Preparation method of large-size 7055 aluminum alloy cast ingot

Abstract

The invention provides a preparation method of a large-size 7055 aluminum alloy cast ingot, which comprises the following steps: S1) burdening according to the composition proportion of the 7055 aluminum alloy cast ingot, and refining the burdened mixed raw material, including smelting furnace refining for three times and holding furnace refining for one time in sequence; s2) carrying out slagging-off, component adjustment and standing on the melt obtained in the step S1), and then carrying out online refining; (S3) the melt obtained in the step (S2) sequentially enters a first degassing box and a second degassing box to be subjected to online degassing, then two-stage filtering is conducted, and then casting is conducted; and (S4) the aluminum alloy cast ingot obtained in the step (S3) is subjected to three-stage homogenizing annealing, and the 7055 aluminum alloy cast ingot is obtained. According to the preparation method provided by the invention, the high-strength, high-toughness and large-specification 7055 aluminum alloy cast ingot which is free of cracks, small in grain size, good in internal quality and free of dendritic segregation can be prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy preparation, and in particular to a method for preparing a large-size 7055 aluminum alloy ingot. Background Art

[0002] With the rapid development of the aerospace industry, the requirements for the strength, fracture toughness, corrosion resistance, and fatigue resistance of high-performance aluminum alloys for aerospace applications are becoming increasingly stringent. 7055, a new aluminum alloy developed based on the 7050 alloy by increasing the Zn / Mg ratio and further reducing the content of impurities such as Fe, Si, and Mn, is currently the strongest wrought aluminum alloy. 7055 aluminum alloy can be produced into large-scale aerospace rings through the ring forging process, which also places higher demands on the specifications and quality of 7055 aluminum alloy ingots.

[0003] Large-sized 7055 aluminum alloy ingots, with alloying content exceeding 12%, experience a wide crystallization range, large linear shrinkage during solidification, and high thermal stresses within the ingot. Furthermore, their large cross-sectional dimensions lead to uneven temperature distribution during cooling, resulting in uneven thermal stress distribution and a high tendency to thermal cracking. This wide crystallization range also results in coarse dendrites during solidification of the aluminum alloy melt, which are prone to shrinkage. Coarse dendrites also lead to dendritic segregation, reducing the material's strength, toughness, and corrosion resistance. Shrinkage, interdendritic compounds, and coarse dendrites themselves within the ingot are all sources of stress concentration and cracking.

[0004] Therefore, in order to improve the application range of large-size 7055 aluminum alloy ingots, it is of great significance to provide a preparation method of large-size 7055 aluminum alloy ingots to solve the problems of coarse dendrites, easy cracking and poor internal quality. Summary of the Invention

[0005] The technical problem solved by the present invention is to provide a method for preparing large-scale 7055 aluminum alloy ingots. The preparation method provided in this application can prepare high-strength and high-toughness large-scale 7055 aluminum alloy ingots with no cracks, small grain size, good internal quality and no dendrite segregation.

[0006] In view of this, the present application provides a method for preparing a large-scale 7055 aluminum alloy ingot, comprising the following steps:

[0007] S1) batching the raw materials according to the composition ratio of a 7055 aluminum alloy ingot, and refining the batched mixed raw materials, wherein the refining comprises three smelting furnace refinings and one holding furnace refining performed in sequence, wherein the three smelting furnace refinings are refining agent refinings and the one holding furnace refining is argon refining; the 7055 aluminum alloy ingot comprises: Zn 7.6-8.4wt%, Mg 1.8-2.3wt%, Cu 2.0-2.6wt%, Zr 0.08-0.15wt%, Fe≤0.15wt%, Si≤0.10wt%, Mn≤0.05%, Cr≤0.04wt%, Ti≤0.06wt%, and Al balance;

[0008] S2) skimming, adjusting the composition and allowing the melt obtained in step S1) to stand, and then performing online refinement;

[0009] S3) the melt obtained in step S2) is sequentially passed into a first degassing box and a second degassing box for online degassing, and then subjected to double-stage filtration, and then cast;

[0010] S4) The aluminum alloy ingot obtained in step S3) is subjected to three-stage homogenization annealing to obtain a 7055 aluminum alloy ingot.

