Large-melting-amount melt preparation method capable of reducing oxidation air suction of aluminum-lithium alloy

Abstract

The invention discloses a large-melting-amount melt preparation method capable of reducing aluminum-lithium alloy oxidation air suction. A small amount of rare earth elements are introduced into the aluminum lithium alloy to form a compact, continuous and ultrathin rare earth oxide film layer on the surface of a melt, and the compactness of the film layer and the wettability of the film layer and the melt are regulated and controlled by multi-element compounding of heavy rare earth elements and light rare earth elements and an alloying adding mode, so that the high-temperature resistance of the aluminum lithium alloy is improved. The contact between the aluminum-lithium alloy melt and air is effectively isolated, and the oxidation suction of the high-activity aluminum-lithium alloy melt is reduced; and meanwhile, the internal stress of the rare earth oxide film layer is reduced, and film layer cracking is avoided. The method is environmentally friendly, high in operability, low in cost and very suitable for engineering preparation of the aluminum-lithium alloy melt with the large smelting amount, and further application of the aluminum-lithium alloy in the fields of aerospace, national defense military industry, underwater domain and the like is facilitated.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aluminum alloy, and relates to a preparation method of an aluminum-lithium alloy melt, in particular to a large-melt-quantity melt preparation method for reducing oxidation and air absorption of an aluminum-lithium alloy. BACKGROUND

[0002] Compared with existing high-strength aluminum alloy series such as 2xxx series and 7xxx series, the aluminum-lithium alloy has lower density and higher specific strength and specific stiffness. Research shows that, when 1wt% of lithium is added to the aluminum alloy, the density of the aluminum alloy is reduced by about 3%, and the stiffness is increased by about 6%. Therefore, the aluminum-lithium alloy has broad application prospects in aircrafts, carrier rockets, space vehicles, underwater weapons and the like.

[0003] The preparation of the aluminum-lithium alloy cannot be implemented without the process links of melting and casting. However, lithium has very active chemical properties, and the aluminum-lithium alloy melt is extremely easy to be oxidized and air absorbed during the preparation process. Relevant research shows that the air absorption amount of the aluminum-lithium alloy melt at high temperature is tens to hundreds of times that of conventional aluminum alloys, which leads to a significant increase in the number of pores in the alloy after solidification. Meanwhile, the aluminum-lithium alloy melt is also extremely easy to be oxidized and combusted, and a large amount of oxidation inclusions formed thereby can seriously reduce the purity of the alloy. Therefore, how to effectively protect the aluminum-lithium alloy melt has been one of the key problems in the preparation and forming of the aluminum-lithium alloy material.

[0004] In order to overcome the above problems, academia and industry have conducted in-depth research, and at present there are three kinds of aluminum lithium alloy melt protection methods, namely vacuum melting, inert gas protection and covering agent protection. In the aspect of vacuum melting, patent ZL202011482102.3 (device and method for deep purification of aluminum lithium alloy melt) discloses an aluminum lithium alloy melt purification method, which uses vacuum melting to reduce the oxidation and air absorption of the aluminum lithium alloy melt, but the method has poor engineering applicability in the preparation of large melt. In the aspect of inert gas protection, patent ZL201110459806.3 (an online hydrogen removal device for aluminum lithium alloy melt) discloses an aluminum lithium alloy melt treatment method under the protection of inert gas (mainly Ar gas), that is, the inert gas is continuously introduced into the alloy melt surface under sealed conditions to isolate air, but the method has large gas consumption, high sealing requirement for equipment, easy air entrapment and high use cost. In the aspect of covering agent (mainly composed of a mixture of fluorine salt and chlorine salt) protection, patent ZL201811620924 (an aluminum lithium alloy melt covering agent and a preparation method thereof) discloses a formula and a preparation method of an aluminum lithium alloy covering agent, which isolates air by sprinkling covering agent on the surface of the aluminum lithium alloy melt. The method has good protection effect, strong operability and good economic applicability. However, the method has two shortcomings: first, because the aluminum lithium alloy melt mostly needs to be refined by argon gas rotary spraying, the covering agent on the surface of the melt is easily entrapped into the melt during refining to form secondary molten salt inclusions; second, under the hindering effect of the covering agent on the surface of the melt, hydrogen bubbles separated from the melt during refining are difficult to escape from the surface of the melt, which reduces the refining effect of the melt.

[0005] In summary, in view of the problem that the aluminum lithium alloy melt is easy to oxidize and absorb air during preparation, a new aluminum lithium alloy melt preparation method must be developed. The method at least needs to have the following three characteristics: first, it can effectively hinder the contact between the melt and air and reduce the oxidation and air absorption of the melt; second, it can avoid the formation of secondary molten salt inclusions in the melt and cannot affect the refining effect of the melt; third, it needs to have good economic applicability and engineering applicability. Through the application of the method, the purpose of effectively reducing the oxidation and air absorption of the aluminum lithium alloy during melt preparation is achieved, the preparation quality of the aluminum lithium alloy melt is improved, and the service performance of the aluminum lithium alloy product is improved, which has important significance for promoting the application of aluminum lithium alloy in key fields such as aerospace, national defense and military industry. SUMMARY

[0006] In view of the above shortcomings of the prior art, the present application provides a large melt preparation method for reducing the oxidation and air absorption of aluminum lithium alloy, which not only effectively avoids the secondary molten salt inclusions from being entrapped into the melt during refining, but also has little effect on the escape of hydrogen bubbles in the melt, and has good operability and economic applicability for engineering treatment of large melt.

