JPS62224602A - Production of sintered aluminum alloy forging - Google Patents

Abstract

PURPOSE:To suppress the generation of a blister in the stage of forging and to stabilize the mechanical characteristics of a product by sintering a preform obtd. by molding Al alloy powder, then forging the sintered body to increase the density, and resintering the same, thereby decreasing the gas contained therein. CONSTITUTION:The preform having 70-95% true density ratio is formed by molding the Al alloy powder. After the preform is sintered at 450-550 deg.C in a vacuum or inert atmosphere, the sintered body is held at 200-550 deg.C and is forged to have >=95% true density ratio. The forged sintered body is further resintered at 450-550 deg.C in the inert atmosphere to decrease the amt. of the total gas contained therein to <=about 5cc/100g.Al. The sintered Al alloy forging having the excellent high-temp. strength and wear resistance is obtd. by the above-mentioned method.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing an aluminum alloy with excellent high-temperature strength and wear resistance using a powder metallurgy method. (Prior art and problems to be solved) In recent years, aluminum alloy powder with high wear resistance and high temperature strength has been manufactured using powder metallurgy using aluminum alloy powder to which a large amount of alloying elements have been added by rapid solidification. Development is becoming more active. As a forming method in this case, hot extrusion is generally used, and methods of compacting, sintering, and coining are not used. In order to sinter aluminum alloy powder, it is necessary to destroy the oxide film formed on its surface to promote sintering. Since the alloy powder containing a large amount of alloying elements has high hardness, the ordinary method of compacting, sintering, and coining does not sufficiently sinter the powder and cannot provide excellent properties. However, in hot extrusion, the powder is deformed by plastic flow during extrusion and the oxide film is destroyed, so that sintering progresses sufficiently and a molded body with excellent properties is obtained. As described above, the hot extrusion method is excellent as a method for plastically deforming hard powder, such as powder obtained by the rapid solidification method, in a heated and softened state to destroy the oxide film and promote sintering. However, since it is not a N ear Net Shape (approximate to a linear shape) processing, secondary processing such as cutting and forging is required to finish it into a machine part, and the processing cost for this is high. Alternatively, there are drawbacks such as high material cost due to low material yield. Furthermore, the mechanical properties are different between parallel and perpendicular directions to the extrusion direction. There are also problems such as restrictions on the shape of applicable mechanical parts due to so-called anisotropy. A hot forging method has been considered as a forming method to improve this point, and this method has already been proposed in JP-A-60-145349. The key points of the method proposed in the above publication are AQ - (10-20)%5i-(2-12)%F
The AQ alloy powder mouth of e has (1-12)% Cu and (
0,1~3) A'Q alloy powder with 3Mg added is cold isostatically pressed or molded to a true density ratio of 95%.
After creating the above preform, change the preform to 2
This is a method for producing a highly heat-resistant and wear-resistant aluminum alloy, which is characterized by heating to 50°C to 550°C and forging in a mold. However, this proposal fails to reduce the amount of contained gas, mainly hydrogen gas, which causes blistering (abnormal expansion phenomenon during heat treatment process) and deterioration of mechanical properties, and does not disclose any measures to reduce contained gas. Not yet. An object of the present invention is to provide a method for suppressing the occurrence of blisters in a hot forging process for aluminum alloy powder and obtaining a forged material with stable mechanical properties. (Means for Solving the Problems) In a series of studies to produce a compact having excellent properties using aluminum alloy powder as a raw material, the present inventors discovered that after hot forging, We encountered problems such as blistering occurring in the molded product, or large variations in mechanical properties in the hot forged state. As a result of intensive study to solve this problem,
It was determined that the cause of blisters and variations in mechanical properties was the large amount of gas components, mainly hydrogen gas, contained in the molded product. Therefore, in order to solve the above-mentioned problems, the present inventors investigated in detail a method for degassing aluminum alloy powder compacts, and as a result, they formed aluminum alloy powders with a true density ratio of 70 to 70.