[0011] In some specific embodiments, the refining temperature in the three smelting furnace refinings is independently 740-760° C., the refining time is independently 18-22 min, the standing time for the first two refinings is ≥20 min, and the standing time for the third refining is ≥30 min.

[0012] In some specific embodiments, in step S1), the refining temperature of the smelting furnace to the holding furnace refining is 765-770°C, and / or the refining temperature of the holding furnace refining is 745-765°C, the refining time is 18-22 minutes, and the standing time is ≥20 minutes.

[0013] In some specific embodiments, in step S2), the online refining agent is aluminum titanium boron wire, and the amount used is 2 to 4 kg / (t·Al).

[0014] In some specific embodiments, in step S3), the first degassing box is a snif degassing box, and the second degassing box is a vacuum degassing box.

[0015] In some specific embodiments, in step S3), the filter plate of the double-stage filtration is 40+60ppi.

[0016] In some specific embodiments, in step S3), the starting temperature of the casting melt is 755-768°C, and the steady-state tail temperature is 690-700°C.

[0017] In some specific embodiments, in step S3), the amount of aluminum used for paving the bottom of the casting ladle is 800-900 kg, and the temperature is 760-770°C.

[0018] In some specific embodiments, in step S3), after the casting is completed, tempering treatment is performed when the thickness of the solidified layer in the cross section at the ingot gate is 1 / 2 of the ingot radius, and the tempering treatment time is 20 to 30 minutes.

[0019] In some specific embodiments, the first-stage uniform heating temperature of the homogenization annealing is 400-420°C, the holding time is 8-12h, the second-stage uniform heating temperature is 455-465°C, the holding time is 8-12h, and the third-stage uniform heating temperature is 465-470°C, the holding time is 40-50h.

[0020] The present application provides a preparation method of large-size 7055 aluminum alloy ingots, which first batches the ingredients according to the composition ratio of the 7055 aluminum alloy ingots, sequentially subjects the batched mixed raw materials to three smelting furnace refinings and one holding furnace refining, then skims the obtained melt, adjusts the composition and holds the melt, then performs online refinement on the obtained melt, then sequentially performs two-stage online degassing and two-stage filtration on the obtained melt, casts it after the two-stage filtration, and finally performs three-stage homogenization annealing to obtain large-size 7055 aluminum alloy ingots; in the process of preparing the 7055 aluminum alloy ingots, the present application uses multiple refinings to facilitate removal of impurities in the aluminum liquid, and uses argon refining in the holding furnace to ensure the purity of the aluminum liquid. At the same time, the use of two-stage degassing and two-stage filtration can effectively reduce the hydrogen and impurity contents of the aluminum liquid, improve the purity of the melt, thereby ensuring that the finally prepared large-size 7055 aluminum alloy ingots are free of defects such as cracks, small grain size, good internal quality, and no dendritic segregation, and have the characteristics of high strength and toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Macroscopic and metallographic photographs of the 7055 aluminum alloy ingot prepared in Example 1 of the present invention;

[0022] Figure 2 Macroscopic and metallographic photographs of the 7055 aluminum alloy ingot prepared in Example 2 of the present invention;

[0023] Figure 3 These are macroscopic and metallographic photographs of the 7055 aluminum alloy ingot prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0024] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0025] In view of the problems in the prior art of preparing large-scale 7055 aluminum alloy ingots that are prone to cracks, coarse dendrites, and poor internal quality, the present application provides a method for preparing large-scale 7055 aluminum alloy ingots. By introducing multiple refining steps and combining two-stage degassing, two-stage filtration, and three-stage homogenization annealing, on the basis of improving the purity of the melt, a high-strength and high-toughness large-scale 7055 aluminum alloy ingot with no defects such as cracks, small grain size, good internal quality, and no dendrite segregation is finally prepared. Specifically, the embodiment of the present invention discloses a method for preparing large-scale 7055 aluminum alloy ingots, comprising the following steps:

[0026] S1) batching the raw materials according to the composition ratio of the 7055 aluminum alloy ingot, and refining the batched mixed raw materials, wherein the refining comprises three smelting furnace refinings and one holding furnace refining performed in sequence, wherein the three smelting furnace refinings are refining agent refinings and the one holding furnace refining is argon gas refining;

[0027] S2) skimming, adjusting the composition and allowing the melt obtained in step S1) to stand, and then performing online refinement;

[0028] S3) the melt obtained in step S2) is sequentially passed into a first degassing box and a second degassing box for online degassing, and then subjected to double-stage filtration, and then cast;

[0029] S4) The aluminum alloy ingot obtained in step S3) is subjected to three-stage homogenization annealing to obtain a 7055 aluminum alloy ingot.

