JPH11209839A - High strength aluminum alloy powder excellent in workability, preformed body thereof, forming method therefor, and manufacture of high strength aluminum alloy member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy powder having high speed superplasticity for manufacturing a high strength aluminum alloy member with economical advantage, a preformed body of the aluminum alloy powder, and a plastic working method therefor. SOLUTION: This aluminum alloy powder has a composition consisting of 1-15% of one or >=2 kinds among transition metals of Fe, Cr, Ni, Zr, and Mn, 10-30% Si, 0.5-5% Cu, 1-5% Mg, and the balance Al and also has <=2 μm microcrystal structure and 150 μm powder grain size. If necessary, proper amounts of ceramic powder of Al2 O3 , SiC, Si3 N4 , etc., having fine grain size are blended. This powder is preformed by means, preferably, of electric discharge plasma sintering and then subjected to compression plastic working. The compression plastic working is performed in the region right under the liquidus line. Strain working rate is regulated to >=10<-2> /sec. High ductility of >=200% elongation percentage is provided, and working stress is <=20 MPa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy powder having excellent workability for economically and advantageously producing a high-strength aluminum alloy member useful as various equipment and equipment members such as engine parts for automobiles. The present invention relates to a preform, a forming method, and a method of manufacturing an aluminum alloy member by hot plastic working.

[0002]

2. Description of the Related Art Aluminum alloys have a specific gravity as small as about one third of iron and are widely used as lightweight materials. However, mechanical properties such as heat resistance and abrasion resistance are inferior to iron-based materials. As a measure to improve the characteristics, development of a new aluminum alloy by powder metallurgy has been advanced in recent years. This is because the molten aluminum alloy with a large amount of alloying elements is subjected to a quenching spray treatment such as gas atomization to form powder,
It is formed into a required shape by hot extrusion or the like.
According to powder metallurgy, S
Aluminum alloy members containing a large amount of i, Fe, Mn, Ni, etc. can be manufactured, and as an effect of enriching the amount of alloy elements,
Excellent functional properties result.

[0003]

As described above, the application of powder metallurgy makes it possible to enhance the mechanical properties of aluminum alloy parts, but they have not yet become widespread. The reason is that the processing cost including the raw material powder is high. The first factor is that the production yield of the raw material powder is low. In a powder production method using a gas or the like as a cooling medium, only powders having a particle size of 50 μm or less are targeted, and coarse particles exceeding the particle size need to be classified and removed, and the powder yield is extremely low at about 30%. It becomes.

[0004] The second factor is that the processability of the powder is poor. That is, since a powder containing a large amount of alloy elements is hard and has heat resistance, the forming process is generally performed for about 500 times.
It requires a high pressing force of 200 MPa or more in a temperature range of not less than ℃. In addition, the service life of the mold is short due to high-pressure processing, and it is difficult to accurately mold a component having a complicated shape. An object of the present invention is to solve the above problems, and an aluminum alloy powder excellent in workability for economically and advantageously producing an aluminum alloy member excellent in mechanical properties, and the powder is solidified. Provided are a preform, a forming method thereof, and a compression plastic working method for forming a target member.

[0005]

The aluminum alloy powder of the present invention comprises one or more elements selected from transition metal elements of Fe, Cr, Ni, Zr and Mn: 1 to 15 wt.
%, Si: 10 to 30 wt%, Cu: 0.5 to 5 wt%, M
g: 1 to 5 wt%, the balance being substantially composed of Al, having a fine crystal grain size of 2 μm or less, and a powder particle size of 50 μm or more. This aluminum alloy powder is blended with ceramic powder particles, if desired. Ceramic powder
It is a fine powder with a particle size of 5 μm or less.
Adjusted to the l% range.

The above-mentioned aluminum alloy powder and a mixed powder obtained by mixing the same with a ceramic powder (hereinafter, both may be simply referred to as an aluminum alloy) may be used as a powder or as a solidified body (sintered body) having an appropriate shape. After being preformed, it is formed into a target product member by compression plastic working. The formation of the preform is preferably achieved by a spark plasma sintering method as described later.

