Heat treatment method for improving strength, plasticity, corrosion resistance and fatigue resistance of aluminum-lithium alloy

Abstract

The invention provides a heat treatment method for improving the strength, plasticity, corrosion resistance and fatigue resistance of an aluminum-lithium alloy, and belongs to the technical field of aluminum-lithium alloys. The method comprises the following steps: carrying out solution treatment and first quenching on the aluminum-lithium alloy, and enabling the aluminum-lithium alloy to form a pre-treated aluminum-lithium alloy in an over-solid-solution state; the pretreated aluminum-lithium alloy is subjected to ultralow-temperature cold rolling treatment, the dislocation density of the aluminum-lithium alloy is increased, heterogeneous nucleation and refinement of a T1 phase are promoted, meanwhile, the corrosion potential difference between a matrix and a grain boundary is reduced through narrowing of a grain boundary precipitation-free precipitation zone (PFZ), and therefore the corrosion resistance of the aluminum-lithium alloy is enhanced while the strength of the aluminum-lithium alloy is improved; the intermittent aging treatment is carried out on the ultralow-temperature cold-rolled aluminum-lithium alloy, so that the number density of precipitated phases is increased, the width of PFZ is reduced, and the tensile property, fracture toughness and fatigue resistance of the aluminum-lithium alloy are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum-lithium alloys, and in particular to a heat treatment method for improving the strength, plasticity, corrosion resistance and fatigue resistance of aluminum-lithium alloys. Background Art

[0002] Aluminum-lithium alloys are widely used in aerospace applications due to their excellent properties, including low density, high elastic modulus, high strength, and good damage tolerance. However, the interaction between precipitates and dislocations in aluminum-lithium alloys leads to the accumulation of precipitates at subgrain boundaries, where stress concentrations form. This in turn triggers the initiation and propagation of microcracks, significantly reducing the fatigue resistance of aluminum-lithium alloys. Furthermore, the potential difference between the precipitates and the matrix easily forms localized corrosion microcells in corrosive environments, leading to corrosion failure. Consequently, aluminum-lithium alloys exhibit relatively poor corrosion resistance and fatigue resistance.

[0003] The type, size, and morphology of the precipitated phases in aluminum-lithium alloys are closely related to the aging temperature. Currently, relevant research has been conducted to control the type, size, and morphology of the precipitated phases in aluminum-lithium alloys through heat treatment, optimizing the microstructure of high-strength aluminum-lithium alloys and, in turn, optimizing the performance of aluminum-lithium alloys. Examples include isothermal aging (T6 aging), thermomechanical treatment (T8 aging), and intermittent aging. Isothermal aging can be used to increase the hardness and strength of aluminum-lithium alloys, but the elongation of aluminum-lithium alloys is reduced. Thermomechanical treatment involves pre-deformation by stretching, rolling, or extrusion between the solution and aging processes. This deformation increases the dislocation density and accelerates the aging process, thereby improving the mechanical properties of aluminum-lithium alloys, such as hardness and strength. However, it also increases the corrosion sensitivity of aluminum-lithium alloys and reduces their fatigue life. Intermittent aging is a new aging system developed in recent years both domestically and internationally. It improves the hardness, strength, and corrosion resistance of aluminum-lithium alloys, but exhibits poor fatigue crack growth resistance.

[0004] It can be seen that although there have been many studies on regulating the type, size and morphology of the precipitation phase of aluminum-lithium alloys and optimizing the microstructure of high-strength aluminum-lithium alloys, how to synergistically improve the strength, corrosion resistance and fatigue resistance of aluminum-lithium alloys is still a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] The object of the present invention is to provide a heat treatment method for improving the strength, plasticity, corrosion resistance and fatigue resistance of aluminum-lithium alloy.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a heat treatment method for improving the strength, plasticity, corrosion resistance and fatigue resistance of aluminum-lithium alloy, comprising the following steps:

