阅读说明：本技术 一种大规格空心铸锭及铸锭方法 (Large-size hollow ingot casting and ingot casting method ) 是由 王鹏 李永卉 王明坤 韩正乾 吴茂来 刘博� 赵吉峰 冯骥 张新峰 孔令均 周庆 于 2020-09-25 设计创作，主要内容包括：本发明属于铝合金技术领域,具体涉及一种大规格空心铸锭及铸锭方法。所述大规格空心铸锭,以质量百分比计,其化学成分为：Si≤0.4%,Fe≤0.4%,Cu≤0.1%,Mn0.7-1.1%,Mg5.5-6.5%,Cr≤0.1%,Ni≤0.04%,Zn≤0.2%,Ti≤0.15%,Be0.001-0.005%,Zr0.05-0.15%,Na≤10ppm,Ca≤10ppm,余量为Al和不可避免的杂质元素,Fe＞Si且m%(Fe-Si)=0.06-0.1%；所述铸造方法包括配料、熔炼净化、铸造和均质处理,通过研究加料结构、熔炼温度、精炼介质、精炼气体以及操作方式,确定最优的熔体净化工艺；通过选择最优铸造温度、铸造速度克服开裂倾向缺陷；通过两级均质处理工艺确保组织均匀,促进变形的均匀性,抑制再结晶,提高合金的最终性能；增加电磁线圈实现铸造工装改造升级,提供外场辅助,大规格铸棒易于铸造成型。(The invention belongs to the technical field of aluminum alloy, and particularly relates to a large-size hollow ingot and an ingot casting method. The large-size hollow ingot comprises the following chemical components in percentage by mass: si is less than or equal to 0.4 percent, Fe is less than or equal to 0.4 percent, Cu is less than or equal to 0.1 percent, Mn0.7-1.1 percent, Mg5.5-6.5 percent, Cr is less than or equal to 0.1 percent, Ni is less than or equal to 0.04 percent, Zn is less than or equal to 0.2 percent, Ti is less than or equal to 0.15 percent, Be0.001-0.005 percent, Zr0.05-0.15 percent, Na is less than or equal to 10ppm, Ca is less than or equal to 10ppm, and the balance is Al and inevitable impurity elements, Fe is more than Si and m% (Fe-Si) = 0; the casting method comprises the steps of material preparation, smelting purification, casting and homogenizing treatment, and an optimal melt purification process is determined by researching a charging structure, a smelting temperature, a refining medium, a refining gas and an operation mode; the defect of cracking tendency is overcome by selecting the optimal casting temperature and casting speed; the two-stage homogenization treatment process ensures the uniformity of the structure, promotes the uniformity of deformation, inhibits recrystallization and improves the final performance of the alloy; the electromagnetic coil is added to improve the casting tool, so that the outfield auxiliary is provided, and the large-specification casting rod is easy to cast and form.)

1. The large-size hollow ingot is characterized by comprising the following chemical components in percentage by mass: less than or equal to 0.4 percent of Si, less than or equal to 0.4 percent of Fe, less than or equal to 0.1 percent of Cu, 0.7-1.1 percent of Mn, 5.5-6.5 percent of Mg, less than or equal to 0.1 percent of Cr, less than or equal to 0.04 percent of Ni, less than or equal to 0.2 percent of Zn, less than or equal to 0.15 percent of Ti, 0.001-0.005 percent of Be, 0.05-0.15 percent of Zr0.05, less than or equal to 10ppm of Na, less than or equal to 10ppm of Ca, and the balance of Al and inevitable impurity elements, wherein Fe is more than Si and m.

2. The large-size hollow ingot according to claim 1, wherein the large-size hollow ingot comprises the following chemical components in percentage by mass: less than or equal to 0.15 percent of Si, less than or equal to 0.25 percent of Fe, less than or equal to 0.05 percent of Cu, 0.8-1.0 percent of Mn, 6.1-6.4 percent of Mg, less than or equal to 0.04 percent of Cr, less than or equal to 0.04 percent of Ni, less than or equal to 0.1 percent of Zn, 0.03-0.05 percent of Ti, 0.001-0.003 percent of Be, 0.06-0.11 percent of Zr0.06, less than or equal to 10ppm of Na, less than or equal to 10ppm of Ca, and the balance of Al and inevitable impurity elements, wherein Fe is more than Si and m% (Fe-Si.

