WO2018181107A1 - Sintered aluminum alloy material and method for producing same - Google Patents

Abstract

This sintered aluminum alloy material is obtained by compression molding a starting material powder, which contains a pure aluminum powder and an aluminum alloy powder that contains 1-30% by weight of magnesium, into a powder compact and subsequently sintering the powder compact. The proportions of the pure aluminum powder and the aluminum alloy powder in the starting material powder are set to 70-95% by weight and 5-30% by weight, respectively.

Description

Sintered aluminum alloy material and manufacturing method thereof

The present invention relates to a sintered aluminum alloy material and a manufacturing method thereof.

In recent years, light-weight and high-strength lightweight metal materials are required in various fields such as automobiles, industrial machines, information equipment, daily necessities and the like. Typical lightweight metal materials include aluminum and magnesium. Aluminum and magnesium are alloyed with other metals to improve properties such as strength, toughness, corrosion resistance, and workability, and are mainly used for the above-mentioned applications. In particular, aluminum alloys are suitably used for machine parts because of their good formability. This aluminum alloy is mostly manufactured by stretching and casting, but is also mass-produced by a powder metallurgy method that solidifies rapidly solidified powder obtained by a gas atomization method.

Powder metallurgy methods include a hot extrusion method, a powder forging method, and a sintering method. Among them, the sintering method has an advantage that it can be formed into a net shape or a near net shape at a low cost. Therefore, it is suitable for mass production of machine parts.

However, in the sintering method, the aluminum alloy powder easily adheres to the mold when the green compact is formed, and the oxide film formed on the surface of the aluminum alloy powder inhibits necking bonding during sintering. It is mentioned as a problem. As a measure against the former, for example, means described in Patent Document 1 has been proposed. In Patent Document 1, warm molding is used together with mold lubrication when molding a green compact. This makes it possible to form a high-density green compact while preventing the powder from adhering to the mold. As the latter countermeasure, for example, the means described in Patent Document 2 has been proposed. In Patent Document 2, a nitrogen compound is generated on the powder surface by heat-treating an aluminum alloy powder compact containing magnesium in a nitrogen atmosphere to which a reducing gas component is added. This nitrogen compound promotes sintering.

Japanese Patent No. 3945455 JP-A-6-57363

However, since the technique described in Patent Document 1 uses warm forming, it is less economical than cold forming. In the technique described in Patent Document 2, the powder hardness is lowered by pre-annealing the powder at 250 to 450 ° C. in order to increase the density of the green compact. However, even if an aluminum alloy powder containing magnesium is annealed, the powder hardness cannot be lowered as compared with pure aluminum powder. Therefore, it is insufficient for densification of the green compact. In addition, the introduction of reducing gas requires special atmosphere management, which leads to higher costs, which is problematic in terms of mass productivity.

In view of the above circumstances, in the present invention, it is a technical problem to be solved to form a dense green compact so that a high-strength sintered aluminum alloy material can be manufactured at low cost.

The solution to the above problem is achieved by the sintered aluminum alloy material according to the present invention. That is, this sintered material is formed by compacting a raw powder containing aluminum alloy powder containing 1 to 30% by weight of magnesium and pure aluminum powder to form a green compact, and sintering the green compact. Characterized by the fact that the proportion of pure aluminum powder in the raw material powder is set to 70 to 95% by weight and the proportion of aluminum alloy powder to 5 to 30% by weight, respectively. It is done.