[0007] In order to achieve the above technical effects, the present application proposes a brand new aluminum lithium alloy melt processing and protection method, which is essentially different from the existing inert gas protection and covering agent protection. The existing inert gas protection and covering agent protection mainly use inert gas or covering agent to isolate the melt from the air, thereby reducing the melt oxidation and gas absorption. However, inert gas protection requires a large amount of gas flow, is expensive, and has a protection effect that is not as good as covering agent. When using covering agent protection, the covering agent is easily sucked into the melt during the subsequent rotary inert gas blowing refining process, and the secondary molten salt inclusions formed will have a fatal impact on the mechanical properties and corrosion resistance of the alloy, so the above technologies have certain limitations. The present application innovatively uses multi-element composite rare earth micro-alloying, and a continuous and dense ultra-thin composite rare earth oxide film layer is formed on the surface of the melt by the reaction of rare earth elements with air before the addition of lithium. The physical isolation effect of this composite rare earth oxide film layer avoids the oxidation and gas absorption of the melt. At the same time, during the subsequent rotary inert gas blowing refining process, this ultra-thin composite rare earth oxide film layer will continuously form on the surface of the melt and then be broken and dispersed, and the granular rare earth oxides formed will be dispersed in the melt and effectively improve the mechanical properties of the aluminum lithium alloy as reinforcing phase particles. After the rotary inert gas blowing refining is completed, covering agent is added to the surface of the melt, so that the melt is effectively protected, and the problem of covering agent being sucked into the melt due to melt refining is avoided, and the granular rare earth oxides formed in the melt also have a certain strengthening effect.

[0008] The object of the present application can be achieved by the following scheme:

[0009] In a first aspect, the present application provides a large-melt-volume melt preparation method for reducing the oxidation and gas absorption of aluminum lithium alloy, comprising the following steps:

[0010] S1, adding multi-element composite rare earth elements to the aluminum alloy melt without lithium to form a rare earth oxide film layer on the surface;

[0011] S2, performing first rotary inert gas blowing refining on the aluminum alloy melt, and performing first slagging and standing;

[0012] S3, adding lithium elements to the aluminum alloy melt to obtain an aluminum lithium alloy melt;

[0013] S4, performing second rotary inert gas blowing refining on the aluminum lithium alloy melt, and performing second slagging and standing;

[0014] S5, adding covering agent to the surface of the aluminum lithium alloy melt after standing to obtain an aluminum lithium alloy casting.

[0015] The present invention, by adding a multi-component composite rare earth element to a lithium-free aluminum alloy melt, facilitates the formation of a continuous, dense, ultra-thin composite rare earth oxide film on the surface of the aluminum alloy melt. This composite rare earth oxide film provides physical isolation, preventing oxidative inhalation of the melt. Furthermore, unlike capping agent protection, the rare earth oxide film exhibits much better wettability with the melt. Therefore, although the oxide film is drawn into the melt during the subsequent rotary inert gas refining process, it is easily broken up and dispersed in the melt, without affecting the forming quality of the aluminum-lithium alloy. Instead, the fine, dispersed rare earth oxide particles act as reinforcing phase particles to improve the mechanical properties of the alloy. However, when a capping agent is used for melt protection and drawn into the melt, the capping agent, primarily composed of a mixture of chloride and fluoride salts, not only has no reinforcing effect on the alloy, but also severely fractures the alloy matrix and causes electrochemical corrosion, devastating the mechanical properties and corrosion resistance of the aluminum-lithium alloy.

[0016] As an embodiment of the present invention, in step S1, the aluminum alloy includes any one of Al-Cu series and Al-Mg series. In some embodiments, the chemical formula of the aluminum alloy is Al-4Cu-0.5Mg-0.5Mn.

[0017] Furthermore, the aluminum alloy melt is obtained by mixing and melting aluminum alloy raw materials.

[0018] As one embodiment of the present invention, in step S1, the multi-component composite rare earth element includes a light rare earth element and a heavy rare earth element; wherein the light rare earth element includes one or more of neodymium, cerium, and lanthanum, and the heavy rare earth element includes one or more of gadolinium, yttrium, and the like. The reason for using a multi-component rare earth element composite of heavy and light rare earth elements is to adjust the Pilling-Bedworth ratio (PB ratio), density, and wettability of the rare earth oxide film on the surface of the aluminum alloy melt, thereby reducing the internal stress of the rare earth oxide film, avoiding cracking of the film, and reducing oxidative gas absorption by the melt while ensuring that the rare earth oxide film is continuous and dense and can effectively isolate air.

[0019] Further, the mass ratio of the light rare earth element to the heavy rare earth element is 1:3-1:2, and the total amount of the multi-component composite rare earth element added is 0.1-3% of the mass of the melt. When the mass ratio of the light rare earth element to the heavy rare earth element is too low, the structure of the rare earth oxide film layer formed on the surface of the melt is relatively loose, which reduces the protection effect of the melt. When the mass ratio of the light rare earth element to the heavy rare earth element is too high, the stress of the rare earth oxide film layer formed on the surface of the melt is relatively large, the cracking tendency is large, and the protection effect of the melt is also reduced. When the total content of the rare earth is too low, the thickness of the rare earth oxide film layer on the surface of the melt is relatively thin, and the physical protection effect on the melt is weak. When the total content of the rare earth is too high, the rare earth oxide film layer on the surface of the melt is relatively thick, which interferes with the dehydrogenation effect of the melt in the subsequent refining process.

