JPS6210237A - Aluminum alloy for hot forging - Google Patents

Abstract

PURPOSE:To obtain an Al alloy having superior sorgeability at high temp. by forming the billet of Al alloy powder and heating it in vacuum or an inert gas to lower the gas content. CONSTITUTION:The composition of a molten Al alloy is composed of, by weight, 10-30% Si, 1-15% in total of one or more among 1-15% each of Fe, Mn and Ni and the balance Al with inevitable impurities. The composition may further contain 0.5-5% Cu and 0.2-3% Mg. The molten Al alloy is scattere and solidified by rapid cooling and the resulting powder is compacted to form a billet having a structure contg. finely dispersed Si grains of <=15mum grain size and intermetallic compounds of <=20mum grain size. The total gas content in the billet is lowered to <=5cc/100g by heating in vacuum or an inert gas.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an aluminum alloy that has excellent high-temperature forgeability and wear resistance.

(Prior art) Examples of conventional aluminum (A1) alloys with good wear resistance include JIS AC3A, AC4A, and AC8A.
A1 alloy for casting such as JIS ADCl, ADC
3. A1 alloys for die casting such as ADCIO5ADC12 are known.

However, when these high-silicon Al alloys are made into ingots by conventional methods, they have coarse structures and many internal defects, and cracks are likely to occur due to internal defects, resulting in difficulties in strength and workability.

In addition, silicon (Si) is used as an A1 alloy that has wear resistance.
A containing a third element (e.g. Cu, Mg, etc.) other than
380 alloy is known, but these are cast alloys, and although they are somewhat satisfactory in terms of abrasion resistance, they have not yet been fully satisfactory in terms of heat resistance and workability.

In order to overcome the above-mentioned drawbacks of cast A1 alloy, a method of obtaining an A1 alloy powder compact by extrusion molding of A1 alloy powder has been proposed (for example, Japanese Patent Laid-Open No. 52-109
(Refer to Publication No. 415), this method can be used for cylinder liners for internal combustion engines and vanes of various compressors to obtain materials with excellent wear resistance and lubricity, as well as excellent high-temperature strength. It has recently attracted particular attention because it significantly increases lifespan and efficiency, and helps reduce weight.

Known techniques related to these hypereutectic SiA1 alloy powder compacts include JP-A-57-54203 and JP-A-57.
-112922, JP-A-57-177953, and JP-A-59-110702.

(Problems to be Solved by the Invention) However, in conventionally known A1 alloy powder compacts, when hot forging is attempted to form complex shapes such as pistons and connecting rods, forging cracks tend to occur, resulting in unsatisfactory shapes. Even if the product could not be processed or forged successfully, bubbles called blisters were generated during the heat treatment of the product, making it difficult to obtain a product with sufficient strength.

The present inventors investigated and researched these causes and found that the extruded material contained a large amount of gas components, which caused deterioration in forgeability, leading to the present invention.

The so-called C
The annning method is known. (USP-39544
58, USP-41040131) However, this method requires complicated operations and is not suitable for production processes.

[Means for solving problems]

In order to solve the above-mentioned problems, the present inventors investigated in detail a method for degassing an A1 alloy powder compact, and found that after creating a billet of A1 alloy powder, it was heated in a vacuum or in an inert gas. The inventors discovered that a material suitable for forging could be produced by reducing the gas content to an extremely small amount of 5 cc/100 g or less, leading to the present invention.

The A1 alloy of the present invention has a Sil of 0.0 to 30.0 at a weight ratio of 1.
%, Fe, Ni or Mn is 1.0-15.0% (
However, if two or more types are used, the total will be 1.0 to 15.0.
%), and further contains Cu 0.5 to 5.0 as necessary.
%, Mg 0.2 to 3.0%, the remainder is Al containing unavoidable impurities, and the size of Si crystal grains is 15 gm.
It is below.

The object of the present invention is to provide an A1 alloy powder compact in which the intermetallic compound is finely dispersed to a size of 20 μm or less and the total gas amount is 5 cc/100 g or less.

This invention will be explained in more detail below.

First, the alloy composition of the present invention will be explained.

It is well known that an Al-Si alloy of hypereutectic Si generally has a smaller coefficient of thermal expansion than Al and is superior in heat resistance and wear resistance. In hypereutectic Al--Si alloy casting materials, Si is dispersed in the matrix as primary crystals or eutectics, thereby exhibiting excellent high-temperature strength, wear resistance, and seizure resistance. However, since primary Si often crystallizes as coarse crystals, it lowers ductility and impact value and deteriorates machinability. Furthermore, when used in sliding materials, coarse Si crystals must be avoided as they will damage the mating material.

