JP3368600B2 - Manufacturing method of high heat resistant aluminum alloy - Google Patents

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 a high heat resistant aluminum alloy, and more particularly to a method for producing a high heat resistant aluminum alloy by compacting and solidifying rapidly solidified aluminum alloy powder by a hot forging method. is there.

[0002]

2. Description of the Related Art As a conventional method for producing an aluminum alloy, there is a melt casting method. According to this method, an element (transition metal-based element; iron (Fe), which improves the heat resistance of the aluminum (Al) alloy,
Since nickel (Ni), chromium (Cr), etc. form a coarse intermetallic compound, only about 1% at most can be added, and effects such as heat resistance were limited. The JIS standard alloy that is said to have the highest heat resistance is 2618 or an improved alloy thereof, but even such an alloy does not have sufficient strength in the temperature range of 180 ° C or higher.

On the other hand, in the powder metallurgy method, it is possible to obtain a dispersion strengthened alloy powder having a fine and uniform structure even if a large amount of the above transition metal alloy element is added by using a rapid solidification method. In particular, in this case, it is known that the structure becomes finer and excellent characteristics can be obtained by increasing the rapid solidification rate. However, in the rapidly solidified aluminum powder alloy, it is necessary to once solidify the powder obtained in this way, but since the powder surface is covered with a hard aluminum oxide film, this film inhibits the binding between the powders. To do. Therefore, it is necessary to heat the powder to soften the powder to such an extent that it can be plastically deformed, and then to subject the surface oxide film to fragmentation / breakage by applying plastic working to bond and solidify the powders.

The solidification method includes a hot extrusion method and a hot forging method. In the hot extrusion method, when the heated powder is extruded, a sufficiently large extrusion ratio is applied so as to give sufficient plastic deformation to the powder to divide / break the oxide film and obtain a strong bond between the powders. Must be set. When such a large extrusion ratio is set, the size of the powder compact obtained by extrusion becomes large. Therefore, in the preheating after the powder molding, the preheating time becomes long in order to uniformly raise the temperature inside the powder compact. However, when the preheating time at a high temperature becomes long in this way, there is a problem that the fine structure obtained by the rapid solidification method is decomposed by the diffusion of alloying elements and gradually coarsens to deteriorate the characteristics. Materials with excellent strength have not been realized.

On the other hand, in the hot forging method, it is necessary to heat the powder particles to a sufficiently high temperature so that the powder particles are plastically deformed by pressing and compressing without giving a large plastic flow so that the powder particles can be bonded to each other. There is. If the heating temperature is not sufficiently high, the powder particles are not sufficiently bonded, so that cracks occur at the powder grain boundaries, and sufficient solidification cannot be achieved. Since it is necessary to heat at a sufficiently high temperature even in the hot forging method as described above, there is a problem that the fine structure obtained by the rapid solidification method is decomposed by the diffusion of alloying elements and gradually coarsens to deteriorate the characteristics. Occurs.

On the other hand, an example of a method for manufacturing an aluminum powder alloy member is proposed in Japanese Patent Laid-Open No. 63-60265. In the method proposed in the above publication, first, for the purpose of removing the water adsorbed on the surface of the powder particles,
The heat treatment process of the powder compact in the atmosphere is introduced. However, the removed water reacts with aluminum again to form a strong aluminum oxide film on the powder surface and prevent the powder particles from binding to each other. Also, after the heat treatment of the powder compact to sufficiently break the oxide film existing on the powder surface and bond the powders together, a total of two hot forgings are carried out after preliminary heat-sealed die forging. is doing. Therefore, in the manufacturing method proposed in the above publication, the process is complicated and there is an economical problem.

The present invention has been made to solve the above-mentioned problems, and when the rapidly solidified aluminum alloy powder is compacted and solidified by the hot forging method, the powder can be plastically deformed, and the powders can be separated from each other. It is an object of the present invention to provide a method for producing a high heat-resistant strength aluminum alloy which can be firmly bonded and can prevent decomposition and coarsening of a fine structure obtained by a rapid solidification method.

[0008]

In order to achieve the above object, the method for producing a high heat resistant aluminum alloy of the present invention comprises the following steps.

