Super-large aluminum alloy square cast ingot and preparation method thereof

Abstract

The invention provides a preparation method of an oversized aluminum alloy square cast ingot, which comprises the following steps: S1) proportioning according to the composition proportion of the aluminum alloy square cast ingot, and smelting to obtain an aluminum alloy melt; (S2) the aluminum alloy melt is subjected to refining, on-line degassing and on-line filtering; (S3) the aluminum alloy melt obtained in the step (S2) is subjected to grain refinement; s4) casting the aluminum alloy cast ingot obtained in the step S3); the casting water cooling comprises primary water cooling, secondary water cooling and tertiary water cooling; and (S5) the cast ingot obtained in the step (S4) is subjected to soaking treatment, and the aluminum alloy square cast ingot is obtained. According to the super-large aluminum alloy square cast ingot and the preparation method thereof, the problem that the comprehensive performance of materials becomes poor due to structure segregation is solved while the casting performance of the square cast ingot is solved, the mechanical performance of aluminum alloy is improved, the hardness is improved, and forging flaw detection can reach the grade A.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aluminum alloy, in particular to a super large aluminum alloy square ingot and a preparation method thereof. BACKGROUND

[0002] Al-Mg series aluminum alloy has excellent plasticity, corrosion resistance and welding performance, and is widely used in various departments of the national economy. The main elements are Mg and Mn. With the increase of Mg content, the strength of the alloy gradually increases, but when the Mg content exceeds 5%, the stress corrosion resistance and the welding performance of the aluminum alloy material (strength and crack resistance) decrease, so the content of the aluminum alloy is controlled within 5% of Mg content. When the ingot thickness increases to 800-1200mm, the segregation degree of the ingot is inevitably increased compared with the conventional thickness (400-600mm), which may cause the Mg content in the core of the ingot to be too low to meet the material strength, and increasing the Mg content may cause the stress corrosion resistance and the welding performance to be poor. Therefore, while increasing the thickness of the ingot, how to obtain a lower segregation degree is also a difficult problem to be solved.

[0003] For deformed aluminum alloy, in order to obtain more uniform and fine ingot structure, under general conditions, the thicker or the larger the diameter of the ingot, the more prone to porosity in the center of the ingot, the worse the as-cast performance, and the greater the tendency to crack. At the same time, the segregation degree and the non-uniformity of the ingot increase. For square ingots, the tendency to crack is greater. Therefore, the thickness of the general alloy square ingot rarely exceeds 700mm. With the rapid development of transportation and semiconductor materials, the conventional Al-Mg series ingot size cannot meet the demand of high-performance super large size products, and the ingot thickness needs to reach 900-1100mm. In order to obtain good casting performance and uniform structure, the conventional method adjusts the casting parameters, which not only has problems such as cold shut, leakage and crack in casting forming, but most importantly, the structure and performance cannot meet the requirements of the terminal product.

[0004] Therefore, in order to meet the casting performance and comprehensive price performance demand of super large specification high quality square ingot, it is necessary to develop and optimize the design of tooling design, composition design, raw material selection, melt purification, grain refinement, casting process, soaking process, etc. SUMMARY

[0005] The technical problem solved by the present application is to provide a preparation method of a super large aluminum alloy square ingot. The preparation method provided by the present application obtains a high purity melt, excellent casting performance and uniform and fine ingot structure, so that the aluminum alloy square ingot can have high mechanical properties and hardness when applied.

[0006] Therefore, the present application provides a preparation method of a super large aluminum alloy square ingot, comprising the following steps:

[0007] S1) after the ingredients of the aluminum alloy square ingot are proportioned and dosed, melting is performed to obtain an aluminum alloy melt;

[0008] The ingredients of the aluminum alloy melt, in terms of mass percentage, include: Si≤0.06%, Fe≤0.12%, Cu≤0.03%, Mn 0.50~1.0%, Mg 4.5~5.0%, Cr 0.05~0.12%, Zn≤0.03%, Ti 0.02~0.05%, Be 0.0005~0.0020%, single impurity≤0.03%, and the balance is Al;

[0009] S2) the aluminum alloy melt is subjected to refining, online degassing, and online filtering;

[0010] S3) the aluminum alloy melt obtained in step S2) is subjected to grain refinement;

[0011] S4) the aluminum alloy ingot obtained in step S3) is subjected to casting; the water cooling of the casting includes primary water cooling, secondary water cooling, and tertiary water cooling;

[0012] S5) the ingot obtained in step S4) is subjected to soaking treatment to obtain an aluminum alloy square ingot.

[0013] In some specific embodiments, in step S1), the temperature of the melting is 730~755℃, and / or, a combined mechanical stirring and electromagnetic stirring method is adopted during the melting.

[0014] In some specific embodiments, in step S2), during the refining, granular refining agent is sprayed in the melting furnace for powder refining, argon-chlorine mixed gas is used in the holding furnace for refining, the refining time is≥30min, the amount of the granular refining agent is≤0.25ml / 100gAl; and / or, the standing time of the melt after the refining is≥45min; and / or, a high-efficiency rotary degassing device is adopted for the online degassing, and / or, the filtering plate precision of the online filtering is not less than 50ppi.

[0015] In some specific embodiments, in step S2), the hydrogen content of the melt after the refining is≤0.25ml / 100gAl, and the hydrogen content of the melt after the online degassing is≤0.12ml / 100gAl.

[0016] In some specific embodiments, in step S3), the grain refinement agent adopted for the grain refinement is AlTi5B1, and the amount is 1.5~2.5kg / t.

[0017] In some specific embodiments, in step S4), the casting speed is 25~45mm / min; and / or, the temperature of the aluminum liquid at the end of the flow plate is 685~705℃; and / or, the liquid level height of the crystallizer is 40~60mm.