[0030] In the preparation process of large-scale 7055 aluminum alloy ingot, the present application first prepares the ingredients according to the composition ratio of the 7055 aluminum alloy ingot, and the composition of the 7055 aluminum alloy ingot includes: Zn 7.6-8.4wt%, Mg 1.8-2.3wt%, Cu 2.0-2.6wt%, Zr 0.08-0.15wt%, Fe≤0.15wt%, Si≤0.10wt%, Mn≤0.05%, Cr≤0.04wt%, Ti≤0.06wt%, and Al balance; specifically, the content of Zn is 7.8-8.2wt%, the content of Mg is 1.9-2.2wt%, the content of Cu is 2.0-2.5wt%, the content of Zr is 0.09-0.14wt%, the content of Fe is ≤0.10wt%, the content of Si is ≤0.08wt%, and the content of Mn is ≤0.01wt %, Cr content ≤ 0.01wt%, Ti content ≤ 0.02wt%, and Al balance; more specifically, the Zn content is 7.9-8.1wt%, the Mg content is 2.0-2.1wt%, the Cu content is 2.2-2.4wt%, the Zr content is 0.11-0.12wt%, the Fe content is ≤ 0.10wt%, the Si content is ≤ 0.08wt%, the Mn content is ≤ 0.01wt%, the Cr content is ≤ 0.01wt%, the Ti content is ≤ 0.02wt%, and Al balance. The raw materials of the batching are well known to those skilled in the art. Furthermore, in order to reduce the content of impurities in the 7055 aluminum alloy ingot, no secondary scrap or tertiary scrap is added, the proportion of primary scrap additives does not exceed 20%, and only aluminum alloy scrap rods of the same series can be added to the primary scrap. After batching, the mixed raw materials are refined, which includes three smelting furnace refinings and one holding furnace refining in sequence, that is, one holding furnace refining is carried out after three smelting furnace refinings. The pouring furnace temperature from the smelting furnace to the holding furnace is 765-770°C, specifically, the pouring furnace temperature is 766°C, 767°C, 768°C, and 769°C.The refining temperature in the three smelting furnace refinings is independently 740-760°C, the refining time is independently 18-22 minutes, the standing time for the first two refinings is ≥20 minutes, and the standing time for the third refining is ≥30 minutes; in the above three smelting furnace refining processes, the first refining temperature, the second refining temperature and the third refining temperature can be the same or different. Specifically, the temperatures of the three smelting furnace refinings are independently 750-758°C; for example, in this application, the temperatures of the three smelting furnace refinings are independently 741°C, 744°C, 747°C, 749°C, 750°C, 751°C, 753°C, 757°C and 759°C; the first refining time, the second refining time and the third refining time can be the same or different. Specifically, the refining time of the three smelting furnace refinings is independently 19-20 minutes; the standing time for the first two refinings is 20-25 minutes, and the standing time for the third refining is 30-35 minutes. After three refining steps in the smelting furnace, the molten aluminum may be mixed with some inclusions when it is transferred from the smelting furnace to the holding furnace. These inclusions are suspended inside the molten aluminum. After argon refining, the suspended inclusions will float to the surface of the molten aluminum and then be removed by subsequent slag skimming to ensure the purity of the molten aluminum. Argon refining will not introduce foreign inclusions. Therefore, the three smelting furnace refinings also include one holding furnace refining, and the holding furnace refining is argon refining; the temperature of the holding furnace refining is 745-765°C, the refining time is 18-22 minutes, and the standing time is ≥20 minutes; specifically, the temperature of the holding furnace refining is 748-762°C, more specifically, the temperature of the holding furnace refining is 750-760°C, more specifically, the temperature of the holding furnace refining is 755-758°C; specifically, the refining time of the holding furnace is 19-20 minutes, more specifically, the refining time is 25-30 minutes.