First, a rapidly solidified aluminum alloy powder containing iron in an amount of 4% by weight to 12% by weight and the balance being aluminum and inevitable impurities is prepared in a particle size of 100 μm or less. Then, the rapidly solidified aluminum alloy powder is preformed at a temperature from room temperature to 300 ° C. to obtain a powder compact. Then, the powder compact is heated to 450 ° C. or higher and 540
The temperature is raised to a forging temperature of ℃ or less at a heating rate of 50 ℃ / min or more. Al ₃ Fe which is a stable phase as an intermetallic compound
And Al ₁₃ Fe ₄ and Al ₆ Fe which are metastable phases are formed, and the ratio of the metastable phase to the stable phase is 5: 5 to 8: 2 in the comparison of the diffracted X-ray intensities in the X-ray diffraction method. As described above, the powder compact is forged after being held at the forging temperature for 6 minutes or more and 15 minutes or less.

The stable phase, that is, the equilibrium phase, of the alloy containing Al-Fe as the master alloy is Al as shown in the phase diagram.
₃ Fe is an intermetallic compound. However, the metastable phase obtained by rapid solidification of this alloy is Al ₆ Fe when the rapid solidification rate is extremely high, and Al ₁₃ Fe when it is intermediate.
It becomes Fe ₄ .

As a result of various experiments and examinations, the present inventors
The powder obtained by the usual atomization method has a small amount of Al ₃ Fe, and most of the two metastable phases, Al ₆ Fe and Al ₁₃ Fe ₄ , show that the metastable phase gradually becomes stable when heated. It was confirmed to change to Al ₃ Fe.

Furthermore, the inventors of the present invention have found that the metastable phase in the alloy powder obtained by the rapid solidification method gradually becomes a stable phase due to the thermal history (temperature, time, rate of temperature increase) during heating and holding at high temperature. It has been found that by optimizing its heat history, it is possible to efficiently produce a high heat resistant aluminum alloy having excellent strength, toughness and thermal stability.

In the following, in the method for producing a high heat resistant strength aluminum alloy of the present invention, each condition for defining the heat history will be described.

The temperature at which the powder is preformed by, for example, embossing is usually room temperature. However, since the rapidly solidified aluminum alloy powder is hard, when the moldability is not good or when it is necessary to mold with a low pressure, after heating up to 300 ° C to soften the powder, Molding is performed. However, if the temperature exceeds 300 ° C., the powder surface is oxidized and the hot forgeability in the subsequent step is deteriorated. Therefore, it is necessary to set the temperature of the embossing molding to 300 ° C. or lower.

In the preheating for holding the powder compact at the forging temperature for a predetermined time, the forging temperature controls the morphology of the precipitation phase in the alloy powder and is therefore the most important factor in solidifying the powder. That is, the forging temperature is 450 ° C or higher and 540 ° C.
When it is below, excellent strength / toughness and heat resistance can be secured.

When the forging temperature exceeds 540 ° C., the metastable phase having excellent properties is decomposed and gradually coarsened, so that strength / toughness and heat resistance are deteriorated.

On the other hand, when the forging temperature is lower than 450 ° C., the powder is not annealed and is hard, so that the oxide film on the surface of the powder is not sufficiently divided and broken by the pressure applied during forging. Therefore, the bonding between the powders becomes insufficient. As a result, fracture tends to proceed from the old powder grain boundary,
There arises a problem that the toughness (elongation) is reduced.

Regarding the heating time of the preheating, if the heating time is less than 6 minutes, the powder is not sufficiently annealed and is hard. Is insufficient. As a result, the toughness (elongation) of the alloy decreases. On the other hand, when the heating time exceeds 15 minutes , a rapidly solidified structure having excellent properties is decomposed and coarsened, and thus there arises a problem that strength / toughness and heat resistance are deteriorated. Therefore, the appropriate heating time for preheating to obtain a high heat-resistant strength aluminum alloy is 6 minutes or more 1
5 minutes or less.

