JPH05320837A - Manufacture of structural member made of al alloy - Google Patents

Abstract

PURPOSE:To obtain a structural member showing excellent fatigue strength at a high temp. CONSTITUTION:At the time of manufacturing a structural member, an Al alloy in which the recrystallization temp. of an amorphous phase is defined as Tx is subjected to primary heat treatment under the condition in which the heat treating temp. T1 satisfies Tx-100K<=T1<=Tx+100K to crystallize the amorphous phase. and to execute phase decomposition. Next, this Al allay is subjected to secondary heat treatment under the condition in which the heat treating temp. T2, satisfies T2>Tx+100K and is thereafter subjected to hot extrusion under the condition in which the extruding temp. T3 satisfies T3<=T2. In this way, the objective structural member having excellent elongation and toughness at a high temp. can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an Al alloy structural member, and more particularly to a method for manufacturing a structural member using an Al alloy having a metal structure in which the crystallization temperature of the amorphous phase is Tx.

[0002]

2. Description of the Related Art Conventionally, as this type of manufacturing method, the above-mentioned A
The processing temperature T of the alloy is Tx−100K ≦ T ≦ Tx + 10
A method is known in which the temperature is set to 0K, and a molding and solidification process, for example, a hot extrusion process is performed.

[0003]

However, the structural member obtained by the conventional method has a high internal stress of the Al alloy, and the Al crystal grains and the intermetallic compound crystal grains (hereinafter,
Due to the small difference in grain size between IMC crystal grains) and the high resistance to slip deformation, 423 to 473 K (150
There is a problem in that elongation, fatigue strength and toughness at high temperatures such as (~ 200 ° C.) are low, and thus they are unsuitable as structural members such as engine parts. In view of the above, the present invention removes the internal stress of the Al alloy by subjecting it to a specific heat treatment and increases the grain size difference between the Al crystal grains and the IMC crystal grains. It is an object of the present invention to provide the above-mentioned manufacturing method capable of obtaining a structural member having improved strength and toughness.

[0004]

Made of Al alloy according to the present invention
The manufacturing method of the structural member is such that the crystallization temperature of the amorphous phase is Tx.
A heat treatment temperature T is applied to an Al alloy having a certain metallographic structure.₁Is T
x-100K≤T₁Primary heat under the condition of ≦ Tx + 100K
It is treated to crystallize the amorphous phase and to decompose the phase.
Then, the Al alloy is subjected to a heat treatment temperature T₂Is T₂>
Second heat treatment is performed under the condition of Tx + 100K, before
Using Al alloy, processing temperature T₃Is T ₃≤T₂Conditions
It is characterized in that it is formed and solidified below.

[0005]

The metal structure is a metal structure having a mixed phase structure in which fine Al crystals are uniformly dispersed in an amorphous phase, or a metal structure having an amorphous single phase structure. For example, a differential calorimetric method ( D
In SC), when the temperature rising rate is set to 20 K / min, the metallographic structure exhibits a calorific value of 20 J / g or more in the temperature range from crystallization temperature Tx to crystallization temperature Tx + 150K. When the above-described primary heat treatment is applied to an Al alloy having such a metal structure, the metal structure of the Al alloy is fine,
In addition, it becomes a uniform crystalline phase. In this case, the Al alloy has a high internal stress due to crystallization, phase decomposition, etc. However, when the Al alloy is subjected to the secondary heat treatment as described above, the internal stress of the Al alloy is removed and the metal structure thereof is reduced. Can be stabilized. At the same time, Al crystal grains are preferentially grown to
By increasing the grain size difference from the MC crystal grains, the resistance to slip deformation is reduced, and the Al alloy has excellent deformability.

When such an Al alloy is used for forming and solidifying at the processing temperature T ₃ , it does not impair the stable state of the metal structure and the large grain size difference between both crystal grains. A structural member can be obtained, whereby the structural member exhibits excellent elongation, fatigue strength and toughness at high temperatures.

