and a casting method thereof. Background Art

[0002] 7 series aluminum alloy belongs to ultra-high strength aluminum alloy, which has been widely used in transportation, aerospace and military equipment. At present, the aluminum alloy industry generally adopts vertical direct water-cooled semi-continuous casting method to produce round ingots, also known as DC casting. As shown in the Chinese invention with application number 201510721352.0, the smelted and purified aluminum alloy liquid is introduced into the hot top through a chute. When the liquid level rises to 2 / 3 of the hot top height, cooling water is introduced into the crystallizer, the casting machine is started, the ingot block moves downward, and casting begins. During the casting process, the liquid level is controlled to be stable until the casting is completed. This method saves energy and materials, has continuous and compact production, and has high production efficiency. However, with the development of aviation and military industries, in order to improve production efficiency and meet the needs of large-scale processing materials, the market has more and more needs for large-scale ingots. The quality of large-scale ingots directly determines the subsequent processing technology and final quality of the components. Semi-continuous casting has limitations in the production of large-sized ingots. Since the temperature field and flow field are difficult to control during the casting process, especially for high-strength and high-alloyed 7 series aluminum alloys, large-sized ingots are prone to internal stress and cracks, causing the ingots to crack and difficult to form. This has become one of the bottlenecks restricting the development of high-strength aluminum alloys. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a large-size 7 series aluminum alloy and a semi-continuous casting method thereof.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a casting method for large-size 7 series aluminum alloy, comprising the following steps: using electrolytic aluminum water or aluminum ingots as raw materials, sequentially performing smelting treatment, semi-continuous casting treatment and homogenization annealing heat treatment to obtain large-size 7 series aluminum alloy; dry well casting is adopted during the semi-continuous casting treatment.

[0005] Another technical solution adopted by the present invention is: a large-size 7 series aluminum alloy is prepared by the casting method of the large-size 7 series aluminum alloy.

[0006] The beneficial effects of the present invention are as follows: the present invention adopts dry well casting during semi-continuous casting to prevent the generation of cooling stress and inhibit the generation of cracks; homogenization annealing heat treatment is performed after the semi-continuous casting to eliminate casting stress and further avoid ingot cracking, so as to achieve semi-continuous casting of large-size 7 series aluminum alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1This is a physical picture of the large-size 7075 aluminum alloy prepared in Example 1 of the present invention; Figure 2 This is a physical picture of the large-sized 7075 aluminum alloy after polishing prepared in Example 1 of the present invention; Figure 3 This is the metallographic structure diagram of the large-sized 7075 aluminum alloy prepared in Example 1 of the present invention; Figure 4 Another metallographic structure diagram of the large-sized 7075 aluminum alloy prepared in Example 1 of the present invention; Figure 5 This is a physical picture of the large-size 7075 aluminum alloy prepared in Comparative Example 1 of the present invention; Figure 6 Another physical picture of the large-size 7075 aluminum alloy prepared in Comparative Example 1 of the present invention; Figure 7 This is a physical picture of the large-size 7075 aluminum alloy prepared in Comparative Example 2 of the present invention; Figure 8 This is a physical picture of the large-sized 7075 aluminum alloy prepared in comparative example 3 of the present invention. DETAILED DESCRIPTION

[0008] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in combination with the implementation modes and the accompanying drawings.

[0009] A casting method for a large-size 7 series aluminum alloy comprises the following steps: using electrolytic aluminum liquid or aluminum ingot as raw material, sequentially performing smelting treatment, semi-continuous casting treatment and homogenization annealing heat treatment to obtain a large-size 7 series aluminum alloy; dry well casting is used during the semi-continuous casting treatment.

[0010] From the above description, it can be seen that the beneficial effects of the present invention are: the present invention uses dry well casting, and the cooling water in the casting well is evacuated in advance, which can prevent the ingot from cooling down too quickly and generating cooling stress that causes it to crack, improve the shaping of the ingot, and inhibit the generation of cracks; the crystal structure inside the alloy is improved, the casting stress is eliminated, and the ingot cracking is further avoided. The present invention realizes semi-continuous casting of large-scale 7-series aluminum alloy round ingots through the above technical scheme. This method saves energy and materials, and the production is continuous and compact, with high production efficiency.

[0011] Furthermore, a homogenization annealing heat treatment is performed within 1 hour after the dry well casting is completed.

[0012] From the above description, it can be seen that failure to carry out homogenization annealing heat treatment in time will lead to stress accumulation inside the ingot and cause cracks.

[0013] Furthermore, aluminum titanium boron wire is fed during the semi-continuous casting process.

[0014] From the above description, it can be seen that adding aluminum-titanium-boron wire can improve the strength and plastic toughness of aluminum alloy, reduce stress concentration, and avoid ingot cracking during the plastic process.