After creating a 95% preform, if it is sintered in a vacuum or an inert gas atmosphere and then hot forged, the gas content will be less than 5cc/lOOgAQ, which will prevent blisters and variations in mechanical properties. It was discovered that the mechanical properties can be improved compared to the hot forged state by resintering after hot forging if the amount of gas contained is within this range, and the present invention was developed based on this discovery. . That is, 1. The method for producing an aluminum alloy sintered forged product according to the present invention is to mold aluminum alloy powder to make a preform with a true density ratio of 70 to 95%, and to heat the preform in a vacuum at 450 to 550°C or in an inert state. After sintering in the atmosphere,
The true density ratio is made to be 95% or more by forging at 200 to 550°C, and then resintered at a temperature of 450 to 550°C to reduce the total gas amount to 5 cc/100 g-AQ or less. In a more preferred embodiment, the aluminum alloy powder has a weight ratio of Si: 10.0 to 30.0%. Fe: 1.0-15. Q%, Mn: 1.0-15.0%
and Ni: 1.0 to 15.0%, one or two or more (in the case of two or more, the total is 1.0 to 15.0%), and further Cu: 0, 5 to 1, if necessary. 5.0% and Mg:
The object is a composition containing one or two of 0.2 to 3.0% of Afl, with the remainder substantially containing unavoidable impurities. The present invention will be explained in detail below based on examples. Although the aluminum alloy powder used in the present invention is not particularly limited in terms of composition, it is generally used for members that require various properties such as high temperature strength, wear resistance, and low coefficient of thermal expansion. -5i series, AQ-Si-Mg series, A
Fe in Q-8i-Cu series-AQ-S i -Cu-Mg series and alloys thereof. Those to which heavy metals such as Mn and Ni are added, as well as Cr,
It is also possible to add Mo, Go, Ti, Zr, ■, Zn, etc. The formability of aluminum alloy powder varies significantly depending on the hardness of the powder. Figure 1 shows 6061 alloy powder of 100 mesh or less and Afl-
This figure shows the relationship between the true density ratio and the molding pressure when a 30φ×15tman preform was created by molding a 20%5i-3%Cu-1%Mg alloy powder. Generally, the higher the alloy composition, the more difficult it is to increase the density. At a molding pressure of 3 tonf/0 m2, 6061 alloy is approximately 8
Although the true density ratio is 4%, AQ-20%5L-3%Cu
-1% Mg alloy has a true density ratio of about 67%. If the true density ratio is less than 70%, there will be problems in handling, such as part of the corner of the preform being chipped. If the true density ratio is 70% or more, there will be no such problem in handling. However, in order to increase the true density ratio to 95% or more, it is necessary to increase the molding pressure and a large press is required, resulting in high equipment costs. As is clear from FIG. 1, this tendency is remarkable in the case of hard powders such as high alloy powders. Furthermore, setting the true density ratio after compaction to 95% or more has the problem of inhibiting degassing in the subsequent sintering process. When the true density ratio becomes 95% or more, most of the pores existing in the compact become closed pores (C1osed pores), so crystal water or adhesion of the oxide film formed on the surface of the AQ alloy powder, When the adsorbed water is separated by heating, the escape of the generated gas to the outside of the molded body is inhibited, and the molded body after sintering may contain a large amount of gas, or a bulge called a blister may occur on the surface of the molded body. There's a problem. Fig. 2 shows the molded body shown in Fig. 1 being 520cm
These are the results of measuring the amount of gas in a compact that was sintered for 1 hour and then immediately forged in the atmosphere at a pressure of 8 tonf/cta in a mold preheated to 250°C.As is clear from Figure 2. , the true density ratio after compaction is 9
When it is 5% or more, the gas amount is 5cc/100&・AQ
Become more. When the true density ratio after powder compaction is lower than 95%, the gas amount is less than 5cc/100g-All. In addition, when these forged compacts were re-sintered in a vacuum at 520°C x 30win, blisters were generated on the surface of those with a gas amount greater than 5cc/100gAff, and the gas amount was 5cc/100gAff. 1
No blistering was observed when the number was 1 or less. Further, Table 1 shows the gas amount of a molded body which was forged in the same manner as described above immediately after sintering at 520° C. for 1 hr in each atmosphere, with the sintering atmosphere being Ar, N2 or air. In addition,
The sample was AQ-20%5i-3%Cu-1%Mg alloy powder, which was molded at a pressure of 8 tons/c♂ and the true density ratio was 7.
8-80%), sintered in a mold preheated to 250°C.
It is forged at a pressure of tonf/am2. From the same table, 5CC/100g-A in Ar, N, atmosphere
The amount of gas is less than Q, but the molded body sintered in the atmosphere has 5
The amount of gas was more than cc/100g-Al, and blisters were generated due to resintering. Table 1 Total gas amount of compact after forging Next, AQ-20%5L-3%Cu-1%Mg alloy powder was mixed into 55X10x1 at a molding pressure of 8 tonf/0m2.
A 5 mm preform was molded and sintered in vacuum under the same conditions as above. Immediately after sintering, forging was carried out in the air using a mold preheated to 250°C and changing the forging pressure in the range of 3 to 12 tonf/am. A tensile test piece with a parallel part of 5φ x 200III+1 was created from the forged compact. A tensile test was conducted at room temperature.
