Preparation method of aluminum-lithium alloy

Abstract

The invention provides a preparation method of an aluminum-lithium alloy, and belongs to the technical field of aluminum alloy smelting. The method comprises the following steps: smelting pure aluminum, an aluminum-copper alloy, an aluminum-manganese alloy, an aluminum-zirconium alloy, a magnesium ingot and silver particles to obtain an initial melt; adding a deslagging agent into the initial melt, and stirring to obtain a purified melt; argon is introduced into the purified melt for refining, and a refined melt is obtained; and after the refined melt and lithium are subjected to vacuum melting, argon is introduced for refining, and the aluminum-lithium alloy is obtained. The pure aluminum, the intermediate alloy, the magnesium and the silver are added in batches for smelting at different temperatures according to the refractory degree of the intermediate alloy in the intermediate frequency furnace smelting stage, so that the burning loss rate of alloy elements can be reduced; hexachloroethane deslagging and stirring blowing refining can improve the degassing efficiency and control the cost, and the process matching is flexible; lithium is added into the melt in an argon state, so that the melt is prevented from being in contact with the atmosphere, the oxidation hydrogen absorption of the melt is reduced, and the high-purity melt is obtained.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy smelting technology, and more particularly to a method for preparing an aluminum-lithium alloy. Background Technology

[0002] Aluminum-lithium alloys, as lightweight and high-strength structural materials, have significant application value in aerospace, transportation, and other fields due to their low density, high specific strength, and excellent corrosion resistance. Adding 1% Li by mass to aluminum alloys can reduce the alloy density by 3% and increase the elastic modulus by 6%. Aluminum-lithium alloys also possess excellent low-temperature performance, good corrosion resistance, and outstanding plasticity. Replacing conventional aluminum alloys with them can reduce the mass of components by 10-20% and increase stiffness by 15-20%. However, lithium is chemically extremely reactive (low density, volatile, and easily oxidized and combustible), causing aluminum-lithium alloys to readily react with oxygen, nitrogen, and water vapor during smelting, generating inclusions such as lithium oxide (Li₂O) and lithium nitride (Li₃N), and significantly increasing the hydrogen content of the melt. Lithium is highly oxidized, resulting in a poorly dense oxide film that is difficult to remove, and the melt readily absorbs gases, more than 50 times more readily than conventional aluminum alloys.

[0003] Existing technologies employ inert gas purging, flux purification, and filtration purification methods, but still suffer from the following drawbacks: (1) While inert gas purging can partially remove hydrogen from the melt, its removal efficiency for micron / submicron inclusions is low. (2) Although traditional fluxes can remove some inclusions through adsorption, their high reactivity with lithium may trigger flux-melt interface reactions, leading to fluctuations in alloy composition and even the introduction of impurity elements such as Na and K, thus deteriorating material properties. (3) While they have a certain interception effect on larger inclusions, their removal efficiency for small inclusions is insufficient. Furthermore, existing technologies often focus on a single purification target (such as hydrogen removal or impurity removal), lacking a synergistic removal mechanism for gas-solid-liquid multiphase impurities in aluminum-lithium alloy melts, resulting in the cleanliness of the purified melt failing to meet the requirements for the preparation of high-performance aluminum-lithium alloys.

[0004] Therefore, a method for purifying aluminum-lithium alloy melts by synergistically controlling hydrogen content, inclusions, and lithium loss has become a key technological requirement for improving the overall performance of materials and promoting industry applications. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing aluminum-lithium alloy, thereby achieving better purification of the aluminum-lithium alloy melt.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing an aluminum-lithium alloy, comprising the following steps: 1) Smelt pure aluminum, aluminum-copper alloy, aluminum-manganese alloy, aluminum-zirconium alloy, magnesium ingots and silver granules to obtain an initial melt; 2) Add a slag remover to the initial melt and stir to obtain a purified melt; 3) Argon gas is introduced into the purified melt for refining to obtain a refined melt; 4) After vacuum melting of the refined melt and lithium, argon gas is introduced for further refining to obtain an aluminum-lithium alloy.

[0007] Preferably, the melting temperature in step 1) is 700~800℃.

[0008] Preferably, the smelting process in step 1) is as follows: pure aluminum is smelted for the first time, then aluminum-copper alloy, aluminum-manganese alloy, and aluminum-zirconium alloy are added for the second smelting, and then magnesium ingots and silver granules are added for the third smelting; the temperature of the first smelting is 700~750℃, the temperature of the second smelting is 760~800℃, and the temperature of the third smelting is 700~720℃.