3. The large-size hollow ingot casting method disclosed by any one of claims 1-2, which is characterized by comprising the steps of batching, smelting purification, casting and homogenizing treatment, and comprises the following specific steps:

(1) preparing materials;

(2) smelting purification

(a) Feeding structure: adopting a self-feeding solid mode to feed materials, and charging the materials in sequence: 99.85 percent of high-purity aluminum ingot → first-level waste, when charging, the hearth temperature of the smelting furnace is 600-;

(b) the Na content is effectively controlled to be less than 10ppm and the fusion casting time is controlled as follows: except that Na-free flux is used, high-temperature smelting at the temperature of 700 ℃ and 750 ℃ is adopted; the smelting time is shortened to 4-6h, a sodium-free covering agent pyrotek sodium-free C2 is scattered after furnace burden collapses, the sodium-free covering agent is uniformly scattered to cover the furnace burden completely, and the temperature of the alloy melt is measured after the furnace burden is completely melted;

(c) improving the purity of the melt: b, introducing the alloy melt obtained in the step b into a heat preservation furnace, adding a refining agent into the heat preservation furnace, wherein the dosage of the refining agent is 1.5-2kg/tAl, and spraying 10-15kg of Na-free covering agent to completely cover after refining; the smelting time is 4-6h, and the standing time from the completion of slag removal after refining to the time before casting is 1-1.5 h; degassing in a holding furnace, blowing air for 30-35min from bottom to top through a furnace bottom air brick, and degassing again through a degassing box in the subsequent on-line treatment process to ensure that the content of hydrogen detected on line is less than 0.15ml/100 gAl; the last on-line treatment procedure is to filter and purify the melt by using a 40-60ppi high-quality foamed ceramic filter plate through an on-line filter box;

(3) casting

According to the characteristics of the alloy, secondary cooling in the casting process is increased, and a high-quality grain refiner inlet AMG5Ti1B is selected for refining grains, wherein the casting speed is 14-20 mm/min, and the cooling water flow is 40-60m³The cooling water temperature is 20-30 ℃, and the speed of feeding the grain refiner wire rod is controlled at 20-30 cm/min;

(4) homogenizing treatment

Carrying out a two-stage homogenization treatment mode on the alloy ingot obtained in the step (3): 350 plus or minus 5 ℃ multiplied by 8h +465 ℃ multiplied by 24 h; then naturally cooling to room temperature.

4. The method of claim 3, wherein the feeding of step (a) is performed by charging small pieces or thin pieces of primary scrap, and then adding the stub or other large pieces of primary scrap, according to the primary scrap form.

5. A large format hollow ingot casting method as claimed in claim 3 wherein the primary scrap material in step (a) comprises no more than 40% of the metalliferous feed material.

6. The method for casting the large-size hollow ingot as claimed in claim 3, wherein the temperature of the melt is measured once at an interval of 1-1.5 hours after the furnace charge is completely melted in the step (b), so as to ensure that the temperature of the melt is within 700-750 ℃, and the temperature is strictly kept from being over-heated; after the furnace burden is completely melted, the process time of adjusting components, refining, slagging off, adjusting the temperature of the converter and the like is controlled within 3-5 h.

7. The method of casting a large-format hollow ingot as claimed in claim 3, wherein during the online degassing of step (d), the hydrogen content is monitored online at < 0.15mol/100 gAl.

8. The large-size hollow ingot casting method according to claim 3, wherein the hot-top tool in the step (3) is additionally provided with an electromagnetic coil (2), and the electromagnetic coil (2) is positioned in water-cooling annular cavities of the upper water plate (1) and the lower water plate (3) of the cooling water device.

9. The large-size hollow ingot casting method according to claim 3, wherein the two-stage homogenization treatment in the step (4) is specifically as follows: furnace gas is fed into the furnace at 200 ℃, a step temperature rise control program is used, the step temperature rise time is 5 hours, the furnace gas is heated to 350 +/-5 ℃, the temperature is kept for 8 hours, the secondary temperature rise is 1.5 hours, the furnace gas is heated to 465 +/-5 ℃, and the temperature is kept for 24 hours.

Technical Field

The invention belongs to the technical field of aluminum alloy, and particularly relates to a large-size hollow ingot and an ingot casting method.