A tensile test was similarly conducted on the forged compact that was re-sintered in vacuum at 520°C x 30wins. After re-sintering, a tensile test was also conducted on the specimens which were subjected to T6 treatment at 475°C for 1 hr and WQ→175°C for 8 hr. These results are shown in FIG. From the same figure, the tensile strength of the as-forged state is determined by the forging pressure of 5.
tonf/am2 or less, low, 8tonf/C
It rises when it exceeds m2. Also, although the tensile strength increases by resintering, the forging pressure is 8 tonf/cm
This tendency is remarkable when the number is 2 or more. In addition, when the forging pressure is 5 tonf/am2 and 8 tonf/aJ, the as-forged true density ratio is 91% and 97%, respectively.
Met. As mentioned above, after creating a preform with a true density ratio of 70 to 95% after compaction, this is sintered in a vacuum or an inert atmosphere, and then hot forged to a true density ratio of 95%. If above, the amount of gas contained is 5cc/100g-
If the AQ is below, blistering and variations in mechanical properties will be reduced, and if the gas content is within this range, resintering after hot forging will improve the mechanical properties compared to hot forging. can. Next, the reason for limiting the conditions of the present invention will be explained. First, the true density ratio of a preform obtained by molding AQ alloy powder is 70 to 95%. If the true density ratio is lower than 70%, there will be problems such as part of the corner being chipped when handling the preform. In addition, if the true density ratio is higher than 95%, degassing in the next sintering process, which is one of the features of the present invention, will be inhibited, and the 5cc/100g-A Q
Not only would it not be possible to obtain a molded product with the gas amount below, but it would also require a molding press with an unnecessarily large capacity.
Undesirable. Note that mold molding or cold isostatic pressing can be used to mold the preform. Sintering of the preform is performed in a vacuum or inert atmosphere at 450-550°C. In the atmosphere, degassing does not proceed sufficiently, and a molded article having a gas amount of 5 cc/100 g-AQ or less cannot be obtained. For this reason, it is necessary to sinter in a vacuum or in an inert atmosphere. In the case of vacuum, the degree of vacuum is 0. I
Torr or less, preferably 0, OI Torr or less. In an inert atmosphere such as Ar or Nz, it is preferable to control the inert atmosphere so that the dew point is below 110°C, preferably below 120°C. If the sintering temperature is lower than 450"C, the sintering progresses slowly, and
Moisture and crystal water adsorbed on the surface of aluminum oxide cannot be completely removed. If the temperature is higher than 550°C, sintering will proceed, but the structure will become coarser and the mechanical properties will deteriorate, which is not preferable. Forging is performed at 200 to 550°C, and the true density ratio of the forged compact is 95% or more. In order to give sufficient plastic deformation to the AQ alloy powder by forging and destroy the oxide film formed on its surface to reveal a new active surface,
It is preferable to heat the AQ alloy powder to 200° C. or higher to soften it. For this purpose, it is preferable not only to maintain the preform at a temperature of 200° C. or higher, but also to heat and maintain the forging die at a temperature of 200° C. or higher. If the temperature exceeds 550°C, it is undesirable because the structure will coarsen and the mechanical properties will deteriorate. It is also desirable to heat the preform at the same time as heating during sintering, so that the temperature of the preform decreases and the atmosphere In order to reduce the increase in the amount of gas due to exposure to the inside, it is desirable to forge immediately after taking it out from the sintering furnace. If the preform before forging is heated separately from the heating during sintering, it is necessary to heat it to 450-550℃ in a vacuum or inert atmosphere, and after taking it out of the furnace. The considerations are the same as above. If the true density ratio of the compact after forging is lower than 95%, the mechanical properties will be poor, so resintering after forging is preferably carried out at 450-550°C. The purpose of resintering is to sufficiently sinter the new active surface generated during forging, and for this purpose it is necessary to perform the resintering at a temperature of 450'C or higher. If the temperature is higher than 550°C, the structure will coarsen and the mechanical properties will deteriorate, so it is not preferable.Although resintering can be carried out in the air without any problem, it is preferable to do it in a vacuum or in an inert atmosphere. . During resintering, if the gas amount in the forged compact is more than 5cc/100g-AQ, blisters will occur or mechanical properties will deteriorate, so it is difficult to achieve the original purpose of resintering. becomes difficult to do. Next, the reasons for limiting the preferred composition of the aluminum alloy powder used in the present invention will be explained. If Si is less than 10.0%, the amount of dispersion is small and the effect on heat resistance and abrasion resistance is insufficient. In a hypoeutectic region of about 10% 5i, 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%, no matter what rapid solidification method is adopted for powdering, the coarse Si initial product becomes difficult to disappear. When the quenching rate is about 103° C./see, it is desirable to keep the amount of Si at 25% or less in order to refine the primary Si crystals. 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 this alloy. Fe, Mn or Ni has low solubility in AQ,
It is added to take advantage of the slow diffusion rate to disperse the product as a fine compound and increase its high-temperature strength. The amounts of Fe, Mn, and Ni added are each 1.0% to 15%.
