JPH02194130A - Manufacture of sintered compact of heat resisting al-base alloy powder - Google Patents

Abstract

PURPOSE:To manufacture a sintered compact excellent in heat resistance and toughness by applying plastic deformation to an Al-base alloy powder in which Cr and Zr exist in the form of solid solution at specific temp. to introduce dislocation into the inner part of the powder and then subjecting the above powder to hot compaction. CONSTITUTION:A powder of Al-base alloy in which Cr and Zr are allowed to enter into solid solution as essential components is subjected to plastic deformation by using a ball mill, etc., at a temp. of the recrystallization temp. or below, by which dislocation is introduced into the matrix to carry out work hardening. The above powder is heated to and held at 200-450 deg.C to stabilize grain boundary precipitates and is further hot-compacted at <=500 deg.C, by which the dense sintered compact of the Al-base alloy can be obtained. This sintered compact is suitable for material for various engine parts, aircraft sheath material, and other various parts for use under a high-temp. environment.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing an At-based alloy powder sintered body, which is widely used in various industrial machinery fields such as automobiles, front air planes, railway vehicles, and ships. It is related to.

[Prior art] In recent years, as a new direction for AI powder metallurgy, rapid solidification methods have been applied to obtain Al-based alloy powders containing various transition elements, and sintered bodies have been formed using the Al-based alloy powders. Many techniques have been developed to produce sintered bodies with high hot strength.

According to the above technology, Al-Fe, Al-Cr, and Al-Zr with compositions that cannot normally be obtained in an equilibrium state are produced.
, Al-3L, etc. can be manufactured by using rapidly solidified powder, and by adjusting the grain size and fine mixture, new alloys with excellent heat resistance, wear resistance, and fatigue strength can be produced. materials can be obtained.

For example, Japanese Patent Application Laid-Open No. 59-43802, [io-23
No. 4936, No. 60-2481180, No. 6
Numerous technologies are disclosed in Japanese Patent No. 1-49551, Japanese Patent No. 61-96051, Japanese Patent No. 51-130451, etc., and a similar technology is also disclosed in US Patent No. 4,464,199. There is.

All of the techniques found in the above documents have an F of approximately 8 to 12%.
In addition to containing e, rare earth elements such as Ce or V, Zr, M
Al-Fe-based alloy powder containing transition metal elements such as It is stated that an At-based alloy powder sintered body with high hot strength and heat resistance was obtained by dispersing the aforementioned Ce, V, Zr, Mo, etc.).

Much research and development has been carried out on Al-based alloy powders other than the Al-Fe alloy powders shown above.
Al-Cr-Zr with improved heat resistance by containing r etc.
A sintered body of alloy powder is disclosed.

[Problems to be solved by the invention] In the sintered body obtained from the Al-Fe alloy powder,
All have high tensile strength in the temperature range from room temperature to about 300°C.

However, when the present inventors conducted various studies on the Al-Fe alloy powder sintered body, it was found that the sintered body had low toughness. This is because in Al-Fe alloy powder sintered bodies, large amounts of Fe and other elements are added to increase the volume fraction of the dispersed phase in order to improve strength, but this dispersed phase is brittle. In addition, it tends to act as a crack propagation site and promote crack propagation, and it is thought that these factors lower the toughness of the sintered body.

In addition, even if an attempt was made to improve the toughness by lowering the volume fraction of the dispersed phase, there was a problem in that the tensile strength deteriorated. It is extremely difficult to satisfy both of these requirements at the same time.These problems pose a particularly serious obstacle when applying the sintered body to various parts that require toughness.

On the other hand, it is known that the Al-Cr-Zr alloy powder sintered body is a product in which Cr and Zr are forcibly dissolved in Al when the powder is manufactured by a rapid solidification method. Cr and Z
When the rapidly solidified powder in which r is forcibly dissolved is heated at a temperature of 300 to 450°C, CuAl゜ZrAl. Intermetallic compounds such as these are finely precipitated, and precipitation strengthening can be expected. Moreover, the above-mentioned precipitated compounds are formed at the heat treatment temperature (3
Since it hardly becomes coarse in the temperature range of 00 to 450°C or lower, it is expected to exhibit high strength in the temperature range of 300°C or lower.