[0020] As an embodiment of the present application, in step S1, the multi-component composite rare earth element is added in the form of an aluminum-rare earth intermediate alloy, the content of the rare earth in the aluminum-rare earth intermediate alloy is ≤30wt.%, and the addition temperature is 740-800°C. This is because there is often a rare earth-containing phase with a high melting point and a relatively large size in the aluminum-rare earth intermediate alloy. When the content of the rare earth in the aluminum-rare earth intermediate alloy exceeds 30wt.%, the second phase containing the rare earth in the aluminum-rare earth intermediate alloy is too large, so that the rare earth is difficult to effectively dissolve and diffuse in the aluminum alloy melt, causing segregation of the rare earth element. Only by strictly controlling the content of the rare earth in the aluminum-rare earth intermediate alloy and the temperature of the rare earth alloying can the rare earth be fully dissolved and diffused in the melt, which can effectively ensure the uniformity and density of the rare earth oxide film layer on the surface of the melt, and improve the protection effect of the rare earth oxide film layer on the melt. However, too high alloying temperature can cause serious oxidation and burning loss of the chemically active rare earth element, reducing the yield of the rare earth.

[0021] As an embodiment of the present application, in step S2, the gas flow of the first rotation blowing inert gas refining is 10-20L / min, the rotation speed is 200-400rpm, and the refining temperature is 730-750°C. The purpose of the first-stage refining is to remove hydrogen in the melt without lithium element. Since the melt does not contain active lithium element at this time, the oxidation and absorption tendency of the melt is low, and the refining effect is better within the above parameter range.

[0022] As an embodiment of the present application, in step S2, the standing time is 20-30min.

[0023] As an embodiment of the present application, in step S3, the method of adding lithium element includes: firstly, cooling the aluminum alloy melt to 690-710℃, then, breaking the rare earth oxide film layer on the surface of the aluminum alloy melt, and pressing pure lithium into the aluminum alloy melt from the broken part. After reducing the melt temperature, the rare earth oxide film layer will shrink, the compactness will increase, and the protection effect on the melt will increase. At the same time, the reaction intensity between lithium and the rare earth oxide film at lower temperature is weaker, and the reaction loss between lithium and the rare earth oxide film layer can be reduced. The rare earth oxide film layer on the surface of the aluminum alloy melt is broken to add lithium, which can reduce the area of the melt exposed to air as much as possible, and reduce the oxidation and gettering of the melt while alloying with lithium. However, if the aluminum alloy melt is cooled too low, the melting and diffusion rate of lithium in the aluminum melt will be slowed down, and the uniformity of the distribution of lithium in the aluminum melt will be affected. At the same time, too low melt temperature is not conducive to subsequent refining and degassing.

[0024] Preferably, the addition of lithium element is completed under inert gas protection or vacuum.

[0025] As an embodiment of the present application, in step S3, the amount of lithium element added is 0.1-4% of the mass of the melt.

[0026] As an embodiment of the present application, in step S4, the gas flow of the second rotation blowing inert gas refining is 5-10 L / min, the rotation speed is 100-200 rpm, and the refining temperature is 690-710℃. After adding lithium element, the lithium element will react with the rare earth oxide film layer and form lithium oxide, which not only reduces the compactness of the rare earth oxide film layer and its protection effect on the melt, but also causes the loss of expensive lithium element. Therefore, the gas flow, rotation speed and refining temperature of the second melt refining are lower than those of the first time, and the purpose is to reduce the reaction between lithium element and the rare earth oxide film layer.

[0027] Further, in steps S2 and S4, the present application uses rotation blowing inert gas to refine the melt, the main purpose of which is to use the partial pressure difference effect to make the hydrogen in the melt diffuse into the inert bubbles, and separate the hydrogen from the melt in the process of floating on the inert bubbles. However, when using covering agent protection, part of the covering agent will be rolled into the melt, and a thick layer of covering agent on the surface of the melt will hinder the hydrogen-containing inert bubbles from escaping from the melt, thereby reducing the effect of melt refining. The present application uses a thin and compact rare earth oxide film layer generated in situ to protect the melt, which not only can effectively isolate air, but also can effectively adsorb hydrogen in the melt by the active effect of rare earth in the rare earth oxide film, and accelerate the dehydrogenation of the melt.

[0028] As an embodiment of the present application, in step S4, the standing time is 5-10 min.

[0029] In the present application, the first and second standing are to let the inert bubbles of hydrogen after refining have enough time to float and escape from the surface of the melt, so as to improve the effect of hydrogen removal from the melt. Unlike the use of covering agent protection, because of the large thickness and high viscosity of the covering agent, the inert bubbles containing hydrogen are difficult to effectively escape from the surface of the melt, so the standing process under the condition of covering agent protection has less effect on further improving the effect of hydrogen removal from the melt; and in the present application, the thin rare earth oxide film layer is used to isolate the melt from the air, and the inert bubbles can easily pass through the film layer and escape, so that the present application can effectively protect the melt while avoiding interference with the hydrogen removal effect of the melt. Because the amount of the melt before adding lithium is large, the standing time required after refining is longer, and the standing time required after adding lithium is shorter.