However, in the first heat treatment, when the heat treatment temperature T ₁ is T ₁ <Tx-100K, crystallization and phase decomposition of the amorphous phase become insufficient, so that a rapid phase change occurs in the second heat treatment. Then, the metal structure of the Al alloy becomes non-uniform, and it becomes difficult to remove the internal stress and preferentially grow the Al crystal grains. On the other hand, when T ₁ > Tx + 100K, the metal structure of the Al alloy becomes nonuniform and coarsens. Again 2
In the subsequent heat treatment, the heat treatment temperature T ₂ is T ₂ ≦ Tx + 10
At 0K, the internal stress of the Al alloy cannot be removed and the preferential growth of Al crystal grains cannot be sufficiently performed. Further, in the forming and solidifying process, when the processing temperature T ₃ is T ₃ > T ₂ , the stable state of the metal structure in the Al alloy after the secondary heat treatment and the large grain size difference between both crystal grains are lost, and It is not possible to obtain a structural member that does.

[0008]

【Example】

 [Example 1] Al₉₁Fe₆Y₃Composition of (numerical value is atomic%)
Prepared by a high-frequency melting method, and then
High pressure N using molten metal₂Gas atomization method (pressure 80kgf
/cm ²) Is applied to produce a powdered Al alloy and then classified.
Adjust the particle size of powdered Al alloy to 22μm or less
Arranged

X-ray diffraction and differential calorimetric analysis (DSC) of the powdered Al alloy were carried out, and FIGS.
The result was obtained. From both figures, it was found that the powdered Al alloy had a mixed phase structure composed of an amorphous phase and a crystalline phase, and the crystallization temperature Tx of the amorphous phase was 658K.

Next, using a powdered Al alloy, various structural members were manufactured by continuously performing the following primary heat treatment, secondary heat treatment and hot extrusion as a forming and solidifying process. First, using a powdered Al alloy, 4000 kgf / cm
A plurality of billets having a diameter of about 50 mm and a length of 50 mm were manufactured by performing cold isostatic pressing (CIP) under the conditions of ² . Each billet is loaded into an aluminum alloy (A5056) can body, the lid body is welded to the opening of the can body, an extruded material having a diameter of about 54 mm and a length of 70 mm is manufactured, and then a connecting pipe provided on the lid body. The atmospheric pressure inside the can was maintained below 2 × 10 ⁻³ Torr.

For each extruded material, and thus each billet,
The heat treatment temperature T _{1 is set} to T ₁ = 623K (Tx-35K),
Further, the heat treatment time was set to 1 hour, and the primary heat treatment was performed.

Next, the heat treatment temperature T _{2 is set} to 673K (Tx + 15K) and 698K (Tx + 40) for each billet.
K), 723K (Tx + 65K), 743K (Tx + 8)
5K), 753K (Tx + 95K), 763K (Tx +
105K), 773K (Tx + 115K), and the heat treatment time was set to 1 hour, and the second heat treatment was performed.

Then, each billet is charged into a container having a temperature of 673K, the die diameter is 15 mm, the processing temperature, and therefore the extrusion temperature T ₃ is T ₃ = 673K (T ₃ ≤T ₂ ).
Various structural members were manufactured by performing hot extrusion processing as molding and solidifying processing under the conditions of.

A tensile test was conducted on various structural members under a test temperature of 423 K, and the tensile strength and the elongation until breaking were measured, and the results shown in FIG. 3 were obtained. In FIG. 3, line a indicates tensile strength and line b indicates elongation. As is clear from FIG. 3, the structural member in which the heat treatment temperature T ₂ of the secondary heat treatment is set to T ₂ > Tx + 100K has an elongation of 5% or more. Whether or not it is suitable as a structural member such as an engine part is based on whether or not the member exhibits elongation of about 5% at the test temperature, and therefore, it is suitable as an engine part or the like according to the present invention. A structural member can be obtained.

