High-strength corrosion-resistant aluminum-lithium alloy and preparation method thereof

Abstract

The invention discloses a high-strength corrosion-resistant aluminum-lithium alloy and a preparation method thereof, and relates to the technical field of aluminum-lithium alloys, and the alloy comprises the following element components in percentage by weight: 1.8%-2.2% of Li, 2.8%-3.2% of Cu, 4.2%-4.6% of Mg, 0.15%-0.25% of Ag, 0.08%-0.15% of Sc, 0.06%-0.10% of Zr, 0.03%-0.05% of Y, less than or equal to 0.05% of Fe, less than or equal to 0.03% of Si and the balance of Al. The preparation method of the aluminum-lithium alloy comprises the steps of smelting, gradient cooling casting, homogenization treatment, controlled deformation heat treatment, composite aging strengthening and the like. Through collaborative optimization of the components and the process, the contradiction among mechanical strength, toughness and corrosion resistance of a traditional aluminum-lithium alloy is broken through, and a solution is provided for a high-end light-weight structural material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aluminum alloy materials, and particularly relates to a high-strength and high-toughness corrosion-resistant aluminum-lithium alloy and a preparation method thereof. BACKGROUND

[0002] As a lightweight high-strength material, aluminum-lithium alloy has important application value in the fields of aerospace and transportation. However, the traditional aluminum-lithium alloy still faces the following challenges in the improvement of comprehensive performance:

[0003] (1) Balance problem of strength and toughness: the addition of lithium can significantly reduce the density of the alloy and improve the specific strength, but excessive lithium can cause the alloy to become brittle and reduce the toughness, and cracks are easily generated during the processing. At the same time, the addition of strengthening elements such as copper and magnesium can improve the strength, but may cause intergranular corrosion or form brittle phases (such as Al2CuMg), resulting in a decrease in comprehensive mechanical properties.

[0004] (2) Insufficient corrosion resistance: aluminum-lithium alloy is sensitive to intergranular corrosion, pitting corrosion and stress corrosion cracking, especially in alloys containing impurity elements (such as iron and silicon) or having serious element segregation. The content of impurity elements (such as Fe and Si) in the traditional alloy is not strictly controlled, which can easily form brittle phases such as AlFeSi, and aggravate the tendency of intergranular corrosion and pitting corrosion. At the same time, there is a lack of effective micro-alloying elements to inhibit grain boundary sliding, resulting in local corrosion sensitivity.

[0005] (3) Complex preparation process: the existing alloy preparation process (such as homogenization treatment, hot working and aging strengthening) cannot effectively inhibit dendritic segregation, refine grains and achieve uniform distribution of precipitates, resulting in insufficient performance stability.

[0006] Although there have been studies on optimizing grain structure by adding micro-alloying elements such as scandium (Sc) and zirconium (Zr), it is still difficult to balance high strength, high toughness and corrosion resistance due to the limitation of component ratio control, multi-element synergistic effect and fine matching of process parameters. Therefore, it is a technical problem to be solved in this field to develop an aluminum-lithium alloy combined with precise component design and innovative process. SUMMARY

[0007] In view of the problems existing in the prior art, the purpose of the present application is to provide a high-strength and corrosion-resistant aluminum-lithium alloy and a preparation method thereof. The alloy realizes the balance and optimization of strength, toughness and corrosion resistance by accurately adjusting the ratio of Li, Cu and Mg main elements, combining the synergistic strengthening effect of trace amounts of Sc, Zr, Ag and Y, and innovating the thermal mechanical treatment process, and is suitable for high-end fields such as aerospace structures and new energy vehicle battery packs.

[0008] In order to achieve the above purpose, the aluminum-lithium alloy of the present application comprises the following element components in percentage by weight:

[0009] Li (Lithium): 1.8% to 2.2%;

[0010] Cu (Copper): 2.8% to 3.2%:

[0011] Mg (Magnesium): 4.2% to 4.6%:

[0012] Ag (Silver): 0.15% to 0.25%;

[0013] Sc (Scandium): 0.08% to 0.15%;

[0014] Zr (Zirconium): 0.06% to 0.10%;

[0015] Y (Yttrium): 0.03 to 0.05%;

[0016] Fe (Iron): ≤0.05%;

[0017] Si (Silicon): ≤0.03%;

[0018] Al (Aluminum) and inevitable impurities (≤0.15%): balance.

[0019] The presence of lithium can generate nano δ' phase (Al3Li) with aluminum, which can significantly reduce the density of the alloy, increase the specific strength and specific stiffness, and also improve the corrosion resistance and fatigue resistance of the alloy. Too high lithium content can reduce the corrosion resistance of the alloy, and can also make the alloy too fragile, reduce its toughness, and increase the difficulty of processing, which can easily cause cracks during processing. When the lithium content is less than 1.8%, the effect of reducing the density of the alloy, increasing the specific strength and specific stiffness can be weakened, and the fatigue resistance and corrosion resistance are not obviously improved. When the lithium content is greater than 2.2%, the δ' phase is coarsened, which can reduce the corrosion resistance of the alloy, and can also make the alloy too fragile, reduce its toughness, and increase the difficulty of processing, which can easily cause cracks during processing.