Background

The rapid development of the industries such as aerospace, nuclear power, automobiles, national defense war industry, high-speed rail, rail transit and the like increases the demand for high-performance aluminum alloy seamless aluminum tubes year by year. The preparation of the large-size hollow cast ingot is a precondition for preparing a high-end large-size high-performance aluminum alloy section. However, the external diameter of the large-size hollow ingot is (Inner diameter) The casting is difficult, the defects of tensile cracking, layering, cold shut, compounds, segregation tumors and the like are often generated in the casting process, so that the geometric waste is excessive, and the whole furnace ingot cannot be scrapped due to the fact that some defects cannot be processed through mechanical processing. As the size of the ingot increases, several control difficulties arise: due to the difference between the cooling speed and the diffusion speed of alloy elements, the uniformity of chemical components of each part of the cast ingot is reduced; due to the large diameter of the ingot and the limitation of the cooling speed, under the condition of a certain addition amount of the grain refiner, uniform and fine grain structure is difficult to realize.

Disclosure of Invention

The invention provides a large-size hollow ingot and an ingot casting method, aiming at solving the technical problems of eccentricity, cracks, uneven components and the like of the large-size hollow ingot in the prior art.

The invention is realized by the following technical scheme:

a large-size hollow ingot comprises the following chemical components in percentage by mass: less than or equal to 0.4 percent of Si, less than or equal to 0.4 percent of Fe, less than or equal to 0.1 percent of Cu, 0.7-1.1 percent of Mn, 5.5-6.5 percent of Mg5, less than or equal to 0.1 percent of Cr, less than or equal to 0.04 percent of Ni, less than or equal to 0.2 percent of Zn, less than or equal to 0.15 percent of Ti, 0.001-0.005 percent of Be, 0.05-0.15 percent of Zr0, less than or equal to 10ppm of Na, less than or equal to 10ppm of Ca, and the balance of Al and inevitable impurity elements, wherein Fe is more than Si and m% (.

Further, the chemical components are as follows by mass percent: less than or equal to 0.15 percent of Si, less than or equal to 0.25 percent of Fe, less than or equal to 0.05 percent of Cu, 0.8-1.0 percent of Mn, 6.1-6.4 percent of Mg6.1-6.4 percent of Cr, less than or equal to 0.04 percent of Ni, less than or equal to 0.1 percent of Zn, 0.03-0.05 percent of Ti, 0.001-0.003 percent of Be, 0.06-0.11 percent of Zr0.06, less than or equal to 10ppm of Na, less than or equal to 10ppm of Ca, and the balance of Al and inevitable impurity elements, wherein Fe is more than Si and m% (Fe-Si) is.

The action of the main alloying elements in the present invention is based on the following principle:

si and Fe are harmful impurities in Al-Mg alloy, and the contents of Si and Fe are strictly controlled. Form Mg with Mg₂Si phase, in the case of excess Mg, reduces Mg₂The solubility of the Si phase in the matrix is low, so that the strengthening effect of Si is not great, and the plasticity and the corrosion resistance of the alloy are reduced. Fe forms an insoluble intermetallic compound with Cr in the alloy, so that a hard and brittle compound appears in an ingot structure, and the processing is not facilitated. In addition, Fe can form an anode phase with Al in the alloy, so that the corrosion resistance of the alloy is reduced, and the annual corrosion depth is almost linearly increased along with the increase of Fe content. At the same time, the Fe & gt Si is controlled, which is beneficial to reducing the cracking tendency of the ingot. If Fe is added to be more than Si0.06-0.1%, the generation of beta phase AlFeSi phase is reduced, so that the cracking tendency is greatly reduced.

The addition of Mn element is favorable for improving the corrosion resistance of the alloy and the strength of the alloy. Addition of small amounts of Ti and Zr suppresses recrystallization and refines recrystallized grains. The intermetallic compound primary crystal and the unmelted high melting point pure metal crystal have high melting point and high hardness, are mostly distributed in the alloy material in a blocky, flaky or needle-shaped manner and are unevenly distributed in the alloy material, so that the plasticity of the alloy is reduced, the alloy is easy to crack during processing, the processing performance, the fatigue limit, the fracture toughness and the corrosion resistance of the material are reduced, and the surface quality is coarse. In the application, 0.03-0.05% of Ti and 0.06-0.11% of Zr are added, so that the columnar crystal structure of the cast ingot is reduced, the forging performance of the alloy is improved, and the crystal grains of the product are refined.

