JPH1068053A - Production of aluminum-lithium base alloy thin sheet material excellent in isotropy of toughness - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an Al-Li base alloy thin sheet material having toughness excellent in isotropy and improved in elongation value. SOLUTION: An Al-Li base alloy ingot contg., by weight, 1.0 to 3.0% Li, 1.0 to 3.0% Cu, 0.5 to 2.0% Mg, 0.04 to 0.10% Zr, and the balance Al with inevitable impurities is subjected to homogenizing heat treatment and hot rolling, is thereafter subjected to process annealing treatment at 380 to 420 deg.C for 2 to 10hr and is then subjected to cold rolling at >=60% draft.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an Al--Li alloy sheet, and more particularly to a method for producing an Al--Li alloy sheet having excellent toughness isotropy and an improved elongation value.

[0002]

2. Description of the Related Art Al-Li alloys containing 1.7 to 3.0% of Li and Cu, Mg and Zr are 2020, 2091, 8090, 8091 in accordance with international standards for wrought Al alloys.
And so on. These alloys are capable of increasing the elastic modulus in addition to the low density, and are expected to expand their applications as lightweight structural materials for aerospace equipment, automobiles, rail vehicles, etc. Improvement, particularly toughness without anisotropy, is desired.

[0003] In the prior art relating to the improvement of toughness of these Al-Li alloys, an attempt is made to improve elongation value and toughness by controlling the shape of crystal grains by cold rolling (Japanese Patent Application Laid-Open No. 61-233751). Cooling at a specific speed after quenching treatment, cold rolling, and aging treatment to improve fracture toughness (JP-A-60-2215)
43) have been proposed. However, many applications of this type of alloy are thin sheets, and particularly in the case of aircraft, damage-tolerant designs are often made, and the anisotropy in not only tensile properties but also toughness is a problem. However, in the case of a thin plate, the anisotropy of toughness was not sufficiently eliminated.

Generally, it is considered that the anisotropy of a sheet material is caused by a microstructure, and the anisotropy is reduced by recrystallization of the material structure into a random orientation including a cubic orientation different from the deformed matrix. However, it has been considered that it is extremely difficult to eliminate the anisotropy by stably recrystallizing the material structure to a random orientation, and the conventional method is unclear. there were.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and is an Al-Li-Cu-Mg-Z having excellent isotropic toughness and improved elongation value.
An object of the present invention is to provide a method for producing an r-based alloy sheet material.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have conducted intensive studies on a method for producing an Al-Li-based alloy sheet, and found that under a specific condition between hot rolling and cold rolling. The present inventors have found that the object of the present invention can be achieved by a method of performing an intermediate annealing treatment and then performing cold rolling at a specific reduction rate, and have accomplished the present invention.

That is, the method for producing an Al—Li alloy sheet having excellent toughness isotropic properties according to the present invention is as follows.
3.0%, Cu 1.0-3.0%, Mg 0.5-2.0
%, Zr 0.04 to 0.10%, and after homogenizing an Al-Li alloy ingot consisting of the balance of Al and unavoidable impurities by a conventional method, hot rolling is performed, and then a temperature of 380 to 4%.
It is characterized by performing an intermediate annealing treatment at 20 ° C. for 2 to 10 hours, and then performing cold rolling at a working ratio of 60% or more to finely recrystallize the structure of the Al—Li alloy thin sheet material. In this paper, the cubic orientation is introduced into the texture and the slip is randomized to improve ductility and eliminate anisotropy of toughness.

The reasons for limiting the chemical components in the present invention will be described. Li: Li is a lightening element,
The metastable phase δ ′ precipitates and contributes to strength improvement and high rigidity. If the Li content is less than 1.0%, the effects of weight reduction and strength improvement are insufficient, and if it exceeds 3.0%, casting crack susceptibility increases and a coarse metastable phase δ 'is formed. As a result, the elongation value and the toughness of the alloy are reduced, so the upper limit of the amount of Li is set to 3.0%.

Cu: Cu forms an Al-Cu-based plate-like precipitate (Al ₂ Cu) or an Al-Cu-Li-based plate-like precipitate phase (T ₁ phase) to improve strength and toughness. To contribute.
However, if the content is less than 1.0%, the effect is not sufficient, and if it exceeds 3.0%, the effect is saturated and the weight reduction effect is reduced. When the Mg content is less than 1.0%, the Cu content is desirably 1.5 to 3.0%, and when the Mg content exceeds 1.0%, the effect of improving the strength by Mg is also expected. Because Cu can be 1.0 ~
It may be about 2.5%.

Mg: Mg strengthens the alloy without lowering the elongation value and the toughness due to the solid solution effect, and at the same time, Al-
Cu-Mg based metastable phase plate-like precipitate S 'phase (Al-C
uMg), thereby further contributing to strength improvement. If the Mg content is less than 0.5%, the effect of improving strength is not sufficient, and if it exceeds 2.0%, the strength is improved but the toughness and elongation value are reduced. Therefore, Mg is 0.5 to
A range of 2.0% is desirable.