[0007] The aluminum alloy powder of the present invention and its preform have high-speed superplastic properties. As described later, in the temperature range immediately below the liquidus line, the strain processing speed (ε) 10 ⁻²
It can perform high-speed processing at a rate of not less than / sec, and exhibits high ductility with an elongation of about 200% or more under these processing conditions, and its deformation flow stress is remarkably low at about 20 MPa or less. Aluminum alloys containing a large amount of alloying elements are generally hard and heat-resistant, so plastic working of crystal materials usually requires high working force of 200 MPa or more in a high temperature range of 500 ° C. or more, and processing using superplasticity. Process (crystal grain size: about 10-100 μm)
Even if is applied, the processing speed is about 10 ^-3 ~ 10 ^-4 / sec
Therefore, high speed processing of 10 ^-2 / sec or more is impossible, resulting in poor productivity. The aluminum alloy powder and the preform thereof according to the present invention realize efficient compression plastic working under high speed and low pressure as effects of the chemical composition, ultrafine crystal structure and powder particle size of the alloy powder. ing.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The reason why the chemical composition of the aluminum alloy powder is specified as described above is to ensure the mechanical properties required for structural members and the like and to ensure superplastic properties. That is, Si, Cu, Mg, and the like are elements that increase strength, heat resistance, wear resistance, and the like. If the content is less than the above lower limit, the material improvement effect is insufficient,
On the other hand, if it exceeds the upper limit, the material becomes hard and brittle, and it becomes impossible to secure superplastic properties.

[0009] Transition metal elements of Fe, Cr, Ni, Zr and Mn are elements that are effective for improving mechanical properties.
An object of the present invention is to enhance superplastic properties as an effect of the addition. That is, these elements combine with Al,
By precipitating as a fine compound phase, it is possible to suppress the crystal growth of the aluminum alloy, and to obtain a fine crystal structure required for developing superplastic properties. The content (the total amount when two or more kinds are combined) is set to 1 wt% or more in order to enhance the effect of addition.
The reason for setting the upper limit to% is that if it exceeds this, the material becomes hard and the superplastic properties are impaired.

The crystal grain size of the aluminum alloy powder is 2 μm
It must be: Such an ultrafine structure is used to ensure high-speed superplasticity. The reason why the particle diameter of the powder is limited to 50 μm or more is to improve the compressibility, moldability and plastic deformability of the powder. This is because the finer the powder produced by rapid quenching and solidification, the greater the strain hardening, the higher the frictional resistance at the particle interface in compression plastic working, and the lower the plastic deformability. The aluminum alloy powder having the ultrafine crystal structure and the powder particle size is subjected to a spinning water atomization process (SWAP method: Spinning Water atomi
A high yield can be obtained by spray treatment (cooling rate: 10 ⁴ ° C / sec or more) of the zation process.

The above aluminum alloy powder is mixed with a ceramic powder if desired. Ceramic particles are
It is dispersed in the aluminum alloy matrix to enhance the mechanical properties of the product member, and suppresses the crystal growth of the aluminum alloy in the matrix. The grade of ceramics is
Oxides, nitrides, carbides, borides, etc.
One or more of them are appropriately selected and used. In particular, the use of silicon carbide (SiC), alumina (Al ₂ O ₃ ), silicon nitride (Si ₃ N ₄ ) or the like alone or in combination is effective.

The ceramic powder must be fine particles having a particle size of 5 μm or less. For coarser particle sizes,
This is because the superplastic properties of the aluminum alloy powder are reduced, and high-speed superplastic working becomes difficult, and finishing (machining) becomes difficult. The compounding amount is 1 to 10
The reason for the vol% is that if it is less than 1 vol%, the compounding effect is poor, while if it exceeds 10 vol%, the alloy is embrittled and the high-speed superplastic properties are impaired.

The aluminum alloy powder (single powder or mixed powder with ceramics) of the present invention is formed into a suitably shaped and solidified body (sintered body) prior to molding (compression plastic working such as forging) of a product member. Is preferred. It is possible to obtain the target member by subjecting the powder to compression plastic working, but preforming is advantageous in increasing the efficiency of the compression plastic working.

The preforming is performed by a spark plasma sintering method (SP
S method: Spark plasma sintering). In spark plasma sintering, pressure sintering is performed using pulsed electric current. Internal heat generation sintering that utilizes the high energy of high-temperature plasma generated by instantaneous and intermittent spark discharge generated in the gap between powder particles Is the law. The discharge points in the powder sample move and disperse throughout the sample as the current / voltage application is repeatedly turned on / off. Due to the uniform heating effect due to the internal heat generation, homogeneous sintering can be achieved in a short time and at a low temperature (the crystal grain growth and coarsening are prevented from being suppressed).