[0031] The present application then performs slag removal, composition adjustment and static standing of the refined aluminum liquid; the specific operating means of the slag removal, composition adjustment and static standing are well known to those skilled in the art, and the present application does not impose any particular limitation on this.

[0032] According to the present invention, the aluminum liquid is then refined online, and the online refining agent is aluminum titanium boron wire, and the amount used is 2 to 4 kg / (t·Al). Specifically, the amount of the refining agent is 2.5 to 3.8 kg / (t·Al), and more specifically, the amount of the refining agent is 3.5 kg / (t·Al).

[0033] This application then sequentially directs the melt after online refinement into a first degassing box and a second degassing box for online degassing. Specifically, the first degassing box is a snif degassing box, and the second degassing box is a vacuum degassing box. The snif degassing box injects inert gas (nitrogen or argon) into the molten aluminum in the form of tiny bubbles through a rotating nozzle, and purifies the molten aluminum through physical dehydrogenation, inclusion removal and dynamic stirring. The vacuum degassing box removes hydrogen and inclusions from the molten aluminum by creating a low-pressure environment, thereby significantly improving the purity of the molten aluminum. The vacuum degassing box includes vacuum dehydrogenation, inclusion floating and boiling effects to achieve the removal of hydrogen and inclusions in the molten aluminum.

[0034] After the dual-stage online degassing, the obtained aluminum liquid is subjected to dual-stage filtration, wherein the filter plates of the dual-stage filtration have a 40+60 ppi ratio. The combination of the dual-stage online degassing and dual-stage filtration can effectively reduce the hydrogen and impurity content in the aluminum liquid and improve the purity of the aluminum liquid.

[0035] This application then casts the aluminum liquid after double-stage filtration; the casting operation means are the operation means well known to those skilled in the art, and this application does not impose any special restrictions on this; in this application, the starting melt temperature of the casting is 755-768°C, and the steady-state tail temperature is 690-700°C. Specifically, the starting melt temperature is 757-765°C, and the steady-state tail temperature is 692-698°C. More specifically, the starting melt temperature is 759-762°C, and the steady-state tail temperature is 694-696°C. The amount of aluminum used for the bottom of the casting ladle is 800-900 kg, and the temperature is 760-770°C; specifically, the amount of aluminum used for the bottom of the casting ladle is 820-880 kg, and the temperature is 762-768°C; more specifically, the amount of aluminum used for the bottom of the casting ladle is 830-860 kg, and the temperature is 764-765°C; the aluminum used for the bottom of the ladle can protect the furnace lining, assist in melting, and contain impurities. After the casting is completed, the tempering treatment is carried out when the thickness of the solidified layer in the cross section at the ingot pouring mouth is 1 / 2 of the ingot radius, and the tempering treatment time is 20-30 minutes; the tempering treatment in the field of aluminum alloys is also called self-tempering, which is to stop the flow after the ingot drops to the lower edge of the crystallizer, and stop the water when the thickness of the solidified layer in the cross section at the ingot pouring mouth is 1 / 2 of the ingot radius, so that the temperature of the upper part of the ingot is automatically heated to above 350°C by the residual heat of the residual metal in the liquid cavity. 7055 aluminum alloy ingots have poor low-temperature plasticity, and large-sized 7055 aluminum alloys are very prone to cracking. This application uses tempering to improve the plasticity of the ingot's pouring area, reduce stress, and heat the metal layer near the pouring area to prevent cracking. Failure to properly adjust the tempering time will increase the tendency to crack.

[0036] Finally, the cast aluminum alloy ingot is subjected to a three-stage homogenization treatment to obtain a 7055 aluminum alloy ingot; the three-stage homogenization treatment is beneficial to increasing the solid solubility of solute atoms in the ingot, improving the aging strengthening effect of the alloy, and significantly reducing the residual phase without overburning. The first-stage equalizing temperature of the homogenization annealing is 400-420°C, and the holding time is 8-12h. Specifically, the first-stage equalizing temperature is 405-418°C, and the holding time is 9-10h. More specifically, the first-stage equalizing temperature is 410-416°C; the second-stage equalizing temperature is 455-465°C, and the holding time is 8-12h. Specifically, the second-stage equalizing temperature is 458-462°C, and the holding time is 9-10h. More specifically, the second-stage equalizing temperature is 459-460°C; the third-stage equalizing temperature is 465-470°C, and the holding time is 40-50h. Specifically, the third-stage equalizing temperature is 466-468°C, and the holding time is 42-48h.