[0008] (1) subjecting the aluminum-lithium alloy to a solution treatment and a first quenching in sequence to obtain a pretreated aluminum-lithium alloy;

[0009] (2) subjecting the pretreated aluminum-lithium alloy obtained in step (1) to ultra-low temperature cold rolling to obtain an ultra-low temperature cold-rolled aluminum-lithium alloy; the temperature of the ultra-low temperature cold rolling is below -160°C;

[0010] (3) subjecting the ultra-low temperature cold-rolled aluminum-lithium alloy obtained in step (2) to intermittent aging treatment to obtain a high-strength, plastic, corrosion-resistant and fatigue-resistant aluminum-lithium alloy.

[0011] Preferably, the aluminum-lithium alloy in step (1) includes 2195 aluminum-lithium alloy, 2060 aluminum-lithium alloy, 2099 aluminum-lithium alloy or 8090 aluminum-lithium alloy.

[0012] Preferably, the temperature of the solution treatment in step (1) is 510-540° C., and the time of the solution treatment is 0.5-1.5 h.

[0013] Preferably, the first quenching method in step (1) is water quenching.

[0014] Preferably, the deformation amount of the ultra-low temperature cold rolling treatment in step (2) is 6 to 10%.

[0015] Preferably, the intermittent aging treatment in step (3) includes pre-aging, low-temperature aging and re-aging performed in sequence; the temperature of the low-temperature aging is independently lower than the pre-aging temperature and the re-aging temperature.

[0016] Preferably, the pre-aging temperature is 140-180° C., and the pre-aging time is 20 min-3 h.

[0017] Preferably, the low-temperature aging temperature is 25-65° C., and the low-temperature aging time is 0-10 days.

[0018] Preferably, the re-aging temperature is 140-180° C., and the re-aging time is 0-96 h.

[0019] Preferably, the intermittent aging treatment includes pre-aging, second quenching, low-temperature aging, third quenching, re-aging and fourth quenching performed in sequence.

[0020] The present invention provides a heat treatment method for improving the strength, plasticity, corrosion resistance and fatigue resistance of an aluminum-lithium alloy, comprising the following steps: subjecting the aluminum-lithium alloy to a solution treatment and a first quenching in sequence to obtain a pretreated aluminum-lithium alloy; subjecting the pretreated aluminum-lithium alloy to an ultra-low temperature cold rolling treatment to obtain an ultra-low temperature cold-rolled aluminum-lithium alloy; the temperature of the ultra-low temperature cold rolling treatment is below -160°C; and subjecting the ultra-low temperature cold-rolled aluminum-lithium alloy to an intermittent aging treatment to obtain an aluminum-lithium alloy with high strength, plasticity, corrosion resistance and fatigue resistance. The present invention performs a solution treatment and a first quenching on an aluminum-lithium alloy to form a pre-treated aluminum-lithium alloy in an over-solution state; the pre-treated aluminum-lithium alloy is subjected to an ultra-low temperature cold rolling treatment, which can increase the dislocation density of the aluminum-lithium alloy, promote the heterogeneous nucleation and refinement of the T1 phase, and at the same time, the narrowing of the precipitation-free zone (PFZ) at the grain boundary reduces the corrosion potential difference between the matrix and the grain boundary, thereby improving the strength of the aluminum-lithium alloy while enhancing its corrosion resistance; the present invention performs an intermittent aging treatment on the ultra-low temperature cold-rolled aluminum-lithium alloy to increase the number density of the precipitated phase, reduce the width of the PFZ, and improve the tensile properties, fracture toughness, and fatigue resistance of the aluminum-lithium alloy. The results of the embodiment show that when the cold rolling pre-deformation amount is 6-10%, the Vickers hardness can reach above 200HV, the tensile strength is above 560MPa, and the yield strength is above 530MPa, while maintaining a plasticity of 10.3%; the maximum corrosion depth of the alloy is less than 36μm, and its fatigue life is increased by more than 60%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of a heat treatment method for improving the strength, plasticity, corrosion resistance and fatigue resistance of an aluminum-lithium alloy according to the present invention;