In the intermetallic compound present in the Al--Fe alloy powder obtained by the rapid solidification method, the metastable phase (Al
₁₃ Fe ₄ , Al ₆ Fe) occupy the majority, but as described above, this metastable phase gradually becomes stable (Al ₃ F
e). Therefore, in the present invention, not only the above-mentioned thermal history but also the metastable phase and the stable phase (equilibrium phase) are uniformly dispersed in the matrix, and their diffracted X-ray intensity ratio by the X-ray diffraction method is 5: It has been found that the heat resistance of the alloy is improved when it is present in the ratio of 5 to 8: 2.

The specific amount of iron added to achieve the above diffracted X-ray intensity ratio is 4% by weight or more and 12% by weight or less. If it is less than 4% by weight, the metastable phase does not exist in the above proportion, and the effects such as heat resistance are insufficient.
If it exceeds 12% by weight, coarse Al-Fe
Since the intermetallic compound is formed, the strength / toughness or heat resistance decreases.

When the Al--Fe rapidly solidified powder is compacted and solidified by the hot forging method as described above, the heating history (temperature, time, temperature rising rate) in the solidifying step is optimized and stable with the metastable phase. Diffraction X-ray intensity ratio with phase 5: 5
By 8: 2, the conventional hot powder extrusion method or 2
It is possible to efficiently manufacture such an excellent high heat-resistant strength aluminum alloy that cannot be obtained by the hot forging method. Further, unlike the conventional heat-resistant strength aluminum alloy, since it is not necessary to add various refractory metal elements for improving the heat-resistant strength, the cost of the powder itself becomes low, and it is molded and solidified based on the manufacturing method of the present invention. As a result, it can be economically molded. As a result, it can be applied to automobile parts that are required to be lightweight and heat resistant, such as connecting rods, valve guides, and valve lifters.

Further, rapidly solidified aluminum alloy powder 1
It is prepared with a particle size of 00 μm or less.

For example, when the particle size of the rapidly solidified aluminum alloy powder obtained by the atomization method exceeds 100 μm, the cooling rate during solidification (rapid solidification rate) becomes small.
Therefore, the amount ratio of the stable phase and the metastable phase is 5: 5 to 5
A metastable phase satisfying 8: 2 is not generated, and as a result, there arises a problem that the heat resistance of the alloy obtained by solidifying such powder is remarkably lowered. Also powder molding
In the process of raising the temperature of the body to the forging temperature, the heating rate is 50 ° C / min.
That is all. For example, the rate of temperature rise in rapid induction heating is
If it is less than 50 ° C / min, until the temperature rises to the forging temperature
The heating time becomes longer. Therefore, it can be obtained by rapid solidification.
The microstructure of the metastable phase becomes coarse and, as a result,
The characteristic deteriorates because the diffracted X-ray intensity ratio is not satisfied.
It Therefore, the heating rate should be 50 ° C / min or more.
is necessary.

According to preferred have stations surface of the present invention, the step of heating the powder compact to forging temperature takes place in one of an atmosphere of air and inert gas. When the powder compact is induction-heated, for example, the above properties of the alloy can be secured by heat treatment in either atmosphere or an inert gas atmosphere.

[0025]

According to preferred have stations surface of the present invention, the forging temperature is 450 ° C. or higher 500 ° C. or less. When the heat resistance of the alloy is required preferentially, it is effective to allow the metastable phase to remain as much as possible and to have a certain degree of toughness (elongation). For that purpose, the forging temperature of the powder compact is preferably 450 ° C. or higher and 500 ° C. or lower.

As described above, according to the manufacturing method of the present invention, the tensile strength at room temperature is 35 kgf / mm ² or more and the elongation is 5 to 10%, and the tensile strength at 200 ° C. at high temperature is 30 kgf / mm ² or more. It is possible to easily and inexpensively manufacture a highly heat-resistant aluminum alloy, which is extremely superior to the conventional ones.

[0028]

EXAMPLES Characteristics of rapidly solidified aluminum alloy powder having the composition and grain size shown in Table 1 and solidified into a 10 × 55 × 10 mm shape by hot forging under the various conditions shown in Table 2 (strength / toughness). , High temperature strength and precipitation phase ratio)
Are shown in Table 2.

