阅读说明：本技术 铝锂合金复合锭的铸造方法 (Casting method of aluminum-lithium alloy composite ingot ) 是由 王俊升 于 2019-10-14 设计创作，主要内容包括：本发明涉及铸造含锂铝合金的方法,通过半连续铸造锂所占比重大于0.25％的含锂合金复合锭和锂所占比重小于0.25％或者更少不含锂的合金复合锭,达到隔离易挥发性铝锂合金与氧气和水接触的效果,实现安全可靠铸造环境,并为后续低成本的挤压或者轧制创造条件。本发明采用氩气有效地隔离铝锂合金与空气的接触,使用不含锂的铝合金作为外壳,提供了铸造铝锂合金复合锭的一种新方法。(The invention relates to a method for casting lithium-containing aluminum alloy, which achieves the effect of isolating volatile aluminum-lithium alloy from contacting oxygen and water by semi-continuously casting a lithium-containing alloy composite ingot with lithium accounting for more than 0.25 percent of the proportion and an alloy composite ingot with lithium accounting for less than 0.25 percent of the proportion or less without lithium, realizes a safe and reliable casting environment, and creates conditions for subsequent low-cost extrusion or rolling. The invention adopts argon to effectively isolate the contact between the aluminum lithium alloy and air, and uses the aluminum alloy without lithium as a shell, thereby providing a new method for casting the aluminum lithium alloy composite ingot.)

1. The process flow design and the equipment structure design for casting the aluminum alloy round ingot or flat ingot containing lithium elements are as follows:

the aluminum-lithium alloy composite ingot comprises an aluminum alloy without lithium on the outer layer and an ingot with an inner core for strictly controlling the components of the aluminum-lithium alloy, wherein the aluminum alloy without lithium on the outer layer presents a beaker structure and is metallurgically combined with the aluminum alloy with lithium on the inner core, and the aluminum-lithium alloy on the inner core is completely isolated from external cooling water and air and does not have oxidation.

2. The composite ingot of claim 1, wherein the dummy head forms a strong and sealed beaker structure with the first solidified lithium-free aluminum alloy, completely isolating the aluminum-lithium alloy from the external environment.

3. The composite ingot according to claim 1, wherein the aluminum lithium alloy is solidified under the argon protective atmosphere, heat is taken away through a beaker-shaped outer wall formed by the aluminum alloy without lithium, a solid-liquid two-phase region with controllable thickness exists at a bonding interface of the two alloys in the solidification process, and the two alloys form an adjacent layer which is tightly bonded with the two alloys along with the chilling of external cooling water.

4. The composite ingot according to claim 1, wherein the lithium-free aluminum alloy is based on an aluminum-copper-magnesium alloy, and the lithium-containing aluminum alloy is based on an aluminum-copper-magnesium-lithium alloy.

5. The composite ingot according to claim 1, wherein the composite round ingot can be processed into fatigue-resistant and corrosion-resistant aircraft and rocket load-bearing structural member products after extrusion, hot and cold rolling of the slab ingot, and heat treatment.

6. The composite ingot according to claim 1, wherein the composite ingot is processed and peeled to produce a round rod or a flat ingot product of aluminum-lithium alloy having no internal oxidation defects and excellent surface quality.

Technical Field

The invention is suitable for the fusion casting production of lithium-containing aluminum alloy, the product form is a composite cast ingot (round or flat), the product can be used as a raw material in the processing processes of extrusion, rolling, forging and the like, and the final application can be used as a part material in the fields of aerospace and the like.

Background

The aluminum-lithium alloy has complex casting process, but has the effects of replacing the conventional aluminum alloy, reducing weight by about 15 percent and improving rigidity by about 15 percent due to low density, high specific strength and specific stiffness, excellent low-temperature mechanical property, higher high-temperature strength and the like, better fatigue resistance and certain superplasticity forming property, so that the performance improvement and economic benefit brought to the design of aerospace aircrafts are very obvious, and the aluminum-lithium alloy is more and more widely applied as a high-end new material. For example, in the design of an airplane, an aluminum-lithium alloy plate can be used as a skin and a wall plate, an extruded section can be used as parts such as a stringer, a reinforcing rib and a floor beam, and the traditional aluminum alloy is replaced to reduce the weight and improve the performance of the airplane. In the design of the rocket, the aluminum-lithium alloy can be used as a fuel tank and a liquid oxygen tank, the excellent forming performance is convenient for manufacturing a common-bottom storage tank, the effective load can be increased, the height of the rocket can be reduced, and the overall performance of the rocket can be improved.

