JPH11124648A - Aluminum material excellent in high temperature strength - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum material excellent in high temp. strength without deteriorating workability. SOLUTION: This material is an aluminum material produced by subjecting a billet to hot extrusion and then to cold working. This aluminum material has an alloy composition which consists of, by weight, 0.5-1.8% Mn and the balance Al with impurities and in which, as impurities, the contents of Fe, Si, Mg, Cu, and other elements are controlled to <=0.4%, <=0.4%, <=0.5%, <=0.5% and <=0.2 respectively, and also has an alloy structure in which an Al-Mn type precipitate has <=0.4 μm major axis and is present by >=1 piece/μm<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an aluminum material having excellent strength in a high temperature range.

[0002] In this specification, the term "aluminum" is used to include aluminum and its alloys.

[0003]

2. Description of the Related Art Al-Mn alloys are widely used as materials for various objects, building materials and the like because of their excellent strength. In addition, because extrudability and processability are good,
These products are often subjected to cold working such as drawing after extrusion to produce required shapes.

[0004]

However, since cold working generally lowers the recrystallization temperature, the product must be 300 to
When used in a high temperature range of about 400 ° C. for a long time, there is a problem that the state becomes the same as that of annealed, and the strength is significantly reduced.

Accordingly, the present applicant has previously filed an application as an Al-Mn-based aluminum material having excellent high-temperature strength, in which the size and number of intermetallic compounds are regulated (Japanese Patent Application No. 9-1 / 1991).
No. 27037). Specifically, the number of intermetallic compounds having a major axis of 1 μm or more was specified to be less than 1 × 10 ⁴ / mm ² .

However, subsequent studies have shown that, among intermetallic compounds, crystallized substances become nuclei for recrystallization in a high-temperature environment and promote recrystallization to lower the strength. But Al-Mn
It has been found that it is desirable that a small amount of the systemic precipitates be present in a certain amount or more because the high-temperature strength can be improved.

The present invention has been made in view of such technical background,
It is an object of the present invention to provide an aluminum material excellent in high-temperature strength with little strength reduction even when used in a high-temperature range.

[0008]

Means for Solving the Problems The aluminum material having excellent high temperature strength according to the present invention is an aluminum material produced by extruding a billet hot and then performing cold working to achieve the above object. In addition, in the alloy composition, Mn: 0.5 to 1.8 wt% is contained, and the balance consists of Al and impurities, and Fe as impurities is 0.4 wt%.
Hereinafter, Si is 0.4 wt% or less, Mg is 0.5 wt% or less,
Cu is regulated to 0.5 wt% or less, and other elements are regulated to 0.2 wt% or less, respectively. In the alloy structure, the Al—Mn-based precipitate has a major axis of 0.4 μm or less and 1 piece / μm.
It is characterized in that there are ^two or more.

Preferably, the aluminum material is subjected to hot extrusion without subjecting the billet to a homogenizing treatment. Further, the hot extrusion is preferably performed at a temperature of 500 ° C. or less and an extrusion speed of 20 m / min or more. Further, it is preferable that the cold working is performed at a working ratio of 5% or more and less than 35%.

In the alloy composition of the aluminum material according to the present invention, the significance of addition of each element and the reason for limiting the content and the reason for controlling impurities are as follows.

Mn is an element that contributes to an improvement in strength by suppressing the growth of recrystallized grains, making the recrystallized grains finer, and suppressing the movement of grain boundaries. Mn content,
If the content is less than 0.5 wt%, the above effect is poor, while 1.5 wt%
If the amount exceeds Mn, the amount of undissolved Mn increases to generate a coarse intermetallic compound, which may cause recrystallized grains to grow and lower the strength. Therefore, the Mn content is 0.5-1.
It must be 8 wt%. A preferred lower limit of the Mn content is 0.8 wt%, and a preferred upper limit is 1.3 wt%.

The balance of Mn is Al and impurities.
When Fe and Si are present as impurities in the alloy, A
This increases the amount of crystallized substances such as l-Fe-Mn and Fe-Si, and also causes Al-Mn-based precipitates to become coarse. Therefore, each of Fe and Si needs to be regulated to 0.4 wt% or less. The preferred upper limit of the Fe content is 0.3 wt%, and the preferred upper limit of Si is 0.2 wt%.
%. Further, when Mg as an impurity is contained in a large amount, deformation resistance at the time of cold working is increased, and productivity is deteriorated. The preferred upper limit of Mg is 0.1% by weight. Cu is an element that contributes to the improvement of the strength. However, if the content is too large, it may cause the formation of coarse crystals, so it is necessary to regulate the content to 0.5 wt% or less. The preferred upper limit of Cu is 0.3 wt%. Other impurity elements must be regulated to 0.2 wt% or less, respectively, in order to suppress coarse crystals, and particularly preferably 0.1 wt% or less.