[0037] Taking the first-stage soaking temperature as 400℃, the second-stage soaking temperature as 460℃, and the third-stage soaking temperature as 468℃ as an example, the homogenization process is as follows: the aluminum alloy ingot is hoisted onto the soaking rack, and after thermocouples are inserted at different positions, it is transported to the soaking furnace for homogenization annealing; the soaking furnace gas temperature is set at 430℃, and when one thermocouple temperature reaches 400℃, the furnace gas temperature is immediately adjusted to the holding temperature (400℃), and when all thermocouple temperature values ​​reach the metal temperature control lower limit (395℃), the holding time is calculated; when the first-stage soaking is completed, the furnace gas is immediately adjusted to the holding temperature (400℃). The temperature is set to the second-stage soaking temperature (490°C). When a thermocouple temperature reaches 460°C, the furnace gas temperature is adjusted to the holding temperature (460°C). When all thermocouple temperatures reach the metal temperature control lower limit (455°C), the second-stage soaking and holding time begins to be calculated. After the second-stage soaking is completed, the furnace gas temperature is immediately set to the third-stage soaking temperature (470°C). When a thermocouple holding temperature reaches 468°C, the furnace gas temperature is adjusted to the holding temperature (468°C). When all thermocouple temperatures reach the metal temperature control lower limit (465°C), the holding time can be calculated. After the homogenization annealing is completed, the cooling method is natural cooling.

[0038] The preparation method of the 7055 aluminum alloy ingot provided in the present application is applicable to aluminum alloy ingots with a specification of 630 to 830 mm.

[0039] The present application provides a method for preparing large-size 7055 aluminum alloy ingots, which includes multiple refining-online refinement-two-stage online degassing-two-stage filtration-casting-three-stage homogenization annealing; during the preparation process, the present application adopts multiple refining to facilitate the removal of impurities in the aluminum liquid, the combination of refining agent refining and argon refining is conducive to the purity of the aluminum liquid, the use of two-stage degassing and two-stage filtration can effectively reduce the hydrogen and impurity content of the aluminum liquid, improve the purity of the melt, and combined with the final three-stage homogenization annealing, finally produce high-strength and high-toughness large-size 7055 aluminum alloy ingots with no cracks, small grain size, good internal quality, and no defects such as dendritic segregation.

[0040] In order to further understand the present invention, the preparation method of the large-size 7055 aluminum alloy ingot provided by the present invention is described in detail below in conjunction with the examples. The protection scope of the present invention is not limited by the following examples.

[0041] Example 1

[0042] 1) Material preparation: The materials are prepared according to the mass percentage of the elements in Table 1; secondary and tertiary scraps are not selected as raw materials for the materials, and the proportion of primary scrap added is controlled at 10%, and only aluminum alloy scrap rods of the same series can be added to the primary scrap;

[0043] Table 17055 aluminum alloy ingot composition data (wt%)

[0044] element Si Fe Cu Mg Zn Ti Zr Al Actual value 0.042 0.065 2.35 2.08 8.12 0.038 0.15 margin

[0045] 2) The mixed material after batching was first refined three times in a refining furnace, the melt after refining in the refining furnace was poured into a furnace at 765°C, and then refined once in an argon holding furnace. The specific refining parameters are shown in Table 2;

[0046] Table 2 Refining parameter data of melting furnace and holding furnace

[0047]

[0048] 3) The aluminum liquid obtained in step 2) is subjected to deslagging, composition adjustment, and standing, and then 3 kg / (t·Al) of aluminum titanium boron wire is added for online refinement;

[0049] 4) The aluminum liquid after online refinement is degassed online using a snif degassing box and a vacuum degassing box in sequence, and then double-stage filtered using an imported Zhuokai filter plate 40+60ppi;

[0050] The obtained aluminum liquid is cast, the starting temperature of the aluminum liquid is 759℃, the casting speed is 30mm / min, the steady-state tail temperature is 690℃, the amount of aluminum used for the bottom of the ladle is 800kg, the temperature is 760℃, and after the casting is completed, when the thickness of the solidified layer on the cross section of the ingot gate reaches 1 / 2 of the ingot radius, it is tempered for 20 minutes to ensure that no cooling water contacts the gate. Specifications of crystallizer;

[0051] 5) After the aluminum alloy ingot obtained in step 4) is produced, it is sent to a soaking furnace for soaking, using a three-stage soaking process: 400℃ / 10h, 460℃ / 10h, 468℃ / 48h, and finally naturally cooled to obtain a 7055 aluminum alloy ingot with a size of φ630mm.