As a result of intensive investigations, the present inventors have found that magnesium contained in the green compact diffuses into the sintered aluminum alloy material in the sintering process and becomes highly concentrated in the surface layer portion. According to Non-Patent Document 1, magnesium has a lower free energy of formation of oxide than aluminum and forms an oxide film of magnesium. In consideration of this point, in the green compact of the composition according to the present invention, as the sintering proceeds, the aluminum oxide film is reduced at the surface layer portion of the green compact, thereby causing a strong necking bond, resulting in a result. It is speculated that a high-strength sintered body can be obtained. The present invention has been made on the basis of the above knowledge, and decided to compress and sinter a raw material powder containing an aluminum alloy powder containing 1 to 30% by weight of magnesium and a pure aluminum powder. Thereby, a strong necking bond can be produced | generated and a high intensity | strength sintered compact can be obtained. Further, by allowing pure magnesium powder to be contained, the green compact can be molded at a high density even in the case of cold molding. This is because the hardness of the raw material powder can be significantly reduced by containing pure aluminum powder as the majority of the raw material powder. In addition, since this sintered body (sintered aluminum alloy material) can be manufactured without performing processing that leads to cost increase such as warm forming or introduction of reducing gas, the manufacturing cost can be reduced. This enables mass production. The ratio of pure aluminum powder to the raw material powder is set to 70 to 95% by weight, and the ratio of aluminum alloy powder to 5 to 30% by weight, respectively. If it is small, the green compact is deformed during heat treatment (sintering), and in some cases, there is an increased risk of cracking. Moreover, it is because it becomes difficult to generate | occur | produce the reduction | restoration phenomenon mentioned above stably, when the aluminum alloy powder of the said composition is not a fixed quantity (at least 5 weight%).

Further, in the sintered aluminum alloy material according to the present invention, the magnesium concentration in a region within 0.3 mm from the surface may be higher than the magnesium concentration in a region deeper than 0.3 mm from the surface.

Thus, in the surface layer portion (region within a depth of 0.3 mm from the surface) of the sintered aluminum alloy material, the magnesium oxide film is highly concentrated, so that the oxide film of aluminum is sufficiently reduced. Therefore, it is possible to generate a stronger necking bond and to further increase the strength of the sintered body.

In the sintered aluminum alloy material according to the present invention, the relative density may be 90% or more by weight. The relative density referred to here is obtained by dividing the density of the sintered aluminum alloy material measured according to the Archimedes method in accordance with JIS Z 2501: 2000 by the true density of the raw material powder of the sintered aluminum alloy material. It shall refer to the value obtained.

According to the sintered aluminum alloy material of the present invention, by containing pure aluminum powder, it is possible to form a very dense green compact while containing the aluminum alloy powder. Therefore, by setting the relative density of the sintered aluminum alloy material to 90% or more by weight, the mechanical strength of the green compact itself that becomes the base of the sintered body can be ensured. Therefore, it is possible to sufficiently and stably develop the high strength of the sintered body.

In the sintered aluminum alloy material according to the present invention, the crushing strength may be 120 MPa or more. The crushing strength here refers to the crushing strength evaluated according to JIS Z 2507 “Sintered bearing—crushing strength test method”.

According to the sintered aluminum alloy material according to the present invention, a very high strength sintered body can be obtained by strong necking bonding. Therefore, by setting the crushing strength to 120 MPa or more, it is possible to exhibit the mechanical strength of a level required as a machine part.

The solution to the above problem can also be achieved by the method for producing a sintered aluminum alloy material according to the present invention. That is, this manufacturing method includes a mixing step in which an aluminum alloy powder containing 1 to 30% by weight of magnesium and a pure aluminum powder are mixed to produce a raw material powder containing the aluminum alloy powder and the pure aluminum powder; A method for producing a sintered aluminum alloy material comprising a green compacting step of forming a green compact by compression molding, and a sintering step of obtaining a sintered body by sintering the green compact, It is characterized in that the aluminum alloy powder and the pure aluminum powder are mixed so that the proportion of the pure aluminum powder in the raw material powder is 70 to 95% by weight and the proportion of the aluminum alloy powder is 5 to 30% by weight in the mixing step. Attached.