[0018] In some embodiments, in step S4, the water flow rate of the casting is 60-120 m 3 / h. root, and the water temperature is 20-30℃.

[0019] In some embodiments, in step S4, the device for the three times of water cooling is a water tank arranged at the lower edge of the crystallizer, and the inner wall of the water tank is provided with holes.

[0020] In some embodiments, in step S5, the heating rate of the homogenization treatment is 50-90℃ / h, the heating time is 10-20h, the heating temperature is 500-550℃, the holding temperature is 480-510℃, and the holding time is 30-60h; and / or, the thickness of the aluminum alloy square ingot is 900-1100mm, the width of the ingot is 1300-2000mm, the length of the ingot is ≥3500mm, and the weight is more than 14 tons.

[0021] The application also provides an aluminum alloy square ingot prepared by the preparation method described in the above scheme, which comprises, in mass percentage: Si≤0.06%, Fe≤0.12%, Cu≤0.03%, Mn 0.50-1.0%, Mg 4.5-5.0%, Cr 0.05-0.12%, Zn≤0.05%, Ti 0.02-0.05%, Be 0.0005-0.0020%, single impurity≤0.03%, and the balance being Al.

[0022] The application provides a preparation method of a super-large aluminum alloy square ingot, which comprises the following steps: first, ingredients are prepared according to the component ratio of the aluminum alloy square ingot, and then the aluminum alloy melt is obtained by melting; then, the aluminum alloy melt is refined, on-line degassed and on-line filtered; then, the grain of the obtained aluminum alloy melt is refined; then, the melt after grain refinement is cast; and finally, homogenization treatment is performed; in the above process, the ingot size, component design and homogenization process are reasonably selected, so that a super-large square ingot with excellent comprehensive performance is obtained; at the same time, by reasonably controlling the melting process, melt purification, grain refinement and matching the appropriate casting process, and by increasing the three times of water cooling in the casting process, the uniformity of the edge and core of the large-size square ingot is realized, the organization segregation is reduced, the square ingot with high purity melt, excellent casting performance and uniform and fine ingot organization is obtained, and thus the mechanical properties and hardness of the aluminum alloy are improved, the aluminum alloy forging piece is A-level in the flaw detection, the performance requirements of the rail transit and semiconductor aluminum material are met, the yield is increased, and the production cost is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The crystallizer structure after the three times of water cooling of the application is shown in the figure. DETAILED DESCRIPTION

[0024] For a further understanding of the present application, preferred embodiments thereof will be described in detail in connection with the following examples, although it is to be understood that various changes can be made and equivalents employed without departing from the scope of the application as defined by the claims.

[0025] In order to develop the square ingot for the super large size high performance product, the Al-Mg series ingot of the present application has a high Mg content, and continuous network β (Al3Mg2) phase precipitates easily appear along the grain boundary, thereby affecting the comprehensive performance of the product; meanwhile, there is no related production control technology for the super large aluminum alloy with a thickness of 900-1100 mm, the present application provides a super large aluminum alloy square ingot and a preparation method thereof, which solves the problems of the casting performance of the square ingot and the poor comprehensive performance of the aluminum alloy caused by segregation, and improves the mechanical properties and hardness of the aluminum alloy, so that the forging detection can reach A level. Specifically, the present application discloses a preparation method of a super large aluminum alloy square ingot, comprising the following steps:

[0026] S1) After the ingredients of the aluminum alloy square ingot are proportioned and matched, melting is carried out to obtain an aluminum alloy melt;

[0027] The composition of the aluminum alloy melt comprises, in mass percent: Si≤0.06%, Fe≤0.12%, Cu≤0.03%, Mn 0.50-1.0%, Mg 4.5-5.0%, Cr 0.05-0.12%, Zn≤0.03%, Ti 0.02-0.05%, Be 0.0005-0.0020%, single impurity≤0.03%, and the balance is Al;

[0028] S2) The aluminum alloy melt is refined, on-line degassed and on-line filtered;

[0029] S3) The aluminum alloy melt obtained in step S2) is grain refined;

[0030] S4) The aluminum alloy ingot obtained in step S3) is cast; the water cooling of the casting comprises primary water cooling, secondary water cooling and tertiary water cooling;

[0031] S5) The ingot obtained in step S4) is subjected to soaking treatment to obtain an aluminum alloy square ingot.

[0032] In the process of preparing the super-large aluminum alloy square ingot, in step S1, after the ingredients of the aluminum alloy square ingot are proportioned and ingredients are prepared, the aluminum alloy melt is obtained; in this process, in order to meet the good casting performance and the comprehensive performance requirements of the aluminum alloy product, high-purity aluminum ingots and other raw materials with good uniformity are used to ensure that the impurities and trace elements such as Si, Fe, Cu, and Zn are controlled at a very low level; in specific embodiments, Al99.90 or above grade raw aluminum ingots, Mg99.9 or above grade magnesium ingots, Zn99.99 or above grade zinc ingots, AlCr, AlTi, AlMn (or Mn agent) intermediate alloy, AlBe intermediate alloy, and high-purity first-class waste are used for ingredients. In the process of melting, in order to reduce the generation of more oxidation slag in the melting process, the raw aluminum ingots are first laid in a layer to protect the furnace bottom, then the intermediate alloy, magnesium ingot, and zinc ingot of smaller size in the raw materials are added to the furnace, then the remaining raw aluminum is added, and if there is waste, the bulk waste is finally added; in order to obtain uniform and consistent composition, the temperature control during melting is 730-755℃, and mechanical stirring + electromagnetic stirring combined treatment is used during melting. Specifically, the melting temperature is 740-755℃.