[0030] As an embodiment of the present application, in step S5, the covering agent includes any one of KCl-LiCl, LiCl-LiF.

[0031] As an embodiment of the present application, the adding method of the covering agent includes: first heating and melting the covering agent, and then pouring it into the surface of the aluminum-lithium alloy melt, and the heating temperature is 500-600℃. Because the melt already contains lithium at this time, and lithium will react with the rare earth oxide film layer. Therefore, during the waiting for casting process, the covering agent should be added to protect the melt, to prevent the rare earth oxide film layer from reducing the protection effect due to containing more lithium oxide. At the same time, because the melt has completed the lithium alloying and refining process at this time, therefore, at this time, the covering agent is scattered on the surface of the melt, and the problem of the covering agent being rolled into the melt to form secondary molten salt inclusions does not occur. However, most of the existing aluminum-lithium alloy covering agents are mixed by chlorides and fluorides, and the covering agent has a strong tendency to absorb moisture. The crystallization water formed after absorbing moisture is difficult to remove by simple drying and heating processes. In order to reduce the influence of moisture absorption of the covering agent on the quality of the melt, the covering agent is first heated to 500-600℃ and melted to remove all the crystallization water in the covering agent, and then poured into the surface of the aluminum-lithium alloy melt. In addition, because the covering agent is poured onto the surface of the melt in a liquid state, the covering agent has better fluidity and can effectively cover the melt in a shorter time, and the covering effect is more excellent.

[0032] In a second aspect, the present application provides an aluminum-lithium alloy casting prepared by the preparation method of the large-melt-volume melt.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] 1. The present application introduces a small amount of rare earth elements into the aluminum-lithium alloy to form a dense and continuous ultra-thin rare earth oxide film layer on the surface of the melt, and by using multi-element composite heavy and light rare earth elements and adopting the addition method of alloying, the density of the film layer and its wettability with aluminum melt are controlled, effectively isolating the aluminum-lithium alloy melt from the air and reducing the oxidation and adsorption of the high-activity aluminum-lithium alloy melt; at the same time, the internal stress of the rare earth oxide film layer is reduced, avoiding the cracking of the film layer.

[0035] 2. The present application uses an in-situ formed rare earth oxide film layer to protect the aluminum-lithium alloy melt, which can be broken and dispersed during the subsequent rotary blowing of inert gas refining process, and the formed granular rare earth oxide not only does not affect the quality of the melt, but also improves the mechanical properties of the aluminum-lithium alloy as a reinforcing phase particle, avoiding the problem of secondary molten salt inclusions caused by the covering agent being rolled into the melt when using the covering agent for protection.

[0036] 3. The active role of rare earth in the rare earth oxide film layer can also effectively adsorb hydrogen in the melt and accelerate the dehydrogenation of the melt; at the same time, the ultra-thin rare earth oxide film layer is more easily penetrated by hydrogen-containing inert bubbles and escapes, thereby further improving the dehydrogenation effect of the melt.

[0037] 4. The method used in the present application is green and environmentally friendly, requires a small amount of covering agent, is easy to operate, has low cost, and is very suitable for the engineering preparation of large smelting amount of aluminum-lithium alloy melt, and is helpful to promote the further application of aluminum-lithium alloy in the fields of aerospace, national defense and military industry, underwater domain, etc. DETAILED DESCRIPTION

[0038] The present application will be described in detail below in conjunction with specific embodiments. The following examples are implemented under the premise of the technical scheme of the present application, and provide detailed implementation methods and specific operation processes, which will help those skilled in the art to further understand the present application. It should be pointed out that the protection scope of the present application is not limited to the following examples, and several adjustments and improvements made under the premise of the concept of the present application all belong to the protection scope of the present application.

[0039] Example 1

[0040] The alloy composition (mass percent) for smelting is: Al-4Cu-0.5Li-0.5Mg-0.5Mn-0.075Gd-0.025Nd.

[0041] Other element alloying: the calculated and weighed pure aluminum ingot, Al-Cu intermediate alloy, pure Mg, Al-Mn intermediate alloy were melted in a resistance heating furnace. After the furnace charge was melted, Al-20wt.% Gd and Al-20wt.% Nd intermediate alloys were added at 740℃. The total amount of rare earth elements added was 0.1% of the mass of the melt, of which the amount of Nd added was 0.025%, and the amount of Gd added was 0.075%, i.e. the mass ratio of light rare earth elements to heavy rare earth elements was 1:3.

[0042] First refining: after the rare earth elements were completely melted, the temperature of the aluminum alloy melt was reduced to 730℃, and the aluminum alloy melt was subjected to first rotary inert gas blowing refining, with a gas flow rate of 10 L / min and a rotation speed of 200 rpm. After refining, slagging was performed, and the melt was allowed to stand for 20 min.

[0043] Lithium alloying: the temperature of the aluminum alloy melt was reduced to 690℃, and a pure lithium ingot was pressed into the aluminum alloy melt through an opening in the rare earth oxide film layer on the surface of the aluminum alloy melt. The amount of lithium added was 0.5% of the mass of the melt, and an aluminum-lithium alloy melt was obtained. The lithium addition process was completed in an argon gas protective atmosphere.