[0020] The addition of copper forms θ' phase (Al2Cu) to strengthen the matrix, improve the aging response, increase the strength and hardness of the alloy, and also improve the heat resistance and corrosion resistance of the alloy. In the alloy of the present application, the copper content is controlled between 2.8% and 3.2%, which can effectively play its strengthening effect, and can also avoid the decrease of toughness and increase of processing difficulty caused by too high content. When the copper content is less than 2.8%, the strength and hardness of the alloy can be reduced, and the heat resistance and corrosion resistance can be limitedly improved. When the copper content is greater than 3.2%, Al2CuMg brittle phase can be easily generated, which can make the alloy brittle, reduce its toughness, and also can cause intergranular corrosion, which can damage the corrosion resistance and strength of the alloy.

[0021] The addition of magnesium can play a role of solid solution strengthening, inhibit the oxidation of Li element, improve the strength and heat resistance of the alloy, and can improve the welding performance and corrosion resistance of the alloy. In the aluminum-lithium alloy of the present application, the content range of magnesium can make magnesium fully play a role in the alloy, improve the comprehensive performance of the alloy, and at the same time avoid the problem of intergranular corrosion caused by too high magnesium content. If the content of magnesium is less than 4.2%, the strength and heat resistance of the alloy will be reduced, and the welding performance and corrosion resistance will be limited. If it is higher than 4.6%, it may cause the deterioration of hot working performance, increase the risk of intergranular corrosion, damage the corrosion resistance of the alloy, and at the same time may make the alloy too sensitive, and require higher processing technology.

[0022] The presence of silver can promote the uniform precipitation of Omega phase (Al2CuMg), improve the high temperature stability and the tensile strength and yield strength of the alloy, and also improve the corrosion resistance and stress corrosion cracking resistance of the alloy. In the alloy of the present application, the content of silver is controlled in the range of 0.15% to 0.25%, although the content is low, but it plays an important role in improving the performance of the alloy. If the content of silver is less than the above range, the effect of refining the grain may be reduced, the tensile strength and yield strength of the alloy are not obviously improved, and the corrosion resistance and stress corrosion cracking resistance are limitedly improved. If the content of silver is higher than the above range, the cost will be increased and the effect will be saturated.

[0023] The addition of scandium can generate Al3Sc nanoparticles (size ≤ 15 nm) with aluminum, refine the grain to ≤ 10 μm, have a significant effect of refining the alloy, improve the strength and toughness of the alloy, and also improve the heat resistance and corrosion resistance of the alloy. In the aluminum-lithium alloy of the present application, the content of scandium is 0.08% to 0.15%, which can effectively play the role of refining the grain and improving the performance. If the content of scandium is insufficient, the effect of refining the grain may be reduced, the strength and toughness of the alloy are not obviously improved, and the heat resistance and corrosion resistance are limitedly improved. If the content of scandium exceeds the standard, the cost will be increased, and at the same time, coarse ScAl phase may be formed, which will adversely affect the processing performance of the alloy.

[0024] The addition of zirconium can inhibit recrystallization (recrystallization fraction < 3%) with Sc, play a role of refining the grain and stabilizing the phase structure, improve the strength and toughness of the alloy, and also improve the corrosion resistance and welding performance of the alloy. In the alloy, the content of zirconium is controlled in the range of 0.06% to 0.10%, which has a certain effect on the stability and improvement of the performance of the alloy. If the content of zirconium is insufficient, the effect of refining the grain and stabilizing the phase structure may be reduced, the strength and toughness of the alloy are not obviously improved, and the corrosion resistance and welding performance are limitedly improved. If the content of zirconium exceeds the standard, the hardness of the alloy may be increased, the toughness may be reduced, and at the same time, the welding performance of the alloy may be adversely affected.

[0025] Yttrium as a grain boundary strengthening element, can inhibit the grain boundary slip, improve the grain boundary binding force, and has the effect of refining the dendritic structure, which helps to obtain more uniform, fine grain structure, thereby improving the grain boundary plasticity and toughness of the alloy, and improving the high temperature strength and corrosion resistance of the alloy, in the alloy of the application, the content of yttrium is controlled at 0.03% to 0.05%, if the content of yttrium is insufficient, the gain of yttrium will be weakened. If the content of yttrium exceeds the standard, it may cause difficulties in the processing of the alloy, such as increasing the hardness and brittleness of the alloy, reducing its processability, and increasing the production cost of the alloy.

[0026] In addition, iron is an impurity element in aluminum-lithium alloy, and the Fe impurity is controlled to avoid the formation of AlFeSi brittle phase, and the content of iron is too high, which will reduce the corrosion resistance and toughness of the alloy, so the content of iron needs to be strictly controlled below 0.05%. Silicon is also an impurity element, and the control of Si impurity can reduce the grain boundary embrittlement, and the content of silicon is too high, which will reduce the strength and corrosion resistance of the alloy, so the content of silicon in the alloy is controlled below 0.03%.

[0027] The content of unavoidable impurities is less than or equal to 0.15%, and the impurities specifically include: calcium (Ca), lead (Pb), vanadium (V), sodium (Na), bismuth (Bi), antimony (Sb), beryllium (Be) and the like. It is pointed out that when the unavoidable impurities are described, since the undesirable impurities from the raw materials or the surrounding environment are inevitably mixed in the typical manufacturing process, they cannot be excluded. Since these impurities are known to those skilled in the art during the manufacturing process, all the details thereof are not specifically mentioned in the present specification. Since the above-mentioned impurity element components may have adverse effects on the flowability, mechanical strength, corrosion resistance, thermal conductivity and the like of the aluminum alloy, it is preferred that the total amount of impurity elements is controlled to be below 0.10%, and more preferably, the total amount of impurity elements is controlled to be below 0.05%.