The high magnesium alloy enters H in the melt due to the existence of Mg (Mg6.0-6.5)₂O is more liable to react with Mg at high temperature to generate H, and because H cannot react with Al and Mg, part of H is combined into H₂Molecules, forming bubbles; the other part of H is dissolved in the aluminum melt. The solubility of H in the aluminum melt is very high, the solubility is sharply reduced along with the temperature reduction in the crystallization process, and the solubilities of H in liquid aluminum and solid aluminum are respectively 0.65cm³/(100gAl) and 0.10 to 0.034cm³/(100 gAl). Thus, H is formed from H precipitated from the melt during crystallization₂Possibly in the form of bubbles, from the surface of the crystallized pockets. However, under the crystallization conditions of semi-continuous casting, H can be released from the surface of the liquid cavity₂Rarely, the majority is wrapped in the melt in a viscous plastic state, and casting defects such as porosity and porosity are formed in the subsequent casting. The subsequent melt purification treatment needs degassing, but from the chemical composition, a small amount of Be (Be0.001-0.005) can Be added to form a melt protective film, and an oxide film on the surface of the melt is not damaged in the casting process, so that the hydrogen absorption is greatly reduced.

The high magnesium alloy enters H in the melt due to the existence of Mg (Mg6.0-6.5)₂O is more liable to react with Mg at high temperature to generate H, and because H cannot react with Al and Mg, part of H is combined into H₂Molecules, forming bubbles; the other part of H is dissolved in the aluminum melt. The solubility of H in the aluminum melt is very high, the solubility is sharply reduced along with the temperature reduction in the crystallization process, and the solubilities of H in liquid aluminum and solid aluminum are respectively 0.65cm³/(100gAl) and 0.10 to 0.034cm³/(100 gAl). Thus, H is formed from H precipitated from the melt during crystallization₂Possibly in the form of bubbles, from the surface of the crystallized pockets. However, under the crystallization conditions of semi-continuous casting, H can be released from the surface of the liquid cavity₂Rarely, the majority is wrapped in the melt in a viscous plastic state, and casting defects such as porosity and porosity are formed in the subsequent casting. Subsequent melt purification treatment requires degassingHowever, a small amount of Be (Be0.001-0.005) can Be added to the alloy to form a melt protective film, and hydrogen absorption can Be greatly reduced without damaging an oxide film on the melt surface during casting.

Controlling the content of alkali metal to be less than or equal to 10ppm of Na and less than or equal to 10ppm of Ca; the trace impurity Na increases the viscosity of the aluminum alloy melt, the casting tension crack tendency is increased, and when the Na content is higher, the spherical particles at the grain boundary of the aluminum-magnesium alloy casting structure are more and more dense, and the volume fraction of the second phase is increased. Na can strongly damage the thermal deformation performance of the alloy, and sodium brittleness is generated, and is particularly prominent in high-magnesium aluminum alloy. The trace element Na causes brittle fracture of the aluminum-magnesium alloy. Sodium brittleness is caused by the concentration of free Na, which is insoluble in aluminum, at the grain boundaries, due to the low melting point.

The invention also aims to provide a method for casting the large-size hollow ingot, which comprises the steps of material preparation, smelting purification, casting and homogenizing treatment, and comprises the following specific steps:

(1) ingredients

The formula of the large-size hollow cast ingot based on the burdening is as follows: according to weight percentage, Si is less than or equal to 0.15 percent, Fe is less than or equal to 0.25 percent, Cu is less than or equal to 0.05 percent, Mn0.8-1.0 percent, Mg6.1-6.4 percent, Cr is less than or equal to 0.04 percent, Ni is less than or equal to 0.04 percent, Zn is less than or equal to 0.1 percent, Ti0.03-0.05 percent, Be0.001-0.003 percent, Zr0.06-0.11 percent, Na is less than or equal to 10ppm, Ca is less than or equal to 10ppm, the balance is Al and inevitable impurity elements, Fe is more than Si, and m% (Fe-Si) is 0.06-0.1 percent;

(2) smelting purification

(a) Feeding structure: adopting a self-feeding solid mode to feed materials, and charging the materials in sequence: 99.85 percent of high-purity aluminum ingot → first-level waste, when charging, the hearth temperature of the smelting furnace is 600-;