Due to the chemical activity of lithium, lithium must be produced by melting and casting under a protective atmosphere, usually with inert gas or vacuum, in order to prevent oxidation and explosion accidents. If the traditional casting mode is adopted, oxidation is easily generated in the casting process, and an oxidation layer is formed on the surface, so that the cooling efficiency is reduced, and the condition of leakage is easy to occur. Weeping refers to a phenomenon similar to the spilling of liquid from a candle wick to the outer surface. If a leakage accident occurs, the high-temperature aluminum-lithium alloy liquid can be directly contacted with water, the capability of generating hydrogen is more than 10 times of that of the common aluminum alloy, and the explosion accident can be rapidly caused. In addition, the casting speed, the lubrication degree, the size of the cast ingot, the casting temperature, the radial distribution of the liquid metal, the quality and the temperature of cooling water, the level of the liquid level, power failure accidents, the change of the cooling water pressure and the like can cause the occurrence of leakage accidents. Therefore, many patents have invented cooling fluids without water to improve heat transfer stability and reduce explosion hazards. Meanwhile, a plurality of invention patents propose new lubricants for reducing the friction coefficient of the contact surface of the aluminum lithium alloy and the crystallizer and reducing the occurrence of leakage accidents. In addition, many documents report that the thickness of an oxide layer can be reduced, the surface quality can be improved and the occurrence of a leakage accident can be avoided by adding toxic bismuth (Bi) elements. However, bismuth (Bi) is a great harm to human body, and its use is strictly controlled, and is not generally used in the nonferrous metal industry.

Therefore, the invention mainly solves the problem of realizing safe and reliable semi-continuous casting of the aluminum-lithium alloy composite ingot by the process flow design and the equipment structure design of the cylindrical or flat composite ingot. For example, the 2099 aluminum lithium alloy is coated by the 2039 aluminum copper alloy, so that the 2099 aluminum lithium alloy is prevented from being directly contacted with water, the phenomenon of leakage is effectively inhibited, a 2039/2099 composite ingot is cast, the surface of the 2039/2099 composite ingot is coated with 1000 series aluminum alloy to prevent corrosion, and the improvement of the overall performance is realized through subsequent processing. When the conventional aluminum lithium alloy is completely exposed to an environment containing oxygen and moisture, a special lubricant and a reversible rolling mill with a heating function are required in the hot rolling process, and the environment atmosphere needs to be controlled in the heat treatment process. However, special protection measures are not needed in the processing process of the composite ingot with the aluminum-lithium alloy coated inside, so that the cost is greatly reduced. In addition, because the casting process adopts the outer beaker-shaped shell which is firstly solidified, then the aluminum lithium alloy solution is injected under the protective atmosphere of argon, and the outer part of the shell adopts multi-stage cooling water chilling, the hot cracking tendency of the aluminum lithium alloy is effectively reduced, and the casting yield is improved.

In order to solve the safety and reliability of aluminum-lithium alloy casting, U.S. Kaiser aluminum patent 4567936 in 1986 describes a method of casting a lithium-containing aluminum alloy composite ingot by casting a lithium-free aluminum alloy as an outer layer and a lithium-containing aluminum alloy as an inner layer. Wherein the higher solidus outer layer is first solidified into a beaker structure and then the lower solidus inner core aluminum lithium alloy is cast. The patent emphasizes that the lower solidus temperature aluminum lithium alloy must have a fully solidified, strong outer shell as the outer layer prior to casting. The invention has the defects that an argon protection and sealing device in the inner core casting process is not considered, and in addition, the liquid level of the aluminum-lithium alloy in the inner part is basically equal to that of the alloy on the outer wall, so that the solid-liquid mixing area is necessarily overlarge, and the situations of casing burning and liquid leakage are easy to occur.