[0033] After obtaining the aluminum alloy melt, in step S2, the aluminum alloy melt is refined, degassed online, and filtered online; in the process of refining, granular refining agent is used for powder spraying refining in the melting furnace, and argon-chlorine mixed gas is used for refining in the holding furnace, the refining time is ≥30min, and the amount of the granular refining agent is ≤0.25ml / 100gAl; specifically, the refining time is 30-40min, and the amount of the granular refining agent is 0.20-0.25ml / 100gAl; the granular refining agent is well known to those skilled in the art and includes KCl and MgCl2; the standing time of the melt after refining is 50-60min to make the removed slag fully float or precipitate; the hydrogen content of the melt after refining is ≤0.25ml / 100gAl, and specifically, the hydrogen content of the melt after refining is 0.20-0.23ml / 100gAl; high-efficiency rotary degassing device is used for online degassing, and the hydrogen content of the melt after online degassing is ≤0.12ml / 100gAl, and specifically, the hydrogen content of the melt after online degassing is 0.10-0.11ml / 100gAl. In order to obtain very good filtering effect, plate filter is used for online filtering, and the filtering plate precision of the online filtering is not less than 50ppi, and specifically, the online filtering uses 30ppi+50ppi double-stage filtering mode.

[0034] The application then carries out grain refinement on the obtained aluminum alloy melt; the grain size of the ingot grain gradually increases from the surface to the core, and for the super-thick specification ingot, the core temperature is high and the cooling speed is slow, which provides a convenient condition for the growth of the grain and the primary crystalline compound, in order to obtain a cast structure with fine and uniform grains, and at the same time, the primary crystalline compound is refined; the application not only meets the grain refinement requirement, but also avoids the harm caused by excessive refiner, the application uses AlTi5B1 refiner on line, the amount is 1.5~2.5kg / t, specifically, the amount of the refiner is 1.6~2.3kg / t, more specifically, the amount of the refiner is 1.8~2.0kg / t.

[0035] After the grain refinement, the obtained aluminum alloy melt is cast in step S4; in order to obtain a cast ingot with excellent performance, a faster casting speed is generally adopted, which can make the grain and structure of the cast ingot small and the density of the cast ingot high, but too high speed for an ultra-thick specification cast ingot can cause the cooling gradient of the cast ingot to increase sharply, resulting in an increase in tensile deformation and an increase in the tendency of hot cracking; with the increase of the cooling intensity, the size of the primary crystalline compound can be refined and the regional segregation can be reduced, and in the present application, the three water cooling is increased, which causes the original temperature field and stress field to change, the effective crystallization height (i.e. the direct distance from the contact point of the melt and the crystallizer wall to the cast ingot and the secondary direct water cooling) is lower, the cooling speed is faster, the solute elements cannot diffuse in time, the intracrystalline structure is small, and the surface of the cast ingot is smooth. The water cooling device of the conventional square cast ingot crystallizer is a water tank type, and the crystallization surface in direct contact with the aluminum liquid is generally aluminum or copper, the rapidly flowing water in the water tank carries away the heat of the aluminum liquid through the crystallization surface to form the primary water cooling of the cast ingot, and the primary water cooling mainly plays a role of forming a solid shell, generally accounting for 10-15% of the total cooling intensity; a row of water spray holes is distributed along the lower edge of the crystallizer, the center line of the water holes is at an angle of 45° with the axis of the cast ingot, and the water after the primary cooling is sprayed from the water spray holes to the surface of the cast ingot and flows down evenly along the surface of the cast ingot, thereby forming the secondary water cooling of the cast ingot, which is the main cooling source for the solidification of the cast ingot and accounts for more than 80% of the total cooling amount; the heat conduction of the cast ingot itself can also play a certain role in solidification, mainly in the starting casting stage, and under the steady state condition, this part of the role is very small. According to the design of the crystallizer of the prior art, the cooling water flow is mainly increased, when the flow increases to a certain extent, the sprayed water splashes, and the cooling becomes weaker, while the present application increases the primary water cooling along the lower edge of the crystallizer, i.e. the three water cooling, which can increase the intensity of the secondary water cooling by more than 50%, and at the same time, the three water cooling is adjustable, the position of the three water cooling can be adjusted according to the product demand, the best matching of the casting performance and the comprehensive performance of the product can be realized according to the height adjustment, and the individualized demand of the product can be realized. In summary, the aluminum alloy casting cooling is all relying on the rapidly flowing water in the water tank of the crystallizer to carry away the heat through the crystallizer wall to perform the primary water cooling, there is one row or two rows or even more rows of water holes along the lower edge of the crystallizer, and the water in the water tank is sprayed on the surface of the cast ingot at a certain angle from the water holes to perform the secondary water cooling; the three water cooling of the present application is to increase one water tank (as shown in Figure 1 ), only the water sprayed on the surface of the cast ingot from the water holes in the inner wall of the water tank performs the three water cooling; the primary water cooling and the secondary water cooling are the same water, only the ways of carrying away the heat are different; the three water cooling and the primary and secondary water cooling are the total water flow of the water tank.

[0036] Further, in order to obtain good cast ingot quality and comprehensive performance of the product, during the above casting process, the casting speed is 25-45 mm / min, the water flow is 60-120 m 3h. root, the temperature of the aluminum liquid at the end of the flow plate is 685~705℃, the water temperature is 20~30℃, the liquid level height of the crystallizer is 40~60mm; specifically, the casting speed is 28~42mm / min, the water flow is 75~110m 3 h. root, the temperature of the aluminum liquid at the end of the flow plate is 690~700℃, the water temperature is 21~27℃, the liquid level height of the crystallizer is 45~55mm; more specifically, the casting speed is 32~40mm / min, the water flow is 80~95m 3 h. root, the temperature of the aluminum liquid at the end of the flow plate is 695~700℃, the water temperature is 23~25℃, the liquid level height of the crystallizer is 50~55mm.