[0028] The preparation method of the high-strength corrosion-resistant aluminum-lithium alloy of the application comprises the following steps:

[0029] S1-raw material preparation: according to the weight percentage of the element composition, prepare industrial high-purity aluminum ingot, Al-Li intermediate alloy, Al-Cu intermediate alloy, Al-Mg intermediate alloy, Al-Ag intermediate alloy, Al-Sc intermediate alloy, Al-Zr intermediate alloy and Al-Y alloy.

[0030] S2-protection atmosphere smelting: argon-nitrogen-hydrogen mixed gas protection, wherein the volume ratio of argon, nitrogen and hydrogen is (56±1%):(42±1%):2%, the oxygen content is below 50ppm, and the smelting adopts staged charging:

[0031] ① First melt Al, Al-Cu, Al-Mg intermediate alloy, the temperature of the molten pool is 710±5℃, electromagnetic stirring for 30-40 minutes, covered with 0.5% LiCl-KCl molten salt protection;

[0032] ② Then add Al-Li intermediate alloy, the temperature of the molten pool is 685±5℃, electromagnetic stirring for 20-30 minutes;

[0033] ③ Then add Al-Ag, Al-Sc, Al-Zr, Al-Y intermediate alloy, the temperature of the molten pool is 700±5℃, adopt rotary spray refining for 8-10 minutes, and remove slag after 10 minutes of standing;

[0034] By adopting argon-nitrogen mixed gas protection, the oxidation and air absorption of the alloy in the melting process are effectively prevented, the oxygen content is reduced, and the purity of the alloy is ensured; the staged feeding is helpful for the gradual melting and uniform mixing of the alloy elements, and local overheating and composition segregation are avoided, thereby laying a foundation for obtaining uniform alloy liquid;

[0035] S3-Gradient cooling casting: adopt multi-stage water-cooled copper mold, the surface layer is cooled by high-pressure water mist, and the core is cooled by circulating water, the pouring temperature is 690±5℃, the blank drawing speed is 80mm / min; and an axial static magnetic field is applied to inhibit dendrite growth, the obtained ingot is packaged by heat sealing to prevent surface oxidation; the multi-stage water-cooled copper mold is adopted to realize gradient cooling, the surface layer of the ingot is rapidly cooled to form a fine grain zone, and the core is slowly cooled to form a uniform dendritic network structure, and such structure is helpful to improve the strength and toughness of the alloy.

[0036] Homogenization treatment: adopt three-stage temperature rising process, the homogenization temperature of the first stage is 300±5℃ / 4h (to dissolve non-equilibrium eutectic phase), the homogenization temperature of the second stage is 450±5℃ / 12h (to eliminate Cu / Mg segregation), and the homogenization temperature of the third stage is 470±5℃ / 6h (to promote Sc / Zr atomic cluster formation); gradient temperature control (temperature rising rate 20℃ / h) is adopted during the process to eliminate dendritic segregation, and final cooling is realized by staged water quenching (470℃→300℃→150℃→room temperature), wherein, in the first stage (470℃→300℃), 80-90℃ hot water is adopted, and the cooling rate is 15-25℃ / s; in the second stage (300℃→150℃), 50-60℃ hot water is adopted, and the cooling rate is 20-30℃ / s; in the third stage (150℃→room temperature), 20-30℃ hot water is adopted, and the cooling rate is 30-40℃ / s; the thermal stress is reduced by staged cooling to avoid quenching cracking, and Li element segregation is inhibited.

[0037] S4-Deformation heat treatment control:

[0038] The first pass is rolling at a temperature of 425℃, a deformation amount of 25%, and a strain rate of 0.8s -1 ;

[0039] Second pass, rolling temperature is 405℃, deformation 30%, strain rate 1.2s -1 ;

[0040] Third pass, rolling temperature is 385℃, deformation 35%, strain rate 2.0s -1 ;

[0041] Fourth pass, rolling temperature is 370℃, deformation 40%, strain rate 3.5s -1 .

[0042] Immediately after deformation, double medium quenching (water cooling + liquid nitrogen spraying) is carried out, and the quenching transfer time is ≤10 seconds (to prevent the precipitation of coarse phase). Among them, the water temperature of water cooling is controlled at 20-30℃, the cooling method adopts immersion type water tank, and the temperature is reduced to 140-160℃ (to avoid direct cooling to room temperature to cause excessive stress); the atomization pressure of liquid nitrogen (LN2) atomization spraying is 0.3-0.6MPa, the nozzle spacing is 100-200mm, the infrared temperature instrument feeds back in real time, and the final temperature is ensured to be ≤-50℃.

[0043] Multi-pass rolling is carried out at different temperatures, by controlling the rolling temperature, deformation and strain rate, so that the alloy occurs dynamic recrystallization and static recrystallization during hot deformation, the grain is refined, the crystal orientation is optimized, and the strength and toughness of the alloy are improved. After final rolling, the surface roughness Ra≤0.8μm, so that the alloy surface has high smoothness and flatness, reduces the surface defects and stress concentration points, and helps to improve the fatigue strength and corrosion resistance of the alloy. The advantage of double medium quenching is that it is rapidly cooled in the unstable region of austenite, and slowly cooled in the martensite transformation region, which reduces the organizational stress and thermal stress, and reduces the internal stress of the alloy and the possibility of deformation and cracking caused thereby. Through double medium quenching, the alloy can not only maintain high hardness, but also obtain good toughness and wear resistance, and the comprehensive mechanical properties are significantly improved.