[0022] Figure 2 A schematic diagram of the evolution process of the intragranular precipitation phase in the heat treatment method for improving the strength, plasticity, corrosion resistance and fatigue resistance of the aluminum-lithium alloy according to the present invention;

[0023] Figure 3 The intracrystalline high-angle annular dark field morphology images of the aluminum-lithium alloys treated by the methods of Example 1 and Comparative Examples 1 to 3 of the present invention are shown;

[0024] Figure 4 The high-angle annular dark field morphology images of the grain boundaries of the aluminum-lithium alloys treated by the methods of Example 1 and Comparative Examples 1 to 3 of the present invention are shown;

[0025] Figure 5 The engineering stress-strain curves of the aluminum-lithium alloys treated by the methods of Example 1 and Comparative Examples 1 to 3 of the present invention are shown;

[0026] Figure 6 This is the aN curve of the aluminum-lithium alloy treated by the methods of Example 1 and Comparative Examples 1 to 3 of the present invention. DETAILED DESCRIPTION

[0027] The present invention provides a heat treatment method for improving the strength, plasticity, corrosion resistance and fatigue resistance of aluminum-lithium alloy, comprising the following steps:

[0028] (1) subjecting the aluminum-lithium alloy to a solution treatment and a first quenching in sequence to obtain a pretreated aluminum-lithium alloy;

[0029] (2) subjecting the pretreated aluminum-lithium alloy obtained in step (1) to ultra-low temperature cold rolling to obtain an ultra-low temperature cold-rolled aluminum-lithium alloy; the temperature of the ultra-low temperature cold rolling is below -160°C;

[0030] (3) subjecting the ultra-low temperature cold-rolled aluminum-lithium alloy obtained in step (2) to intermittent aging treatment to obtain a high-strength, plastic, corrosion-resistant and fatigue-resistant aluminum-lithium alloy.

[0031] The present invention sequentially performs solid solution treatment and first quenching on the aluminum-lithium alloy to obtain a pretreated aluminum-lithium alloy.

[0032] In the present invention, the aluminum-lithium alloy preferably includes 2195 aluminum-lithium alloy, 2060 aluminum-lithium alloy, 2099 aluminum-lithium alloy, or 8090 aluminum-lithium alloy, with 2195 aluminum-lithium alloy being more preferred. The present invention does not specifically limit the source of the aluminum-lithium alloy; any conventional commercially available product may be used. In an embodiment of the present invention, the composition of the 2195 aluminum-lithium alloy may be: 4.09% Cu, 1.1% Li, 0.34% Mg, 0.35% Ag, 0.34% Mn, 0.08% Zr, and the balance Al.

[0033] In the present invention, the solution treatment temperature is preferably 510-540°C, more preferably 520-530°C; the solution treatment time is preferably 0.5-1.5 hours, more preferably 1 hour. The present invention uses solution treatment to convert the aluminum-lithium alloy into a pretreated aluminum-lithium alloy in an over-solution state. The present invention does not specifically limit the method of solution treatment; conventional solution treatment methods can be used, and solution treatment can be performed at the above-mentioned temperature and time.

[0034] In the present invention, the first quenching method is preferably water quenching. In the present invention, the temperature of the water used for the water quenching is preferably room temperature. Water quenching at room temperature in the present invention has a relatively fast cooling rate. Rapid cooling can inhibit the diffusion of solute atoms, forming a supersaturated solid solution and producing a solid solution strengthening effect.

[0035] After obtaining the pretreated aluminum-lithium alloy, the present invention performs ultra-low temperature cold rolling on the pretreated aluminum-lithium alloy to obtain the ultra-low temperature cold rolled aluminum-lithium alloy.