(b) the Na content is effectively controlled to be less than 10ppm and the fusion casting time is controlled as follows: except that Na-free flux is used, high-temperature smelting at the temperature of 700 ℃ and 750 ℃ is adopted; the smelting time is shortened to 4-6h, a sodium-free covering agent pyrotek sodium-free C2 is scattered after furnace burden collapses, the sodium-free covering agent is uniformly scattered to cover the furnace burden completely, and the temperature of the alloy melt is measured after the furnace burden is completely melted;

(c) improving the purity of the melt: b, introducing the alloy melt obtained in the step b into a heat preservation furnace, adding a refining agent into the heat preservation furnace, wherein the dosage of the refining agent is 1.5-2kg/tAl, and spraying 10-15kg of Na-free covering agent to completely cover after refining; the smelting time is 4-6h, and the standing time from the completion of slag removal after refining to the time before casting is 1-1.5 h; degassing in a holding furnace, replacing nitrogen with high-purity argon, blowing the furnace bottom air brick for 30-35min from bottom to top, diffusing free hydrogen into bubbles of inert gas, and taking out aluminum liquid along with the rising of the bubbles of the inert gas to achieve the purpose of degassing; in the process of rising the high-purity inert gas, the fine impurities adsorbed on the surface can be taken out of the aluminum liquid, so that the aim of removing slag is fulfilled, only very fine particles can be adsorbed and removed, and the impurities of larger particles still need to be removed in a filtering manner; in the subsequent on-line treatment process, degassing is carried out again through a degassing box, and the content of hydrogen detected on line is ensured to be less than 0.15ml/100gAl so as to reduce the loosening tendency; the last on-line treatment procedure is to filter and purify the melt by using a 40-60ppi high-quality foamed ceramic filter plate through an on-line filter box;

(3) casting

According to the characteristics of the alloy, secondary cooling in the casting process is increased, and a high-quality grain refiner inlet AMG5Ti1B is selected for refining grains, wherein the casting speed is 14-20 mm/min, and the cooling water flow is 40-60m³The cooling water temperature is 20-30 ℃, and the speed of feeding the grain refiner wire rod is controlled at 20-30 cm/min; the stability of parameters such as speed, water quantity, lubricating oil flow and the like in the process of oil-slip casting of the large-size cast rod is ensured;

(4) homogenizing treatment

Carrying out a two-stage homogenization treatment mode on the alloy ingot obtained in the step (3): the temperature of furnace gas in the furnace is ensured to be more than 200 ℃ by multiplying the temperature by 350 +/-5 ℃ for 8h and 465 ℃ for 24 h; the first-stage heating time is 300min, and the number of heating stages is 75; the temperature rise time of the second stage is 60min, and the homogenizing temperature is the temperature of furnace gas; then naturally cooling to room temperature.

Wherein the content of the first and second substances,

according to the form of the primary waste in the step (a), the small or thin primary waste is firstly filled in the feeding process, and then the rod head or other large primary waste is added.

The primary scrap material in step (a) comprises no more than 40% of the metal feedstock. The high power structure of the added Al-Mn and Al-Ti-B intermediate alloy is uniform, fine, slag-free, pore-free and defect-free; in addition, coarse compounds in the sometimes used master alloys do not melt or melt incompletely and remain as the melt enters the ingot. When the recycled materials or the casting process is improper, the high-melting-point alloy elements are locally enriched when the cast ingot is solidified, and are preferentially solidified and nucleated to form coarse compound primary crystals. Because the proportion of the first-grade waste material used while the first-grade waste material is repeatedly used is higher, the heat preservation time of the melt is too long, the coarse compounds containing Mn and Ti grow up, and the fine oxide particles of Al and Mg are adsorbed around the coarse compounds to form coarse oxide slag inclusion, so that a crack source is formed, and finally, the ingot casting is cracked. Ensuring the cleanness of raw materials, a smelting holding furnace, a launder and tools for smelting the alloy.