[0044] S5-Composite aging strengthening:

[0045] Solution treatment: the temperature is controlled at 480±5℃, and the holding time is controlled at 2h, and then water quenching to room temperature. This process is used to dissolve the strengthening phase to obtain a supersaturated solid solution;

[0046] Pre-deformation treatment: 2% tensile pre-strain is carried out at room temperature, and this process promotes the nucleation of aging precipitates by introducing dislocations, and improves the strength and uniformity. Aging is carried out immediately after deformation to avoid dislocation recovery.

[0047] Aging process: The aging treatment is carried out at two stages with temperatures controlled at 120±5℃ and 160±5℃, for 10h and 16h respectively, followed by air cooling. The two-stage aging treatment allows the precipitates to develop in different sizes and distributions, forming high-density, uniformly distributed precipitates, thereby significantly improving the strength and corrosion resistance of the alloy.

[0048] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0049] Li-Cu-Mg synergy: Li and Al form a nano-δ' phase (Al3Li), which reduces density and increases specific strength; Cu forms a θ' phase (Al2Cu) to strengthen the matrix; Mg inhibits Li oxidation and enhances heat resistance.

[0050] Sc / Y / Zr microalloying: Sc and Y form Al3(Sc,Y) nano-precipitates (<50nm), refining the grain size to 5-8μm. Zr synergistically inhibits recrystallization, significantly improving strength and toughness. This invention improves corrosion resistance by strictly limiting Fe and Si to avoid the formation of brittle phases.

[0051] In terms of manufacturing process, this invention combines high-pressure water mist (120℃ / s) on the surface with circulating water cooling (25℃ / s) in the core to form a fine-grained region on the surface and a uniform dendritic structure in the core, thus suppressing segregation. This invention employs multi-pass rolling (deformation 25%-40%) combined with dual-medium quenching (water cooling + liquid nitrogen spray) to refine dynamically recrystallized grains, achieving a final surface roughness Ra≤0.8μm and reducing stress concentration. This invention uses a two-stage aging process (120℃ / 10h + 160℃ / 16h) to promote the uniform distribution of high-density nano-precipitates (T1, θ' phases), balancing strength and corrosion resistance. Detailed Implementation

[0052] The specific embodiments of the present invention will be further described below with reference to the examples. The following examples are only used to illustrate the technical solutions of the present invention more clearly, and should not be used to limit the scope of protection of the present invention.

[0053] Example 1

[0054] Embodiment 1 of this application discloses a high-strength, tough, and corrosion-resistant aluminum-lithium alloy, comprising the following elemental composition by weight percentage, as shown in Table 1 below:

[0055] Table 1:

[0056]

[0057] Based on the above ingredients, the preparation method of aluminum-lithium alloy in Example 1 mainly includes the following steps:

[0058] S1-Preparation: Prepare industrial high-purity aluminum ingots (purity ≥ 99.95%), Al-Li intermediate alloy, Al-Cu intermediate alloy, Al-Mg intermediate alloy, Al-Ag intermediate alloy, Al-Sc intermediate alloy, Al-Zr intermediate alloy, and Al-Y alloy.

[0059] S2-Protection atmosphere melting: argon-nitrogen-hydrogen mixed gas protection, wherein the volume ratio of argon, nitrogen and hydrogen is 55%:43%:2%, the oxygen content is less than 50 ppm, and the melting adopts staged feeding:

[0060] ① First melt Al, Al-Cu, Al-Mg intermediate alloy, the molten pool temperature is 705℃, electromagnetic stirring (frequency 15Hz) for 40 minutes, cover 0.5% LiCl-KCl molten salt protection;

[0061] ② Then add Al-Li intermediate alloy, the molten pool temperature is 680℃, electromagnetic stirring (frequency 15Hz) for 30 minutes;

[0062] ③ Then add Al-Ag, Al-Sc, Al-Zr, Al-Y intermediate alloy, the molten pool temperature is 695℃, adopt rotary spray refining (add C2Cl6 equivalent to 0.15% of the mother liquor mass + nitrogen carrier), refine for 8 minutes, then stand for 10 minutes, then remove slag;

[0063] S3-Gradient cooling casting: adopt multi-stage water-cooled copper mold, the surface layer is cooled by high-pressure water mist (120℃ / s), the core is cooled by circulating water (25℃ / s), the pouring temperature is 685℃, the blank drawing speed is 80mm / min; and an axial static magnetic field (0.5T) is applied to suppress dendrite growth, and the obtained ingot is packaged by hot sealing (395℃ into the furnace).

[0064] Homogenization treatment: adopt three-stage heating process, the first stage homogenization temperature is 295℃ / 4h, the second stage homogenization temperature is 445℃ / 12h, and the third stage homogenization temperature is 465℃ / 6h; during the period, gradient temperature control (heating rate 20℃ / h) is adopted to eliminate dendritic segregation. The final cooling adopts staged water quenching, wherein the first stage (470℃→300℃) adopts 80℃ hot water with a cooling rate of 25℃ / s; the second stage (300℃→150℃) adopts 50℃ hot water with a cooling rate of 30℃ / s; the third stage (150℃→room temperature) adopts 20℃ hot water with a cooling rate of 40℃ / s.

[0065] S4-Shape control heat treatment:

[0066] First pass, rolling temperature is 425℃, deformation amount is 25%, strain rate is 0.8s -1 ;

[0067] Second pass, rolling temperature is 405℃, deformation 30%, strain rate 1.2s -1 ;

[0068] Third pass, rolling temperature is 385℃, deformation 35%, strain rate 2.0s -1 ;

[0069] Fourth pass, rolling temperature is 370℃, deformation 40%, strain rate 3.5s -1 .