[0037] After the melt is cast, in order to eliminate the stress of the ingot, reduce the segregation of the ingot and obtain fine and dispersed compounds, the ingot needs to be subjected to high-temperature soaking treatment. This treatment can make the continuous network β (Al3Mg2) phase generated by unbalanced crystallization during casting melt, except for a small amount of insoluble AlFeMnSi phase, be melted and uniformly dissolved, and can further reduce the size of the compound. The soaking treatment of the present application has a heating rate of 50~90℃ / h, a heating time of 10~20h, a heating temperature of 500~550℃, a holding temperature of 480~510℃, and a holding time of 30~60h; specifically, the heating rate is 60~80℃ / h, the heating time is 11~18h, the heating temperature is 510~540℃, the holding temperature is 490~500℃, and the holding time is 40~50h.

[0038] Further, after the soaking treatment, the ingot is sawn to remove the unstable head and tail of 350mm, and the surface quenching layer is removed by 10~15mm, so that the thickness of the aluminum alloy square ingot is 900~1100mm, the width of the ingot is 1300~2000mm, the length of the ingot is ≥3500mm, and the weight of the ingot is more than 14 tons. As the size of the ingot increases, the composition segregation also increases significantly. For the ingot with a thickness of 900~1100mm, the elements are inversely segregated (i.e., the edge part is high, and the element content gradually decreases along the thickness direction, and the lowest part is the center of the ingot), especially the main element Mg. The larger the thickness of the ingot, the greater the Mg segregation. Since the aluminum alloy needs high strength and hardness, the hardness cannot meet the product requirements when the Mg content is too low. Increasing the element content can increase the hardness, but when the Mg content exceeds 5%, the stress corrosion resistance, weldability and stability of the aluminum alloy decrease. The matching of the composition of the ingot with the increase in the size of the ingot needs to meet the product strength and hardness while also having good corrosion resistance and weldability stability. Therefore, the composition of the aluminum alloy square ingot is designed.

[0039] The application further provides the aluminum alloy square ingot prepared by the preparation method.

[0040] In the aluminum alloy square ingot provided by the application, the components are controlled, Mg element is the main component of the 5xxx alloy, increasing the Mg content in the alloy can increase the tensile strength, especially the yield strength, but when the Mg content exceeds 5%, the stress corrosion resistance, welding and stability are reduced, the tendency of welding crack formation is increased, when the Mg content is higher or lower, the crack tendency is significantly reduced, and too low Mg content will cause the strength to not meet the material requirements due to segregation. Specifically, the content of Mg is 4.5-5.0%, specifically, the content of Mg is 4.62-4.86%, more specifically, the content of Mg is 4.70-4.85%, and more specifically, the content of Mg is 4.76-4.83%.

[0041] The addition of Mn and Cr in the Al-Mg alloy can improve the strength of the base material and the welding part, and can also improve the heat crack resistance (the crack tendency is the smallest when the content of Mn is 0.8%) and the stress corrosion resistance of the material during welding; when the content of Cr is too high, coarse Cr-containing compounds are prone to occur, which causes the product to not meet the A-level flaw detection requirements; Be can prevent the alloy from being oxidized during melting, processing and welding process heating, and can also prevent the alloy from being pulled apart during the casting process, so a certain amount of Be element is added in the alloy. The content of Mn is 0.50-1.0%, specifically, the content of Mn is 0.58-0.86%, more specifically, the content of Mn is 0.63-0.75%, more specifically, the content of Mn is 0.65-0.72%, and more specifically, the content of Mn is 0.68-0.70%. The content of Cr is 0.05-0.12%, specifically, the content of Cr is 0.06-0.11%, more specifically, the content of Cr is 0.08-0.10%. The content of Be is 0.0005-0.0020%, specifically, the content of Be is 0.008-0.0016%, more specifically, the content of Be is 0.0010-0.0014%.

[0042] Further, the application needs to reduce the content of Si, Fe, Cu and Zn elements; Si will reduce the mechanical properties of the alloy, especially the elongation, and the content is ≤0.06%, more specifically, the content of Si is 0.02-0.03%; Fe not only makes the mechanical properties worse, but also makes the corrosion resistance of the alloy worse, especially when Mn exists, which is more obvious, Fe ≤0.12%, specifically, the content of Fe is 0.03-0.08%, more specifically, the content of Fe is 0.05-0.07%; impurity Cu can reduce the corrosion resistance of 5xxx alloy, Cu ≤0.03%, specifically, the content of Cu is 0.01-0.02%; impurity Zn will affect the casting performance and welding performance of the material, Zn ≤0.05%, specifically, the content of Zn is 0.03-0.04%.

[0043] In order to further understand the application, the preparation method of the super-large aluminum alloy square ingot provided by the application will be described in detail below in combination with examples, and the protection scope of the application is not limited by the following examples.

[0044] Example 1

[0045] The aluminum alloy is prepared according to the following method, which includes the following steps: tooling design, composition design, raw material selection, melting process, melt purification, grain refinement, casting process, soaking process and ingot processing; specifically including the following steps:

[0046] Tooling design: a water cooling is added at the lower edge of the crystallizer, i.e. three times water cooling, three times water cooling is to add a water tank at the lower edge of the crystallizer, only the water holes in the inner wall of the water tank spray water onto the surface of the ingot, which is called three times water cooling; primary water cooling and secondary water cooling are the same water, only the ways of taking away heat are different; three times water cooling and primary and secondary water cooling are the total water flow of the water tank; three times water cooling can increase the intensity of secondary water cooling by more than 50%, at the same time, three times water cooling is adjustable, which can adjust the position of three times water cooling to realize the matching with the casting parameters according to the product process requirements;

[0047] Composition design: impurity elements are controlled by raw material selection, main elements Mn 0.70%, Mg 4.85%, Cr 0.10%, Ti 0.03%, Be 0.0020%;

[0048] Raw material selection: Al99.90 primary aluminum ingot, Mg99.90 primary magnesium ingot, aluminum-based Mn agent, rod-shaped AlTi intermediate alloy and AlBe intermediate alloy are used;