However, most of the previous research on Al-Cr-Zr based alloy powder sintered bodies
This is related to the ternary alloy material itself, and because it does not take into account the thermal history associated with solidification and forming after rapid cooling, it has not reached a level of strength sufficient for practical use as an extruded rod or forged material. This is the current situation. That is, the Al-based alloy powder sintered body was developed based on the above-mentioned purpose, and after sintering and hot forming, it can be processed by hot forging, rolling, extrusion, etc. in the same way as ordinary forged ingots. It is common that these processes are carried out, and it is necessary to develop a practically sufficient strength level even after these processes.

As is clear from the above purpose, the "sintered body" in the present invention refers to a molded material (simply referred to as Al) before being processed into a product.
The meaning also includes (generally referred to as base alloy).

The technique disclosed in JP-A-59-116352 further adds Mn to the ternary alloy of Al-Cr-Zr,
Although the resulting sintered body has increased strength, this sintered body has the following problems.

For example, Materials published in April 1986
Science and Technology, Vo
1, 2, pp. 394-399, Al-Cr-Zr-M
Research on n-alloy powder has been published, and it is disclosed that sintered bodies obtained from this alloy powder are easily affected by heating conditions during hot extrusion and the like. Therefore, in order to develop sufficient strength in the sintered body obtained from this Al-based alloy powder, measures such as extruding the rapidly solidified powder at room temperature are required, such as hydrostatic extrusion and special press equipment with extremely high power. It was difficult to put it into practical use because it required

The present invention was made to solve these technical problems, and its purpose is to provide a method for obtaining a sintered body that is excellent in both heat resistance (high temperature strength) and toughness. It is in the point of doing.

[Means for Solving the Problems] The method of the present invention that achieves the above object contains C as an essential component.
Al-based alloy powder containing r and Zr as a solid solution is plastically deformed in a temperature range below the recrystallization temperature to introduce dislocations into the matrix, and then the powder is heated and held at a temperature of 200 to 450°C to form grains. The key points are that interfacial precipitates are stabilized and that hot compression molding is performed at a temperature of 500° C. or lower.

In addition to Cr and Zr, as the Al-based alloy powder, Fe
It is even more effective to use IMi selected from Mn and Mn, or a solid solution of the two.

[Function] The present inventors focused on the fact that the properties of the Al-Cr-Zr alloy powder sintered body can be improved by adding a relatively small amount of elements, and compared it with the Al-Fe-based one. Based on the idea that this material may have the potential to develop a sintered body with high toughness, we have been conducting intensive research for some time. As a result, it was found that the properties of Al-Cr-Zr alloy powder sintered bodies largely depend on the interaction between the dislocation structure and precipitates in the alloy powder, and that by skillfully controlling both, the strength can be improved. The present invention was completed based on the discovery that an Al-based alloy powder sintered body having excellent toughness and toughness can be obtained.

The present invention will be described in detail below along with the steps of the method of the present invention.

Powder production> The Al-based alloy powder used in the present invention is produced by processing a molten alloy into fine powder by a rapid solidification method in order to forcefully dissolve elements (such as Cr and Zr) that have small solid solubility limits in an equilibrium state into a supersaturated state. This is what I did. Regarding the specific means for producing this powder, various atomization methods are exemplified and not limited in any way, but in order to obtain the desired fine powder, the quenching rate should be set at 100%.
It is preferable to set the temperature to 0°C/sec or more. In the present invention, the term "powder" is not limited to a spherical shape, but includes various shapes such as a two-piece foil shape and an irregular shape.

The Al-based alloy powder used in the present invention contains Cr and Zr as essential components, but in order to achieve the purpose, the content should be Cr: 2 to 5% and Zr: 0.5 to 2.
% is desirable. Furthermore, in order to achieve higher strength, Fe and Mn are added to Fe: 0.5 to 3%, Mn:
It is recommended to contain about 0.5 to 3% (however, 0.5 to 3% in total). However, these additive elements (Cr, Z
(r, Fe, Mn) in an amount exceeding the above range is not preferable because it causes a decrease in fatigue properties and toughness in the final product.