[0015] Furthermore, the mass of the aluminum-titanium-boron wire accounts for more than 0.01% of the mass of the 7 series aluminum alloy.

[0016] Furthermore, a pure aluminum core is used as a bottom layer during the semi-continuous casting process.

[0017] From the above description, it can be seen that the bottom laying of pure aluminum core billets can inhibit the bottom cracking of large-sized ingots. The present invention adopts the bottom laying technology of pure aluminum core billets for semi-continuous casting, and does not need to use special equipment to inject liquid aluminum water for bottom laying and top laying operations, and the operation is simple.

[0018] Furthermore, in the semi-continuous casting process, dry well casting is continuously maintained and the ingot is sprayed with secondary cooling water. The secondary cooling water is turned off 10 to 60 seconds after the casting is completed, and the ingot is then cooled in the casting well for 1 to 2 hours.

[0019] From the above description, it can be seen that adopting a specific cooling process after casting is completed can reduce cooling stress and avoid cracks.

[0020] Furthermore, the casting speed during the semi-continuous casting process is 30-45 mm / min.

[0021] Furthermore, a flat bottom starter is used in the semi-continuous casting process.

[0022] From the above description, it can be seen that conventional starter heads include two types: flat-bottom starter heads and planar boss starter heads. If a planar boss starter head is used for casting of aluminum alloy, cracks may occur.

[0023] Furthermore, the titanium content in the product obtained by smelting treatment is ≥ 0.02wt%.

[0024] From the above description, it can be seen that the content of titanium in the smelting furnace is greater than 0.02wt%, which can play a role in refining grains.

[0025] Furthermore, the products obtained from the smelting process also include magnesium, copper, zinc, manganese and chromium.

[0026] Furthermore, it also includes refining treatment, slag removal treatment, static treatment, degassing and impurity removal treatment and filtering treatment carried out in sequence after the smelting treatment.

[0027] From the above description, it can be seen that the refining treatment, slag removal treatment, static treatment, degassing and impurity removal treatment and filtering treatment carried out in sequence after the smelting treatment can obtain a pure and uniform alloy melt.

[0028] Furthermore, the refining time of the refining process is ≥10 min.

[0029] Furthermore, the homogenization annealing heat treatment is followed by natural cooling.

[0030] From the above description, it can be seen that natural cooling after homogenization annealing heat treatment can prevent the ingot from deformation and cracking.

[0031] Another technical solution adopted by the present invention is: a large-size 7 series aluminum alloy is prepared by the casting method of the large-size 7 series aluminum alloy.

[0032] From the above description, it can be seen that the large-size 7 series aluminum alloy can be made without cracking at a diameter of 457 mm.

[0033] Embodiment 1 of the present invention is: a casting method of a large-size 7075 aluminum alloy with a diameter of 457 mm, the steps are as follows: S1: electrolytic aluminum liquid is used as raw material, added into the smelting furnace, and electromagnetic stirring is performed evenly after the raw material is completely melted. The smelting temperature is 740℃, the smelting time is 230min, and samples are taken twice to detect the alloy composition; S2: According to the test results of S1, add flux, continue smelting until the solvent is completely melted and fully alloyed, then take samples to test the alloy composition, until the alloy melt contains 2.45wt% magnesium, 1.54wt% copper, 5.33wt% zinc, 0.24wt% manganese, 0.20wt% chromium, and 0.02wt% titanium, which is qualified; S3: After the alloy melt composition is tested to be qualified, add 2wt% of the weight of the alloy melt He's refining agent for 20 minutes of refining treatment, and then use a multifunctional slag removal vehicle to remove slag, and let it stand for 30 minutes after the treatment is completed; S4: The alloy melt treated in S3 is transferred to a holding furnace and allowed to stand for 30 minutes; then, vacuum and rotary spray composite online purification technology is used to remove gas and impurities, and then plate filtration is performed to remove non-metallic inclusions and solid inclusions to obtain a pure and uniform alloy melt; S5: The alloy melt treated with S4 is cast using the oil-gas lubricated semi-continuous casting technology: first, the bottom pure aluminum core billet is placed on the flat-bottom ingot starter, the casting machine is turned on, and the ingot starter with the pure aluminum core billet installed is raised into the crystallizer; the alloy melt treated with S4 is introduced into the crystallizer through the flow channel for semi-continuous direct cooling casting, with a casting speed of 35 mm / min. During the process, a wire feeder is used to feed double wires of aluminum-titanium-boron wires, and the mass of the aluminum-titanium-boron wires is 0.02% of the mass of the alloy melt; during casting, the cooling water is evacuated in advance and dry well casting is used, and the dry well casting is continuously maintained and the ingot is sprayed with secondary cooling water, and the wiper is turned on to clamp the outer periphery of the ingot to prevent the cooling water from contacting the ingot; S6: 20 seconds after the casting is completed, the secondary cooling water is immediately turned off, and the ingot is cooled in the well for 1 hour before being subjected to homogenization annealing. After being kept at 465°C for 24 hours, it is naturally cooled to prepare a large-size 7075 aluminum alloy. The actual picture of the aluminum alloy is shown in Figure 1 , see the actual picture after polishing Figure 2 , the aluminum alloy was subjected to metallographic testing, and the test results are shown in Figure 3 and 4 ;Depend on Figures 1 to 4 It can be seen that the metallographic structure of the large-size 7075 aluminum alloy with a diameter of 457 mm cast by the casting method of the present invention is uniform and free of cracks.