Next, the test temperature 42 for various structural members
Tensile-compression type fatigue test was performed at 3K and the number of repetitions was 10 ⁷
When the fatigue strength was measured once, the results shown in FIG. 4 were obtained. In various structural members, the tensile strength σ _B (FIG. 3, line a) gradually decreased with increasing heat treatment temperature T ₂ , but
As is clear from FIG. 4, the fatigue strength σ _f is the heat treatment temperature T ₂
Is almost unchanged when T ₂ ≤Tx + 100K, while T
₂ > Tx + 100K, and the structural member with T ₂ = 773K showed a high value of σ _f / σ _B = 0.51. For structural members such as engine parts, temperature 423
Fatigue strength is more important than tensile strength at ˜473 K, and according to the present invention, it is possible to obtain a structural member that can sufficiently meet such requirements.

Further, the test temperature of various structural members is 4
When the Charpy impact test was performed under the condition of 23K, the result of FIG. 5 was obtained. As is clear from FIG. 5, the Charpy impact value shows the same tendency as the fatigue strength, and the heat treatment temperature T
_The structural member in which ₂ is set to T ₂ > Tx + 100K has high toughness.

For comparison, various structural members were manufactured by the following method.

Using the powdered Al alloy, a plurality of extruded materials were manufactured through the same steps as described above, and the atmospheric pressure inside the can body of each extruded material was maintained at 2 × 10 ⁻³ Torr or less as described above. For each extruded material, and thus each billet,
Primary heat treatment was performed while changing the heat treatment temperature T ₁ and setting the heat treatment time to 1 hour. Then, for each billet, the heat treatment temperature T ₂ was set to 773K (Tx + 115K),
Further, the secondary heat treatment in which the heat treatment time was set to 1 hour was performed. Thereafter, each of the billets was subjected to hot extrusion under the same conditions (extrusion temperature T ₃ = 673K, T ₃ ≦ T ₂ ) as described above to produce various structural members.

A tensile test was conducted on various structural members at a test temperature of 423 K, and the tensile strength and the elongation until breaking were measured, and the results shown in FIG. 6 were obtained.
Line a represents tensile strength and line b represents elongation.

[0020] As apparent from FIG. 6, the primary heat treatment temperature in the heat treatment _{Tx-100K ≦ T 1 ≦ Tx} + 100
When set to K, the tensile strength and elongation of various structural members can be improved. However, the heat treatment temperature T ₁ is T
_{When 1} <Tx-100K, a rapid phase change occurs in the secondary heat treatment, so that the metal structure of the Al alloy becomes nonuniform, and the elongation of the structural member is greatly reduced. On the other hand, T ₁ > Tx +
At 100K, not only the metal structure of the Al alloy becomes non-uniform but also coarsens in the primary heat treatment, and the tensile strength and elongation of the structural member are greatly reduced.

Next, for each structural member, a transmission electron microscope is used.
Heat treatment temperature of secondary heat treatment by observing metallographic structure with a mirror
T₂And the average grain size of Al and IMC grains
When the person in charge was examined, the results shown in FIG. 7 were obtained. Line c in the figure
₁Is the Al crystal grain and the line c ₂For IMC crystal grains
Applicable

As is apparent from FIG. 7, by setting the heat treatment temperature T ₂ of the secondary heat treatment to T ₂ > Tx + 100K, the average grain size of Al crystal grains (line c ₁ ) is changed to IMC crystal grains (line c ₂ The average particle size can be increased rapidly.

Thus, the heat treatment temperature T _{2 is set} to T ₂ > Tx
When set to + 100K and increasing the average grain size difference between the Al crystal grains and the IMC crystal grains, the resistance to slip deformation is reduced and the IMC crystal grains can be rolled at the Al crystal grain interface. It is considered that each of the above-mentioned characteristics could be obtained because the deformability of No. 1 was improved. IMC is Al ₈ YFe ₄ , Al ₃ Y, etc.,
Their shape and average particle size were substantially the same.