Plastic processing〉 The purpose of this process is to plastically deform the alloy powder and introduce dislocations into the powder, and there are no specific limitations on the specific means, but the most common method is, for example, a ball mill. or high-speed ball mill (atroughter)
It would be interesting to mention some methods etc. In short, the powder produced in the previous step may be plastically deformed into various shapes such as flat, irregular, etc., and then work-hardened by introducing dislocations.

However, the degree of work hardening and processing conditions vary depending on the blending ratio of each alloy component and processing method, and are not limited in any way. Furthermore, the term "plastic working" as used herein means carrying out within a temperature range in which recrystallization does not occur, and includes not only cold working but also so-called warm working.

Heating and holding> In this step, a metal compound mainly containing Cr and Zr''lr is precipitated at grain boundaries on the dislocations introduced into the powder in the previous step, and the dislocations are fixed and stabilized by the binding effect of the precipitates. This heating step can also serve as heating for hot working for densification, which will be described later.

Regarding the heating method, the powder that has gone through the previous process is heated to a powder state or c.
It may be heated in the air or atmosphere in a state that has been preliminarily solidified by TP molding or the like, but from the viewpoint of preventing oxidation, it is preferable to heat in a non-oxidizing atmosphere such as an inert gas.

Regarding the heating temperature, the lower the heating temperature, the finer the precipitates on the dislocations, so it is preferable, but if the processing time is also taken into account, it is better to set the heating temperature to 200°C or higher.
The temperature was 0°C or higher. Furthermore, if heated at a temperature exceeding 450°C, the precipitates will become coarse and no strength improvement effect can be expected, so the upper limit of the heating temperature was set at 450°C.

On the other hand, the distribution of precipitates is almost determined by nucleation at the initial stage of heat treatment.
Heating at 50° C. for 0.5 to several hours is effective. The heating time is determined in relation to the temperature, and the lower the temperature, the longer it takes, but at a temperature of 300°C, it takes approximately 6 to
Good retention time of 24 hours.

Hot Compression Molding> The powder that has undergone the above steps is densified by hot compression molding to obtain an Al-based alloy powder sintered body.

The processing means at this time is not limited in any way, but examples include hot pressing, extrusion, and HIP processing. The processing temperature is 500°C or less when the processing heat is small, such as hot pressing or HIP processing, and 500°C or less when the processing heat is large, such as extrusion.
It is sufficient to heat at a temperature obtained by subtracting the temperature rise due to processing heat from For example, the temperature is preferably 350°C or higher.

In addition, "densification" in the present invention means a state as dense as that of conventional wrought materials, in other words, a state free of coarse defects such as blowholes and shrinkage found in castings, etc. This does not mean that the molding is completely defect-free, and the atmosphere for compression molding is preferably a vacuum, so hot pressing under vacuum is more effective. Examples of such methods include, for example, using a vacuum hot press machine, , a method of filling powder into a capsule in advance, deaerating and sealing the capsule, and compression molding the capsule.

The method of the present invention will be explained in more detail below with reference to examples, but the following examples are not intended to limit the present invention.
Any design changes in accordance with the above and below intentions are included within the technical scope of the present invention.

[Example] Preparation ■± An alloy with a composition of Al-3,5% Cr-1,5% Zr was melted and rapidly solidified by N2 gas atomization to a particle size of 7.
A powder of less than 4 μI was obtained. The powder was immersed in a dry high-speed ball mill loaded with zirconia balls, treated for various times, and then recovered. At this time, the powder was repeatedly agglomerated and pulverized while being plastically deformed in a ball mill, and was recovered in an irregular shape. A relatively coarse agglomerated portion was collected from the recovered powder, and the Vickers hardness was measured on its cross section to determine the degree of work hardening, and the results shown in FIG. 1 were obtained. From the results shown in FIG. 1, it was confirmed that the powder was work hardened due to cold working.

Next, the powder that had been cold-processed for 7 hours using a ball mill was collected, filled into an Al alloy capsule (AA standard 5052), heated at 350°C for 2 hours, vacuum degassed inside the capsule, and further heated to 350°C. 15m hot extruded with
A round bar of mφ was obtained.

On the other hand, as a comparative example, a round bar was obtained by using the same alloy powder that had not been subjected to cold working and extruding it after degassing treatment at 350° C. for 2 hours.