[0070] Immediately after deformation, double medium quenching (water cooling + liquid nitrogen spraying) is carried out, and the quenching transfer time is ≤10 seconds. Among them, the water temperature of water cooling is controlled at 20℃, the cooling mode adopts immersion type water tank, and the temperature is reduced to 160℃; the atomization pressure of liquid nitrogen (LN2) atomization spraying is 0.3MPa, the nozzle spacing is 100mm, the infrared temperature instrument feedbacks in real time, and the final temperature is ensured to be ≤-50℃.

[0071] S5-Composite aging strengthening:

[0072] Solution treatment (in vacuum environment, oxygen partial pressure <10 -3 Pa): the temperature is controlled at 475℃, the holding time is controlled at 2h, and then water quenching (20℃ deionized water, cooling rate is 100℃ / s) is carried out to room temperature.

[0073] Pre-deformation treatment: 2% tensile pre-strain is carried out at room temperature.

[0074] Aging process: the two-stage temperature of aging treatment is controlled at 120±5℃ and 160±5℃ respectively, the time is 10h and 16h respectively, and then air cooling is carried out.

[0075] Example 2

[0076] The example 2 of the application discloses a high-strength and high-toughness corrosion-resistant aluminum-lithium alloy, which comprises the following element components in percentage by weight, as shown in the following ingredient table 2:

[0077] Table 2:

[0078]

[0079] Based on the above ingredients, the preparation method of the aluminum-lithium alloy of the example 2 mainly comprises the following steps:

[0080] S1-Preparation of materials: preparation of industrial high-purity aluminum ingot (purity ≥ 99.95%), Al-Li intermediate alloy, Al-Cu intermediate alloy, Al-Mg intermediate alloy, Al-Ag intermediate alloy, Al-Sc intermediate alloy, Al-Zr intermediate alloy and Al-Y alloy.

[0081] S2-Protective atmosphere melting: argon-nitrogen-hydrogen mixed gas protection, wherein the volume ratio of argon, nitrogen and hydrogen is 56%:42%:2%, the oxygen content is less than 50ppm, and the melting adopts staged feeding:

[0082] ①First, melt Al, Al-Cu, Al-Mg intermediate alloy, the temperature of the molten pool is 710℃, electromagnetic stirring (frequency 15Hz) for 35 minutes, cover 0.5% LiCl-KCl molten salt protection;

[0083] ②Then add Al-Li intermediate alloy, the temperature of the molten pool is 685℃, electromagnetic stirring (frequency 15Hz) for 25 minutes;

[0084] ③Then add Al-Ag, Al-Sc, Al-Zr, Al-Y intermediate alloy, the temperature of the molten pool is 700℃, adopt rotary spray refining (add C2Cl6 equivalent to 0.15% of the mother liquor mass + nitrogen carrier), refine for 9 minutes, then stand for 10 minutes, and then remove slag;

[0085] S3-Gradient cooling casting: adopt multi-stage water-cooled copper mold, the surface layer is cooled by high-pressure water mist (120℃ / s), the core is cooled by circulating water (25℃ / s), the pouring temperature is 690℃, the pulling speed is 80mm / min; and an axial static magnetic field (0.5T) is applied to inhibit dendrite growth, and the obtained ingot is packaged by hot sealing (400℃ into the furnace).

[0086] Homogenization treatment: adopt three-stage heating process, the homogenization temperature of the first stage is 300℃ / 4h, the homogenization temperature of the second stage is 450℃ / 12h, and the homogenization temperature of the third stage is 470℃ / 6h; during the period, gradient temperature control (heating rate 20℃ / h) is adopted to eliminate dendritic segregation. The final cooling adopts staged water quenching, wherein, in the first stage (470℃→300℃), 85℃ hot water is used, and the cooling rate is 20℃ / s; in the second stage (300℃→150℃), 55℃ hot water is used, and the cooling rate is 25℃ / s; in the third stage (150℃→room temperature), 25℃ hot water is used, and the cooling rate is 35℃ / s.

[0087] S4-Shape control heat treatment:

[0088] The first pass, the rolling temperature is 425℃, the deformation amount is 25%, and the strain rate is 0.8s -1 ;

[0089] The second pass, the rolling temperature is 405℃, the deformation amount is 30%, and the strain rate is 1.2s -1 ;

[0090] The third pass, the rolling temperature is 385℃, the deformation amount is 35%, and the strain rate is 2.0s -1 ;

[0091] The fourth pass is rolled at a temperature of 370℃, a deformation of 40%, and a strain rate of 3.5s -1 .

[0092] Immediately after deformation, double medium quenching (water cooling + liquid nitrogen spraying) is performed, and the quenching transfer time is ≤10 seconds. Among them, the water temperature of water cooling is controlled at 25℃, the cooling method adopts immersion type water tank, and the temperature is reduced to 150℃; the atomization pressure of liquid nitrogen (LN2) atomization spraying is 0.5MPa, the nozzle spacing is 200mm, the infrared temperature instrument feeds back in real time, and the final temperature is ensured to be ≤-50℃.

[0093] S5-composite aging strengthening:

[0094] Solution treatment (in a vacuum environment, oxygen partial pressure <10 -3 Pa): the temperature is controlled at 480℃, the holding time is controlled at 2h, and then water quenching (25℃ deionized water, cooling rate is 110℃ / s) is performed to room temperature.