Although the heat treatment times in the primary and secondary heat treatments depend on the heat treatment temperature, the primary heat treatment time t ₁ is 0.01 hours ≦ t ₁ ≦ 3 hours and the secondary heat treatment time t within the above temperature range. ₂ is suitable for 0.01 hours ≦ t ₂ ≦ 2 hours. This time condition is the same in each of the following examples. It is also possible to carry out the primary heat treatment at a continuous temperature rise of 10 K / min or less. It is not always necessary to carry out the primary heat treatment and the secondary heat treatment in succession, but it is desirable to carry out the secondary heat treatment and the forming and solidifying process in succession. The reason is that, if a time interval is provided between the secondary heat treatment and the forming and solidifying process, the billet is subjected to a thermal history at the time of temperature decrease and temperature increase, which makes control of the metal structure complicated.

Example 2 The powdery Al alloy (Al ₉₁ Fe ₆ Y ₃ ) of Example 1 was subjected to the same conditions as in Example 1 in an N ₂ gas atmosphere, that is, the heat treatment temperature T ₁ was T ₁ = 623K
(Tx-35K) and the heat treatment time was set to 1 hour, and the primary heat treatment was performed.

The hardness of the powdery Al alloy after the primary heat treatment was measured by using a micro Vickers hardness tester. The hardness was 240 DPN, and the hardness before the primary heat treatment was 30.
It turned out that it is lower than 0DPN. Therefore, a uniaxial die press was used instead of the cold isostatic press (CIP), and a billet with a diameter of 50 mm and a length of 50 mm was manufactured from the powdered Al alloy after the primary heat treatment under the condition of 30 kgf / mm ^2. did. As in Example 1, the billet was charged into an aluminum alloy can body to produce an extruded material, and the pressure inside the can body was maintained at 2 × 10 ⁻³ Torr or less.

Then, the heat treatment temperature T ₂ of the billet is set to 7
63 K (Tx + 105 K) and the heat treatment time is set to 1 hour to carry out the secondary heat treatment. Immediately after the heat treatment time elapses, the billet is charged into a container at a temperature of 673 K, and under the same conditions as in Example 1. Hot extrusion was carried out to manufacture a structural member.

When various tests were conducted on this structural member at a temperature of 423 K, the structural member was found to have tensile strength σ _B 4
The fatigue strength was 70 MPa, the elongation was 6.5%, and the fatigue strength was σ _f 220 MPa after the number of repetitions was 10 ⁷ and it was found that the structural member had the same or higher mechanical properties as the structural member manufactured under the same conditions in Example 1. ..

As described above, the primary heat treatment is performed in the powder state of A.
When applied to an L alloy, the billet can be easily manufactured by a uniaxial press without cold isostatic pressing, so that the structural member can be manufactured in a line and its mass productivity can be improved. Becomes

[Example 3] A molten metal having various compositions was prepared, and then a powdered Al alloy was produced in the same manner as in Example 1,
After that, classification treatment is performed to reduce the particle size of the powdered Al alloy to 22 μm.
It was adjusted to m or less. When the metal structure of each powdered Al alloy was examined by the same method as in Example 1, it was found to have a multiphase structure as described above.

Table 1 shows powdered Al alloys (1) to (20).
The composition and the crystallization temperature Tx of are shown. In the table, Mm is misch metal.

[0032]

[Table 1] Using various powdered Al alloys, a plurality of extruded materials were manufactured through the same steps as in Example 1, and the atmospheric pressure inside the can body of each extruded material was maintained at 2 × 10 ⁻³ Torr or less as described above. .. Each extruded material, and thus each billet, was sequentially subjected to a first heat treatment, a second heat treatment and a hot extrusion process under the same conditions as in Example 1 (extrusion temperature T ₃ = 673K),
Various structural members (1) to (20) [Structural members (1) to (2
0) corresponds to Al alloys (1) to (20), respectively. ] Was manufactured.

Tables 2 and 3 show various structural members (1) to (3).
The production conditions of (20), the average grain sizes of Al crystal grains and IMC crystal grains, and the mechanical strength at 423K are shown.
The heat treatment time in the primary and secondary heat treatments was set to 1 hour. In the evaluation, “◯” indicates that the mechanical strength is excellent, and “X” indicates that the mechanical strength is inferior.

