Efficient Aging Methods for Aluminum-Lithium Alloys Based on Dynamic Strain Precipitation

This application is a continuation-in-part application of International Application No. PCT/CN2023/128326, filed on Oct. 31, 2023, which claims priority of Chinese Patent Application No. 202310999059.5, filed on Aug. 9, 2023, the entire contents of each of which are incorporated herein by reference.

The present disclosure relates to the technical field of heat treatment of aluminum-lithium alloys, and in particular, to an efficient aging method for an aluminum-lithium alloy based on dynamic strain precipitation.

The new aluminum-lithium alloy (Al—Cu—Li system) is an aging-strengthened deformed aluminum alloy with excellent specific strength, specific stiffness, and fracture toughness, which is an ideal structural material for aerospace vehicles. The excellent comprehensive mechanical properties of the new aluminum-lithium alloy depend on the precipitation of a main reinforcing phase-Tphase during the aging process. An important direction for research of the new aluminum-lithium alloy is how to increase the precipitation amount of the Tphase during the aging process.

Therefore, it is necessary to provide an efficient aging method for an aluminum-lithium alloy based on dynamic strain precipitation to effectively increase the precipitation amount of the Tphase during the aging process, thereby ensuring the comprehensive mechanical properties of the new aluminum-lithium alloy.

One or more embodiments of the present disclosure provide an efficient aging method for an aluminum-lithium alloy based on dynamic strain precipitation, comprising ingot casting, homogenization treatment, hot rolling, solution heat treatment and quenching, and aging treatment, wherein the method further comprises temperature-controlled and rate-controlled deformation treatment between the solution heat treatment and quenching and the aging treatment, the temperature-controlled and rate-controlled deformation treatment includes performing preheating, temperature-controlled and rate-controlled hot rolling, and cooling treatment on an aluminum-lithium alloy sheet after the solution heat treatment and quenching in sequence, the temperature-controlled and rate-controlled hot rolling has a rolling temperature of 250° C.-330° C., a rolling reduction of 10%-30%, and a strain rate of 0.001 s-0.5 s, and an alloy chemical composition of the aluminum-lithium alloy includes Cu: 2.7 wt %-2.8 wt %, Li: 1.7 wt %-1.9 wt %, Mg: 0.3 wt %-0.5 wt %, Mn: 0.3 wt %-0.5 wt %, Zn: 0.5 wt %-0.7 wt %, Zr: 0.08 wt %-0.12 wt %, Si≤0.05 wt %, and Fe≤0.07 wt %.

One or more embodiments of the present disclosure provide an efficient aging method for an aluminum-lithium alloy based on dynamic strain precipitation, comprising: (1) preparing an aluminum-lithium alloy ingot by a vacuum melting and casting method, wherein alloy chemical composition of the aluminum-lithium alloy includes Cu: 2.7 wt %-2.8 wt %, Li: 1.7 wt %-1.9 wt %, Mg: 0.3 wt %-0.5 wt %, Mn: 0.3 wt %-0.5 wt %, Zn: 0.5 wt %-0.7 wt %, Zr: 0.08 wt %-0.12 wt %, Si≤0.05 wt %, Fe≤0.07 wt %, and the balance is aluminum; (2) performing homogenization treatment on the aluminum-lithium alloy ingot at a range of 510° C.-530° C. for 70 h-80 h; (3) preheating the homogenized aluminum-lithium alloy ingot at a range of 420° C.-460° C., and after the whole homogenized aluminum-lithium alloy ingot reaches a preheat temperature, holding for 20 min-40 min, and then performing hot rolling on the homogenized aluminum-lithium alloy ingot to obtain an aluminum-lithium alloy sheet; (4) performing solution heat treatment on the aluminum-lithium alloy sheet at a range of 535° C.-545° C. for 0.5 h-1.5 h, followed by quenching in cold water at 25° C.; (5) preheating the quenched aluminum-lithium alloy sheet to the rolling temperature of temperature-controlled and rate-controlled hot rolling within a range of 2 min-8 min, and then performing the temperature-controlled and rate-controlled hot rolling, wherein the temperature-controlled and rate-controlled hot rolling has the rolling temperature of 250° C.-330° C., a rolling reduction of 10%-30%, and a strain rate of 0.001 s-0.1 s, followed by air cooling to room temperature; and (6) aging the aluminum-lithium alloy sheet after the temperature-controlled and rate-controlled hot rolling at 160° C. for 8 h-15 h, followed by air cooling to the room temperature.

The accompanying drawings, which are required to be used in the description of the embodiments, are briefly described below. The accompanying drawings do not represent the entirety of the embodiments.