The sintering temperature is preferably regulated to 500 ° C. or less. This is for preventing growth coarsening of crystal grains and maintaining high-speed superplastic properties based on a fine crystal structure.
The processing temperature can be easily controlled by the pulse current, ON / OFF cycle, processing time, and the like. The pressure is suitably in the range of about 70 to 180 MPa. If the pressure is lower than this, high-temperature sintering is required, which causes inconvenience of coarsening of crystal grains. On the other hand, it is not necessary to use a high pressure exceeding 180 MPa, and a further increase in the pressing force is not preferable because it promotes the consumption of the mold.

In the spark plasma sintering, various intermetallic compounds (Cu-Al,
Mg-Si, Al-Cu-Fe, Al-Mn). Although the aluminum alloy powder of the present invention contains a large amount of alloying elements, it is subjected to ultra-rapid solidification treatment such as a SWAP method (cooling rate: 10 ⁴ ° C).
/ sec or more), there is almost no generation of precipitates, and even if they precipitate, the amount of generation is small and they are in a supersaturated solid solution state. These elements precipitate as intermetallic compounds during the spark plasma sintering process. Since the sintering is achieved under low-temperature and short-time conditions, the precipitated compound phase is fine (particle size 1).
μm or less) and contributes to strengthening the mechanical properties of the aluminum alloy product without impairing the superplastic properties of the powder.

In the compression plastic working of the aluminum alloy powder (single powder or mixed powder with ceramics) and the preform of the present invention, the strain working rate is 10 ⁻ in the temperature range just below the liquidus line (T _liq ) of the alloy. ^It is performed under the condition of ² / sec or more. The optimal region for the plastic working temperature (T) is T _liq −
35 ° C. ≦ T ≦ T _liq −10 ° C. FIG. 1 shows the superplastic properties of the aluminum alloy powder (preformed body) and its flow deformation stress (strain processing speed: 10 ^-1 / sec) (sample material:
Chemical composition (wt%) Si 17.1, Cu 0.96, Mg 1.86, Fe 1.92, N
i 1.0, Mo 0.56, Al Bal, crystal particle size 2μm, powder particle size 50
μm, liquidus 550 ° C). As shown in the drawing, in high strain rate processing in a temperature range (approximately 515 to 540 ° C.) immediately below the liquidus line, a high ductility with an elongation of 200% or more is exhibited, and its deformation flow stress is extremely low at 20 MPa or less.

As described above, the aluminum alloy powder and the preform thereof according to the present invention enable efficient compression plastic working under a high speed and a low pressing force, enhance the productivity of various members by powder metallurgy, and The present invention is effective in improving the useful life of the mold by reducing and alleviating the wear of the mold, and at the same time, it is possible to enhance the shape accuracy of a member having a complicated shape.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Aluminum alloy powder (single powder and mixed powder) is preformed and subjected to forging to produce a member. (1) Aluminum alloy powder The powder by SWAP method and the powder by gas atomization method are used. The SWAP powder has a particle size of 50 to 420 μm, and the gas atomized powder has a coarse particle size (powder particle size: 50 μm).
420420 μm) and a fine particle size (<50 μm). (2) Ceramic powder a: Silicon carbide (SiC) b: Alumina (Al ₂ O ₃ ) c: Silicon nitride (Si ₃ N ₄ )

(3) Preforming (formation of a solidified body) A cylindrical block (φ60 × 30 l, mm) is formed by spark plasma sintering or hot extrusion. [SPS sintering and sintering] Sintering temperature 400 ° C, processing time 20 min, pressure 1.5tf / cm
² . [Hot extrusion molding] Molding temperature 480 ° C, extrusion ratio 11.

(4) Compression plastic working The piston member (outer diameter: 62, length:
65, wall thickness: Top part 3, side part 5, mm). Processing speed: 10 ^-1 / sec Processing temperature: Liquidus line -35 to 10 ° C

Tables 1 and 2 show raw material powders, molding / processing conditions, processing results, and the like. In the table, "W" in the "Type of alloy powder" column is a SWAP powder, "G" is a gas atomized powder, powder particle size: 50 to 420 μm, and powder particle size: <50
μm. Further, the crystal grain diameter of W powder ≦ 1 μm, the crystal grain diameter of G powder ≧ 1 μm, and the crystal grain diameter of G powder <1 μm. The “forging result” is an inspection result by visual observation and color check of the member obtained by forging, and a mark “○” indicates that there is no crack and sound quality. Blanks (No. 114 and No. 115) in the same column indicate that a preform that could be used for forging could not be formed in the preforming step, and forging could not be performed.