[0095] Pre-deformation treatment: 2% tensile pre-strain is performed at room temperature.

[0096] Aging process: the two-stage temperature of aging treatment is controlled at 120℃ and 160℃ respectively, the time is 10h and 16h respectively, and then air cooling is performed.

[0097] Example 3

[0098] The example 3 of the present application discloses a high strength and toughness corrosion resistant aluminum lithium alloy, which comprises the following element components in percentage by weight as shown in the following ingredient table 3:

[0099] Table 3:

[0100]

[0101] Based on the above ingredients, the preparation method of the aluminum lithium alloy of the example 3 mainly includes the following steps:

[0102] S1-preparation of materials: prepare industrial high-purity aluminum ingot (purity ≥ 99.95%), Al-Li intermediate alloy, Al-Cu intermediate alloy, Al-Mg intermediate alloy, Al-Ag intermediate alloy, Al-Sc intermediate alloy, Al-Zr intermediate alloy and Al-Y alloy.

[0103] S2-protection atmosphere smelting: argon-nitrogen-hydrogen mixed gas protection, wherein the volume ratio of argon, nitrogen and hydrogen is 57%:41%:2%, and the oxygen content is lower than 50ppm, and the smelting adopts staged feeding:

[0104] ① First melt Al, Al-Cu, Al-Mg intermediate alloy, the temperature of the molten pool is 715℃, electromagnetic stirring (frequency 15Hz) for 30 minutes, cover 0.5% LiCl-KCl molten salt protection;

[0105] ② Then add Al-Li intermediate alloy, the temperature of the molten pool is 690℃, electromagnetic stirring (frequency 15Hz) for 20 minutes;

[0106] ③ Then add Al-Ag, Al-Sc, Al-Zr, Al-Y intermediate alloy, the temperature of the molten pool is 705℃, adopt rotary spray refining (add C2Cl6 equivalent to 0.15% of the mother liquor mass + nitrogen carrier), refine for 10 minutes, then stand for 10 minutes, then remove slag;

[0107] S3-Gradient cooling casting: adopt multi-stage water-cooled copper mold, the surface layer is high-pressure water mist cooling (120℃ / s), the core is circulating water cooling (25℃ / s), pouring temperature is 695℃, the pulling speed is 80mm / min; and apply axial static magnetic field (0.5T) to inhibit dendrite growth, and the obtained ingot is subjected to hot packaging (405℃ into the furnace).

[0108] Homogenization treatment: adopt three-stage heating process, the first stage homogenization temperature is 305℃ / 4h, the second stage homogenization temperature is 455℃ / 12h, and the third stage homogenization temperature is 475℃ / 6h; during the period, adopt gradient temperature control (heating rate 20℃ / h) to eliminate dendritic segregation. The final cooling adopts staged water quenching, wherein, in the first stage (470℃→300℃), 90℃ hot water is adopted, and the cooling rate is 15℃ / s; in the second stage (300℃→150℃), 60℃ hot water is adopted, and the cooling rate is 20℃ / s; in the third stage (150℃→room temperature), 30℃ hot water is adopted, and the cooling rate is 30℃ / s.

[0109] S4-Shape control heat treatment:

[0110] The first pass, the rolling temperature is 425℃, the deformation amount is 25%, and the strain rate is 0.8s -1 ;

[0111] The second pass, the rolling temperature is 405℃, the deformation amount is 30%, and the strain rate is 1.2s -1 ;

[0112] The third pass, the rolling temperature is 385℃, the deformation amount is 35%, and the strain rate is 2.0s -1 ;

[0113] The fourth pass, the rolling temperature is 370℃, the deformation amount is 40%, and the strain rate is 3.5s -1 .

[0114] Immediately after deformation, dual medium quenching (water cooling + liquid nitrogen spraying) was carried out, and the quenching transfer time was ≤10 seconds. Among them, the water temperature of water cooling was controlled at 30°C, the cooling mode adopted immersion type water tank, and the temperature dropped to 140°C; the atomization pressure of liquid nitrogen (LN2) atomization spraying was 0.6 MPa, the nozzle spacing was 100 mm, the infrared temperature instrument was fed back in real time, and the final temperature was ensured to be ≤-50°C.

[0115] S5 - composite aging strengthening:

[0116] Solution treatment (vacuum environment, oxygen partial pressure <10 -3 Pa): the temperature was controlled at 485°C, the holding time was controlled at 2h, and then water quenching (30°C deionized water, cooling rate was 120°C / s) was carried out to room temperature.

[0117] Pre-deformation treatment: 2% tensile pre-strain was carried out at room temperature.

[0118] Aging process: the two-stage temperature of aging treatment was controlled at 125°C and 165°C respectively, the time was 10h and 16h respectively, and then air cooling was carried out.

[0119] Comparative Example 1

[0120] Comparative Example 1 discloses an aluminum lithium alloy.

[0121] Composition: Li 2.0%, Cu 3.0%, Mg 4.4%, Ag 0.20%, Sc / Y 0%, and the others are the same as Example 2.

[0122] Process: the same as Example 2, but the Al-Sc, Al-Y intermediate alloy addition is omitted.

[0123] Comparative Example 2

[0124] Comparative Example 2 discloses an aluminum lithium alloy.

[0125] Composition: the same as Example 2.

[0126] Process: the aging treatment is changed to single stage (160°C / 26h), and the other steps are the same.

[0127] Comparative Example 3

[0128] Comparative Example 3 discloses an aluminum lithium alloy.

[0129] Composition: the same as Example 2.