[0034] Embodiment 2 of the present invention is: The only difference between Example 2 and Example 1 is that aluminum ingots are used as raw materials, the melting temperature is 730° C., the casting speed is 30 mm / min, and the secondary cooling water is turned off 10 seconds after the dry well casting is completed, and the casting is cooled in the casting well for 2 hours.

[0035] Embodiment 3 of the present invention is: The only difference between Example 3 and Example 1 is that the melting temperature is 760° C.; the casting speed is 45 mm / min; the secondary cooling water is turned off 60 seconds after the dry well casting is completed, and the casting is cooled in the casting well for 1 hour.

[0036] Embodiment 4 of the present invention is: a large-size 7 series aluminum alloy prepared by the preparation method of embodiment 1.

[0037] Comparative Example 1 of the present invention is: The only difference between Comparative Example 1 and Example 1 is that the cooling water is not evacuated during casting, and the cooling water is not prevented from contacting the ingot. Figure 5 and 6 .

[0038] Comparative Example 2 of the present invention is: The difference between the comparative example 2 and the embodiment 1 is that the casting is directly water-cooled for 1 hour. Figure 7 .

[0039] Comparative Example 3 of the present invention is: The only difference between the comparative example 3 and the embodiment 1 is that liquid aluminum is injected to perform the bottom and top laying operations. The actual picture of the comparative example 3 is shown in FIG. Figure 8 .

[0040] In summary, the casting method of large-size 7 series aluminum alloy provided by the present invention has the following advantages: 1. The scraper-coupled dry-well casting process is adopted, and a flat-bottomed ingot starter is used to release stress, increase the plasticity of the ingot, and avoid ingot cracking; after casting, a specific cooling process is adopted to reduce cooling stress and avoid cracks.

[0041] 2. Use pure aluminum core billet as the bottom to suppress bottom cracking of large-sized ingots.

[0042] 3. Perform homogenization annealing heat treatment within 1 hour after casting, followed by natural cooling, to prevent the ingot from deformation and cracking.

[0043] 4. Adding titanium in a content greater than 0.02wt% to the raw materials can help refine the grains.

[0044] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A casting method for a large-size 7 series aluminum alloy, characterized in that: The following steps are involved: Electrolytic aluminum liquid or aluminum ingot is used as raw material, and smelting treatment, semi-continuous casting treatment and homogenization annealing heat treatment are carried out in sequence to obtain large-size 7 series aluminum alloy; dry well casting is used in the semi-continuous casting treatment.

2. The casting method of large-size 7 series aluminum alloy according to claim 1, characterized in that: A homogenization annealing heat treatment is performed within 1 to 2 hours after the dry well casting is completed.

3. The casting method of large-size 7 series aluminum alloy according to claim 1, characterized in that: The semi-continuous casting process is carried out by feeding aluminum titanium boron wire.

4. The casting method of large-size 7 series aluminum alloy according to claim 1, characterized in that: The semi-continuous casting process uses a pure aluminum core as the bottom layer.

5. The casting method of large-size 7 series aluminum alloy according to claim 1, characterized in that: In the semi-continuous casting process, dry well casting is continuously maintained and the ingot is sprayed with secondary cooling water. The secondary cooling water is turned off 10 to 60 seconds after the casting is completed, and then the ingot is cooled in the casting well for 1 to 2 hours.

6. The casting method of large-size 7 series aluminum alloy according to claim 1, characterized in that: The semi-continuous casting process uses a flat bottom starter.

7. The casting method of large-size 7 series aluminum alloy according to claim 1, characterized in that: The titanium content of the product obtained by the smelting treatment is ≥ 0.02wt%.

8. The casting method of large-size 7 series aluminum alloy according to claim 1, characterized in that: It also includes refining treatment, slag removal treatment, static treatment, degassing and impurity removal treatment and filtering treatment carried out in sequence after smelting treatment.

9. The casting method of large-size 7 series aluminum alloy according to claim 1, characterized in that: The homogenization annealing heat treatment is followed by natural cooling.

10. A large-size 7 series aluminum alloy prepared by the casting method of any one of claims 1 to 9.

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