In Comparative Examples, No. 101 (excessive Si content in aluminum alloy powder), No. 103 (excessive Cu content), No. 105 (excessive Cu content)
The reason why cracks occurred in the forged members of No. 107 (excess amount of transition metal element) and No. 107 (excess amount of transition metal element) is that the alloy powder became too hard due to the excessive content of the alloy element, and the crack sensitivity of the material was increased. No.102 (Insufficient amount of Si in aluminum alloy powder), No.104
No. 106 (insufficient amount of Mg) and No. 108 (insufficient amount of transition metal element) are forged with low processing stress due to coarsening of the crystal grain size due to insufficient element content of the alloy powder. Despite the conditions, cracking has occurred. This is because the optimum processing speed region has shifted to the lower speed side. No.109 and No.1
The cracks occurred in the forged members of No. 10 because the former was excessively mixed with ceramic powder, and the latter was because the ceramic particle size was large, and the superplastic properties of the preforms were impaired. .

No. 111 [fine crystalline SWAP powder (powder particle size ≧
50μm) use] forged member is cracked,
This is because the crystal grains became coarse during the preforming (hot extrusion) process, and the superplastic deformability of the preformed body was reduced. The cracking of the forged member of No. 112 is caused by alloy powder (gas atomized powder)
Is due to the coarse (grain size> 2 μm) and low superplasticity of the preformed body. As shown in No. 113, even if spark plasma sintering is applied as a preforming method, the superplastic deformability of the preformed body is low, and cracking during forging cannot be avoided. Also, like No.114 and No.115,
When a fine powder (powder particle size <50 μm) is used as the alloy powder, the powder is inferior in compressibility and moldability, and a preform that can be used for forging cannot be formed.

On the other hand, in the example of the invention, under a condition of a high working speed (working speed: 10 ^-1 / sec), forging is efficiently achieved at a low pressing force of 20 MPa or less to obtain a sound part without cracks. ing. The mechanical properties are also good. For example, the tensile strength of No. 2 member is 398 MPa, that of No. 5 is 376 MPa.
And improved high strength required for structural members such as a piston member for an automobile engine.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

According to the present invention, various structural members requiring high strength, for example, pistons and gears of an automobile engine, and other various electric / precision machine parts, can be manufactured at high speeds.
It can be manufactured efficiently under low pressure processing conditions. High-speed machining enables a significant increase in productivity, while low machining stress is effective in reducing mold wear and improving service life, as well as improving product shape accuracy and improving material yield through net shaping.・ Effects such as shortening of the process are provided. As described above, the present invention not only enhances the functional characteristics of the high-strength aluminum alloy member but also greatly contributes to energy saving and cost reduction.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the plastic deformation ability of aluminum alloy powder and the processing temperature.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tadashi Yoshino 5-6 Koyodai, Ryugasaki, Ibaraki Pref.

Claims (7)

[Claims] 1. One or more elements selected from transition metal elements of Fe, Cr, Ni, Zr and Mn: 1-1
5wt%, Si: 10-30wt%, Cu: 0.5-5wt
%, Mg: 1 to 5% by weight, with the balance being substantially Al, a high-strength aluminum alloy powder excellent in workability and having a crystal grain size of 2 μm or less and a powder particle size of 50 μm or more. 2. The aluminum alloy powder according to claim 1, wherein 1 to 10 vol% of ceramic powder having a particle size of 5 μm or less.
High-strength aluminum alloy powder with excellent workability, which is a mixed powder containing 3. The high-strength aluminum alloy powder having excellent workability according to claim 2, wherein the ceramic powder is one or more powders selected from alumina, silicon carbide, and silicon nitride. 4. An aluminum alloy preform having excellent workability, which is a sintered body of the powder according to any one of claims 1 to 3. 5. The high-strength aluminum alloy preform having excellent workability according to claim 4, wherein the powder according to claim 1 is solidified by spark plasma sintering. Formation method. 6. The method for forming a high-strength aluminum alloy preform having excellent workability according to claim 5, wherein the sintering temperature is 500 ° C. or lower. 7. A strain of the powder according to any one of claims 1 to 3 or the preform according to claim 4 in a temperature range immediately below a liquidus line, of 10 ⁻² / sec or more. A method for producing a high-strength aluminum alloy member, comprising compression plastic working at a high speed.