JPH0689439B2 - Method for producing structural Al-Cu-Mg-Li aluminum alloy material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention shows that solid solution elements do not precipitate by quenching (cooling) following solution heat treatment by air cooling or forced air cooling. The present invention relates to a method for manufacturing a structural aluminum alloy material that can obtain strength (50 kgf / mm ² or more).

Quenching as used here means that elements such as Cu and Li in the aluminum alloy are melted into the matrix by heating at 500 ° C or higher. After the solution treatment, the element is melted by rapid cooling such as water cooling. The hardenability referred to here means that the melted element is not precipitated even if the cooling rate after the solution treatment is small (for example, by air cooling). The more dissolved elements, the higher the strength obtained by artificial aging treatment.

[Prior Art] Conventionally known aluminum alloys, like JIS A2024 and A7075 alloys, do not have sufficient strength after aging treatment unless quenched at a high cooling rate such as water cooling when quenching after solution treatment. Not so-called alloy with poor hardenability,
There are so-called hardenable alloys such as JIS A6063, A 7003, and 7NO1 alloys that can obtain a tensile strength of 40 kgf / mm ² or less even at a cooling rate of about air cooling.

Heretofore, in order to obtain a tensile strength of 50 kgf / mm ² or more, an age-hardening type aluminum alloy that has undergone the steps of solution treatment, quenching, and aging, that is, an alloy having poor quenchability has been used.

That is, as the structural aluminum alloy material, an aging / precipitation type alloy is generally used, and after it is formed into a product shape such as a plate or a bar, it is subjected to heat treatment such as solution heat treatment, quenching, and artificial aging, which results in a fine grain in the alloy. A large intermetallic compound is deposited to obtain high strength.

As such an alloy, one in which the ductility and toughness are improved by controlling the crystal grain shape of an Al-Li alloy by cold working (Japanese Patent Laid-Open No. 61-23751), Al-Li-Mg- C
u-based alloy, which is solution-quenched, water-quenched, and aged at 170 ° C (JP-A-58-157942), Al-L
i, Al-Li-Cu, Al-Li-Cu-Mg based alloys, which have improved electric resistance and tensile strength (Japanese Patent Laid-Open No. 59-118848), Al-Li-Cu-Zr based alloys. An alloy, which is cooled by blast air cooling or the like after solution treatment (water cooling in the example), is overaged, and is then cold worked (Japanese Patent Publication No. 60-2644), Al-Li-Cu-
Mg-based alloy, in which homogenization, solution treatment, quenching and tempering are performed for a long time so that the dimension of the intermetallic compound after quenching is 0 to 5 μm in the steps of homogenizing, solutionizing, quenching and tempering. (JP-A-60-215735), Al-Li-Cu-
Mg-Zr-Mn-Zn alloy, 100 ° F / s after solution treatment
It has been proposed that the fracture toughness is improved by aging treatment after cooling with a steel, cold working, and the like (JP-A-60-221543).

[Problems to be Solved by the Invention] As described above, in the conventional structural aluminum alloy material, unless it is quenched at a large cooling rate such as water cooling from the solution heat treatment temperature, a large compound is precipitated and sufficient strength is obtained. There is a drawback that you can't. Further, when the material is cooled at a high cooling rate, distortion occurs in the material, and there is a drawback that a step such as straightening is required.

Therefore, the present invention is an aluminum alloy material that can sufficiently dissolve the element even if the cooling rate after the solution treatment is small (1 to 5 ° C / s) and can obtain high strength (50 kgf / mm ² or more) by the subsequent artificial aging treatment. It aims at providing the manufacturing method of.

[Means for Solving the Problems] The alloy according to the present invention is configured as follows to achieve the above object. That is, Cu: 0.5-3.5%, Mg: 0.
5 to 4.0% and Li: 2.0 to 4.0%, and Zr0.05 to 0.3
0%, Cr0.05-0.30%, Mn0.05-1.0%, V0.05-0.30%
Of the aluminum alloy containing one or more of the above and the balance Al and inevitable impurities, and melting and casting.
1 to 5 after carrying out in an Ar atmosphere, performing homogenization treatment and plastic working in the usual way, and subjecting it to solution treatment at 500 ° C or higher.
A structural Al-Cu-Mg-Li system with excellent hardenability, characterized in that the average particle size of the precipitates was 100 nm or less by performing artificial aging treatment after cooling at a cooling rate of ° C / sec. It is a manufacturing method of an aluminum alloy material.

[Operation] The meaning and limitation reason of the component composition according to the present invention are as follows.

Cu: Cu is effective in improving the strength of alloy materials. This effect is 0.5
% Less, and more than 3.5%, coarse plate-like T ₁ phase (Al ₂ CuLi) and T ₂ phase (Al ₆ Li) at grain boundaries during cooling after heating.
₃ Cu) tends to precipitate and the strength after aging treatment decreases. This upper limit is preferably 2.4% or less because the inclusion of transition elements such as Zr, Cr, Mn and V promotes precipitation of the T ₁ phase and the T ₂ phase.

Mg: Mg, like Cu, is effective in improving the strength of alloy materials. This effect cannot be obtained if it is less than 0.5%, and if it exceeds 4.0%, hot brittleness occurs during rolling, making hot working difficult.