Zr: Zr is contained for the purpose of refining the cast structure and suppressing recrystallization, but the content is 0.2%.
If it exceeds, a coarse intermetallic compound of Al-Zr is formed to lower the strength, toughness and elongation value, so that it is often limited to 0.2% or less. When the content exceeds 0.1%, recrystallization of the material structure is suppressed. Therefore, when the purpose is to obtain a recrystallized structure as in the present invention, only the structure refining effect of Zr is expected, It is necessary to limit the content of Zr to a range where the effect of suppressing the recrystallization does not reach. Therefore, the content is set in the range of 0.04 to 0.1% by weight.

The other elements are equivalent to the amounts of impurities allowed in general Al alloys. That is, Fe0.
The content of 30% or less, Si 0.20% or less, Zn 0.25% or less, Cr 0.10% or less, and Mn 0.10% or less may be included. However, since it is necessary to further reduce the anisotropy of toughness, it is preferable that Fe0.10% or less and Si0.
10%, Zn 0.10% or less, Ti 0.05% or less, C
It is desirable to restrict r to 0.05% or less.

[0013] Ti is 0.01-0.05% Al-T
i or an alloy such as Al-Ti-B or a Ti-containing compound is positively added and refined to refine the ingot structure. Mn has the effect of becoming a recrystallization nucleus during hot rolling and trapping the transition in the stretch after solution treatment, and has the effect of becoming a nucleation site for precipitation in the subsequent aging treatment. To produce the compound,
The content is limited to 0.10%.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, the manufacturing method will be described. The molten Al-Li alloy having the above-mentioned chemical components is converted into A according to a conventional method.
It is cast by a semi-continuous casting (DC casting) method while protecting Li in an inert atmosphere such as r. The obtained ingot has a microstructure in which a Zr compound is finely dispersed, and after subjecting the ingot to beveling, a two-stage soaking treatment is performed. In the first stage, Al3Zr is precipitated by a homogenization treatment at 450 ± 20 ° C. for about 4 to 48 hours. Next, in the second stage, the additive element and the impurity element are dissolved by a soaking treatment at 520 ± 20 ° C. for about 2 to 12 hours.

After the above soaking treatment, hot rolling is performed at a rolling ratio of 60% or more in a temperature range of 500 to 250 ° C. If the hot rolling temperature exceeds 500 ° C., there is a risk that hot cracks will occur. On the other hand, if the hot rolling temperature is less than 250 ° C., plate breakage due to edge cracks will occur, making it difficult to manufacture hot rolled coils. On the other hand, when the hot rolling ratio is less than 60%, it is insufficient to make the ingot structure completely rolled, and the toughness of the cold rolled sheet is insufficient. Also, the higher the hot rolling ratio, the finer the work structure becomes, so there is no need to set an upper limit, but it is industrially limited by ear cracks, temperature drop during rolling, and the like.

In the present invention, the hot-rolled sheet is subjected to an intermediate annealing treatment in a temperature range of 380 to 420 ° C. for 2 to 10 hours before cold rolling, and further cold-rolled by 60% or more. If the rolling reduction in the cold rolling after annealing is less than 60%, randomization of the structure by recrystallization is insufficient and the elongation value is improved, but the anisotropy of toughness remains and the rolling reduction is 80%. If it exceeds, there is a concern about rolling troubles such as plate breakage due to edge cracks or the like, and reduction in product yield due to trimming or the like. Therefore, the upper limit is preferably about 80% industrially.

After the cold rolling, heat treatment for tempering the sheet is performed by a conventional method. The heat treatment is usually T6 (artificial aging treatment after solution treatment) or T8 (cold working after solution treatment, then artificial aging treatment), but T8 treatment has higher specific strength than T6.
The result which is excellent in the isotropy of the elongation value and the toughness together with the specific rigidity is obtained.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.
Al-Li alloy (Li: 2.23%, Cu: 2.30%, M
g: 1.60%, Zr: 0.08%, Ti: 0.03%, Fe: 0.05
%, Si: 0.03%, Zn: 0.01%, and the balance of Al) were dissolved in an Ar gas atmosphere, formed into an ingot by a semi-continuous casting method, and surface-polished into a slab. The slab is heated at 450 ° C. for 24 hours.
Then, a two-stage soaking treatment was performed at 520 ° C. for 6 hours, and then hot rolling was performed. The starting temperature of the hot rolling is 470 ° C., the ending temperature is 270 ° C., the rolling reduction is 90%, and the sheet thickness is 6.0 mm. Hot rolled sheet.

After subjecting the hot-rolled sheet to intermediate annealing at a temperature of 360 to 440 ° C. for 1 to 12 hours, a rolling reduction of 20 to 8 hours
0% cold rolling was performed to obtain a sheet thickness of 1.2 to 4.8 mm. Was obtained. Next, the sheet material was heated at 520 ° C. for 30 minutes to perform a solution treatment, and then subjected to a stretch of 3.0 ± 0.5% and an aging treatment at 150 ° C. for 24 hours.