[0009] Preferably, the slag remover in step 2) is hexachloroethane, and the mass of the slag remover is 0.5 to 2% of the initial melt mass.

[0010] Preferably, the stirring temperature in step 2) is 720~760℃ and the stirring time is 20~30min.

[0011] As a preferred embodiment, the refining process described in steps 3) and 4) is as follows: refining is carried out by blowing argon gas through a baked graphite rotor, the temperature of the argon gas blowing refining is 710~750℃, the time is 20~40min, and the argon gas flow rate is 1~5L / min.

[0012] Preferably, the graphite rotor is baked at a temperature of 300~500℃ for 3~7h; refining is carried out under stirring at a stirring rate of 200~500r / min.

[0013] Preferably, the vacuum melting temperature in step 4) is 720~760℃, the vacuum degree is ≤50Pa, and the vacuum melting atmosphere is argon atmosphere with argon purity ≥99.99%.

[0014] Preferably, in step 4), after the argon gas refining is completed, the melt is allowed to stand for 20-30 minutes.

[0015] The beneficial effects of this invention are: This invention involves adding pure aluminum, the master alloy, magnesium, and silver in batches at different temperatures during the medium-frequency furnace smelting stage, based on the degree of refractory nature of the master alloy. This helps reduce the burn-off rate of alloying elements. The hexachloroethane slag removal and stirring-blowing refining process improves degassing efficiency, controls costs, and allows for flexible process combinations. Adding lithium to the melt under argon atmosphere avoids contact with the atmosphere, reducing oxidation and hydrogen absorption, resulting in a high-purity aluminum-lithium alloy melt. This invention effectively improves the cleanliness of the aluminum-lithium alloy melt and enhances the quality of aluminum-lithium alloy materials. Attached Figure Description

[0016] Figure 1 Metallographic images of the aluminum-lithium alloys prepared in Examples 1-3; Figure 2 This is a process flow diagram for preparing the aluminum-lithium alloy of the present invention. Detailed Implementation

[0017] This invention provides a method for preparing an aluminum-lithium alloy, comprising the following steps: 1) Smelt pure aluminum, aluminum-copper alloy, aluminum-manganese alloy, aluminum-zirconium alloy, magnesium ingots and silver granules to obtain an initial melt; 2) Add a slag remover to the initial melt and stir to obtain a purified melt; 3) Argon gas is introduced into the purified melt for refining to obtain a refined melt; 4) After vacuum melting of the refined melt and lithium, argon gas is introduced for further refining to obtain an aluminum-lithium alloy.

[0018] In this invention, the melting temperature in step 1) is preferably 700~800℃, more preferably 720~780℃, and even more preferably 750~760℃.

[0019] In this invention, the preferred smelting process in step 1) is as follows: pure aluminum is smelted for the first time, followed by the addition of aluminum-copper alloy, aluminum-manganese alloy, and aluminum-zirconium alloy for the second smelting, and then magnesium ingots and silver granules for the third smelting; the preferred temperature for the first smelting is 700~750℃, more preferably 710~740℃, and even more preferably 720~730℃; the preferred temperature for the second smelting is 760~800℃, more preferably 780~790℃; and the preferred temperature for the third smelting is 700~720℃, more preferably 710℃.

[0020] In this invention, the slag remover in step 2) is preferably hexachloroethane, and the mass of the slag remover is preferably 0.5-2% of the initial melt mass, more preferably 1-1.5%.

[0021] In this invention, the stirring temperature in step 2) is preferably 720~760℃, more preferably 730~750℃, and even more preferably 740℃, and the stirring time is preferably 20~30min, more preferably 22~28min, and even more preferably 25~26min.

[0022] In this invention, the refining process described in steps 3) and 4) is preferably as follows: refining is performed by blowing argon gas through a baked graphite rotor; the temperature for refining with argon gas is preferably 710~750℃, more preferably 720~740℃, and even more preferably 730℃; the time is preferably 20~40min, more preferably 25~35min, and even more preferably 30min; and the argon gas flow rate is preferably 1~5L / min, more preferably 2~4L / min, and even more preferably 3L / min.

[0023] In this invention, the baking temperature of the graphite rotor is preferably 300~500℃, more preferably 350~450℃, and even more preferably 400℃, and the baking time is preferably 3~7h, more preferably 4~6h, and even more preferably 5h; the refining is preferably carried out under stirring, and the stirring rate is preferably 200~500r / min, more preferably 300~400r / min, and even more preferably 350r / min.