Unless the context clearly suggests an exception, at least one of the words “one”, “a”, “an”, or “the” do not refer specifically to the singular, but may also include the plural. Generally, the terms “including” and “comprising” only suggest the inclusion of explicitly identified steps and elements that do not constitute an exclusive list, and the method or devices may also include other steps or elements.

The precipitation process of the new aluminum-lithium alloy is complex. Due to the influence of alloying elements, precipitation phases of the alloy include δ′ (AlLi), θ′ (AlCu), S′ (AlCuMg), and T1 (AlCuLi), and different precipitation phases have different structural characteristics and precipitation features, which brings different effects on alloy properties. During plastic deformation, the δ′ phase leads to stress concentration and deterioration of alloy plasticity. In corrosive environments, the θ′ phase leads to pitting of matrix. In the aluminum-lithium alloys with low or medium Cu/Li ratios, the Tphase has the best aging-strengthening effect on the alloy, and the Tphase grows by consuming the δ′ phase and the θ′ phase during the aging process.

However, during the heat treatment process, atomic polarization zones (GP zones) are generated in the matrix, in which the atoms are Cu and the strengthening effect of Cu on the matrix is much smaller than that of the Tphase. However, there is a competitive precipitation relationship between the Tphase and the GP zones, and an increase of the GP zones may lead to a reduction in strength, hardness, and other properties of the alloy. To improve the strengthening effect on the matrix, it is necessary to increase the content of the Tphase and reduce the generation of the GP zones.

In the prior art, dislocations are introduced in the matrix by cold deformation treatment before aging treatment to promote Tphase precipitation. In processing technology of the aluminum-lithium alloys, there are many heat treatment processes to improve the mechanical properties of the matrix, among which T6 treatment (cold deformation+solution heat treatment+aging) and T8 treatment (solution heat treatment+cold deformation+aging) are used. It has been reported that 2195 aluminum-lithium alloy undergoes the solution heat treatment, followed by 3%-6% pre-deformation and aging treatment, and the amount of the Tphase effectively increases with the prolonging of the aging time. However, the T8 treatment requires a longer aging time and does not completely inhibit the formation of the GP zones, which reduces the amount density of the Tphase precipitation. For example, when double-stage aging is used, the cold deformation combined with the double-stage aging is capable of increasing the generation of the Tphase in the matrix and reducing the formation of the GP zones, but a plurality of the GP zones still exists in the aluminum-lithium alloy treated in this way, and the aging time used in the T8 treatment is long, which also leads to high energy consumption.

To avoid the above problems, some embodiments of the present disclosure provide an efficient aging method for an aluminum-lithium alloy based on dynamic strain precipitation, which can effectively improve the comprehensive mechanical properties of the aluminum-lithium alloy while saving time and energy consumption.

is an exemplary flowchart illustrating an efficient aging method for an aluminum-lithium alloy based on dynamic strain precipitation according to some embodiments of the present disclosure. In some embodiments, one or more additional operations not described herein may be added and/or one or more operations discussed herein may be deleted when completing a process. Additionally, the order of the operations shown inis not limiting. As shown in, the processincludes operations-.

In some embodiments, the efficient aging method for the aluminum-lithium alloy based on dynamic strain precipitation includes ingot casting, homogenization treatment, hot rolling, solution heat treatment and quenching, and aging treatment of the aluminum-lithium alloy. The method further includes temperature-controlled and rate-controlled deformation treatment between the solution heat treatment and quenching and the aging treatment. The temperature-controlled and rate-controlled deformation treatment includes performing preheating, temperature-controlled and rate-controlled hot rolling, and cooling treatment on an aluminum-lithium alloy sheet after the solution heat treatment and quenching in sequence. The temperature-controlled and rate-controlled hot rolling has a rolling temperature of 250° C.-330° C., a rolling reduction of 10%-30%, and a strain rate of 0.001 s-0.5 s, and an alloy chemical composition of the aluminum-lithium alloy includes Cu: 2.7 wt %-2.8 wt %, Li: 1.7 wt %-1.9 wt %, Mg: 0.3 wt %-0.5 wt %, Mn: 0.3 wt %-0.5 wt %, Zn: 0.5 wt %-0.7 wt %, Zr: 0.08 wt %-0.12 wt %, Si≤0.05 wt %, and Fe≤0.07 wt %.