[0036] In the present invention, the temperature of the ultra-low temperature cold rolling treatment is below -160°C, preferably -196°C. The present invention forms a uniformly distributed dislocation substructure through ultra-low temperature cold rolling treatment, increases the dislocation density of the aluminum-lithium alloy, promotes the heterogeneous nucleation and refinement of the T1 phase, and simultaneously narrows the PFZ to reduce the corrosion potential difference between the matrix and the grain boundary, thereby improving the strength of the aluminum-lithium alloy while enhancing its corrosion resistance.

[0037] In the present invention, the ultra-low temperature cold rolling treatment method preferably includes immersing the pretreated aluminum-lithium alloy in liquid nitrogen and then performing a rolling treatment.

[0038] In the present invention, the deformation amount of the ultra-low temperature cold rolling process is preferably 6-10%. As an embodiment of the present invention, the deformation amount of the ultra-low temperature cold rolling process can be 6%, 7%, 8%, 9%, or 10%. By controlling the deformation amount of the ultra-low temperature cold rolling process within the above range, the present invention can improve the hardness, yield strength, plasticity, and corrosion resistance of the aluminum-lithium alloy.

[0039] In the present invention, the ultra-low temperature cold rolling process is preferably performed in multiple passes. The number of passes is not particularly limited, and may be adjusted to achieve a deformation of 6 to 10% during the ultra-low temperature cold rolling process. In the present invention, the aluminum-lithium alloy is preferably immersed in liquid nitrogen after each rolling pass before the next rolling pass is performed.

[0040] After obtaining the ultra-low temperature cold-rolled aluminum-lithium alloy, the present invention performs intermittent aging treatment on the ultra-low temperature cold-rolled aluminum-lithium alloy to obtain a high-strength, plastic, corrosion-resistant and fatigue-resistant aluminum-lithium alloy.

[0041] In the present invention, the interrupted aging treatment preferably includes pre-aging, low-temperature aging, and re-aging, performed sequentially; the low-temperature aging temperature is independently lower than the pre-aging temperature and the re-aging temperature. The present invention utilizes the interrupted aging treatment to control the microstructure of the aluminum-lithium alloy by adjusting the temperature range.

[0042] In the present invention, the intermittent aging treatment preferably includes pre-aging, second quenching, low-temperature aging, third quenching, re-aging and fourth quenching performed in sequence.

[0043] In the present invention, the pre-aging temperature is preferably 140 to 180°C. As an embodiment of the present invention, the pre-aging temperature may be 140°C, 150°C, 160°C, 170°C or 180°C. In the present invention, the pre-aging time is preferably 20 minutes to 3 hours. As an embodiment of the present invention, the pre-aging time may be 20 minutes, 30 minutes, 40 minutes, 50 minutes, 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours. The present invention can form a GP zone through pre-aging.

[0044] The present invention has no particular limitation on the second quenching method. Conventional quenching methods can be used to reduce the temperature of the pre-aging aluminum-lithium alloy to room temperature. In an embodiment of the present invention, the second quenching method can be oil quenching.

[0045] In the present invention, the temperature of the low-temperature aging is preferably 25 to 65°C. As an embodiment of the present invention, the temperature of the low-temperature aging may be 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C or 65°C. In the present invention, the time of the low-temperature aging is preferably 1 to 10 days. As an embodiment of the present invention, the time of the low-temperature aging may be 1 day, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 8 days, 9 days or 10 days. The present invention can increase the number density of the precipitated phase, reduce the width of the PFZ, and improve the tensile properties and fracture toughness of the aluminum-lithium alloy through low-temperature aging treatment.

[0046] The present invention does not specifically limit the method for the third quenching. Conventional quenching methods can be used to reduce the temperature of the aluminum-lithium alloy after the low-temperature long-aging treatment to room temperature. In embodiments of the present invention, the third quenching method can be salt bath quenching. The present invention does not specifically limit the method for the salt bath quenching. Conventional salt bath quenching methods can be used.