[0052] After testing, the H content in the flow channel is 0.77mL / 100gAl, the final ingot grain size is level one, loose level one, without cracks, pores, inclusion defects, no residual phase at the grain boundary, and the metallographic structure is uniform and without overburning. Figure 1 shown.

[0053] Example 2

[0054] 1) Material preparation: The materials are prepared according to the mass percentage of the elements in Table 3; secondary and tertiary scraps are not selected as raw materials for the materials, the proportion of primary scrap added is controlled at 10%, and only aluminum alloy scrap rods of the same series can be added to the primary scrap;

[0055] Table 3 7055 aluminum alloy ingot composition data (wt%)

[0056] element Si Fe Cu Mg Zn Ti Zr Al Actual value 0.046 0.063 2.41 2.16 8.13 0.042 0.14 margin

[0057] 2) The mixed material after batching was first refined three times in a refining furnace, the melt after refining in the refining furnace was poured into a furnace at 765°C, and then refined once in an argon holding furnace. The specific refining parameters are shown in Table 4;

[0058] Table 4 Refining parameter data of melting furnace and holding furnace

[0059]

[0060]

[0061] 3) The aluminum liquid obtained in step 2) is subjected to deslagging, composition adjustment, and standing, and then 3 kg / (t·Al) of aluminum titanium boron wire is added for online refinement;

[0062] 4) The aluminum liquid after online refinement is degassed online using a snif degassing box and a vacuum degassing box in turn, and then double-stage filtered using an imported Zhuokai filter plate 40+60ppi. The obtained aluminum liquid is cast. The starting temperature of the aluminum liquid is 759°C, the casting speed is 30mm / min, the steady-state tail temperature is 690°C, the amount of aluminum used for the bottom of the ladle is 800kg, and the temperature is 760°C. After the casting is completed, when the thickness of the solidified layer on the cross section of the ingot gate reaches 1 / 2 of the ingot radius, it is tempered for 25 minutes to ensure that no cooling water contacts the gate. During the casting process, Specifications of crystallizer;

[0063] 5) After the aluminum alloy ingot obtained in step 4) is produced, it is sent to a soaking furnace for soaking. The soaking process is 400°C / 10h, 460°C / 10h, and 468°C / 48h. Finally, it is naturally cooled to obtain a 7055 aluminum alloy ingot with a size of Φ700mm.

[0064] After testing, the H content of the launder is 0.82mL / 100gAl, the final ingot has a grain size of one level and a looseness of one level, without cracks, pores, or inclusion defects, and some residual phases appear at the grain boundaries. The metallographic structure is uniform and there is no overburning. Figure 2 shown.

[0065] Example 3

[0066] 1) Material preparation: The materials are prepared according to the mass percentage of the elements in Table 5; secondary and tertiary scraps are not selected as raw materials for the materials, and the proportion of primary scrap added is controlled at 10%, and only aluminum alloy scrap rods of the same series can be added to the primary scrap;

[0067] Table 57055 aluminum alloy ingot composition data (wt%)

[0068] element Si Fe Cu Mg Zn Ti Zr Al Actual value 0.046 0.063 2.41 2.16 8.13 0.042 0.14 margin

[0069] 2) The mixed material after batching was first refined three times in a refining furnace, the melt after refining in the refining furnace was poured into a furnace at 765°C, and then refined once in an argon holding furnace. The specific refining parameters are shown in Table 6;

[0070] Table 6 Refining parameter data of melting furnace and holding furnace

[0071]

[0072] 3) The aluminum liquid obtained in step 2) is subjected to deslagging, composition adjustment, and standing, and then 3 kg / (t·Al) of aluminum titanium boron wire is added for online refinement;