[0034]

[Table 2]

[0035]

[Table 3] As is apparent from Tables 2 and 3, the heat treatment temperatures T ₁ and T ₂ and the extrusion temperature T in the primary and secondary heat treatments
By setting ₃ in the above range, the internal stress of the Al alloy is removed, and a large average grain size difference appears between the Al crystal grains and the IMC crystal grains, so that a structural member having excellent mechanical strength (3 ), (4); (7), (8); (1
1), (12); (15), (16); (19), (2
0) can be obtained.

As the forming and solidifying process, powder forging method, hot pressing, hot isostatic pressing (HIP) and the like are also applied.

[0037]

According to the present invention, a structural member that exhibits excellent elongation, fatigue strength and toughness at high temperature can be obtained by sequentially performing a specific heat treatment and a forming and solidifying process on a specific Al alloy. it can.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction diagram of an Al alloy.

FIG. 2 is a differential calorimetric analysis diagram of an Al alloy.

3 is a graph showing the relationship between the heat treatment temperature T ₂ and the tensile strength sigma _B and elongation of the secondary heat treatment.

It is a graph showing the relationship between FIG. 4 of the second heat treatment heat treatment temperature T ₂ and the fatigue strength sigma _f.

FIG. 5 is a graph showing the relationship between the heat treatment temperature T _{2 of the second} heat treatment and the Charpy impact value.

6 is a graph showing the relationship between the primary heat treatment heat treatment temperature T ₁ of the and the tensile strength sigma _B and elongation.

7 is a graph showing the relationship between the average particle size of the second heat treatment heat treatment temperature T ₂ and the Al crystal grains and IMC grain.

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[Procedure amendment]

[Submission date] July 15, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0024

[Correction method] Change

[Correction content]

Although the heat treatment times in the primary and secondary heat treatments depend on the heat treatment temperature, the primary heat treatment time t ₁ is 0.01 hours ≦ t ₁ ≦ 3 hours and the secondary heat treatment time t within the above temperature range. ₂ is suitable for 0.01 hours ≦ t ₂ ≦ 2 hours. This time condition is the same in each of the following examples. It is also possible to carry out the primary heat treatment at a continuous temperature rise of 10 K / min or less. Not necessarily to the this continuously performing a primary heat treatment and second heat treatment, but who performed continuously in a mold and solidified processing and second heat treatment is desirable. The reason is that, if a time interval is provided between the secondary heat treatment and the forming and solidifying process, the billet is subjected to a thermal history at the time of temperature decrease and temperature increase, which makes control of the metal structure complicated.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction content]

[0034]

[Table 2]

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0035

[Correction method] Change

[Correction content]

[0035]

[Table 3] As is apparent from Tables 2 and 3, the heat treatment temperatures T ₁ and T ₂ and the extrusion temperature T in the primary and secondary heat treatments
By setting ₃ in the above range, the internal stress of the Al alloy is removed, and a large average grain size difference appears between the Al crystal grains and the IMC crystal grains, so that a structural member having excellent mechanical strength (3 ), (4); (7), (8); (1
1), (12); (15), (16); (19), (2
0) can be obtained.

Claims (2)

[Claims] 1. An Al alloy having a metallic structure in which the crystallization temperature of the amorphous phase is Tx, and the heat treatment temperature T ₁ is Tx-10.
A primary heat treatment is performed under the conditions of 0K ≦ T ₁ ≦ Tx + 100K to crystallize the amorphous phase and to perform phase decomposition, and then the heat treatment temperature T _{2 of the} Al alloy is T ₂ > Tx + 1.
A second heat treatment is performed under the condition of 00K, and thereafter, the Al alloy is used for forming and solidifying under the condition that the working temperature T ₃ is T ₃ ≦ T _2. Method. 2. The method for manufacturing an Al alloy structural member according to claim 1, wherein the primary heat treatment is applied to the Al alloy in a powder state.