[0049] Al99.90 primary aluminum ingots, aluminum-based Mn flux, and rod-shaped AlTi master alloy were batched according to the above composition design and then smelted to obtain an aluminum alloy melt. During the smelting process, in order to obtain a pure melt with uniform chemical composition and temperature, a combination of electromagnetic stirring and mechanical stirring was used to treat the melt. The melt temperature during the smelting process was 755℃. To avoid Mg element burn-off, magnesium ingots were added when the melt temperature reached 740℃, along with AlBe master alloy and flux (KCl, MgCl2, and BaCl2). The chemical composition before the furnace was controlled within ±0.10% for Mg, ±0.03% for Mn, and ±0.01% for Cr. Before the melt was transferred to the holding furnace, the surface slag of the melt was removed, and the melt residence time after the composition adjustment was qualified did not exceed 1 hour.

[0050] The above-mentioned aluminum alloy melt was refined in the furnace using permeable bricks at the bottom of the furnace and powdered granular refining agent. The holding furnace was refined using a mixture of argon and chlorine gas. In order to prevent residual contamination of the flux during the refining process, no flux was used in the settling furnace. After refining for 40 minutes, the melt was settling for 50 minutes. The melt was filtered using a 30+50ppi foam ceramic filter plate.

[0051] The refined aluminum alloy melt was subjected to grain refinement. In order to obtain fine and uniform grains and primary crystal compounds, AlTi5B1 wire was used online for grain refinement at a dosage of 1.6 kg / t.

[0052] Cast the refined aluminum alloy melt;

[0053] Tooling selection during casting: Ingot size 1000x1000x4000mm;

[0054] To reduce segregation and obtain a uniform and fine microstructure, the casting process employed three stages of water cooling. The pre-cast melt temperature in the furnace was 750℃, the casting speed was 42 mm / min, the aluminum melt temperature at the end of the runner was 705℃, and the water flow rate was 75 m³ / min. 3 / h.root, water temperature 23℃, crystallizer liquid level height 55mm;

[0055] The cast ingots were subjected to homogenization heat treatment. In order to obtain fine dispersed phases and minimize residual phases, the cast aluminum alloy was homogenized and the heating rate was controlled. The heating rate of the homogenization annealing of the ingots was 50℃ / h, the heating time was 11h, the holding temperature was 500℃, and the holding time was 50h.

[0056] After homogenization and machining, the above-mentioned ingots, after forging and heat treatment, all met the quality requirements for high-quality transportation products in terms of performance and flaw detection. The test results are shown below:

[0057] (1) Ingot macrostructure: grain size 1 level; the detection method is GB / T3246.2 "Deformed aluminum and aluminum alloy products - Part 2: Macrostructure test method";

[0058] (2) Chemical composition: Si 0.03%, Fe 0.08%, Cu 0.01%, Mn 0.70%, Cr 0.10%, Mg 4.85%, Zn 0.05%, Ti 0.03%, Be 0.0020%, the balance is Al; the detection method is GB / T 20975 "Aluminum alloy analysis method" and GB / T 7999 "Aluminum and aluminum alloy optical direct-reading emission spectroscopic analysis method";

[0059] (3) Hydrogen content: 0.102 ml / 100g Al; the detection method is YS / T600 "Aluminum and aluminum alloy liquid state hydrogen detection method - Closed circuit method";

[0060] (4) Mechanical properties: tensile strength 286 MPa, yield strength 135 MPa, elongation 29.5%; the detection method is GB / T16865 "Deformed aluminum, magnesium and their alloy products - Tensile test sample and method";

[0061] (5) Hardness: 86 HV, the detection method is GB / T 4340 "Metallic materials - Vickers hardness test"

[0062] (6) Forging flaw detection: A level; the detection method is GB / T6519 "Deformed aluminum, magnesium alloy product ultrasonic test method".

[0063] Example 2

[0064] The aluminum alloy is prepared according to the following method, which includes the following steps: tooling design, composition design, raw material selection, melting process, melt purification, grain refinement, casting process, soaking process, and ingot processing; specifically including the following steps:

[0065] Tooling design: a water cooling is added at the lower edge of the crystallizer, i.e. three times water cooling, three times water cooling is to add a water tank at the lower edge of the crystallizer, only the water holes in the inner wall of the water tank spray water onto the surface of the ingot, which is called three times water cooling; primary water cooling and secondary water cooling are the same water, only the ways of taking away heat are different; three times water cooling and primary and secondary water cooling are the total water flow of the water tank; three times water cooling can increase the intensity of secondary water cooling by more than 50%, at the same time, three times water cooling is adjustable, which can adjust the position of three times water cooling to match the casting parameters according to the product process requirements;

[0066] Composition design: impurity elements are controlled by raw material selection, main elements Mn 0.72%,

[0067] Mg 4.83%, Cr 0.11%, Ti 0.03%, Be 0.0020%.

[0068] Raw material selection: Al99.90 ingot, Al99.90 primary magnesium ingot, aluminum-based Mn agent, rod-shaped AlTi intermediate alloy, AlBe intermediate alloy are used;

[0069] The Al99.90 ingot, Mg99.90 primary magnesium ingot, aluminum-based Mn agent, and rod-shaped AlTi intermediate alloy are weighed according to the above component design and then smelted to obtain an aluminum alloy melt. In the smelting process, in order to obtain a pure, uniform chemical composition and temperature melt, the melt is treated by a combination of electromagnetic stirring and mechanical stirring during the melting process, and the melt temperature is 755℃ during the smelting process. In order to avoid the burning loss of Mg element, the melt is heated to 740℃, and then Mg element, AlBe intermediate alloy and flux are synchronously added. The Mg control range is ±0.10%, the Mn control range is ±0.03%, and the Cr control range is ±0.01% before the melt is transferred into the holding furnace. The surface dross of the melt is removed before the melt is transferred into the holding furnace, and the melt stays for no more than 1h after the component adjustment is qualified.