[0130] Process: the axial static magnetic field in S3 is cancelled, and the other parameters are the same as Example 2.

[0131] Comparative Example 4

[0132] Comparative Example 4 discloses an aluminum lithium alloy.

[0133] Composition: same as Example 2.

[0134] Process: homogenization treatment changed to single stage (450℃ / 22h), three-stage temperature rising cancelled.

[0135] Comparative Example 5

[0136] Comparative Example 5 discloses an aluminum-lithium alloy.

[0137] Composition: same as Example 2.

[0138] Process: S4 quenching only uses water cooling (final temperature ≤20℃), liquid nitrogen spraying is cancelled.

[0139] Test Example

[0140] The aluminum-lithium alloys prepared in the above Examples 1-3 and Comparative Examples 1-5 were subjected to the following performance tests, and the test results are shown in Tables 4 and 5 below:

[0141] I. Tensile strength, yield strength, elongation: tested according to GB / T 228.1 “Metallic materials— Tensile testing— Part 1: Method of test at room temperature”;

[0142] II. Fracture toughness: reference GB / T 4161 “Metallic materials— Plane-strain fracture toughness KIC test method”, fracture toughness value is tested by loading pre-cracked sample;

[0143] III. Corrosion resistance detection

[0144] 3.1. Salt spray test (corrosion weight loss and pitting depth): GB / T 10125-2012 “Artificial atmosphere corrosion testing— Salt spray tests” is adopted, neutral salt spray test (NSS) or copper-accelerated acetic acid salt spray test (CASS) is used to evaluate the corrosion resistance of aluminum-lithium alloy;

[0145] 3.2. Intergranular corrosion sensitivity: method C (electrochemical polarization method) in GB / T 36174-2018 “Determination of the resistance of aluminum alloys to intergranular corrosion after solid solution heat treatment for corrosion” is used to evaluate the intergranular corrosion of aluminum-lithium alloy;

[0146] Table 4: Mechanical properties and toughness test data of aluminum-lithium alloy

[0147] Group Tensile strength (MPa) Yield strength (MPa) Elongation (%) Fracture toughness (MPa-m 1 / 2 )]]> Example 1 620 580 8.5 32.5 Example 2 645 605 7.8 30.8 Example 3 670 630 7.0 29.0 Comparative Example 1 580 540 6.2 25.4 Comparative Example 2 600 560 6.8 27.1 Comparative Example 3 595 550 5.5 23.6 Comparative Example 4 560 520 4.9 20.3 Comparative Example 5 610 570 6.0 26.0

[0148] From the above Table 4, it can be analyzed that:

[0149] The tensile strength (620-670 MPa) and yield strength (580-630 MPa) of the examples (1-3) were significantly higher than the comparative examples (1-5, tensile strength 560-610 MPa, yield strength 520-570 MPa). Example 3 exhibited the highest strength (tensile 670 MPa, yield 630 MPa), which was about 10% higher than the highest value of the comparative examples (tensile 610 MPa, yield 570 MPa).

[0150] The elongation of the examples (7.0-8.5%) was overall better than the comparative examples (4.9-6.8%). As the strength increased (Example 1→3), the elongation decreased from 8.5% to 7.0%, indicating a trade-off between strength and ductility, but still higher than most of the comparative examples.

[0151] The fracture toughness of the examples (29.0-32.5 MPa·m 2 ) was significantly higher than the comparative examples (20.3-27.1 MPa·m 2 ). The toughness of Example 1 was the best (32.5 MPa·m 2 ), which was about 20% higher than the highest value of the comparative examples (27.1 MPa·m 2 ).

[0152] Table 5: Corrosion resistance test data

[0153]

[0154]

[0155] From the above Table 5, it can be analyzed that:

[0156] The corrosion weight loss of the examples (1-3) (9.2-12.5 g / m 2 ) was significantly lower than the comparative examples (1, 3, 4: 18.7-30.1 g / m 2 ), indicating that the uniform corrosion resistance of the examples was better. The corrosion weight loss of Example 3 (9.2 g / m 2 ) was about 51% lower than the best value in the comparative examples (Comparative Example 3: 18.7 g / m 2 ), which had a significant improvement effect.

[0157] The maximum pitting depth of the examples (32-45 μm) was much lower than the comparative examples (65-95 μm), indicating that the examples had stronger inhibition ability to local pitting. The pitting depth of Example 3 (32 μm) was only about 49% of that of Comparative Example 3 (65 μm), further verifying its advantage in pitting resistance.

[0158] Four, Microstructure analysis

[0159] Example 1-3: The alloy has uniform fine equiaxed grains (grain size 5-8 μm), T1 phase (Al2CuLi) and θ' phase (Al2Cu) are uniformly distributed, Sc / Y forms Al3(Sc,Y) nano-precipitates (size < 50 nm).

[0160] Comparative Example 1: Coarse grains (15-20 μm), precipitates are clustered, no Al3(Sc,Y) phase.

[0161] Comparative Example 3: Columnar dendrite structure is obvious, serious segregation at grain boundaries.

[0162] Comparative Example 5: Precipitates size increases (200-300 nm), uneven distribution.

[0163] The above only the preferred embodiments of the present application have, and not for limiting the present application, although with reference to the foregoing embodiments of the present application are described in detail, for those skilled in the art, it still can be modified, or part of the technical features of the equivalent replacement of the technical solutions recorded in the foregoing embodiments. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application, should be included within the scope of the present application.