After the furnace charge is completely melted in the step (b), measuring the temperature of the melt once at an interval of 1-1.5 hours to ensure that the temperature of the melt is within 700-750 ℃, and strictly prohibiting overtemperature; after the furnace burden is completely melted, the process time of adjusting components, refining, slagging off, adjusting the temperature of a converter and the like is controlled within 3-5h, because the melting temperature is high, particularly under the liquid state condition, the residence time of the melt is too long, the air suction quantity of the melt is increased, the oxidation burning loss is increased, the non-spontaneous crystal nucleus is reduced, and the tendency of forming cracks, coarse crystals and feather-like crystals of the cast ingot is increased.

In the smelting and purifying process in the step (c), the operation of feeding or diluting is not carried out in the heat preservation furnace, so that the probability of generation of impurities and coarse compounds can be effectively reduced.

And (d) in the online degassing process in the step (d), monitoring the hydrogen content to be less than 0.15mol/100gAl online so as to reduce the loosening tendency.

And (3) additionally arranging electromagnetic coils in the hot top tool, wherein the electromagnetic coils are positioned in water cooling annular cavities of the water tray upper plate and the water tray lower plate of the cooling water device. The hot-top casting is a continuous casting method in which a storage tank (i.e., a hot top) made of refractory heat-insulating material is installed above a short mold, and the melt in the storage tank is maintained at least at the same level as the melt in a distribution flow plate without using a conventional float funnel. The hot top part is used for keeping the temperature of the melt, keeping a liquid column at the upper part of the cast ingot all the time, keeping a certain static pressure of the molten aluminum and simultaneously reducing the solidification position of the melt in the crystallizer. The height of the cooling part is very small, usually only 15-40mm, and the cooling part has the function of making the effective crystallization area of the ingot forming hot top crystallizer very small, effectively preventing the secondary remelting of the solidified shell, thereby inhibiting the generation of segregation tumors on the inner and outer surfaces. On the premise of hot top casting, an electromagnetic coil is newly added, an electromagnetic field generated by alternating current (the current intensity is 8-15A, and the frequency is 10-20Hz) in an induction coil is used as an external field for assistance in the electromagnetic casting process, a good electromagnetic stirring casting effect is obtained, the same horizontal current supply is realized, the temperature field is balanced, the cooling speed of the cast ingot is improved, the intragranular structure of the cast ingot is thinner, and the problems of difficult crack forming and coarse grains of the large-size cast ingot can be realized by matching with an online refining process.

The two-stage homogenization treatment in the step (4) comprises the following specific steps: furnace gas is charged at 200 ℃, a step temperature rise control program is used, the step temperature rise time is 5 hours, the furnace gas is heated to 350 +/-5 ℃, the temperature is kept for 8 hours, and ZrAl is enabled to be in a low-temperature stage₃The particles are uniformly pre-nucleated in a high-concentration area in the crystal and do not grow up too fast, so that the particles are dispersed and fine; simultaneously dissolving part of eutectic phase with low melting point; heating for 1.5h in the second stage to 465 +/-5 ℃, preserving heat for 24h, and reducing adverse effects of high-melting-point impurity phase transformation and diffusion, thereby improving the comprehensive performance of the material; and then naturally cooling to room temperature to obtain the large-size hollow cast ingot subjected to homogenization treatment. The influence of overburning is generally considered in the homogenization treatment process, if the content of the alloy elements is high, the corresponding low-melting-point phase cannot be diffused into the substrate in time in the homogenization heating process, and the overheating or overburning phenomenon can occur, so that the product is invalid and even scrapped. Al in the whole process under a homogenization system of 465 ℃ for 24h₃Mg₂The phase and the AlMgSi phase are both greatly reduced, and the Al has low melting point₃Mg₂Relatively high melting point Al₈(FeMn)₂The dissolution speed of the Si phase and the AlMgSi phase is high; when 24 is turned onAfter h homogenization, Al can be seen₃Mg₂The phase is substantially completely redissolved in the matrix, leaving only a small amount of particulate Al₃Mg₂Phase, AlMgSi phase, also gets better re-dissolution. And (3) final verification result: the cast ingot has the best homogenization degree and has no overburning. The dendritic network at the edge of the ingot is discontinuous, most of the continuous dendritic network structure at the central part and the radius of 1/2 are dissolved and are in a thin line shape, and a beta phase (Mg) is precipitated from the matrix₅Al₆) Open and small particles of the equal phase.