When tensile tests were conducted using both of these round bars at room temperature and high temperature (250° C.), the results shown in Table 1 below were obtained. In addition, σ in Table 1. 2 indicates 0.2% proof stress, σB indicates tensile strength, and δ indicates elongation at break.

As is clear from the results in Table 1, the strength of the sintered body can be improved by cold working the alloy powder.

In order to investigate the influence of heating conditions after gradual opening processing, the following experiment was conducted. That is, AI-3,5Cr- which was subjected to ball mill treatment (7 hours) in the same manner as in Example 1 above.
The 1,52r alloy powder was subjected to CIP molding, then heated under the conditions shown in Table 2 below, and extruded into a 15 mm + φ round bar in the CEP state (400°C). The obtained round bar was subjected to the same tensile test as in Example 1. The results are also listed in Table 2.

As is clear from the results in Table 2 above, optimal strength can be obtained by heating and holding the cold worked powder in an appropriate temperature range. Especially no.

As shown in 2.3, heat treatment at a low temperature in advance and then extrusion at a relatively high temperature is more effective in improving strength.

Fugori 1 Alloys with various compositions shown in Table 3 below were melted and rapidly solidified by N gas atomization to obtain powder with a particle size of 74 μm or less, and the powder was subjected to dry ball milling ( After 7 hours), the powder was collected and subjected to CIP molding to form a billet. This billet was heated at 300° C. for 5 hours, then further heated at 400° C. for 1 hour, and hot extruded into a round bar with a diameter of 15 mm.

For each sample obtained, A S T M B 55
A tensile test was conducted in accordance with 7M, A37M602 and ASTM E21.
% proof stress (σ.2) and strength (σB), strength of notched test piece (
σNTS ) and high temperature strength (σ, ) at 250°C were measured. Furthermore, the notch tensile strength/yield strength ratio (ONrs//00.2) was calculated from the obtained results, and this was used as a parameter for toughness evaluation.

On the other hand, as a conventional example, an extruded rod was made from AI-8, 5% Fe-7% Ce alloy powder, and the above-mentioned tensile test was also conducted on this extruded rod. In addition, this conventional material is a powder with the above composition (
A billet (particle size of 74 μm or less) was formed by CIP without cold working, and this billet was extruded at 400° C. to form a round bar.

These results are also listed in Table 3 below.

No. 6.11 shown in Table 3 and No. 2 in Table 2 above.
As is clear from the comparison of the properties, an improvement in tensile strength at room temperature and high temperature is observed, confirming the effect of adding Fe and Mn. Also, the conventional example shown in No. 13 and No. 6
As is clear from comparing the Examples shown in 1 to 12, it is understood that the Al-based alloy powder sintered body obtained by the method of the present invention exhibits high values in both strength and toughness. .

[Effects of the Invention] As described above, by following the method of the present invention, it is possible to obtain an Al-based alloy powder sintered body that has high strength and excellent toughness at room temperature and high temperature. According to this method, it is not necessary to perform processing using large amounts of force such as extrusion at room temperature, so products of various shapes can be easily processed.

Furthermore, the sintered body obtained by the method of the present invention has excellent toughness as well as heat resistance, so it can be used in various engine parts, exterior materials for aircraft and ladder flying vehicles, and other areas under high-temperature environments. It is ideal as a material for various parts, and can reduce weight and improve functionality.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the influence of ball milling time on work hardening of AI-3,5Cr-1,52r alloy powder.

Claims (2)

[Claims] (1) Al-based alloy powder containing Cr and Zr as essential components is plastically deformed in a temperature range below the recrystallization temperature to introduce dislocation into the matrix, and then the powder is
A method for producing a heat-resistant Al-based alloy powder sintered body, which comprises heating and holding at a temperature of 50°C to stabilize grain boundary precipitates, and further hot compression molding at a temperature of 500°C or less. (2) In addition to solid solution of Cr and Zr as essential components, Fe
Al-based alloy powder containing one or two selected from
A method for producing a heat-resistant Al-based alloy powder sintered body, which comprises heating and holding at a temperature of 450°C to stabilize grain boundary precipitates, and further hot compression molding at a temperature of 500°C or less.