[0047] In the present invention, the re-aging temperature is preferably 140-180°C. As an embodiment of the present invention, the re-aging temperature may be 140°C, 150°C, 160°C, 170°C or 180°C. In the present invention, the re-aging time is preferably 1-96h. As an embodiment of the present invention, the re-aging time may be 1h, 6h, 12h, 24h, 36h, 48h, 60h, 72h, 84h or 96h. The present invention can form a strengthening phase precursor GP zone in the alloy through pre-aging and low-temperature aging, so that more θ' can be precipitated during re-aging, forming a bimodal distribution of the strengthening phase together with the T1 phase, thereby improving the strength and plasticity of the aluminum-lithium alloy.

[0048] The present invention does not specifically limit the method for performing the fourth quenching. Conventional quenching methods can be used to reduce the temperature of the aluminum-lithium alloy after the re-aging treatment to room temperature. In embodiments of the present invention, the fourth quenching method can be step quenching. The present invention does not specifically limit the method for performing the step quenching. Conventional step quenching methods can be used.

[0049] In the present invention, the schematic diagram of the heat treatment method for improving the strength, plasticity, corrosion resistance and fatigue resistance of the aluminum-lithium alloy is preferably as follows: Figure 1 As shown. Figure 1It can be seen that in the present invention, the 2195 aluminum-lithium alloy is immersed in liquid nitrogen and then subjected to ultra-low temperature pre-deformation, and then subjected to intermittent aging treatment.

[0050] In the present invention, the schematic diagram of the evolution process of the intragranular precipitation phase of the heat treatment method for improving the strength, plasticity, corrosion resistance and fatigue resistance of the aluminum-lithium alloy is preferably as follows: Figure 2 As shown. Figure 2 It can be seen that the method provided by the present invention first performs solution treatment and quenching treatment on the aluminum-lithium alloy, and then performs low-temperature pre-rolling by liquid nitrogen cooling to form dislocations and atomic clusters; after pre-aging and quenching, GP zone (GPI / GPII zone) is formed; after low-temperature long aging, T1 phase and dislocation cells are formed; and after re-aging, θ' is precipitated.

[0051] The heat treatment method provided by the present invention first forms a pretreated aluminum-lithium alloy in a solid solution state; the pretreated aluminum-lithium alloy is subjected to ultra-low temperature cold rolling treatment to increase the dislocation density of the aluminum-lithium alloy, promote the heterogeneous nucleation and refinement of the T1 phase, and at the same time, the narrowing of the PFZ reduces the corrosion potential difference between the matrix and the grain boundary, thereby improving the strength of the aluminum-lithium alloy while enhancing its corrosion resistance; the present invention increases the number density of the precipitated phase, reduces the width of the PFZ, and improves the tensile properties, fracture toughness and fatigue resistance of the aluminum-lithium alloy by performing intermittent aging treatment on the ultra-low temperature cold-rolled aluminum-lithium alloy.

[0052] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0053] Example 1

[0054] A heat treatment method for improving the strength, plasticity, corrosion resistance and fatigue resistance of aluminum-lithium alloy, comprising the following steps:

[0055] (1) 2195 Al-Li alloy was solution treated at 530 °C for 1 h and then quenched in room temperature water to room temperature to obtain a pretreated Al-Li alloy;

[0056] (2) soaking the pretreated aluminum-lithium alloy obtained in step (1) in liquid nitrogen to a temperature of -196°C, and then performing ultra-low temperature cold rolling treatment, controlling the deformation amount to 6%, to obtain an ultra-low temperature cold rolled aluminum-lithium alloy;

[0057] (3) The ultra-low temperature cold-rolled aluminum-lithium alloy obtained in step (2) is heated to 160° C. and kept warm for 1 hour for pre-aging treatment, then quenched to room temperature, heated to 65° C. and kept warm for 10 days for low-temperature aging, then quenched to room temperature, heated to 160° C. and kept warm for 24 hours for re-aging treatment, and quenched to room temperature to obtain a high-strength, plastic, corrosion-resistant and fatigue-resistant aluminum-lithium alloy.