[0029]

[Table 1]

[0030]

[Table 2]

The pressure applied during stamping and forging was 6 t / cm ² , and the strength of the alloy at 200 ° C. was
It is data when a tensile test was performed after the sample was heated and held at 200 ° C. for 100 hours. The ratio of metastable phase to stable phase in the alloy is the relative ratio of its diffraction intensities obtained by X-ray diffractometry.

Nos. 1 to 10 shown in Table 2 are examples of the present invention. The alloy obtained by the production method of the present invention is excellent in strength / toughness and high temperature strength, and is stable with metastable phases in the alloy. The ratio with the phase is within the target range.

On the other hand, Nos. 11 to 19 shown in Table 2 are comparative examples, and in the sample No. 11, the iron content exceeds 12% by weight, so that the intermetallic compound becomes coarse and the toughness decreases.

In the sample of No. 12, the iron content for improving the heat resistance of the alloy is less than 4% by weight, so that the strength at high temperature decreases.

In the sample of No. 13, the powder particle size is 100 μm.
Since it is larger than m, a sufficient rapidly solidified structure cannot be obtained and heat resistance is lowered.

Sample No. 14 had a heating temperature of 450 ° C.
Since it is lower than that, the bonding between the powders becomes insufficient and the toughness decreases.

Sample No. 15 had a heating temperature of 540 ° C.
Since it is higher than the above, the metastable phase decomposes and coarsens, and the heat resistance decreases.

In the sample of No. 16, since the heating temperature is less than 6 minutes, the bonding between the powders becomes insufficient and the toughness decreases.

In the sample of No. 17, since the heating time exceeds 20 minutes, the metastable phase decomposes and coarsens, and the heat resistance decreases.

In the sample of No. 18, the heating rate during heating is smaller than 50 ° C./minute, so that heat treatment is required for a long time, and the heat resistance decreases due to decomposition and coarsening of the metastable phase.

In the sample of No. 19, the temperature at the time of embossing exceeds 300 ° C., the oxidation of the powder surface progresses, and a strong bond between the powders cannot be obtained, resulting in a decrease in toughness.

[0042]

[Effects of the Invention] When the Al-Fe system rapidly solidified powder is compacted and solidified by the hot forging method, the heating history (temperature, time, temperature rising rate) in the solidification step is optimized and the metastable phase and stable phase are formed. By setting the diffracted X-ray intensity ratio to 5: 5 to 8: 2, an excellent high heat-resistant aluminum alloy that cannot be obtained by the conventional hot powder extrusion method or double hot forging method can be efficiently produced. . Further, unlike the conventional high heat-resistant strength aluminum alloy, since it is not necessary to add various refractory metal elements for improving the heat resistance, the cost of the powder itself is low, and the solidification is performed based on the manufacturing method of the present invention. By doing so, it can be manufactured economically.
As a result, it can be applied to automobile parts that are required to be lightweight and heat resistant, such as connecting rods, valve guides, and valve lifters.

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Claims (3)

(57) [Claims] 1. A step of preparing a rapidly solidified aluminum alloy powder containing 4% to 12% by weight of iron and the balance being aluminum and unavoidable impurities in a particle size of 100 μm or less, and the rapidly solidified aluminum alloy powder. Above room temperature 300 ° C
A step of obtaining a powder compact by preforming at the following temperature, a step of raising the powder compact to a forging temperature of 450 ° C. or higher and 540 ° C. or lower at a heating rate of 50 ° C./min or higher, and an intermetallic compound As a stable phase, Al ₃ Fe and metastable phases, Al ₁₃ Fe ₄ and Al ₆ Fe, are formed, and the metastable phase and the stable phase are compared with each other in the comparison of the diffracted X-ray intensities in the X-ray diffraction method. So as to exist at a ratio of 5: 5 to 8: 2, and then forging the powder compact after holding at the forging temperature for 6 minutes or more and 15 minutes or less,
Method for producing high heat resistant aluminum alloy. 2. The high heat-resisting strength aluminum according to claim 1, wherein the step of raising the temperature of the powder compact to the forging temperature is performed in an atmosphere of either air or an inert gas. Alloy manufacturing method. 3. The forging temperature is 450 ° C. or higher and 500 ° C.
It is the following, The manufacturing method of the high heat resistant aluminum alloy of Claim 1 or 2 characterized by the following.