[0013] In the alloy structure of the aluminum material having such a composition, Al-Mn-based precipitates must be fine and numerous densely present in order to suppress the growth of recrystallized grains in a high temperature environment after cold working. is necessary. Specifically, it is necessary that the precipitate has a major axis of 0.4 μm or less and one / μm ² or more. Preferably, 0.3 μm or less, 2
It is preferable that the number of particles / μm ² or more be present. in this way,
The reason why the growth of recrystallized grains in a high-temperature environment can be suppressed by making the Al-Mn-based precipitates fine and densely present is not clear, but the pinning effect of the grain boundaries by these Al-Mn-based precipitates is unknown. Is presumed to have been exhibited. In addition, as for the crystallized substance in the aluminum material, those having a major axis of 1 μm or more are desirably regulated to less than 1 × 10 ⁴ particles / mm ² .

The aluminum material of the present invention is formed into a product having a required shape by subjecting a billet to cold working after hot extrusion, in which Al-Mn-based precipitates are finely and densely distributed as described above. For this reason, it is preferable to process by the following method.

First, it is preferable that the billet is not homogenized. This is because, when the homogenization treatment is performed, the Al-Mn-based compound may precipitate as coarse crystals in the heating process and the subsequent cooling process.

As for the extrusion conditions, it is recommended that the extrusion temperature is 500 ° C. or less and the extrusion speed is 20 m / min or more as the product speed. This is because, at low temperature and low speed extrusion, the crystal structure becomes fibrous and the strength is significantly reduced in a high temperature environment. Because there is. A particularly preferred upper limit of the extrusion temperature is 450
° C, and the lower limit is 400 ° C. A particularly preferred lower limit of the extrusion speed is 30 m / min.

For the cold working, any working method such as drawing and rolling can be applied, and the cold working ratio represented by the following equation is reduced to 5%.
It is preferable that the content is not less than 35%.

Cold working rate (%) = (1−A ₁ / A ₀ ) × 100 where A ₀ : cross-sectional area before cold working A ₁ : cross-sectional area after cold working Cold working rate is 5 %, The work hardening is insufficient and the strength after cold working is insufficient, and accordingly, the strength after holding at a high temperature is also insufficient. In addition, Al-Mn-based precipitates are not sufficiently refined, which causes insufficient strength after high-temperature holding. on the other hand,
When the cold working ratio is 35% or more, the strength increases due to work hardening, but the strength reduction rate due to holding at a high temperature increases, resulting in insufficient strength when used at a high temperature for a long time.

The aluminum material of the present invention contains not only a predetermined amount of Mn in the alloy composition, but also the contents of Fe, Si, Mg, and Cu as impurities, as well as the Al-Mn-based precipitation. Since the objects are finely and densely distributed, the recrystallization temperature is less reduced even when used for a long time in a high-temperature environment, the growth of recrystallization is suppressed, and the decrease in strength is small.

[0020]

EXAMPLES Next, specific examples of the aluminum material of the present invention will be described.

[Experiment I] First, billets having respective alloy compositions shown in Table 1 below were cast. Of these billets,
Each Example and Comparative Examples 7 to 10 were not subjected to the homogenization treatment.
A homogenization treatment for 16 hours was performed. Then, it is preheated to 450 ° C., and has an outer diameter of 7 at a constant extrusion speed of 60 m / min.
A 2 mm x 2.0 mm thick tube was extruded. Further, these extruded tubes were drawn under a constant condition of a reduction (cold working ratio) of 20% and a reduction in outer diameter of 3 mm. Table 1 shows the length and number of Al-Mn-based precipitates in the alloy structures of these drawn tubes. The crystallized product had a major axis of less than 1 × 10 ⁴ particles / mm ² .

Immediately after drawing, each of the drawn tubes thus obtained was kept at 500 ° C. for 3 hours and at 327 ° C. for 440.
After holding for 0 hours, the proof stress was measured by an ordinary method. The results are shown in Table 1. The pass / fail judgment is 5
Those that maintained a proof stress of 70 MPa or more after both holding at a high temperature of 00 ° C. for a short time and 327 ° C. for a long time were evaluated as good (良), and the others were evaluated as defective (×).

[0023]

[Table 1]

From the results shown in Table 1, it was confirmed that by setting the alloy composition of the aluminum material and the distribution state of the Al—Mn-based precipitate within the range of the present invention, it was possible to maintain a high proof stress even at a high temperature for a long time. did it. In addition, it was confirmed that such a distribution state of the precipitate can be achieved by not performing the homogenization treatment on the billet.