In 1952 german patent 844806 invented a mold for casting a layered structure, the inner core was cast earlier than the outer wall and the outer layer alloy was cast after complete solidification. Us patent 3353934 issued in 1967 discloses a casting system wherein internal compartments are provided in the mould cavity to substantially separate regions of different alloy composition. The end of the baffle is referred to as a "mushy zone" that can stop at the solidification portion where the alloy is free to mix under the end of the baffle to form a bond between the layers. However, the alloy composition cast by this method is not controllable, so the so-called baffle is only a flow-blocking baffle, and the alloy composition in the true solid-liquid two-phase region is not controlled. German patent DE4420697 in 1995 invented a casting system, again using internal baffles, allowing the two phases of solid and liquid of the bottom layer to mix, thereby forming a continuous concentration gradient at the interface. In uk patent GB1174764 of 1965, movable partitions were provided to separate common casting troughs, allowing casting of different metals, but the problem of intermixing of the two alloys was still not solved. Us patent WO2003/035305 in 2003 discloses a casting system using barrier material in the form of thin sheets between two different alloy layers. The thin sheet has a melting point higher than the initial temperature of the two alloys so that it can completely separate the two alloys to obtain a composite structure. However, this method is costly and difficult to implement. Us 4828015 in 1989 discloses a single model method of casting two liquid alloys by supplying two zones through a compartment formed in the liquid zone by a magnetic field, the alloy supplied to the upper part of the zone solidifying around the alloy supplied to the lower part, thereby forming a composite structure. Us 391196 discloses an outer flexible wall structure to adjust the ingot mold, the 5947184 patent invented a composite ingot that allows for numerous shape controls, the 4498521 patent invented a metal level control system that uses a float on the metal surface to control the metal level for feedback, the 5526870 patent automatically controls the level using a remote radar to detect the metal level, and the 6260602 patent invented an ingot shape with a variable tapered wall.

In recent two years, with the mass use of third-generation aluminum lithium alloys by air passenger car companies and SpaceX companies, many aluminum alloy companies build new aluminum lithium alloy casting production lines to meet the market demand for the new material. The mature third generation aluminum lithium alloy has wide brand, and the invention of the casting process of the composite ingot not only avoids the occurrence of leakage and explosion accidents, reduces the risk, but also can improve the product quality.

It is therefore an object of the present invention to produce safely, reliably and consistently composite ingots of lithium-free aluminum alloy as an outer layer around a lithium-containing aluminum alloy, round or flat ingot, with metallurgical bonding between the two alloys.

Another object of the present invention is to provide a process for casting a composite ingot, which provides a metallurgical method for injecting molten metal into an inner layer and an outer layer from different positions of an inflow groove, and solidifying the molten metal in sequence to form a cladding structure.

It is another object of the present invention to provide a control method and apparatus structure for isolating two alloys, argon-shielded casting, from oxidation of the aluminum lithium alloy.

The invention also aims to provide a radar monitoring method for liquid level control, an equipment structure for automatically adjusting the metal liquid level at high temperature and a control method.

Another object of the present invention is to provide a casting method for preventing a leak accident, and a control method for preventing contact between an aluminum lithium alloy melt and water at a high temperature.

Disclosure of Invention

The invention aims to provide a set of whole casting process flow and a control method of aluminum alloy round ingots and flat ingots containing lithium elements, which effectively control the cooling of high-temperature liquid metal and solidify the high-temperature liquid metal into ingots for rolling or extrusion. The method comprises the following steps:

1. the feed port is divided into an inner part and an outer part, the inner part and the outer part are completely isolated, the feed port comes from the lithium-free aluminum alloy feed chamber and the lithium-containing aluminum alloy feed chamber respectively, the flow and the temperature are adjusted through the automatic control system, and the incoming material supply is carried out according to a process system.

2. And a discharge port adopts a hydraulic support, and a flat ingot or a round ingot after solidification is drawn out of the crystallizer from top to bottom to form an upright composite ingot.

3. The outer cooling system of composite ingot consists of crystallizer and multiple chilling system, and includes one set of crystallizer commonly used in 2000 and 7000 series aluminum alloy and multiple chilling spraying water cooling system providing secondary, tertiary, quaternary and other multistage convective heat exchange except heat conduction of crystallizer.

4. The inner layer of the composite ingot is provided with an independent cooling system, the composite ingot is of a beaker cover type structure processed by pure aluminum or pure copper, a graphite shell is attached to the outer part of the composite ingot, and the inner part of the composite ingot is cooled by circulating water to keep the temperature of the inner wall not higher than 100 ℃.