0% (However, in the case of two or more types, the total is 1.0~15゜0
%) is appropriate. Fe, Mn or Ni addition amount is 1.0
If it is less than 15%, no effect on high temperature strength or wear resistance will be observed, and if it exceeds 15%, the hardness and wear resistance will be rather low, and when a molded article is made, the material will tend to become brittle. . The AQ gold alloy in this alloy example contains Cu and Mg as necessary.
may be added. Cu and Mg are widely used in A12 alloy as ingredients that impart age hardenability and strengthen the material, and the appropriate amount of Cu to be added is 0.5 to 5.0%.
Mg ranges from 0.2 to 3.0%. In this alloy example as well, Cu and Mg can be contained within the solid solubility limit at the solution treatment temperature.
Adding is effective in strengthening the material. In this alloy example, in order to improve high-temperature strength, C
There is no problem in adding small amounts of r, Mo, Go, Ti, Zr, V, Zn, Li, etc. However, if the amount added is too large, manufacturing problems such as component control and increase in melting temperature will occur. . (Example) Next, an example of the present invention will be described. Using AQ alloy powder of 100 meshes or less and having the composition shown in Table 2 produced by the atmospheric atomization method, 8 t
Mold forming is carried out at a pressure of onf/Cm2, 55X
A 10×15 mm preform was obtained and the true density ratio was determined. Next, these preforms were sintered for 520'CX1 hr in a vacuum of 0°01 Torr or less and an Ar and N2 atmosphere with a dew point of -20°C or less, and then taken out of the sintering furnace and immediately heated and held at 250°C. 8 tons in mold
It was forged in the atmosphere at a pressure of "f/am". After determining the true density ratio, the forged compact was heated in N2 at a dew point of -20°C or lower.
It was re-sintered at 520°C x 30w1n in an atmosphere. A gas analysis and a tensile test were conducted on the molded body after resintering. Gas analysis uses vacuum melt extraction method (using stainless steel pipes)
This was done by The tensile test used a specimen with a parallel part of 5φ x 200ma+,
The test was conducted at room temperature and 200° C., and Nα11 to Nα14 were used as resintered samples, and Nα1 to Nα10 were tested after being subjected to T6 treatment. Note that the tensile test was also conducted on a mold cast material of A390.0 alloy (T6 treated material) for comparison. These results are summarized in Table 2, and it is clear that according to the method of the present invention, AQ alloy sintered forged products with excellent high-temperature strength can be obtained. In addition, some of the products were subjected to tensile tests in the as-forged state, but the gas amount was low at 5 cc/100 g-AQ or less, and no blisters occurred, so the variation in tensile strength was small.

[Left below]

(Effects of the Invention) As described in detail above, according to the present invention, the occurrence of blisters and variations in mechanical materials are significantly reduced, and an aluminum alloy sintered forged product of stable quality can be manufactured.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between molding pressure and true density ratio, and FIG. 2 is a diagram showing the relationship between the true density ratio of a molded body and the total gas amount of the molded body after forging. FIG. 3 is a diagram showing the relationship between tensile strength and forging pressure as-forged and after resintering. Patent applicant Showa Denko K.K. Patent attorney Takashi Nakamura Figure 3 11:'1'J/H, force (moon/cm')0
N” ■
■ 1'L (γ.n) from Omofuo

Claims (1)

[Claims] 1. True density ratio of aluminum alloy powder molded from 70 to 9
For 5% preform, the preform is 450 ~
After sintering in vacuum or inert atmosphere at 550 °C, 20
A sintered forged aluminum alloy with excellent high-temperature strength and wear resistance, characterized by forging at a temperature of 0 to 550°C to achieve a true density ratio of 95% or more, and then resintering at a temperature of 450 to 550°C. method of manufacturing the product. 2 The aluminum alloy powder has a weight ratio of Si:1
0.0-30.0%, Fe: 1.0-15.0%, M
n: 1.0-15.0% and Ni: 1.0-1500%
One or more of the following (however, in the case of two or more types, the total is 1.0 to 15.0%), and further Cu as necessary.
Mg: 0.5 to 5.0% and Mg: 0.2 to 3.0%. A method for producing an aluminum alloy sintered forged product according to scope 1.