[Experiment II] Next, a billet having the same composition as in Example 4 was extruded and drawn without performing homogenization. The extrusion conditions were such that the preheating temperature and the extrusion speed of the billet were changed as shown in Table 2, and the drawing conditions were the same as in Experiment I. Then, for each drawn tube, the distribution state of the Al—Mn-based precipitate was examined, and immediately after drawing, after holding at 500 ° C. for 3 hours, 327
The proof stress after 4400 hours of holding at ℃ was measured by a conventional method.
After holding for 4400 hours, the metal structure was examined. Table 2 shows these results. Note that, in Table 2, Example 14 corresponds to Table 1
Of Example 4 of Example 1. The crystallized product of the drawn tube had a major axis of less than 1 × 10 ⁴ / mm ² .

[0026]

[Table 2]

From the results in Table 2, it can be seen that by setting the extrusion conditions within the range of the present invention, the Al-Mn-based precipitates can be finely and densely distributed, and the proof stress can be maintained even at a high temperature for a long time. I was able to confirm that I could.

[Experiment III] Next, an alloy having the same composition as that of the above-mentioned Example 4 was extruded under the same conditions as in Experiment I without performing homogenization treatment, and was further extracted at each reduction shown in Table 3. The distribution state of the Al-Mn-based precipitates was examined for the drawn tube, and for each of the obtained drawn tubes, the yield strength immediately after drawing was maintained at 500 ° C. for 3 hours, and then maintained at 327 ° C. for 4400 hours. Was measured by Table 3 shows the results. In addition, in Table 3, Example 24 is a repetition of Example 4 of Table 1. The crystallized product of the drawn tube had a major axis of less than 1 × 10 ⁴ / mm ² .

[0029]

[Table 3]

According to the results shown in Table 3, the Al—Mn-based precipitates can be finely and densely distributed by performing cold working under the conditions within the range of the present invention, and even when the alloy is held at a high temperature for a long time. It was confirmed that the proof stress could be maintained.

[0031]

As described above, the aluminum material of the present invention is an aluminum material manufactured by extruding a billet by hot working and then performing cold working. To 1.8 wt%, the balance consisting of Al and impurities, and Fe as impurities of 0.1 wt%.
4 wt% or less, Si 0.4 wt% or less, Mg 0.5 wt%
Hereinafter, Cu is 0.5 wt% or less, and other elements are 0.2 wt% or less, respectively.
wt% or less.
The Mn-based precipitate has a long diameter of 0.4 μm or less, and has a fine and dense structure of 1 / μm ² or more. Therefore, the growth of recrystallization is suppressed even in a high temperature environment. Therefore, a decrease in strength is suppressed, and a high strength can be stably maintained for a long time even in a high temperature range. Further, since the Mg content as an impurity is regulated, there is no possibility that the workability is impaired.

Further, the fine and dense structure of the Al—Mn precipitate as described above may be subjected to hot extrusion without subjecting the billet to a homogenization treatment.
It is obtained by performing the cold working at an extrusion rate of 20 m / min or more at a temperature of not more than 5 ° C. or lower, and furthermore, performing the cold working at a working rate of 5% or more and less than 35%.

────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code FI C22F 1/00 650 C22F 1/00 650A 683 683 685 685Z 694 694A 694B (72) Inventor Yuichi Takami 6,224 Kaiyamacho, Sakai-shi Showa Aluminum Co., Ltd.

Claims (4)

[Claims] An aluminum material manufactured by cold working after hot extruding a billet, the alloy composition containing Mn: 0.5 to 1.8 wt%, with the balance being Al Fe is 0.4 wt% or less, Si is 0.4 wt% or less, Mg is 0.5 wt% or less, Cu is 0.5 wt% or less, and other elements are 0.2 wt% or less. In the alloy structure, the major diameter of the Al-Mn-based precipitate is 0.4
An aluminum material having excellent high-temperature strength, wherein the aluminum material has a size of not more than 1 μm and not less than 1 piece / μm ² . 2. The aluminum material having excellent high-temperature strength according to claim 1, wherein hot extrusion is performed without subjecting the billet to a homogenization treatment. 3. The aluminum material excellent in high-temperature strength according to claim 1, wherein the hot extrusion is performed at a temperature of 500 ° C. or less and an extrusion speed of 20 m / min or more. 4. The aluminum material according to claim 1, wherein the cold working is performed at a working ratio of 5% or more and less than 35%.