The aluminum-lithium alloy refers to an alloy obtained by adding lithium as an alloying element to aluminum. In some embodiments, the alloy chemical composition of the aluminum-lithium alloy includes Cu: 2.7 wt %-2.8 wt %, Li: 1.7 wt %-1.9 wt %, Mg: 0.3 wt %-0.5 wt %, Mn: 0.3 wt %-0.5 wt %, Zn: 0.5 wt %-0.7 wt %, Zr: 0.08 wt %-0.12 wt %, Si≤0.05 wt %, and Fe≤0.07 wt %. In operation, ingot casting.

The ingot casting refers to a process in which molten metal is injected into a casting mold and solidified into a metal ingot. In some embodiments, an aluminum-lithium alloy ingot is obtained by the ingot casting. The aluminum-lithium alloy ingot refers to an ingot that is made of the aluminum-lithium alloy by an ingot casting process.

In some embodiments, the aluminum-lithium alloy ingot may be prepared in a plurality of methods. For example, preparation methods include die casting, sand casting, gravity casting, or the like.

In some embodiments, the aluminum-lithium alloy ingot is prepared using a vacuum melting and casting method. The vacuum melting and casting method refers to a method in which the material is cast directly into products after high-temperature melting in a vacuum environment.

In operation, homogenization treatment.

The homogenization treatment refers to a process of homogenizing structure and eliminating stress of alloy material. Comprehensive performance of the aluminum-lithium alloy ingot may be improved by the homogenization treatment.

In some embodiments, the homogenization treatment of the aluminum-lithium alloy ingot includes performing the homogenization treatment on the aluminum-lithium alloy ingot for a homogenization time at a homogenization temperature. For example, the homogenization treatment is performed on the aluminum-lithium alloy ingot for 70 h-80 h at a range of 510° C.-530° C.

In some embodiments, the homogenization temperature is within a range of 510° C.-530° C. In some embodiments, the homogenization temperature is within a range of 515° C.-525° C. In some embodiments, the homogenization temperature is within a range of 518° C.-525° C. In some embodiments, the homogenization temperature is within a range of 519° C.-522° C.

In some embodiments, the homogenization time is within a range of 70 h-80 h. In some embodiments, the homogenization time is within a range of 71 h-79 h. In some embodiments, the homogenization time is within a range of 74 h-78 h. In some embodiments, the homogenization time is within a range of 75 h-77 h.

In operation, hot rolling.

The hot rolling refers to a metal processing technology in which the metal is rolled above its recrystallization temperature. Recrystallization refers to a process in which when an annealing temperature is high enough and the time is long enough, new grains with strain-free (i.e., cores of the recrystallization) are generated in fiber structures of the deformed metals or the alloys, and the new grains continue to grow until the original deformation structure completely disappears, and the properties of the metals or the alloys also undergo significant changes. The recrystallization temperature of the metal refers to a temperature at which the metal begins to form the new grains.

In some embodiments, the aluminum-lithium alloy ingot after the homogenization treatment is preheated at a preheat temperature, and after the whole reaches the preheat temperature, the preset temperature is held for a holding time, and then the hot rolling is performed on the aluminum-lithium alloy ingot to obtain an aluminum-lithium alloy sheet. For example, the aluminum-lithium alloy ingot after the homogenization treatment is preheated at a preheat temperature of 420° C.-460° C., and after the whole reaches the preheat temperature, the preset temperature is held for a holding time of 20 min-40 min, and then the hot rolling is performed on the aluminum-lithium alloy ingot to obtain the aluminum-lithium alloy sheet.

In some embodiments, the preheat temperature is within a range of 420° C.-460° C. In some embodiments, the preheat temperature is within a range of 430°° C.-450° C. In some embodiments, the preheat temperature is within a range of 435° C.-445° C. In some embodiments, the preheat temperature is within a range of 438° C.-440° C.

In some embodiments, the holding time is within a range of 20 min-40 min. In some embodiments, the holding time is within a range of 25 min-35 min. In some embodiments, the holding time is within a range of 27 min-32 min. In some embodiments, the holding time is within a range of 28 min-30 min.

In operation, solution heat treatment and quenching.

The solution heat treatment and quenching refers to a heat treatment process in which the aluminum-lithium alloy sheet is heated to a high-temperature single-phase zone, and held at a constant temperature, so that an excess phase is fully dissolved into the solid solution and then cooled rapidly to obtain a supersaturated solid solution. The supersaturated solid solution refers to a solid solution in a metastable state in which the amount of dissolved solutes at a given temperature is greater than the amount of soluble at equilibrium at the temperature.