[0044] Second refining: when the temperature of the aluminum-lithium alloy melt was 690℃, the aluminum-lithium alloy melt was subjected to second rotary inert gas blowing refining, with a gas flow rate of 5 L / min and a rotation speed of 100 rpm. After refining, slagging was performed, and the melt was allowed to stand for 5 min.

[0045] Covering agent addition: the covering agent (KCl and LiCl in a mass ratio of 1:1) was heated to 500℃, and after the covering agent was melted, the liquid covering agent was added to the surface of the aluminum-lithium alloy melt, and an aluminum-lithium alloy casting was obtained by casting.

[0046] Analysis and detection: the aluminum-lithium alloy casting obtained above was tested. According to the composition test, hydrogen content test and metallographic analysis, the yield of lithium in the aluminum-lithium alloy reached 92.3%, the inclusion content was 0.54%, and the hydrogen content was 0.136 ml / 100g. According to the standard GB / T 228.1-2021, the room temperature tensile property test was performed on the aluminum-lithium alloy casting sample, and the tensile strength of the sample was 277 MPa, the yield strength was 212 MPa, and the elongation was 3.7%.

[0047] Example 2

[0048] The alloy composition (mass percentage) of the smelted alloy was: Al-4Cu-1Li-0.5Mg-0.5Mn-0.75Y-0.125Ce-0.125La.

[0049] Other element alloying: the calculated and weighed pure aluminum ingot, Al-Cu intermediate alloy, pure Mg, Al-Mn intermediate alloy were melted in a resistance heating furnace. After the furnace charge was melted, Al-25wt.% Y, Al-25wt.% Ce, Al-25wt.% La intermediate alloy were added at 760℃. The total amount of rare earth elements added was 1% of the mass of the melt, among which the amount of Ce added was 0.125%, the amount of La added was 0.125%, and the amount of Y added was 0.75%, i.e. the mass ratio of light rare earth elements to heavy rare earth elements was 1:3.

[0050] First refining: after the rare earth elements were completely melted, the temperature of the aluminum alloy melt was reduced to 740℃, and the aluminum alloy melt was subjected to first rotary inert gas refining, with a gas flow rate of 15L / min and a rotation speed of 300rpm. After refining, slagging was performed, and the melt was left to stand for 25min.

[0051] Lithium alloying: the temperature of the aluminum alloy melt was reduced to 700℃, and a hole was opened in the rare earth oxide film layer on the surface of the aluminum alloy melt. Pure lithium ingot was pressed into the aluminum alloy melt through the hole in the rare earth oxide film layer, and the amount of lithium added was 1% of the mass of the melt, obtaining an aluminum-lithium alloy melt. The lithium addition process was completed in an argon gas protection atmosphere.

[0052] Second refining: when the temperature of the aluminum-lithium alloy melt was 700℃, the aluminum-lithium alloy melt was subjected to second rotary inert gas refining, with a gas flow rate of 7L / min and a rotation speed of 150rpm. After refining, slagging was performed, and the melt was left to stand for 7min.

[0053] Covering agent addition: the covering agent (KCl and LiCl in a mass ratio of 1:1) was heated to 550℃, and after the covering agent was melted, the liquid covering agent was added to the surface of the aluminum-lithium alloy melt, and an aluminum-lithium alloy casting was obtained by casting.

[0054] Analysis and detection: the aluminum-lithium alloy casting obtained above was tested, and according to the composition detection, hydrogen content test and metallographic analysis, the yield of lithium element in the aluminum-lithium alloy reached 91.2%, the inclusion content was 0.65%, and the hydrogen content was 0.147ml / 100g. According to the standard GB / T 228.1-2021, the room temperature tensile property test of the aluminum-lithium alloy casting sample was performed, and the tensile strength of the sample was 288MPa, the yield strength was 241MPa, and the elongation was 3.5%.

[0055] Example 3

[0056] The alloy composition (mass percentage) of the smelted alloy was: Al-4Cu-2Li-0.5Mg-0.5Mn-1.2Y-0.3Ce-0.3La.

[0057] Other element alloying: the calculated and weighed pure aluminum ingot, Al-Cu intermediate alloy, pure Mg, Al-Mn intermediate alloy were melted in a resistance heating furnace. After the furnace charge was melted, Al-30wt.% Y, Al-30wt.% Ce, Al-30wt.% La intermediate alloy were added at 780℃. The total amount of rare earth elements added was 1.8% of the mass of the melt, of which the amount of Ce added was 0.3%, the amount of La added was 0.3%, and the amount of Y added was 1.2%, i.e. the mass ratio of light rare earth elements to heavy rare earth elements was 1:2.

[0058] First refining: after the rare earth elements were completely melted, the temperature of the aluminum alloy melt was reduced to 745℃, and the aluminum alloy melt was subjected to first rotary inert gas refining, with a gas flow rate of 18L / min and a rotation speed of 350rpm. After refining, slagging was performed, and the melt was left to stand for 28min.

[0059] Lithium alloying: the temperature of the aluminum alloy melt was reduced to 710℃, and a pure lithium ingot was pressed into the aluminum alloy melt through an opening in the rare earth oxide film layer on the surface of the aluminum alloy melt. The amount of lithium added was 2% of the mass of the melt, and an aluminum-lithium alloy melt was obtained. The lithium addition process was completed in an argon gas protection atmosphere.