[0070] The above aluminum alloy melt is refined in the furnace by using a bottom gas permeable brick and a granular refining agent. The holding furnace is refined by using argon-chlorine mixed gas. In order to prevent the residue of the flux from polluting the melt during the refining process, no flux is used in the static furnace. The melt is filtered by using a 30+50 ppi foam ceramic filter after being refined for 40min and being static for 50min.

[0071] The refined aluminum alloy melt is subjected to grain refinement. In order to obtain fine and uniform grains and primary crystalline compounds, AlTi5B1 wire is used for grain refinement on line, and the amount is 1.6kg / t.

[0072] The aluminum alloy melt after grain refinement is subjected to casting.

[0073] Tooling selection: the ingot size is 1000x1800x4300mm;

[0074] In order to reduce segregation and obtain uniform and fine structure, three times of water cooling is used in the casting. The melt temperature in the furnace before casting is 750℃, the casting speed is 40mm / min, the aluminum liquid temperature at the end of the flow plate is 705℃, the water flow is 95m 3 / h. root, and the water temperature is 21℃, and the crystallizer liquid level height is 60mm.

[0075] The cast ingot obtained by casting is subjected to soaking treatment. In order to obtain fine dispersed phase and reduce residual phase as much as possible, the cast aluminum alloy is subjected to staged soaking and the heating speed is controlled. The heating speed of the ingot homogenization annealing is 50℃ / h, the heating time is 11h, the holding temperature is 500℃, and the holding time is 50h.

[0076] The ingot is heated and then machined normally, and the performance and flaw detection after forging and heat treatment meet the quality requirements of high-quality transport products, and the test results are as follows:

[0077] (1) Ingot macrostructure: grain size 1 level; the detection method is GB / T3246.2 "Deformed aluminum and aluminum alloy products - Part 2: Macrostructure test method";

[0078] (2) Chemical composition: Si 0.03%, Fe 0.07%, Cu 0.01%, Mn 0.72%, Cr 0.11%, Mg 4.83%, Zn 0.05%, Ti 0.03%, Be 0.0020%, and the balance is Al; the detection method is GB / T 20975 "Aluminum alloy analysis method" and GB / T 7999 "Aluminum and aluminum alloy optical direct-reading emission spectroscopy analysis method";

[0079] (3) Hydrogen content: 0.110 ml / 100g Al; the detection method is YS / T600 "Aluminum and aluminum alloy liquid state hydrogen detection method - Closed circuit method";

[0080] (4) Mechanical properties: tensile strength 291 MPa, yield strength 138 MPa, elongation 30%; the detection method is GB / T16865 "Deformed aluminum, magnesium and their alloy products - Tensile test sample and method";

[0081] (5) Hardness: 80 HV, the detection method is GB / T 4340 "Metallic materials - Vickers hardness test";

[0082] (6) Forging flaw detection: A level; the detection method is GB / T6519 "Deformed aluminum and magnesium alloy products - Ultrasonic testing method".

[0083] Example 3

[0084] The aluminum alloy is prepared according to the following method, including the following steps: tool design, composition design, raw material selection, melting process, melt purification, grain refinement, casting process, soaking process, and ingot processing; specifically including the following steps:

[0085] Tool design: adding a water cooling at the lower edge of the crystallizer, i.e. three times water cooling, which is adding a water tank at the lower edge of the crystallizer, and only the water holes in the inner wall of the water tank spray water onto the surface of the ingot, which is called three times water cooling; primary water cooling and secondary water cooling are the same water, only the ways of taking away heat are different; three times water cooling and primary and secondary water cooling are the total water flow of the water tank; three times water cooling can increase the intensity of secondary water cooling by more than 50%, and at the same time, three times water cooling is adjustable, which can adjust the position of three times water cooling to match the casting parameters according to the product process requirements;

[0086] Component design: impurity elements are controlled by raw material selection, main element Mn 0.75%, Cr 0.11%, Ti 0.03%, Be 0.0020%;

[0087] Mg4.86%, Cr0.11%, Ti0.03%, Be0.0020%;

[0088] Raw material selection: Al99.90 primary aluminum ingot, Al99.90 primary magnesium ingot, aluminum-based Mn agent, rod-shaped AlTi intermediate alloy, AlBe intermediate alloy, 50% first-class scrap are used;

[0089] After the Al99.90 primary aluminum ingot, aluminum-based Mn agent, rod-shaped AlTi intermediate alloy and 50% first-class scrap are dosed according to the above component design, melting is carried out to obtain an aluminum alloy melt; the melting process: in order to obtain a pure, chemically uniform and temperature uniform melt, the melt needs to be treated by electromagnetic stirring + mechanical stirring during the melting process, the melt temperature is 755℃ during the melting process; in order to avoid Mg element burning loss, the magnesium ingot is added when the melt is heated to 740℃, the AlBe intermediate alloy and flux are synchronously added, the Mg control range is ±0.10%, the Mn control range is ±0.03%, the Cr control range is ±0.01% before the melt is transferred into the holding furnace, the surface dross of the melt is removed, and the melt stays for not more than 1h after the component adjustment is qualified;

[0090] The above aluminum alloy melt is refined in the furnace by using a bottom gas permeable brick and a granular refining agent, argon-chlorine mixed gas is used for refining in the holding furnace, in order to prevent the residue pollution of the flux during the refining process, any flux is not used in the static furnace, the melt is placed for 50min after being refined for 40min, and the melt is filtered by using a 30+50 ppi foam ceramic filter plate;

[0091] The refined aluminum alloy melt is subjected to grain refinement; in order to obtain fine and uniform grains and primary crystallization compounds, AlTi5B1 wire is used for grain refinement on line, and the amount is 1.6kg / t;