Claims

1. A high-strength corrosion-resistant aluminum-lithium alloy, characterized by, Comprising the following elemental components in percentage by weight: Li: 1.8%~2.2%, Cu: 2.8%~3.2%, Mg: 4.2%~4.6%, Ag: 0.15%~0.25%, Sc: 0.08%~0.15%, Zr: 0.06%~0.10%, Y: 0.03~0.05%, Fe: ≤0.05%, Si: ≤0.03%; and Al: balance.

2. The high-strength corrosion-resistant aluminum-lithium alloy of claim 1, wherein, Comprising the following elemental components in percentage by weight: Li: 2.0%, Cu: 3.0%, Mg: 4.4%, Ag: 0.20%, Sc: 0.12%, Zr: 0.08%, Y: 0.04%, Fe: ≤0.05%, Si: ≤0.03%; and Al: balance.

3. The high-strength corrosion-resistant aluminum-lithium alloy of claim 1, wherein, Comprising the following elemental components in percentage by weight: Li: 1.8%, Cu: 2.8%, Mg: 4.2%, Ag: 0.15%, Sc: 0.08%, Zr: 0.06%, Y: 0.03, Fe: ≤0.05%, Si: ≤0.03%; and Al: balance.

4. The high-strength corrosion-resistant aluminum-lithium alloy of claim 1, wherein, Comprising the following elemental components in percentage by weight: Li: 2.2%, Cu: 3.2%, Mg: 4.6%, Ag: 0.25%, Sc: 0.15%, Zr: 0.10%, Y: 0.05%, Fe: ≤0.05%, Si: ≤0.03%; and Al: balance.

5. A method of producing the high-strength corrosion-resistant aluminum-lithium alloy according to any one of claims 1 to 4, characterized by, Comprising the following steps: S1-Preparation of raw materials; S2-Smelting Using staged feeding: ①First melt Al, Al-Cu, Al-Mg intermediate alloy, the temperature of the molten pool is 710±5℃, electromagnetic stirring for 30~40 minutes, and covering 0.5% LiCl-KCl molten salt protection; ②Then add Al-Li intermediate alloy, the temperature of the molten pool is 685±5℃, electromagnetic stirring for 20~30 minutes; ③Then add Al-Ag, Al-Sc, Al-Zr, Al-Y intermediate alloy, the temperature of the molten pool is 700±5℃, and rotary spray refining is used, and after refining for 8~10 minutes, it is placed for 10 minutes, and then slag is removed; S3-Gradient cooling casting Using multi-stage water-cooled copper mold, the surface layer is cooled by high-pressure water mist, the cooling temperature is 120℃ / s; the core is cooled by circulating water, the cooling temperature is 25℃ / s, the pouring temperature is 690±5℃, the blank drawing speed is 80mm / min; the obtained ingot is packaged by hot sealing at 400±5℃ into the furnace; Homogenization treatment: using three-stage temperature rising process, the homogenization temperature of the first stage is 300±5℃, the time is 4h, the homogenization temperature of the second stage is 450±5℃, the time is 12h, the homogenization temperature of the third stage is 470±5℃, the time is 6h, during which gradient temperature control is adopted, the heating rate is 20℃ / h, and the final cooling is carried out by staged water quenching, which is sequentially reduced from 470℃ to 300℃, 150℃ and room temperature; S4-Controlled deformation heat treatment: First pass, rolling temperature 425°C, deformation 25%, strain rate 0.8 s -1 ; The second pass, the rolling temperature is 405 ℃, the deformation 30%, the strain rate 1.2 s -1 ; Third pass, rolling temperature 385°C, deformation 35%, strain rate 2.0 s -1 ; The fourth pass, the rolling temperature is 370℃, the deformation is 40%, the strain rate is 3.5s -1 . Immediately after deformation, double-medium quenching, namely water cooling+liquid nitrogen spraying, is carried out; S5-Composite aging strengthening Solution treatment: the temperature is controlled at 480±5℃, and the holding time is controlled at 2h, and then water quenching is carried out; Pre-deformation treatment: 2% tensile pre-strain is carried out at room temperature; Aging process: the two-stage temperature of aging treatment is controlled at 120±5℃ and 160±5℃ respectively, and the time is 10h and 16h respectively, and then air cooling.

6. The preparation method according to claim 5, characterized in that, During the smelting process, argon-nitrogen-hydrogen mixed gas protection is adopted, the volume ratio of argon, nitrogen and hydrogen is (56±1%):(42±1%):2%, and the oxygen content is less than 50ppm.

7. The preparation method according to claim 5, characterized in that, The refining is adding C2Cl6 equivalent to 0.15% of the mass of the mother liquor, and loading by nitrogen.

8. The preparation method according to claim 5, characterized in that, During the casting process, an axial static magnetic field of 0.5T is applied.

9. The preparation method according to claim 5, characterized in that, The first stage of the staged water quenching adopts 80-90℃ hot water, and the cooling rate is 15-25℃ / s; the second stage adopts 50-60℃ hot water, and the cooling rate is 20-30℃ / s; the third stage adopts 20-30℃ hot water, and the cooling rate is 30-40℃ / s.

10. The method of claim 5, wherein, In the double medium quenching, the water temperature of water cooling is controlled at 20-30℃, the cooling mode adopts immersion water tank, the temperature drops to 140-160℃; the atomization pressure of liquid nitrogen atomization spraying is 0.3-0.6MPa, the nozzle spacing is 100-200mm, the infrared temperature measuring instrument feeds back in real time, and the final temperature is ensured to be ≤-50℃.

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