[0058] Example 2

[0059] A heat treatment method for improving the strength, plasticity, corrosion resistance and fatigue resistance of aluminum-lithium alloy, which differs from Example 1 in that the deformation amount of ultra-low temperature cold rolling treatment in step (2) is 10%, and the remaining steps are the same as Example 1.

[0060] Comparative Example 1

[0061] A heat treatment method for an aluminum-lithium alloy comprises: heating a 2195 aluminum-lithium alloy at 160° C. and keeping the temperature for 96 hours, and then quenching the alloy to room temperature to obtain the heat-treated aluminum-lithium alloy.

[0062] Comparative Example 2

[0063] A heat treatment method for aluminum-lithium alloy:

[0064] (1) 2195 Al-Li alloy was solution treated at 530 °C for 1 h and then quenched in room temperature water to obtain a pretreated Al-Li alloy;

[0065] (2) The pretreated aluminum-lithium alloy obtained in step (1) is heated to 160° C. and kept at this temperature for 1 hour for pre-aging treatment, and then quenched to room temperature, heated to 65° C. and kept at this temperature for 10 days for low-temperature aging, and then quenched to room temperature, heated to 160° C. and kept at this temperature for 72 hours for re-aging treatment, and quenched to room temperature to obtain a heat-treated aluminum-lithium alloy.

[0066] Comparative Example 3

[0067] A heat treatment method for aluminum-lithium alloy:

[0068] (1) Pre-rolling 2195 aluminum-lithium alloy, controlling the deformation amount to 6%, to obtain a pre-rolled aluminum-lithium alloy;

[0069] (2) The pre-rolled aluminum-lithium alloy obtained in step (1) is heated to 160° C. and kept at this temperature for 72 hours for aging treatment, and then quenched to room temperature to obtain a heat-treated aluminum-lithium alloy.

[0070] Comparative Example 4

[0071] A heat treatment method for aluminum-lithium alloy, which is different from Example 1 in that the deformation amount of ultra-low temperature cold rolling treatment in step (2) is 2%, and the remaining steps are the same as Example 1.

[0072] Comparative Example 5

[0073] A heat treatment method for aluminum-lithium alloy, which is different from Example 1 in that the deformation amount of ultra-low temperature cold rolling treatment in step (2) is 4%, and the remaining steps are the same as Example 1.

[0074] Comparative Example 6

[0075] A heat treatment method for aluminum-lithium alloy, which is different from Example 1 in that the deformation amount of ultra-low temperature cold rolling treatment in step (2) is 15%, and the remaining steps are the same as Example 1.

[0076] Test Example 1

[0077] The aluminum-lithium alloys obtained by the methods of Examples 1 to 2 and Comparative Examples 1 to 6 were subjected to performance tests, and the test results of the hardness, tensile strength, yield strength, elongation, maximum corrosion depth and fatigue life of the aluminum-lithium alloys were shown in Table 1.

[0078] The hardness is determined according to "Metallic materials Vickers hardness test Part 1: Test method" (GB / T4340.1-2009)

[0079] The tensile properties (tensile strength, yield strength and elongation) were determined according to the "Tension test of metallic materials - Part 1: Test method at room temperature" (GB / T 228.1-2010).

[0080] Fatigue performance (fatigue life) is determined according to the "Metallic Materials Fatigue Crack Growth Rate Test Method" (GB / 6398-2000)

[0081] Intergranular corrosion test (determination of maximum corrosion depth) is based on the "Determination of intergranular corrosion of aluminum alloys" (GB / T7998-2005)

[0082] Table 1 Performance test results of aluminum-lithium alloys obtained by the methods of Examples 1 to 2 and Comparative Examples 1 to 6

[0083]

[0084] It can be seen from Table 1 that when the deformation amount of the ultra-low temperature cold rolling treatment is 6-10%, the Vickers hardness of the aluminum-lithium alloy treated by the method provided by the present invention can reach above 206HV, the tensile strength is above 570MPa, and the yield strength is above 540MPa, while maintaining an elongation of above 10.3%, and having excellent plasticity; the maximum corrosion depth of the aluminum-lithium alloy is less than 30μm, which is much less than the corrosion depth of the aluminum-lithium alloy treated by the method of Comparative Example 1; and the fatigue life of the aluminum-lithium alloy treated by the method of Example 1 of the present invention is increased by more than 60% compared with the aluminum-lithium alloy treated by the method of Comparative Example 1.