As a means of preventing coarse Si crystals, a technique is known in which a hypereutectic Al--Si alloy is rapidly solidified to produce an alloy powder in which primary crystal Si is finely dispersed, and the alloy powder is processed into a mechanical member by extrusion molding.

The hypereutectic Al-Si alloy powder used in the present invention is rapidly solidified by adding Fe, Mn, or Ni, and suppresses coarse crystallization of primary Si and also contains Fe, Mn, or Ni. It has both wear resistance and high temperature strength due to the crystallization of intermetallic compounds.

The reasons for limiting the ingredients in the present invention are as follows.

If Si is less than 10%, the amount of dispersion is small and the effect on heat resistance and wear resistance is insufficient. In a hypoeutectic region of approximately SilO%, primary Si cannot be crystallized and a fine eutectic structure is exhibited. As the amount of Si increases, primary crystals of Si begin to crystallize, resulting in improved heat resistance and wear resistance. However, if the Si content exceeds 30%, coarse Si primary crystals will be difficult to disappear no matter what rapid solidification method is employed for powdering. When the quenching rate is about 103℃/see, primary S
In order to miniaturize i, it is necessary to reduce the amount of Si to 25% or less.

When A1 alloy powder, which has a coarse primary Si structure, is extruded and used, the compressibility of the powder is significantly deteriorated, making it difficult to form a green compact, and the deformation resistance is also increased during hot extrusion. , in addition to requiring large extrusion force,
This results in a significant reduction in the life of the extrusion die.

Therefore, the Si content is preferably 10.0 to 30.0%, preferably 15.0 to 25.0%.

Fe, Mn, and Ni are important components in the present invention. Fe, Mn, or Ni is added for the purpose of increasing high-temperature strength by crystallizing it as a fine compound in a dispersed manner, taking advantage of its low solubility in Al and slow diffusion rate.

When Fe, Mn, Ni, etc. are added beyond the solid solution limit, Al-Si-(Fe, Mn,) system or Al
It precipitates as a -Nt-based intermetallic compound, and its shape becomes coarser as the amount added is larger and the cooling rate is slower. This intermetallic compound exists as a rod-like structure in the alloy powder produced by the dispersion rapid solidification method, and is fragmented in the subsequent hot extrusion step and finely dispersed in the matrix. This compound is stable even at high temperatures, does not grow coarse, and does not lose strength even when kept at high temperatures for a long time.

Therefore, it is suitable as a material for mechanical parts that are exposed to high temperatures and require strength, such as cylinder liners, connecting rods, rocker arms, and compressor vanes.

The amount of Fe, Mn, and Ni added is 1.0 to 15.0%,
(However, in the case of species 2 or more, the total amount is 1.0 to 15.0%.
) is appropriate. Fe or Mn or old addition amount is 1.0
If it is less than 15%, no effect on high temperature strength or abrasion resistance is observed, and if it exceeds 15%, the hardness and abrasion resistance are rather low, and when a molded article is made, the material tends to become brittle.

In the A1 alloy of the present invention, Cu and Mg may be added as necessary. Cu and Mg are widely used in the A1 alloy as ingredients that impart age hardenability and strengthen the material, and appropriate addition. The amount of Cu is 0.5-5.0%,
Mg is in the range of 0.2 to 3.0%. Also in the present invention, adding Cu and Mg within the solid solubility limit at the solution treatment temperature is effective for strengthening the material.

In the alloy of the present invention, for the purpose of improving high temperature strength, Ti, Zr, MOLV, Co, Zn, Li
There is no problem in adding a small amount of the same, but if the amount added is too large, manufacturing problems such as component control and increase in melting temperature will arise.

Next, the reason why the total amount of gas in the A1 alloy was set to 5cc7100g or less was to prevent forging cracks. It is sufficient that the total gas amount is 5 cc/100 g or less at the stage of compression molding the 41 alloy powder. Although it depends on the size of the compression molded product, if the average value of the billet is 5cc/100g or less for up to a billet with a diameter of 300ff and 1 layer and a length of about 500mm, there will be no blistering or cracking during subsequent hot forging or heat treatment. will never occur.

The reason why the size of the Si crystal grains in the A1 alloy is set to 15JJ,I or less is mainly because the size of the primary Si is 15pLff1.
If the temperature exceeds that level, the moldability of the subsequent alloy powder will deteriorate.
This is because the material properties deteriorate.