The beneficial effect of the invention is that,

(1) the large-size hollow ingot provided by the invention determines the optimal melt purification process by optimizing components and a smelting casting process and researching a charging structure, a smelting temperature, a refining medium, a refining gas and an operation mode; the defect of cracking tendency is overcome by selecting the optimal casting temperature and casting speed; the two-stage homogenization treatment process ensures the uniform structure, can reduce the extrusion resistance, improve the extrusion speed, promote the deformation uniformity, inhibit recrystallization and improve the final performance of the alloy; the electromagnetic coil is added to realize the transformation and upgrading of the casting tool, the outfield assistance is provided, and the large-size casting rod is easy to cast and form;

(2) the method provided by the invention effectively solves the problems of eccentricity, cracks and uneven components of the large-size hollow ingot, and the microstructure picture shows that the large-size hollow ingot obtained by the method is not easy to crack and have subcutaneous cracks, has the least unmelted phase and impurity phase and the least crystal grain and meets the requirement of the large-size ingot structure.

Drawings

FIG. 1 is a comparison of the microstructures of example 1, comparative example 1 and comparative example 3, wherein the microstructures of example 1, comparative example 1 and comparative example 3 are shown from left to right;

FIG. 2 is a comparison of the scanning electron micrographs of example 1, comparative example 1 and comparative example 3, wherein the scanning electron micrographs of example 1, comparative example 1 and comparative example 3 are taken from left to right;

FIG. 3 is a schematic structural view of a hot top tool in the American Almex casting production line provided by the invention;

in the figure, 1, a water tray is provided with an upper plate; 2. an electromagnetic coil; 3. a lower plate of the water tray.

Detailed Description

The invention is further described below with reference to specific examples so that a person skilled in the art may better understand the invention, but without thereby restricting the invention.

Example 1

A method for casting a large-size hollow ingot comprises the steps of batching, smelting and purifying, casting and homogenizing, and specifically comprises the following steps:

(1) ingredients

The formula of the large-size hollow cast ingot based on the burdening is as follows: according to weight percentage, Si is less than or equal to 0.2 percent, Fe is less than or equal to 0.3 percent, Cu is less than or equal to 0.1 percent, Mn0.5-1.2 percent, Mg6.0-6.5 percent, Cr is less than or equal to 0.1 percent, Ni is less than or equal to 0.05 percent, Zn is less than or equal to 0.1 percent, Ti is less than or equal to 0.15 percent, Be0.001-0.005 percent, Zr0.05-0.15 percent, Na is less than or equal to 10ppm, Ca is less than or equal to 10ppm, and the balance is Al; proportioning according to the formula components of the large-size hollow ingot, wherein the specific chemical components are shown in table 1, and respectively weighing a high-purity aluminum ingot, a primary waste material, an aluminum-titanium intermediate alloy, an aluminum-manganese intermediate alloy, an aluminum-beryllium intermediate alloy, an aluminum-zirconium intermediate alloy and magnesium metal as raw materials;

(2) smelting purification

a. Feeding structure: and (3) charging sequence: 99.85% aluminum ingot → first grade waste, confirming the furnace charge is clean and dry before feeding, no mixing material, and weighing; when charging, the temperature of the hearth is at 600-; sequentially charging the primary waste, the high-purity aluminum ingot and 90% of intermediate alloy (the estimated amount of the intermediate alloy is 90%, the excessive elements are prevented from being diluted, the production efficiency is greatly influenced and the proportion of other elements) in sequence, and adding the AlTi alloy and the Mg before sampling and stirring in a smelting furnace; in the embodiment, 99.85 percent of low-Fe aluminum ingots are adopted, the impurity content and the alkali metal content are controlled, and the proportion of waste materials is strictly controlled to be less than or equal to 40 percent; the specific feeding structure design is shown in table 2;

b. the Na content is effectively controlled to be less than 10ppm and the fusion casting time is controlled to be as follows: except that Na-free flux is used, high-temperature smelting at the temperature of 700 ℃ and 750 ℃ is adopted; smelting time is 4.5h, after furnace burden collapses, the furnace burden is imported with sodium-free C2 covering agent and evenly scattered into the furnace burden without sodium covering agent to completely cover, after the furnace burden is completely melted, temperature measurement is carried out on the melt temperature once every 1 hour, the melt temperature is ensured to be within the required range of 720 and 750 ℃, and overtemperature is strictly forbidden; after the furnace burden is completely melted, the process time of adjusting components, refining, slagging off, adjusting the temperature of a converter and the like is controlled to be 4.1h, the high melting temperature is avoided, particularly under the liquid state condition, the retention time of a melt is too long, the non-spontaneous crystal nucleus is reduced, and the tendency of generating cracks, coarse crystals and feather-like crystals of the cast ingot is increased;