[0085] As shown in Table 1, the method provided in Example 1 can comprehensively improve the strength, hardness, plasticity, fatigue resistance, and corrosion resistance of the 2195 aluminum-lithium alloy. This is because the ultra-low temperature pre-deformation inhibits the dynamic recovery of dislocations and promotes the accumulation of high-density dislocations, resulting in a smaller grain size and maximum lattice strain in the aluminum-lithium alloy, thereby reducing the grain boundary area and susceptibility to intergranular corrosion. The rough and discontinuously distributed GBPs and narrow PFZ formed by T8I6 offset the adverse effects of T1 phase on alloy corrosion.

[0086] Test Example 2

[0087] The intracrystalline high-angle annular dark field morphology of the aluminum-lithium alloy treated by the methods of Example 1 and Comparative Examples 1 to 3 is shown in FIG. Figure 3 As shown. Figure 3 Among them, (a) represents the aluminum-lithium alloy obtained by the treatment method of Comparative Example 1; (b) represents the aluminum-lithium alloy obtained by the treatment method of Comparative Example 2; (c) represents the aluminum-lithium alloy obtained by the treatment method of Comparative Example 3; (d) represents the aluminum-lithium alloy obtained by the treatment method of Example 1. Figure 3 It can be seen that compared with the heat treatment methods of Comparative Examples 1 to 3, the method provided in Example 1 can make the T1 phase of the aluminum-lithium alloy finer and the number density significantly increased, and the grain boundary precipitation phase of the aluminum-lithium alloy is discontinuously distributed, and the width of the PFZ is the narrowest, only 56 nm.

[0088] The high-angle annular dark field morphology of the grain boundary of the aluminum-lithium alloy treated by the methods of Example 1 and Comparative Examples 1 to 3 is shown in FIG. Figure 4 As shown. Figure 4 Among them, (a) represents the aluminum-lithium alloy obtained by the treatment method of Comparative Example 1; (b) represents the aluminum-lithium alloy obtained by the treatment method of Comparative Example 2; (c) represents the aluminum-lithium alloy obtained by the treatment method of Comparative Example 3; (d) represents the aluminum-lithium alloy obtained by the treatment method of Example 1. Figure 4 It can be seen that ultra-low temperature rolling pre-deformation can refine the grains and introduce a uniformly distributed dislocation substructure into the 2195 Al-Li alloy matrix. In the subsequent aging process, it promotes the dispersion and precipitation of fine intragranular T1 phase and GP zone / θ' phase, significantly improving the strength and elongation of the alloy.

[0089] Test Example 3

[0090] The engineering stress-strain curves of the aluminum-lithium alloys treated by the methods of Example 1 and Comparative Examples 1 to 3 are shown in FIG. Figure 5 As shown. Figure 5 In the table, T6 represents the aluminum-lithium alloy obtained by the treatment method of Comparative Example 1; T6I6 represents the aluminum-lithium alloy obtained by the treatment method of Comparative Example 2; T8 represents the aluminum-lithium alloy obtained by the treatment method of Comparative Example 3; CRYO-T8I6 represents the aluminum-lithium alloy obtained by the treatment method of Example 1. Figure 5 It can be seen that the CRYO-T8I6 heat treatment method enables the 2195 aluminum-lithium alloy to maintain high hardness and strength while also achieving high elongation, with a hardness of 206HV, a tensile strength and yield strength of 570MPa and 541MPa respectively, and an elongation of 10.3%. This is due to the combined effects of strain hardening caused by cold rolling pre-deformation before pre-aging and precipitation strengthening caused by the precipitation of T1 phase during the subsequent aging process.