[0073] 4) The aluminum liquid after online refinement is degassed online using a snif degassing box and a vacuum degassing box in sequence, and then double-stage filtered using an imported Zhuokai filter plate 40+60ppi;

[0074] The obtained aluminum liquid is cast, the starting temperature of the aluminum liquid is 759℃, the casting speed is 30mm / min, the steady-state tail temperature is 690℃, the amount of aluminum used for the bottom of the ladle is 800kg, the temperature is 760℃, and after the casting is completed, when the thickness of the solidified layer at the cross section of the ingot gate reaches 1 / 2 of the ingot radius, it is tempered for 30 minutes to ensure that no cooling water contacts the gate. Specifications of crystallizer;

[0075] 5) After the aluminum alloy ingot obtained in step 4) is produced, it is sent to a soaking furnace for soaking. The soaking process is 400°C / 10h, 460°C / 10h, and 468°C / 50h. Finally, it is naturally cooled to obtain a 7055 aluminum alloy ingot with a size of Φ830mm.

[0076] After testing, the H content of the launder is 0.79mL / 100gAl, the final ingot has a grain size of one level and a looseness of one level, without cracks, pores, or inclusion defects, and some residual phases appear at the grain boundaries. The metallographic structure is uniform and there is no overburning. Figure 3 shown.

[0077] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0078] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a large-size 7055 aluminum alloy ingot, comprising the following steps: S1) batching the raw materials according to the composition ratio of a 7055 aluminum alloy ingot, and refining the batched mixed raw materials, wherein the refining comprises three smelting furnace refinings and one holding furnace refining performed in sequence, wherein the three smelting furnace refinings are refining agent refinings and the one holding furnace refining is argon refining; the 7055 aluminum alloy ingot comprises: Zn 7.6-8.4wt%, Mg 1.8-2.3wt%, Cu 2.0-2.6wt%, Zr 0.08-0.15wt%, Fe≤0.15wt%, Si≤0.10wt%, Mn≤0.05%, Cr≤0.04wt%, Ti≤0.06wt%, and Al balance; S2) skimming, adjusting the composition and allowing the melt obtained in step S1) to stand, and then performing online refinement; S3) the melt obtained in step S2) is sequentially passed into a first degassing box and a second degassing box for online degassing, and then subjected to double-stage filtration, and then cast; S4) The aluminum alloy ingot obtained in step S3) is subjected to three-stage homogenization annealing to obtain a 7055 aluminum alloy ingot.

2. The preparation method according to claim 1, characterized in that The refining temperatures in the three smelting furnace refinings are independently 740-760° C., the refining times are independently 18-22 minutes, the standing time for the first two refinings is ≥20 minutes, and the standing time for the third refining is ≥30 minutes.

3. The preparation method according to claim 1, characterized in that In step S1), the smelting furnace is refined to a pouring furnace temperature of 765-770°C, and / or the refining temperature of the holding furnace is 745-765°C, the refining time is 18-22 minutes, and the standing time is ≥20 minutes.

4. The preparation method according to claim 1, characterized in that In step S2), the online refining agent is aluminum titanium boron wire, and the amount used is 2 to 4 kg / (t·Al).

5. The preparation method according to claim 1, characterized in that In step S3), the first degassing box is a snif degassing box, and the second degassing box is a vacuum degassing box.

6. The preparation method according to claim 1, characterized in that In step S3), the filter plate of the double-stage filtration is 40+60ppi.

7. The preparation method according to claim 1, characterized in that In step S3), the starting temperature of the casting melt is 755-768°C, and the steady-state tail temperature is 690-700°C.

8. The preparation method according to claim 7, characterized in that In step S3), the amount of aluminum used for the bottom of the casting ladle is 800-900 kg, and the temperature is 760-770°C.

9. The preparation method according to claim 8, characterized in that In step S3), after the casting is completed, tempering treatment is performed when the thickness of the solidified layer in the cross section at the ingot gate is 1 / 2 of the ingot radius, and the tempering treatment time is 20 to 30 minutes.

10. The preparation method according to claim 7, characterized in that The first stage of the homogenization annealing is at a temperature of 400-420° C. and a holding time of 8-12 hours; the second stage is at a temperature of 455-465° C. and a holding time of 8-12 hours; and the third stage is at a temperature of 465-470° C. and a holding time of 40-50 hours.

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