The reason why the size of the intermetallic compound in the A1 alloy is set to 204 ra or less is to improve high temperature strength and m-abrasion resistance. Al-Si-(Fe, Ni) system or Al-N
The size of the i-based intermetallic compound is substantially 5 ALm or less,
By finely and uniformly dispersing even large particles to 20 gm or less, mechanical properties can be significantly improved. When the intermetallic compound and Si microcrystals are mixed and distributed uniformly, the effect of crushing is further enhanced.The A1 alloy of the present invention is produced by first atomizing a molten alloy having the target composition, and finely powdering it by centrifugal force. 0.5+am using commonly used means of producing fine powder from molten metal such as
41 alloy powder is obtained by rapid dispersion and solidification to the following particle size. A cooling rate of about 7 seconds or more at 103°C is sufficient, and as the amount of alloy components increases, a microstructure cannot be obtained unless the cooling rate is increased.
1 alloy powder has S1 crystals with a size of 151 Lm or less and metal compound articles whose growth is suppressed, and it is difficult to obtain an alloy with such a structure by a casting method.

Next, the A1 alloy of the present invention is obtained by molding the 41 alloy powder and degassing it. In order to improve high-temperature strength, wear resistance, and seizure resistance during molding,
The size of the primary Si crystal and the size of the seven intermetallic compounds are important factors, and both need to be made as fine as possible.

The A1 alloy powder compact having such a structure can be obtained by compacting the A1 alloy powder according to the invention in advance, degassing it, and then hot extruding it.

Powder compaction is performed as a preparatory work for hot extrusion, and there is no problem with normal methods using cold isostatic presses or hydraulic presses.An example of using a hydraulic press is to compress alloy powder into It is preferable to carry out heating to about 300°C.

If the temperature exceeds 300°C, oxidation will become significant and processing will need to be carried out in an atmosphere of N2, Ar, etc., but processing can be carried out in the air at low temperatures.

Appropriate compacting pressure is about 0.5 w 5 ton/c rn', and the green compact density is set to be 70% or more of the true density.

The degassing step is the most important step in the present invention.

In the process of producing A1 alloy powder, for example, when the air totomization method is used, the gas component is reduced to about 50 cc/(1
00g A1 alloy). This atomized powder is heated, then compacted, and made into a billet. The amount of gas in the A1 alloy material, which is hot extruded in the atmosphere as in the conventional method, is 10 to 20 cc7100 g, although this value is The amount of gas in forged Al is 0. t~0
．． Compared to 3cc7100g, it is about 100 times larger.

When an A1 alloy with a gas amount of 10 to 20 cc/100 g is heated above 450°C, blisters will occur on the alloy surface due to the gas component, and pores of several circles to several hundred IL will be generated inside the alloy. . Therefore, when forging this alloy, if it is heated above about 450°C, cracks will occur on the surface of the product due to the blisters, or the shape will break, making it impossible to obtain the product.
This invention relates to an A1 alloy for forging by removing gas components that cause forging cracks.

The degassing method used in the present invention is a well-known canning method in which powder is placed in a can and evacuated to degas it.

Another method is to compress the powder-formed billet in vacuum or in an inert atmosphere such as Ar or N2.
A method of heating to 20°C can also be used. At temperatures below 400℃, the adhered gas components (mainly N20 and N2) cannot be expected to degas because the temperature is too low, and above 520℃, depending on the alloy composition, they may melt, and even if they do not melt, they become fine due to rapid solidification. This is not preferable because the resulting Si crystals and intermetallic compound particles become coarse.

In the case of vacuum, the degree of vacuum is 0.1 atmosphere or less, preferably 0.1 atmosphere.
It is necessary to keep the O pressure below 1 atmosphere.

This is a process for processing into a hard molded body.

Hot extrusion refines the primary Si phase, eutectic phase, and intermetallic compound phase crystallized in the alloy powder, improves the mechanical properties of the material, and at the same time processes it into a strong compact. This is a process for

Hot extrusion is performed in a temperature range of 350°C or higher.

This is to promote interparticle bonding within a range where the green compact can be easily processed to form a strong compact. Furthermore, the purpose is to finely precipitate the elements in the supersaturated solid solution, and to divide and refine the rod-like structure of primary crystal Si and intermetallic compounds, thereby improving the strength and wear resistance of the compact.

There is no problem in further improving the material properties by subjecting the alloy powder compact obtained by the present invention to various heat treatments. The molded body may be used as a raw material and further subjected to machining, hot forging, or cold forging to be made into a mechanical part.