[0091] Test Example 4

[0092] The aN curves of the aluminum-lithium alloys treated by the methods of Example 1 and Comparative Examples 1 to 3 are shown in FIG. Figure 6 As shown. Figure 6 In the table, T6 represents the aluminum-lithium alloy obtained by the treatment method of Comparative Example 1; T6I6 represents the aluminum-lithium alloy obtained by the treatment method of Comparative Example 2; T8 represents the aluminum-lithium alloy obtained by the treatment method of Comparative Example 3; CRYO-T8I6 represents the aluminum-lithium alloy obtained by the treatment method of Example 1. Figure 6 It can be seen that after the CRYO-T8I6 heat treatment method, the fatigue life of the aluminum-lithium alloy reaches 7.85×10 4 The number of cycles increased by 46.1%, 50.2% and 14.6% respectively compared with the aluminum-lithium alloys obtained by T6, T8 and T6I6 heat treatment methods. This shows that ultra-low temperature pre-deformation + intermittent aging treatment has played a positive role in improving the fatigue properties of the alloy, offsetting the adverse effects of cold rolling pre-deformation on fatigue crack propagation of aluminum-lithium alloy, thereby improving the fatigue crack propagation resistance of aluminum-lithium alloy.

[0093] It can be seen from the above results that the heat treatment method provided by the present invention achieves a synergistic improvement in the comprehensive performance of 2195 aluminum-lithium alloy plate. The aluminum-lithium alloy obtained by this heat treatment method has excellent hardness, strength, plasticity, corrosion resistance and fatigue crack growth resistance.

[0094] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A heat treatment method for improving the strength, plasticity, corrosion resistance and fatigue resistance of aluminum-lithium alloy, characterized in that: The following steps are involved: (1) subjecting the aluminum-lithium alloy to a solution treatment and a first quenching in sequence to obtain a pretreated aluminum-lithium alloy; (2) subjecting the pretreated aluminum-lithium alloy obtained in step (1) to ultra-low temperature cold rolling to obtain an ultra-low temperature cold-rolled aluminum-lithium alloy; the temperature of the ultra-low temperature cold rolling is below -160°C; (3) subjecting the ultra-low temperature cold-rolled aluminum-lithium alloy obtained in step (2) to intermittent aging treatment to obtain a high-strength, plastic, corrosion-resistant and fatigue-resistant aluminum-lithium alloy.

2. The method according to claim 1, characterized in that The aluminum-lithium alloy in step (1) includes 2195 aluminum-lithium alloy, 2060 aluminum-lithium alloy, 2099 aluminum-lithium alloy or 8090 aluminum-lithium alloy.

3. The method according to claim 1, characterized in that The temperature of the solution treatment in step (1) is 510-540° C.; the time of the solution treatment is 0.5-1.5 h.

4. The method according to claim 1, wherein The first quenching method in step (1) is water quenching.

5. The method according to claim 1, wherein The deformation amount of the ultra-low temperature cold rolling treatment in step (2) is 6 to 10%.

6. The method according to claim 1, characterized in that The intermittent aging treatment in step (3) includes pre-aging, low-temperature aging and re-aging performed in sequence; the temperature of the low-temperature aging is independently lower than the pre-aging temperature and the re-aging temperature.

7. The method according to claim 6, characterized in that The pre-aging temperature is 140-180° C.; the pre-aging time is 20 minutes to 3 hours.

8. The method according to claim 6, characterized in that The low-temperature aging temperature is 25 to 65° C., and the low-temperature aging time is 1 to 10 days.

9. The method according to claim 6, characterized in that The re-aging temperature is 140-180° C., and the re-aging time is 1-96 hours.

10. The method according to claim 6, characterized in that The intermittent aging treatment includes pre-aging, second quenching, low-temperature aging, third quenching, re-aging and fourth quenching performed in sequence.

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