In some embodiments, the solution heat treatment is performed on the aluminum-lithium alloy sheet at a solution temperature for a solution time, and quenched using a medium with a medium temperature after the solution heat treatment is completed. The medium may include water, oil, air, liquid nitrogen, or the like. For example, the solution temperature of the solution heat treatment and quenching may be within a range of 535° C.-545° C., the solution time may be within a range of 0.9 h-1.2 h, and the quenching may be carried out with cold water at 25° C. as the medium after the solution heat treatment is completed.

In some embodiments, the solution temperature is within a range of 535° C.-545° C. In some embodiments, the solution temperature is within a range of 536° C.-544° C. In some embodiments, the solution temperature is within a range of 537° C.-543° C. In some embodiments, the solution temperature is within a range of 539° C.-541° C.

In some embodiments, the solution time is within a range of 0.9 h-1.2 h. In some embodiments, the solution time is within a range of 0.9 h-1.1 h. In some embodiments, the solution time is within a range of 1.0 h-1.2 h. In some embodiments, the solution time is within a range of 1.0 h-1.1 h.

In some embodiments, the medium temperature is 25° C. In some embodiments, the medium temperature is 24° C. In some embodiments, the medium temperature is 22° C. In some embodiments, the medium temperature is 20° C.

In operation, temperature-controlled and rate-controlled deformation treatment.

The temperature-controlled and rate-controlled deformation treatment refers to a heat treatment process in which a specific processing effect is achieved by controlling temperature and rate. In some embodiments, the temperature-controlled and rate-controlled deformation treatment includes performing the preheating, the temperature-controlled and rate-controlled hot rolling, and the cooling treatment on the aluminum-lithium alloy sheet after the solution heat treatment and quenching in sequence.

The preheating refers to a process of preheating the aluminum-lithium alloy sheet to the rolling temperature for the temperature-controlled and rate-controlled hot rolling.

In some embodiments, the preheating is to preheat the aluminum-lithium alloy sheet after the solution heat treatment and quenching to the rolling temperature of the temperature-controlled and rate-controlled hot rolling within the preheating time. For example, the preheating is to heat the aluminum-lithium alloy sheet after the solution heat treatment and quenching to a rolling temperature of the temperature-controlled and rate-controlled hot rolling within a range of 2 min-8 min.

In some embodiments, the preheating time is within a range of 2 min-8 min. In some embodiments, the preheating time is within a range of 3 min-5 min. In some embodiments, the preheating time is within a range of 3 min-6 min. In some embodiments, the preheating time is within a range of 4 min-6 min.

The temperature-controlled and rate-controlled hot rolling refers to the hot rolling of the aluminum-lithium alloy sheet after the preheating with controlled the rolling temperature and rate.

In some embodiments, the temperature-controlled and rate-controlled hot rolling is the hot rolling at a rolling temperature, a rolling reduction, and a strain rate. For example, the temperature-controlled and rate-controlled hot rolling is performed at a rolling temperature of 250° C.-330° C., a rolling reduction of 10%-30%, and a strain rate of 0.001 s-0.5 s.

In some embodiments, the rolling temperature is within a range of 250° C.-330° C. In some embodiments, the rolling temperature is within a range of 280° C.-320° C. In some embodiments, the rolling temperature is within a range of 285° C.-310° C. In some embodiments, the rolling temperature is within a range of 290° C.-300° C.

In some embodiments, the rolling reduction is within a range of 10%-30%. In some embodiments, the rolling reduction is within a range of 15%-25%. In some embodiments, the rolling reduction is within a range of 18%-22%. In some embodiments, the rolling reduction is within a range of 19%-20%.

In some embodiments, the strain rate is within a range of 0.001 s-0.5 s. In some embodiments, the strain rate is within a range of 0.01 s-0.5 s. In some embodiments, the strain rate is within a range of 0.1 s-0.5 s. In some embodiments, the strain rate is within a range of 0.025 s-0.1 s.

The cooling treatment refers to a process of cooling down the aluminum-lithium alloy sheet after the hot rolling using physical or chemical methods.

In some embodiments, the cooling treatment may be accomplished in a plurality of methods. For example, oil cooling, water cooling, air cooling, or the like.

In operation, aging treatment.

The aging treatment is a heat treatment process that promotes the phase transformation of metal or alloy material by controlling the temperature and time to improve its mechanical properties.

In some embodiments, the aging treatment may be accomplished in a plurality of methods. For example, high-temperature aging, low-temperature aging, or the like.

In some embodiments, the aging treatment is performing aging for an aging time at an aging temperature. For example, the aging treatment is performing aging for an aging time of 8 h-12 h at 160° C. In some embodiments, the aging treatment is followed by the cooling treatment. For example, air cooling to room temperature. More details regarding the cooling treatment may be found in other contents of the present disclosure (descriptions in connection with above).