[0060] Second refining: when the temperature of the aluminum-lithium alloy melt was 710℃, the aluminum-lithium alloy melt was subjected to second rotary inert gas refining, with a gas flow rate of 9L / min and a rotation speed of 180rpm. After refining, slagging was performed, and the melt was left to stand for 9min.

[0061] Covering agent addition: the covering agent (LiCl and LiF in a mass ratio of 3:1) was heated to 580℃, and after the covering agent was melted, the liquid covering agent was added to the surface of the aluminum-lithium alloy melt, and an aluminum-lithium alloy casting was obtained by casting.

[0062] Analysis and detection: the aluminum-lithium alloy casting obtained above was tested. According to the composition detection, hydrogen content test and metallographic analysis, the yield of lithium in the aluminum-lithium alloy reached 90.3%, the inclusion content was 0.74%, and the hydrogen content was 0.158ml / 100g. According to the standard GB / T 228.1-2021, the room temperature tensile property test of the aluminum-lithium alloy casting sample was performed, and the tensile strength of the sample was 299MPa, the yield strength was 248MPa, and the elongation was 3.3%.

[0063] Example 4

[0064] The alloy composition (mass percentage) of the melting was: Al-4Cu-4Li-0.5Mg-0.5Mn-2Y-0.5Ce-0.5La.

[0065] Other element alloying: the calculated and weighed pure aluminum ingot, Al-Cu intermediate alloy, pure Mg, Al-Mn intermediate alloy were melted in a resistance heating furnace. After the furnace charge was melted, Al-30wt.%Y, Al-30wt.%Ce, Al-30wt.%La intermediate alloy was added at 800℃. The total amount of rare earth elements added was 3% of the mass of the melt, of which the amount of Ce added was 0.5%, the amount of La added was 0.5%, and the amount of Y added was 2%, i.e. the mass ratio of light rare earth elements to heavy rare earth elements was 1:2.

[0066] First refining: after the rare earth elements were completely melted, the temperature of the aluminum alloy melt was reduced to 750℃, and the aluminum alloy melt was subjected to first rotary inert gas refining, with a gas flow rate of 20L / min and a rotation speed of 400rpm. After refining, slagging was performed, and the melt was allowed to stand for 30min.

[0067] Lithium alloying: the temperature of the aluminum alloy melt was reduced to 710℃, and a pure lithium ingot was pressed into the aluminum alloy melt through an opening in the rare earth oxide film layer on the surface of the aluminum alloy melt. The amount of lithium added was 4% of the mass of the melt, and an aluminum-lithium alloy melt was obtained. The lithium addition process was completed in an argon gas protection atmosphere.

[0068] Second refining: when the temperature of the aluminum-lithium alloy melt was 710℃, the aluminum-lithium alloy melt was subjected to second rotary inert gas refining, with a gas flow rate of 10L / min and a rotation speed of 200rpm. After refining, slagging was performed, and the melt was allowed to stand for 10min.

[0069] Covering agent addition: the covering agent (LiCl and LiF in a mass ratio of 3:1) was heated to 600℃, and after the covering agent was melted, the liquid covering agent was added to the surface of the aluminum-lithium alloy melt, and an aluminum-lithium alloy casting was obtained by casting.

[0070] Analysis and detection: the aluminum-lithium alloy casting obtained above was tested. According to the composition detection, hydrogen content test and metallographic analysis, the yield of lithium element in the aluminum-lithium alloy reached 89.9%, the inclusion content was 0.71%, and the hydrogen content was 0.161ml / 100g. According to the standard GB / T 228.1-2021, the room temperature tensile property test of the aluminum-lithium alloy casting sample was performed, and the tensile strength of the sample was 311MPa, the yield strength was 257MPa, and the elongation was 3.2%.

[0071] Comparative Example 1

[0072] The aluminum-lithium alloy preparation process in this comparative example was basically the same as that in Example 1, except that no rare earth elements were added to the alloy.

[0073] The obtained aluminum-lithium alloy castings were tested, and the composition detection, hydrogen content test and metallographic analysis showed that the yield of lithium element in the aluminum-lithium alloy was only 78%, the inclusion content was 2.34%, and the hydrogen content was 0.434 ml / 100g. According to the standard GB / T 228.1-2021, the room temperature tensile properties of the aluminum-lithium alloy casting sample were tested, and the tensile strength of the sample was 211 MPa, the yield strength was 152 MPa, and the elongation was 1.2%. The results showed that the oxidation and absorption of the alloy increased obviously, the main reason was that the rare earth alloying was not used, and the dense and continuous ultra-thin rare earth oxide film layer was not formed on the surface of the aluminum-lithium alloy melt, so the melt was seriously oxidized and absorbed in the atmospheric environment, the gas and slag content was large, and the mechanical properties of the sample were very low.

[0074] Comparative Example 2

[0075] The preparation process of the aluminum-lithium alloy in this comparative example was basically the same as that in Example 1, except that no rare earth element was added to the alloy, but a covering agent was used to protect the melt before adding lithium.

[0076] The obtained aluminum-lithium alloy castings were tested, and the composition detection, hydrogen content test and metallographic analysis showed that the yield of lithium element in the aluminum-lithium alloy was only 78%, the inclusion content was 2.34%, and the hydrogen content was 0.434 ml / 100g. According to the standard GB / T 228.1-2021, the room temperature tensile properties of the aluminum-lithium alloy casting sample were tested, and the tensile strength of the sample was 211 MPa, the yield strength was 152 MPa, and the elongation was 1.2%. The results showed that the oxidation and absorption of the alloy increased obviously, the main reason was that the rare earth alloying was not used, and the dense and continuous ultra-thin rare earth oxide film layer was not formed on the surface of the aluminum-lithium alloy melt, so the melt was seriously oxidized and absorbed in the atmospheric environment, the gas and slag content was large, and the mechanical properties of the sample were very low.