[0092] The aluminum alloy melt after grain refinement is subjected to casting;

[0093] In the casting process, the tooling selection is: the ingot specification is 1100x1300x4500mm;

[0094] In order to reduce segregation and obtain uniform and fine structure, three times of water cooling is used in casting, the melt temperature in the furnace before casting is 750℃, the casting speed is 40mm / min, the aluminum liquid temperature at the end of the flow disc is 705℃, the water flow is 95m 3 / h. root, the water temperature is 25℃, and the crystallizer liquid level height is 60mm;

[0095] The cast ingot is subjected to soaking treatment; in order to obtain fine dispersed phase and reduce residual phase as much as possible, the cast aluminum alloy is subjected to staged soaking and the heating speed is controlled, the heating speed of the ingot homogenization annealing is 50℃ / h, the heating time is 11h, the holding temperature is 500℃, and the holding time is 50h.

[0096] After the above ingot is subjected to soaking and then subjected to normal machining, the performance and flaw detection after the forging heat treatment meet the product quality requirements, and the test results are as follows:

[0097] (1) The grain size of the ingot is 1 level; the detection method is GB / T3246.2 "Deformed aluminum and aluminum alloy products - Part 2: Low magnification inspection method";

[0098] (2) The chemical composition is Si 0.03%, Fe 0.07%, Cu 0.01%, Mn 0.75%, Cr 0.11%, Mg 4.86%, Zn 0.05%, Ti 0.03%, Be 0.0020%, and the balance is Al; the detection method is GB / T 20975 "Aluminum alloy analysis method" and GB / T 7999 "Aluminum and aluminum alloy optical direct-reading emission spectroscopy analysis method";

[0099] (3) The hydrogen content is 0.105ml / 100gAl; the detection method is YS / T600 "Aluminum and aluminum alloy liquid state hydrogen measurement method - Closed circuit method";

[0100] (4) The mechanical properties are tensile strength 284MPa, yield strength 122MPa, and elongation 27.5%; the detection method is GB / T16865 "Deformed aluminum, magnesium and their alloy products - Tensile test sample and method";

[0101] (5) The hardness is 78HV, and the detection method is GB / T 4340 "Metallic materials - Vickers hardness test";

[0102] (6) The flaw detection of the forged piece meets the A level; the detection method is GB / T6519 "Deformed aluminum and magnesium alloy products - Ultrasonic testing method".

[0103] Comparative Example 1

[0104] The preparation method of the aluminum alloy is basically the same as that of Example 1, and the only difference is that the raw material ratio is adjusted according to the composition of the aluminum alloy, and a conventional crystallizer is used without using three times of water cooling.

[0105] After the above ingot is subjected to soaking and then subjected to normal machining, the performance and flaw detection after the forging heat treatment meet the product quality requirements, and the test results are as follows:

[0106] (1) Ingot macrostructure: grain size 1.5 grade; detection method is GB / T3246.2 "Deformed aluminum and aluminum alloy products - Part 2: Macrostructure testing method";

[0107] (2) Chemical composition: Si 0.03%, Fe 0.09%, Cu 0.01%, Mn 0.71%, Cr 0.10%, Mg 4.88%, Zn 0.05%, Ti 0.03%, Be 0.0020%, the balance is Al; detection method is GB / T 20975 "Aluminum alloy analysis method" and GB / T 7999 "Aluminum and aluminum alloy optical direct-reading emission spectroscopy analysis method";

[0108] (3) Hydrogen content: 0.106 ml / 100g Al; detection method is YS / T600 "Aluminum and aluminum alloy liquid state hydrogen detection method closed circuit method";

[0109] (4) Mechanical properties: tensile strength 273 MPa, yield strength 125 MPa, elongation 29%; detection method is GB / T16865 "Deformed aluminum, magnesium and their alloy products Tensile test sample and method";

[0110] (5) Hardness: 62 HV; detection method is GB / T 4340 "Metallic materials Vickers hardness test"

[0111] (6) Forging flaw detection: A level; detection method is GB / T6519 "Deformed aluminum, magnesium alloy product ultrasonic testing method".

[0112] Comparative Example 2

[0113] The preparation method of the aluminum alloy ingot is basically the same as that of Example 2, and the difference is only that the composition design is adjusted: main elements Mn 0.72%, Mg 4.36%, Cr 0.11%, Ti 0.03%, Be 0.0020%.

[0114] The above ingots are heated and then machined normally, and after forging heat treatment, the flaw detection meets the requirements, but the performance and hardness do not meet the product quality requirements, and the detection results are as follows:

[0115] Quality detection:

[0116] (1) Ingot macrostructure: grain size 1 grade; detection method is GB / T3246.2 "Deformed aluminum and aluminum alloy products - Part 2: Macrostructure testing method";

[0117] (2) Chemical composition: Si 0.03%, Fe 0.07%, Cu 0.01%, Mn 0.72%, Cr 0.11%, Mg 4.36%, Zn 0.05%, Ti 0.03%, Be 0.0020%, balance Al; the detection method is GB / T 20975 "Aluminum Alloy Analysis Method" and GB / T 7999 "Aluminum and Aluminum Alloy Photoelectric Direct-reading Emission Spectrometric Analysis Method";

[0118] (3) Hydrogen content: 0.110 ml / 100g Al; the detection method is YS / T600 "Aluminum and Aluminum Alloy Liquid State Hydrogen Detection Method Closed Circuit Method";

[0119] (4) Mechanical properties: tensile strength 244 MPa, yield strength 105 MPa, elongation 19%; the detection method is GB / T16865 "Sample and Method for Tensile Test of Deformed Aluminum, Magnesium and Their Alloy Products";

[0120] (5) Hardness: 57 HV, the detection method is GB / T 4340 "Metallic Materials Vickers Hardness Test";

[0121] (6) Forging piece flaw detection: A level; the detection method is GB / T6519 "Ultrasonic Testing Method for Deformed Aluminum and Magnesium Alloy Products".