From the above-mentioned sheet material, the angle with respect to the rolling direction is 0 °.
An ASTMF1 tensile test piece and two JIS No. 4 Charpy test pieces were sampled from the directions of °, 45 °, and 90 °, and a tensile test and a Charpy test were performed, respectively. The test results are
As shown in Tables 1 to 4. In addition, Table 5 shows, in the above-mentioned use of the Al-Li-based alloy sheet material that is the object of the present invention, target values for generally required characteristic values, namely, tensile strength, proof stress, elongation value, and Charpy value for each rolling direction. In the present invention, this is used as an index of the degree of achievement of the target.

Step A in Table 1 is a case where the rolling ratio before solution treatment is changed in the range of 20 to 80% at an annealing temperature of 400 ° C. (annealing time is 6 hours), and step B in Table 2 is an annealing. Temperature 3
The temperature was changed in the range of 60 to 440 ° C., and the annealing time was 6 hours,
This is the case where the cold rolling reduction before solution treatment is constant at 80%.
Step C in Table 3 is for an annealing temperature of 420 ° C., and Step D in Table 4 is for an annealing temperature of 360, in which the annealing time is changed to 1 to 12 hours. The cold rolling reduction before the solution treatment in Steps C and D was set to 80% in order to make recrystallization of the T8-treated material as little as possible.

[0022]

[Table 1] << Table Note >> Improvement of elongation and isotropic toughness ○: Sufficient effect △: Insufficient effect ×: No effect

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

[Table 4]

[0026]

[Table 5]

In step A of Table 1, the annealing conditions were kept constant at 400 ° C. for 6 hours, and the effect of the cold rolling rate before solution treatment was observed.
Although the elongation value and Charpy value in each direction are high and there is no toughness anisotropy when the cold rolling rate before solution heat is 60 to 80%, it is 50%
Below, either the elongation value or the Charpy value has a problem, and the target value is not satisfied. Therefore, in order to improve the anisotropy of toughness, the cold rolling reduction before solution treatment was evaluated to be appropriately in the range of 60 to 80%.

Looking at the effect of the annealing temperature of the hot-rolled sheet in step B of Table 2, when the annealing temperature is 360 ° C., recrystallization does not proceed sufficiently, so that the anisotropy remains and the elongation value also increases. Low. 38
In the range of 0 to 420 ° C., the elongation value is improved, and the anisotropy of the Charpy value is also improved. However, at a higher temperature of 440 ° C., the recrystallized grains are coarsened during solutionizing, so Although not present, both the elongation value and the Charpy value show a decreasing tendency. Therefore, the annealing temperature of the hot-rolled sheet is suitably from 380 to 420 ° C, and there is a problem if the annealing temperature is higher or lower.

In the process C of Table 3 and the process D of Table 4, the effect of the annealing time of the hot-rolled sheet is observed in the temperature range of 380 to 420 ° C. When the annealing temperature is 380 ° C. or 420 ° C., When the time is 1 hour, the effect of improving both the elongation value and the Charpy value is insufficient. In each case, when the annealing time is 12 hours, the crystal grains are coarsened during the solution treatment, and the anisotropy of toughness disappears, but the Charpy value tends to decrease and is lower than the target value. Therefore, as an appropriate annealing condition that satisfies the target value, the time is 2-1 to 380 to 420 ° C.
It was found to be in the 0 hour range.

[0030]

As described in detail above, according to the present invention, a specific amount of Li, Cu, Mg, Zr is an essential component and the balance is A
In the production of a sheet material of an Al-Li alloy comprising l and impurities, intermediate annealing under specific conditions is performed between hot rolling and cold rolling, and the rolling reduction of cold rolling is adjusted to a specific value or more. By doing so, the microstructure of the sheet material is finely recrystallized, the cubic orientation is introduced into the texture, and the slip is randomized.As a result, the elongation value is improved, and the anisotropy of the toughness is eliminated. An Al-Li-based thin plate material can be manufactured reliably and stably.

As a result, the anisotropy of toughness, which has been a problem of Al-Li alloys which are conventionally used as lightweight structural materials for aircraft and vehicles due to their excellent specific strength and specific elastic modulus, is solved. Al- with improved elongation along with excellent toughness
Since it becomes possible to manufacture a Li-based alloy sheet material, application expansion to this field is expected, and the industrial contribution of the present invention is great.

Claims (1)

[Claims] 1. Li 1.0 to 3% by weight (the same applies hereinafter).
0%, Cu 1.0 to 3.0%, Mg 0.5 to 2.0%,
An Al-Li alloy ingot containing 0.04 to 0.10% of Zr, the balance being Al and inevitable impurities, is subjected to an intermediate treatment at a temperature of 380 to 420 ° C for 2 to 10 hours after a homogenizing heat treatment and hot rolling. A having excellent isotropy of toughness characterized by performing an annealing treatment and then performing cold rolling at a working ratio of 60% or more.
A method for producing an l-Li-based alloy sheet material.