[0077] Comparative Example 3

[0078] The preparation process of the aluminum-lithium alloy in this comparative example was basically the same as that in Example 1, except that the total amount of rare earth elements added to the alloy was 3.5% of the mass of the melt.

[0079] The obtained aluminum-lithium alloy castings were tested, and the composition detection, hydrogen content test and metallographic analysis showed that the yield of lithium element in the aluminum-lithium alloy was only 78%, the inclusion content was 2.34%, and the hydrogen content was 0.434 ml / 100g. According to the standard GB / T 228.1-2021, the room temperature tensile properties of the aluminum-lithium alloy casting sample were tested, and the tensile strength of the sample was 211 MPa, the yield strength was 152 MPa, and the elongation was 1.2%. The results showed that the oxidation and absorption of the alloy increased obviously, the main reason was that the rare earth alloying was not used, and the dense and continuous ultra-thin rare earth oxide film layer was not formed on the surface of the aluminum-lithium alloy melt, so the melt was seriously oxidized and absorbed in the atmospheric environment, the gas and slag content was large, and the mechanical properties of the sample were very low.

[0080] Comparative Example 4

[0081] The preparation process of the aluminum-lithium alloy in this comparative example is basically the same as that in Example 1, except that no covering agent is added after the second refining and the standing is completed.

[0082] The obtained aluminum-lithium alloy castings are tested, and the composition detection, hydrogen content test and metallographic analysis show that the yield of lithium element in the aluminum-lithium alloy is only 81%, the inclusion content is 0.81%, and the hydrogen content is 0.212 ml / 100g. The results show that the oxidation and absorption of the alloy increase, and the yield of lithium element decreases significantly. The main reason is that the lithium element in the melt reacts violently with the rare earth oxide film layer after alloying, and the generated lithium oxide seriously reduces the density of the rare earth oxide film layer, and weakens the physical protection effect of the rare earth oxide film layer on the aluminum-lithium alloy melt.

[0083] Comparative Example 5

[0084] The preparation process of the aluminum-lithium alloy in this comparative example is basically the same as that in Example 1, except that the temperature of adding the rare earth element is 730°C.

[0085] The obtained aluminum-lithium alloy castings are tested, and the composition detection, hydrogen content test and metallographic analysis show that the yield of lithium element in the aluminum-lithium alloy is only 86.5%, the inclusion content is 0.83%, and the hydrogen content is 0.174 ml / 100g. The results show that the oxidation and absorption of the alloy increase, and the main reason is that the temperature of adding the rare earth is low, which causes the non-uniform dissolution and diffusion of the rare earth, affecting the uniformity of the rare earth oxide film layer formed on the surface of the melt, and weakening the physical protection effect of the rare earth oxide film layer on the aluminum-lithium alloy melt.

[0086] Comparative Example 6

[0087] The preparation process of the aluminum-lithium alloy in this comparative example is basically the same as that in Example 1, except that the multi-element composite rare earth alloying is not used in the alloy, but only Gd is used as the rare earth alloying element, and the amount of the rare earth element is unchanged.

[0088] The obtained aluminum-lithium alloy castings are tested, and the composition detection, hydrogen content test and metallographic analysis show that the yield of lithium element in the aluminum-lithium alloy is only 84.3%, the inclusion content is 0.74%, and the hydrogen content is 0.44 ml / 100g. The results show that the oxidation and absorption of the alloy increase, and the main reason is that the multi-element composite rare earth alloying is not used, the density of the rare earth oxide film layer is too large, the thermal stress is high during the cooling process, causing micro-cracks in the film layer, and weakening the physical protection effect of the rare earth oxide film layer on the aluminum-lithium alloy melt.

[0089] Comparative Example 7

[0090] The aluminum-lithium alloy preparation process in this comparative example is basically the same as that in Example 1, except that the process parameters in the second refining are the same as those in the first time.

[0091] The aluminum-lithium alloy castings obtained above are tested, and according to the component detection, hydrogen content test and metallographic analysis, the lithium element yield in the aluminum-lithium alloy is only 81.1%, the inclusion content is 0.88%, and the hydrogen content is 0.41 ml / 100g. The results show that the oxidation and absorption of the alloy increase, and the lithium element yield decreases, the main reason is that the melt contains lithium in the second refining, and the second refining temperature is high and the rotation speed is too fast, which causes the melt to fluctuate obviously, the oxidation and absorption are serious, and the reaction between lithium and rare earth oxide film layer is more intense, which reduces the melt preparation quality.

[0092] Comparative Example 8

[0093] The aluminum-lithium alloy preparation process in this comparative example is basically the same as that in Example 1, except that the covering agent is only dried at 200°C before being added, and the covering agent is not heated to 500-600°C and melted.