[0024] In this invention, the temperature of vacuum melting in step 4) is preferably 720~760℃, more preferably 730~750℃, and even more preferably 740℃. The vacuum degree is preferably ≤50Pa, more preferably ≤20Pa. The atmosphere for vacuum melting is argon atmosphere, and the argon purity is preferably ≥99.99%, more preferably ≥99.999%.

[0025] In step 4) of the present invention, after the argon gas refining is completed, the melt is allowed to stand for a period of 20 to 30 minutes, more preferably 25 minutes.

[0026] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0027] Example 1

[0028] Pure aluminum was added to an intermediate frequency furnace and heated to 720°C until all the pure aluminum was melted. The temperature was then raised to 790°C, and AlZr5 alloy, AlMn10 alloy, and AlCu50 alloy were added. The temperature was held at 790°C for 25 minutes. Then, when the temperature was lowered to 740°C, Ag granules and Mg ingots were added, and the temperature was held at 710°C for 15 minutes to obtain the initial melt.

[0029] Hexachloroethane (0.5% of the initial melt mass) was added to the initial melt, and the melt was stirred at 740℃ for 30 min. The scum on the melt was removed to obtain a purified melt. A graphite rotor, baked at 350℃ for 4 h, was then used for argon refining. The argon refining temperature was 730℃, the time was 30 min, the argon flow rate was 1 L / min, and the stirring rate during the refining process was 250 r / min. Scum was removed after refining.

[0030] The melt from the medium-frequency furnace was transferred to a vacuum induction furnace via a transfer bag. The vacuum induction furnace was evacuated to 45 Pa and filled with 99.999% pure argon gas to a slight negative pressure. The charging chamber door was opened, and metallic lithium was added. Vacuum melting was carried out at 740℃ and 45 Pa for 30 min. After vacuum melting, a graphite rotor baked at 350℃ for 4 h was started to rotate and spray argon gas for refining. The argon gas refining temperature was 730℃, the time was 30 min, the argon gas flow rate was 1 L / min, and the stirring rate during the refining process was 250 r / min. After refining, the mixture was allowed to stand for 30 min to obtain an aluminum-lithium alloy. The average solid hydrogen content was measured to be 0.36 ppm.

[0031] Example 2

[0032] Pure aluminum was added to an intermediate frequency furnace and heated to 715°C until all the pure aluminum was melted. The temperature was then raised to 780°C, and AlZr5 alloy, AlMn10 alloy, and AlCu50 alloy were added. The temperature was held at 780°C for 30 minutes. Then, when the temperature was lowered to 730°C, Ag granules and Mg ingots were added, and the temperature was held at 700°C for 20 minutes to obtain the initial melt.

[0033] Hexachloroethane (1% of the initial melt mass) was added to the initial melt, and the melt was stirred at 720°C for 30 minutes. The scum on the melt was then removed to obtain a purified melt. A graphite rotor, baked at 350°C for 4 hours, was then used for argon refining. The argon refining temperature was 720°C, the time was 30 minutes, the argon flow rate was 3 L / min, and the stirring rate during the refining process was 350 r / min. Scum was removed after refining.

[0034] The melt from the medium-frequency furnace was transferred to a vacuum induction furnace via a transfer bag. The vacuum induction furnace was evacuated to 30 Pa and filled with 99.995% pure argon gas to a slight negative pressure. The charging chamber door was opened, and metallic lithium was added. Vacuum melting was carried out at 740℃ and 30 Pa for 30 min. After vacuum melting, a graphite rotor baked at 350℃ for 4 h was started to rotate and spray argon gas for refining. The argon gas refining temperature was 720℃, the time was 30 min, the argon gas flow rate was 3 L / min, and the stirring rate during the refining process was 350 r / min. After refining, the mixture was allowed to stand for 25 min to obtain an aluminum-lithium alloy. The average solid hydrogen content was measured to be 0.28 ppm.

[0035] Example 3

[0036] Pure aluminum was added to an intermediate frequency furnace and heated to 725°C until all the pure aluminum was melted. The temperature was then raised to 800°C, and AlZr5 alloy, AlMn10 alloy, and AlCu50 alloy were added. The temperature was held at 800°C for 25 minutes. Then, when the temperature was lowered to 750°C, Ag granules and Mg ingots were added, and the temperature was held at 720°C for 10 minutes to obtain the initial melt.

[0037] Hexachloroethane (1.5% of the initial melt mass) was added to the initial melt, and the melt was stirred at 750°C for 30 minutes. The scum on the melt was removed to obtain a purified melt. A graphite rotor, baked at 350°C for 4 hours, was then used for argon refining. The argon refining temperature was 740°C, the time was 25 minutes, the argon flow rate was 5 L / min, and the stirring rate during the refining process was 450 r / min. Scum was removed after refining.