The gas amount of the A1 alloy powder compact produced by performing the degassing treatment according to the present invention is 1 to 5 cc/100 g, which is reduced to 1/2 to 1/20 of that of the untreated compact. It is still 10 to 50 times cheaper than WI-built aluminum.
Although the temperature is about twice as high, there is no problem in practical use, with no blistering occurring even when heated to 500℃.Degassed extruded materials have particularly improved elongation at high temperatures compared to conventional non-degassed materials. This facilitates material flow during hot forging and prevents cracks from occurring. In addition, the A1 alloy powder compact according to the present invention has slightly improved high-temperature strength compared to conventional Al alloy powder compacts, and has excellent wear resistance, seizure resistance, and stress corrosion cracking resistance. It is something that Since it has a relatively small coefficient of friction, it is ideal for sliding members that are used at high temperatures and require wear resistance. Applications include automobile parts such as cylinder liners, connecting rods, pistons, and rocker arms, oil and pneumatic equipment parts such as compressor vanes, liners, and valve plates, home appliance parts such as VTR drums and bearings, and gears for office equipment. In addition to precision parts such as switches, cams, and clutch hubs, it is expected to have a wide range of applications in the aircraft and space industries.

Next, the present invention will be explained with reference to Examples.

Example A molten high-Si aluminum alloy having the composition shown in Table 1 was air atomized to form a powder of 148 segh.

Next, these A1 alloy powders are heated to 1.5 tons/
Compression molded at crn' pressure, diameter 204mm, length 2
00I! It was made into a billet of m.

(Left below) Next, these 10 billets were placed in a degassing furnace, and degassed by heating at 480° C. for 80 minutes in an argon gas flow rate of 2 (IfL/a+in).

Next, these billets were heated to 400° C., inserted into a container with an inner diameter of 206II11 and preheated at the same temperature, and extruded by indirect extrusion (extrusion ratio = 17) using a die with a diameter of 50a+m to obtain a molded body. These molded bodies are T
After treatment or heat treatment (0) at 300° C. for 100 hours, it was processed into a tensile test piece with a gage distance of 50 mm and a parallel part diameter of 6 II m, and a tensile test was conducted at temperatures from room temperature to 250° C. The tensile test was conducted by testing 10 samples at each test temperature.
It was carried out after holding for 0 hours. Further, after the tensile test at each temperature, the hardness was measured using the end of the chuck part of the test piece. In addition, specimens tested at room temperature were cut and microscopically observed to measure the size of the crystal structure. These results are summarized in Table-1.

When the same test piece was subjected to gas analysis using a vacuum melt extraction method (using a stainless steel pipe), the results shown in Table 2 were obtained.

Table 2 Next, the hot extrusion molded body was cut, and a material with a diameter of 70 mm and a length of 10III11 was made by hot forging, and various test pieces were made by machining to perform wear resistance tests and seizure resistance tests. , the friction coefficient was measured.

The abrasion resistance test was performed using a 5x5x1 disk-shaped specimen with a diameter of 70mm.
Spheroidal graphite cast iron with 0mm Cr plating was used as the mating material, speed 5m/sec, pressing force 100Kg/c.
The amount of wear was measured with rn' and a sliding pressure gi of 500 Km.

Note that 5AE20 engine oil (temperature 90° C.) was dropped onto the sliding surface as a lubricating oil at a rate of 500 ml/min.

The seizure resistance test was conducted in the same way as the wear resistance test above, and the suppression was from 100Kg/cm" to 5Kg/cm" *
The surface pressure when seizure occurred was measured by increasing the pressure at a rate of 1 inch.

The friction coefficient was calculated by measuring the torque at the time of running 200 km in the wear resistance test.

These results are shown in Table 3.

(The following is a blank space) Table 3 Hot forging was also performed on sample materials Nos. 1 to 5. Extruded material with a diameter of 50 mm was cut into lengths of 100 mm and heated at 480°C.
heated to. This is heated to 350°C in a mold. 1
An automobile piston with a diameter of 80 mm was produced at a speed of 0.00 mm/sec. Because the extruded material has a small gas component, no blisters occur even when heated to 480°C, and the sample has good elongation at high temperatures, resulting in Not~N
Five O5 pistons were found to be in good condition with no cracking.

From the above results, it is clear that the A1 alloy powder compact of the present invention is a material that has excellent high temperature strength, wear resistance, and seizure resistance, and also has good hot forgeability.

Claims (1)

[Claims] Weight ratio: Si10.0-30.0%, Fe1.0-1
5.0% or Mn1.0-15.0% or Ni1.
One or more of 0 to 15.0% (in the case of two or more, the total is 1.0 to 15.0%), and if necessary, Cu0.5 to 5.0% and Mg0. 2-3.0%
This is a dispersed rapidly solidified powder extruded material of a molten alloy consisting of Al, the remainder of which contains unavoidable impurities, in which the size of Si crystal grains is 15 μm or less, and the size of intermetallic compounds is 20 μm or less.
It has a finely dispersed structure of less than μm, and the total gas amount is 5c.
An aluminum alloy for hot forging, characterized in that it is less than c/100g.