[0094] The aluminum-lithium alloy castings obtained above are tested, and according to the component detection, hydrogen content test and metallographic analysis, the lithium element yield in the aluminum-lithium alloy is only 82.3%, the inclusion content is 0.74%, and the hydrogen content is 0.78 ml / 100g. The results show that the oxidation and absorption of the alloy increase, especially the hydrogen content of the melt increases significantly, the main reason is that there is still a lot of crystal water in the covering agent, which reacts with the alloy melt to form hydrogen, and intensifies the hydrogen absorption of the melt.

[0095] Comparative Example 9

[0096] The aluminum-lithium alloy preparation process in this comparative example is basically the same as that in Example 1, except that the amount of Nd added is 0.02%, and the amount of Gd added is 0.08%, i.e. the mass ratio of light rare earth element to heavy rare earth element is 1:4.

[0097] The aluminum-lithium alloy castings obtained above are tested, and according to the component detection, hydrogen content test and metallographic analysis, the lithium element yield in the aluminum-lithium alloy is only 87.6%, the inclusion content is 0.76%, and the hydrogen content is 0.52 ml / 100g. The results show that the oxidation and absorption of the alloy increase, especially the hydrogen content of the melt increases significantly, the main reason is that the proportion of light rare earth element to heavy rare earth element is too low, so that the structure of the rare earth oxide film layer formed on the surface of the melt is relatively loose, and the melt protection effect is reduced.

[0098] Comparative Example 10

[0099] The preparation process of the aluminum-lithium alloy in the present comparative example is basically the same as that in Example 1, except that the addition amount of Nd is 0.05%, the addition amount of Gd is 0.05%, i.e. the mass ratio of light rare earth element to heavy rare earth element is 1:1.

[0100] The aluminum-lithium alloy castings obtained above are tested. According to the component detection, hydrogen content test and metallographic analysis, the yield of lithium element in the aluminum-lithium alloy is only 88.1%, the inclusion content is 0.74%, and the hydrogen content is 0.49 ml / 100g. The results show that the oxidation and absorption of the alloy increase, especially the hydrogen content in the melt increases significantly. The main reason is that the ratio of light rare earth element to heavy rare earth element is too high, so that the structure of the rare earth oxide film layer formed on the surface of the melt is too dense, the stress in the film layer is large and causes cracking, and the protection effect of the melt is reduced.

[0101] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the specific embodiments described above, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application.

Claims

1. A method for preparing a large melt volume to reduce oxidation absorption of aluminum-lithium alloy, characterized in that: The steps include: S1. Adding a multi-component composite rare earth element to a lithium-free aluminum alloy melt to form a rare earth oxide film on the surface; S2, performing a first rotary inert gas refining on the aluminum alloy melt, and performing a first slag removal and standing; S3, adding lithium element to the aluminum alloy melt to obtain an aluminum-lithium alloy melt; S4, performing a second rotary inert gas refining on the aluminum-lithium alloy melt, and performing a second slagging and standing; S5. Add a covering agent to the surface of the aluminum-lithium alloy melt after the standing is completed, and cast to obtain an aluminum-lithium alloy casting.

2. The method for preparing a large melting point melt according to claim 1, wherein: In step S1, the aluminum alloy includes any one of Al-Cu series and Al-Mg series; the aluminum alloy melt is obtained by mixing and melting aluminum alloy raw materials.

3. The method for preparing a large melting point melt according to claim 1, wherein: In step S1, the multi-component composite rare earth elements include light rare earth elements and heavy rare earth elements; wherein the light rare earth elements include one or more of neodymium, cerium, and lanthanum, and the heavy rare earth elements include one or more of gadolinium, yttrium, and the like.

4. The method for preparing a large melting point melt according to claim 3, wherein: The mass ratio of the light rare earth element to the heavy rare earth element is 1:3 to 1:2, and the total amount of the multi-component composite rare earth element added is 0.1 to 3% of the mass of the melt.

5. The method for preparing a large melting point melt according to claim 1, wherein: In step S1, the multi-component composite rare earth element is added in the form of an aluminum-rare earth master alloy, the rare earth content in the aluminum-rare earth master alloy is ≤30wt.%, and the adding temperature is 740-800°C.

6. The method for preparing a large melting point melt according to claim 1, wherein: In step S2, the gas flow rate of the first rotary inert gas refining is 10-20 L / min, the rotation speed is 200-400 rpm, and the refining temperature is 730-750°C; In step S4, the gas flow rate of the second rotary blowing inert gas refining is 5-10 L / min, the rotation speed is 100-200 rpm, and the refining temperature is 690-710°C.

7. The method for preparing a large melting point melt according to claim 1, wherein: In step S2, the standing time is 20 to 30 minutes; In step S4, the standing time is 5 to 10 minutes.

8. The method for preparing a large melting point melt according to claim 1, wherein: In step S3, the method for adding lithium element includes: first cooling the aluminum alloy melt to 690-710° C., then scratching the rare earth oxide film layer on the surface of the aluminum alloy melt, and pressing pure lithium into the aluminum alloy melt through the scratched portion; The amount of lithium added is 0.1-4% of the mass of the melt.

9. The method for preparing a large melting point melt according to claim 1, wherein: In step S5, the covering agent includes any one of KCl-LiCl and LiCl-LiF; the method of adding the covering agent includes: first heating and melting the covering agent, and then pouring it onto the surface of the aluminum-lithium alloy melt, and the heating temperature is 500-600°C.

10. An aluminum-lithium alloy casting produced by the large-melting-capacity melt production method according to any one of claims 1 to 9.