[0038] The melt from the medium-frequency furnace was transferred to a vacuum induction furnace via a transfer bag. The vacuum induction furnace was evacuated to 20 Pa and filled with 99.995% pure argon gas to a slight negative pressure. The charging chamber door was opened, and metallic lithium was added. Vacuum melting was carried out at 740℃ and 20 Pa for 30 min. After vacuum melting, a graphite rotor baked at 350℃ for 4 h was started to rotate and spray argon gas for refining. The argon gas refining temperature was 740℃, the time was 25 min, the argon gas flow rate was 5 L / min, and the stirring rate during the refining process was 450 r / min. After refining, the mixture was allowed to stand for 30 min to obtain an aluminum-lithium alloy. The average solid hydrogen content was measured to be 0.23 ppm.

[0039] The metallographic structures of the aluminum-lithium alloys prepared in Examples 1-3 are shown below. Figure 1 As shown; among them, the comparative example is the low magnification microstructure of aluminum-lithium alloy prepared by lithium melting with argon gas directly without adding slag remover and without vacuuming, while Examples 1 to 3 are the low magnification microstructures of aluminum-lithium alloy prepared by lithium melting with lithium added under vacuum and argon gas conditions after adding slag remover.

[0040] Compared to traditional aluminum alloy melts, the aluminum-lithium alloy melt of this invention is more likely to absorb hydrogen. Therefore, under vacuum and argon-filled conditions, direct contact between the aluminum-lithium alloy melt and the atmosphere can be minimized. Before adding lithium, pure aluminum and other intermediate alloys, silver, and magnesium are melted. The melt is then efficiently degassed and slag removed by hexachloroethane and stirring. The melt is then transferred to a vacuum induction furnace, vacuumed, and argon is introduced for lithium addition. This effectively reduces the contact between the aluminum-lithium alloy melt and the atmosphere, resulting in a high-purity aluminum-lithium alloy melt.

[0041] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an aluminum-lithium alloy, characterized in that, It includes the following steps: 1) Smelt pure aluminum, aluminum-copper alloy, aluminum-manganese alloy, aluminum-zirconium alloy, magnesium ingots and silver granules to obtain an initial melt; 2) Add a slag remover to the initial melt and stir to obtain a purified melt; 3) Argon gas is introduced into the purified melt for refining to obtain a refined melt; 4) After vacuum melting of the refined melt and lithium, argon gas is introduced for further refining to obtain an aluminum-lithium alloy.

2. The method for preparing the aluminum-lithium alloy according to claim 1, characterized in that, The melting temperature in step 1) is 700~800℃.

3. The method for preparing the aluminum-lithium alloy according to claim 2, characterized in that, Step 1) The smelting process is as follows: pure aluminum is smelted for the first time, then aluminum-copper alloy, aluminum-manganese alloy, and aluminum-zirconium alloy are added for the second smelting, and then magnesium ingots and silver granules are added for the third smelting; the temperature of the first smelting is 700~750℃, the temperature of the second smelting is 760~800℃, and the temperature of the third smelting is 700~720℃.

4. The method for preparing the aluminum-lithium alloy according to claim 2 or 3, characterized in that, Step 2) The slag remover is hexachloroethane, and the mass of the slag remover is 0.5~2% of the initial melt mass.

5. The method for preparing the aluminum-lithium alloy according to claim 4, characterized in that, Step 2) The stirring temperature is 720~760℃ and the stirring time is 20~30min.

6. The method for preparing the aluminum-lithium alloy according to claim 5, characterized in that, The refining process described in steps 3) and 4) is as follows: argon gas is injected into a baked graphite rotor for refining. The temperature of the argon gas injection for refining is 710~750℃, the time is 20~40min, and the argon gas flow rate is 1~5L / min.

7. The method for preparing the aluminum-lithium alloy according to claim 6, characterized in that, The graphite rotor is baked at a temperature of 300~500℃ for 3~7 hours; refining is carried out under stirring at a speed of 200~500 r / min.

8. The method for preparing the aluminum-lithium alloy according to claim 6, characterized in that, Step 4) The vacuum melting temperature is 720~760℃, the vacuum degree is ≤50Pa, and the vacuum melting atmosphere is argon atmosphere with argon purity ≥99.99%.

9. The method for preparing the aluminum-lithium alloy according to claim 8, characterized in that, In step 4), after the argon gas refining is completed, the melt is allowed to stand for 20-30 minutes.

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