5. Argon gas passes through the beaker cover type internal cooling tank, after cooling, the argon gas is blown to the inner wall of the outer layer alloy to provide a secondary cooling effect, and the cooling protective atmosphere is recycled to the beaker cover through the internal cavity.

6. In the process implementation of the invention, firstly, the lithium-free liquid metal raw material is injected into the outer layer, and the beaker-shaped shell is formed through the purging and cooling of the base, the external water-cooled crystallizer and the internal cover type crystallizer and the argon.

7. In the process implementation of the invention, the solidified shell is pulled out of the crystallizer from top to bottom by adopting the hydraulic prop, and the secondary, tertiary, quaternary and other multi-stage cooling of the cooling water injection is carried out to form the firm self-supporting shell.

8. In the process implementation of the invention, after the shell formed by the alloy without lithium reaches a certain height and strength, the liquid metal containing lithium is injected from the center, and is guided to the edge through the distribution groove and is contacted with the inner wall of the shell, so that the heat is released, and the solidification is realized from the edge to the center.

9. In the process implementation of the invention, the injection amount of the two raw materials is matched with the drawing speed of the hydraulic prop, and the stable liquid level position is realized through an infrared or radar liquid level control system.

10. In the process implementation of the invention, metallurgical bonding exists between two metal interfaces, certain inner wall remelting exists because the lithium-containing liquid metal heats the inner wall of the solid shell, but the heat carrying rate of the spray chilling of the cooling water received by the outer wall is far greater than the heating rate of the inner wall, so that the occurrence of burning-through and liquid leakage can be controlled sufficiently.

11. In the process implementation of the invention, the solidus line of the lithium-containing aluminum alloy is lower than the solidus line of the shell without the lithium-aluminum alloy, the liquidus line of the lithium-aluminum alloy is higher than the liquidus image of the lithium-aluminum alloy, and the temperature of the shell without the lithium-aluminum alloy is always controlled below the solidus line of the lithium-aluminum alloy.

12. In the process implementation of the invention, the lithium-free aluminum alloy shell has a self-supporting beaker-shaped structure in strength and does not have defects such as cracks and the like.

13. In a preferred embodiment, the lithium-free aluminum alloy housing is cast with more than 2 feed ports to ensure stable liquid level and uniform temperature.

14. In a preferred scheme, the argon blowing pressure formed by the internal cooling device is close to the atmospheric pressure, and the argon is blown to the cylindrical inner wall and is higher than the liquid level of the lithium-containing aluminum alloy in the cylinder.

15. The sectional shape of the composite ingot can be circular or rectangular, the principle is applicable, and the composite ingot is characterized in that the aluminum alloy without lithium on the outer wall forms a self-supporting beaker-shaped structure, a closed piston structure of graphite and pure aluminum is adopted in the beaker-shaped structure, the structure is provided with a circulating water cooling device to keep constant temperature, the piston structure begins to rise along with the complete solidification of the newly formed aluminum alloy wall and has self-supporting capacity, argon is injected from the position of the top of the piston close to the inner wall, the argon fills the whole inner cavity, and the aluminum lithium alloy is isolated from the atmosphere by the argon.

16. The lithium-containing liquid aluminum alloy is injected only after the height of the beaker reaches a set value, generally the radius of a round ingot or the thickness of a flat ingot is more than that of the round ingot, the liquid aluminum alloy is conveyed to the inner walls of the peripheral shell from a central nozzle through a guide pipe under the atmosphere of argon protection, the liquid aluminum-lithium alloy is solidified under the condition of heat conduction and cooling, the liquid level of the aluminum-lithium alloy is maintained at the set value, a dummy ingot head starts to descend under the traction of a hydraulic device, the conveying guide pipe starts to incline along with the gravity, and finally a conical structure is formed and is located.

17. After the casting is finished, the supply of liquid aluminum-lithium alloy is stopped firstly, then the supply of aluminum alloy liquid without lithium outside is stopped, then the hydraulic system is stopped from descending, argon gas is purged continuously, and cooling water is sprayed until the composite ingot is completely solidified.

Drawings

FIG. 1 is a schematic view of a fusion casting process of an aluminum-lithium alloy composite plate according to the present invention.

Detailed Description

The invention is described in detail below with reference to the drawings and specific examples, but the invention is not limited thereto.