c. improving the purity of the melt: on the premise of completely cleaning the furnace, a refining agent is scattered into the furnace before charging and guiding the furnace, and the dosage of the refining agent is 1.5-2 kg/tAl; 10-15kg of imported pyrotek sodium-free C2 covering agent is scattered into the mixture after refining to completely cover the mixture; the standing time from the completion of slag skimming to the time before casting after refining is 1.2 h; degassing in a holding furnace, replacing nitrogen with high-purity argon, blowing the furnace bottom air brick for 35min from bottom to top, diffusing free hydrogen into bubbles of inert gas, and taking out aluminum liquid along with the rising of the bubbles of the inert gas to achieve the purpose of degassing; in the process of rising the high-purity inert gas, the fine impurities adsorbed on the surface can be taken out of the aluminum liquid, so that the aim of removing slag is fulfilled, only very fine particles can be adsorbed and removed, and the impurities of larger particles still need to be removed in a filtering manner; in the subsequent on-line treatment process, degassing is carried out again through a degassing box, and the content of hydrogen detected on line is ensured to be less than 0.15ml/100gAl so as to reduce the loosening tendency; the last on-line treatment procedure is to filter the melt by using a 40-60ppi high-quality foamed ceramic filter plate through an on-line filter box;

(3) casting

According to the characteristics of the alloy, secondary cooling in the casting process is increased, and a high-quality grain refiner (imported AMG company 5Ti1B) is selected for grain refinement, wherein the casting speed is as follows: 14mm/min-20mm/min, cooling water flow: 40-60m³Cooling water at 20-30 deg.c for grain refiningThe speed of the agent line rod is controlled to be 20cm/min-30 cm/min;

the relevant fusion casting process configuration is shown in table 3;

(4) homogenizing treatment

The two-stage homogenization treatment specifically comprises the following steps: furnace gas is charged at 200 ℃, a step temperature rise control program is used, the step temperature rise time is 5 hours, the furnace gas is heated to 350 +/-5 ℃, the temperature is kept for 8 hours, and ZrAl is enabled to be in a low-temperature stage₃The particles are uniformly pre-nucleated in a high-concentration area in the crystal and do not grow up too fast, so that the particles are dispersed and fine; simultaneously dissolving part of eutectic phase with low melting point; the secondary heating is carried out for 1.5h, the temperature is raised to 465 +/-5 ℃, the heat is preserved for 24h, the transformation and the diffusion of the high-melting-point impurity phase are carried out, the adverse effect is reduced, the extrusion resistance can be reduced, the extrusion speed is improved, the deformation uniformity can be promoted, the recrystallization is inhibited, and the final performance of the alloy is improved.

The relevant homogenization parameters are shown in Table 4.

Comparative example 1: 2030106 melt-processing 1561 alloy cast bars with a specification of phi 816/phi 325, and is shown in tables 1-4.

Comparative example 2: 2030107 smelting 1561 alloy cast rod with phi 816/phi 325 specification, and is shown in tables 1-4

Comparative example 3: 2030108 melt-processing 1561 alloy cast bars with a specification of phi 816/phi 325, and is shown in tables 1-4.

Table 1 example 1 and comparative examples 1-4 ingredient design

TABLE 2 feeding structure design

TABLE 3 fusion casting Process configuration

TABLE 4 homogeneous treatment process design

Test examples

The above example 1 and comparative examples 1 to 3 were subjected to the performance test, and the specific results are shown in Table 5.

TABLE 5 results of Performance test of example 1 and comparative examples 1 to 3

As can be seen from Table 5, the comparative example 2 has no modification and upgrade of casting tools, the electromagnetic coil is added to realize the external field assistance, and the large-size casting rod is difficult to cast and form. By combining the 3 groups of microstructure analysis diagrams of the example 1, the comparative example 2 and the comparative example 4, the eutectic phase, the impurity phase and the crystal grain of the example 1 are the minimum, and the requirement of large-size cast ingot structure is met.