Li: Li, like Cu, is effective in improving the strength of the alloy. The inclusion of Li precipitates a metastable phase δ ', which contributes to the improvement of strength. This metastable phase does not easily become a stable phase, and since it prevents coarsening of Cu-based precipitates, high tensile strength can be obtained after aging even if the cooling rate after solution treatment is small. effective. This effect cannot be obtained when the Li content is low. On the other hand, if it is more than 4.0%, the stable phase δ (A1Li) is likely to precipitate, the strength is lowered, and the elongation and the toughness are also remarkably lowered.

Zr, Cr, Mn, V: Zr, Cr, Mn, V are fine (0.05-0.2μ) during homogenization treatment.
m) In order to precipitate as an intermetallic compound, suppress recrystallization of the alloy material, form fine crystal grains, and improve strength, they may be contained alone or in plural. However, if these contained elements are contained in excess of the upper limit values, a large amount of intermetallic compounds are formed by the process heat treatment from homogenization treatment to the product, and if they are air-cooled after the solution treatment, they are surrounded by these compounds. A large amount of stable phase δ precipitates, and the strength decreases. In addition, a huge intermetallic compound crystallizes during casting, which becomes a defect in the subsequent plastic working.

If it is less than the lower limit, the effect of refining the crystal grains is small.

Melting and casting: It is an active metal that melts and casts in Ar atmosphere.
This is for efficiently containing Li.

Cooling after solution treatment: Cooling after solution treatment is performed by air cooling or forced air cooling in order to reduce strain generated during cooling.

Furthermore, as an application example, even when hot working such as extrusion, quenching is performed as it is with air cooling without water cooling (precipitation of precipitates does not occur even with air cooling), and for forgings and superplastic forming products. On the other hand, since it is easy to burn even with air cooling (precipitation does not occur even with air cooling), solution treatment (cooling that completely dissolves precipitation hardening elements) without causing large (quenching) strain is performed. It is possible.

[Examples] Examples of alloys according to the present invention are shown below.

Example 1 The alloys shown in Table 1 were melted in an Ar atmosphere, the cross section was 150 m.
It was cast into a m × 200 mm ingot. After homogenizing the ingot at 520 ° C for 8 hours in Ar1 atm, 30mm in the length direction of the ingot
It was cut into pieces to obtain a test ingot having a thickness of 30 mm. Next, this ingot was heated to 480 ° C. and hot rolled to a thickness of 6 mm. this
After softening at 350 ° C, a plate with a thickness of 1 mm was obtained by cold rolling. After the solution treatment of the obtained plate in Ar at 520 ° C. for 40 minutes,
It was cooled under the conditions of water cooling (1000 ° C / s), forced air cooling (7 ° C / s), air cooling (2 ° C / s), and furnace cooling (1 x 10 ^-2 ° C / s). Numbers in brackets indicate approximate cooling rate. Then, artificial aging was performed under aging conditions (175 ° C x 24 hr), and the tensile properties were investigated.

The test results are shown in Table 2. In Invention Examples Nos. 1 to 7, the tensile strength of the air-cooled material was 50 kg / mm ² or more, and the reduction rate of the strength of the air-cooled material to the water-cooled material was 97% or more, and the hardenability (hardenability) was high. Good.

However, in No. 8 of the comparative example, none of Zr, Cr, Mn, and V is contained, so that the tensile strength of the air-cooled material is 49.5 kg / mm ²
And 50 kg / mm ² could not be obtained. Since No. 9 and 10 have a small Li content, precipitates are likely to become coarse and hardenability deteriorates,
The tensile strength of the air-cooled material dropped significantly to 28.1 and 34.0 kg / mm ² . No. 11 has a large Li content, so the hot workability is poor,
Could not be rolled. Further, as in No. 12, when the content of Mn and Cr was large, a huge intermetallic compound was generated and a sound product could not be obtained. No. 13 shows 7075 alloy as a typical example of an aluminum alloy having poor hardenability. This alloy is an air-cooled material and its precipitates become coarse and the strength is extremely reduced.

[Effects of the Invention] The alloy material of the present invention can be manufactured without giving strain to the product because sufficient strength can be obtained after aging treatment even if quenching after solution heat treatment is cooled at a cooling rate of about air cooling. it can.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-58-157942 (JP, A) JP-A-59-118848 (JP, A) JP-A-60-2644 (JP, A) JP-A-60- 215735 (JP, A) JP 60-221543 (JP, A) JP 61-23751 (JP, A)

Claims (1)

[Claims] 1. Cu: 0.5 to 3.5% (% is the same as% by weight or less), M
g: 0.5-4.0% and Li: 2.0-4.0%, further Zr: 0.05
~ 0.30%, Cr: 0.05 ~ 0.30%, Mn: 0.05 ~ 1.0%, V: 0.05
~ 0.30% of one or more of the above, with the balance being an aluminum alloy composed of Al and unavoidable impurities,
Casting is performed in an Ar atmosphere, homogenization treatment and plastic working are performed by a normal method, and after solution treatment at 500 ° C. or higher,
A structural Al-Cu-Mg-Li-based aluminum alloy material characterized in that the average particle size of the precipitates is 100 nm or less by artificial aging treatment after cooling at a cooling rate of 1 to 5 ° C / sec. Manufacturing method.