[0122] Comparative Example 3

[0123] The preparation method of the aluminum alloy ingot is basically the same as that of Example 3, and the only difference is that the melt temperature in the furnace before casting is 750°C, the casting speed is 48 mm / min, the aluminum liquid temperature at the end of the flow disc is 705°C, the water flow is 95 m 3 / h. root, the water temperature is 25°C, and the crystallizer liquid level height is 60 mm;

[0124] The above ingots are normal after heating and machining, and the performance meets the requirements after forging and heat treatment, but the surplus is small, and the hardness does not meet the product quality requirements. The detection results are as follows:

[0125] (1) Ingot macrostructure: grain size 1 level; the detection method is GB / T3246.2 "Deformed Aluminum and Aluminum Alloy Products Organization Test Method-Part 2 Macrostructure Test Method";

[0126] (2) Chemical composition: Si 0.03%, Fe 0.07%, Cu 0.01%, Mn 0.74%, Cr 0.11%, Mg 4.81%, Zn 0.05%, Ti 0.03%, Be 0.0020%, balance Al; the detection method is GB / T 20975 "Aluminum Alloy Analysis Method" and GB / T 7999 "Aluminum and Aluminum Alloy Photoelectric Direct-reading Emission Spectrometric Analysis Method".

[0127] (3) Hydrogen content: 0.113 ml / 100g Al; the detection method is YS / T600 "Aluminum and Aluminum Alloy Liquid Hydrogen Measurement Method Closed Circuit Method";

[0128] (4) Mechanical property: tensile strength 260 MPa, yield strength 116 MPa, elongation 29.5%; the detection method is GB / T16865 "Aluminum, Magnesium and Their Alloys Machined Products Tensile Test Sample and Method";

[0129] (5) Hardness: 64 HV; the detection method is GB / T 4340 "Metallic Materials Vickers Hardness Test";

[0130] (6) Forging piece flaw detection: A level; the detection method is GB / T6519 "Aluminum, Magnesium Alloy Product Ultrasonic Inspection Method".

[0131] The above description of the embodiments is only used to help understand the method of the present application and its core idea. It should be noted that for those skilled in the art, some improvements and modifications can be made to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

[0132] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an ultra-large aluminum alloy square ingot, comprising the following steps: S1) After batching the materials according to the composition ratio of the aluminum alloy square ingot, the materials are smelted to obtain the aluminum alloy melt; The composition of the aluminum alloy melt, by mass percentage, includes: Si≤0.06%, Fe≤0.12%, Cu≤0.03%, Mn0.50~1.0%, Mg4.5~5.0%, Cr0.05~0.12%, Zn≤0.03%, Ti0.02~0.05%, Be0.0005~0.0020%, individual impurities≤0.03%, and the balance being Al; S2) The aluminum alloy melt is refined, degassed online, and filtered online; S3) Refine the grain size of the aluminum alloy melt obtained in step S2); S4) Cast the aluminum alloy ingot obtained in step S3); the water cooling of the casting includes primary water cooling, secondary water cooling and tertiary water cooling. S5) The ingot obtained in step S4) is subjected to homogenization heat treatment to obtain an aluminum alloy square ingot.

2. The preparation method according to claim 1, characterized in that, In step S1), the melting temperature is 730~755℃, and / or, the melting process employs a combination of mechanical stirring and electromagnetic stirring.

3. The preparation method according to claim 1, characterized in that, In step S2), during the refining process, granular refining agent is sprayed into the smelting furnace for refining, and argon-chlorine mixed gas is used for refining in the holding furnace. The refining time is ≥30 min, and the amount of granular refining agent used is ≤0.25 ml / 100 g Al; and / or, the settling time of the melt after refining is ≥45 min; and / or, the online degassing uses a high-efficiency rotary degassing device; and / or, the filter plate of the online filter has a filter accuracy of not less than 50 ppi.

4. The preparation method according to claim 3, characterized in that, In step S2), the hydrogen content of the refined melt is ≤0.25ml / 100gAl, and the hydrogen content of the online degassing melt is ≤0.12ml / 100gAl.

5. The preparation method according to claim 4, characterized in that, In step S3), the grain refiner used is AlTi5B1, and the dosage is 1.5~2.5 kg / t.

6. The preparation method according to claim 1, characterized in that, In step S4), the casting speed is 25~45 mm / min; and / or, the temperature of the molten aluminum at the end of the flow plate is 685~705℃; and / or, the liquid level height in the crystallizer is 40~60 mm.

7. The preparation method according to claim 6, characterized in that, In step S4), the water flow rate for casting is 60~120m³. 3 / h.root, water temperature is 20~30℃.

8. The preparation method according to claim 7, characterized in that, In step S4), the device for the three-stage water cooling is a water tank located at the lower edge of the crystallizer, and the inner wall of the water tank is provided with holes.

9. The preparation method according to claim 8, characterized in that, In step S5), the heating rate of the homogenization heat treatment is 50~90℃ / h, the heating time is 10~20h, the heating temperature is 500~550℃, the holding temperature is 480~510℃, and the holding time is 30~60h; and / or, the thickness of the aluminum alloy square ingot is 900~1100mm, the ingot width is 1300~2000mm, the ingot length is ≥3500mm, and the weight exceeds 14 tons.

10. The aluminum alloy square ingot prepared by the preparation method according to any one of claims 1 to 9, comprising, by mass percentage: Si≤0.06%, Fe≤0.12%, Cu≤0.03%, Mn0.50~1.0%, Mg4.5~5.0%, Cr0.05~0.12%, Zn≤0.05%, Ti0.02~0.05%, Be0.0005~0.0020%, single impurity≤0.03%, balance Al.

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