Thus, by compressing and sintering the raw material powder containing magnesium alloy powder containing 1 to 30% by weight of magnesium and pure aluminum powder, it is strong like the sintered aluminum alloy material according to the present invention. A high-strength sintered body can be obtained by generating a simple necking bond. Further, by allowing pure magnesium powder to be contained, the green compact can be molded at a high density even in the case of cold molding. In addition, since this sintered body (sintered aluminum alloy material) can be manufactured without performing processing that leads to cost increase such as warm forming or introduction of reducing gas, the manufacturing cost can be reduced. This enables mass production.

In the method for producing a sintered aluminum alloy material according to the present invention, the green compact may be formed from the raw material powder by cold forming in the green compact forming step.

According to the sintered aluminum alloy material of the present invention, by containing pure aluminum powder, it is possible to form a very dense green compact while containing the aluminum alloy powder. Therefore, even when the green compact is formed from the raw material powder by cold forming, a very dense green compact can be stably formed.

In the method for producing a sintered aluminum alloy material according to the present invention, the green compact may be sintered at a maximum temperature of 560 to 640 ° C. in the sintering step.

In this way, when heating in the sintering process, the maximum temperature is set in the range of 560 to 640 ° C., and the details will be shown in the experimental results to be described later. Bonding) is promoted, and a strong sintered body can be stably produced.

In the method for producing a sintered aluminum alloy material according to the present invention, the green compact may be sintered in a nitrogen atmosphere in the sintering step.

Aluminum tends to generate oxides more easily than other metals. Therefore, by sintering in a nitrogen atmosphere, the generation of oxide can be suppressed and the progress of sintering can be promoted. Therefore, the strength of the sintered body can be improved.

As described above, according to the present invention, a dense green compact can be formed, and a high-strength sintered aluminum alloy material can be manufactured at low cost.

It is an example of the temperature pattern in the sintering process which concerns on this invention.

Hereinafter, an embodiment of the present invention will be described.

As the pure aluminum powder according to the present invention, it is possible to use a high-purity aluminum metal manufactured by the gas atomization method. Pure aluminum powder may contain inevitable impurities. The particle size distribution of the pure aluminum powder is not particularly limited, but is preferably a fine powder capable of forming a dense green compact. The average particle size is 100 μm or less. Of course, the production method is not limited to the gas atomization method, and various powder methods such as a centrifugal atomization method, a known powder production technique such as a mechanical alloying method and a reduction method can be applied.

The aluminum alloy powder according to the present invention can have any alloy composition as long as it contains 1 to 30% by weight of magnesium. A molten metal prepared to have a predetermined alloy composition and manufactured by a gas atomizing method can be used. Since magnesium easily burns, it is preferable to prepare the composition within a range not exceeding 30% by weight. Further, a metal other than magnesium may be added to the alloy composition as long as the effects of the present invention are not impaired. Further, a lubricant may be blended for the purpose of preventing adhesion to the mold when the green compact is formed. This type of lubricant may be added to the alloy composition, or may be added to a mixed powder of pure aluminum powder and aluminum alloy powder described later. The particle size distribution of the aluminum alloy powder is not particularly limited, but is preferably a fine powder capable of forming a dense green compact. The average particle size is preferably 100 μm or less. Of course, for aluminum alloy powder, the production method is not limited to the gas atomization method, and it is possible to apply known powder production techniques such as mechanical alloying method and reduction method, including various atomization methods such as centrifugal atomization method. It is.

Pure aluminum powder and aluminum alloy powder can be mixed by a known mixing method to obtain a raw material powder according to the present invention (mixing step). Specific examples of the mixing method include a V-type mixer and a double cone type mixer. In addition, it is also possible to add arbitrary components to this raw material powder as long as the effects of the present invention are not impaired.

Using the mixed raw material powder, a green compact is formed by cold forming using a press die (compact forming process). At this time, a lubricant may be applied to the surface of the press mold to be used. The molding pressure is set, for example, to 400 to 800 MPa, preferably 550 to 650 MPa. If the molding pressure is too high (for example, 800 MPa or more), the mass productivity is poor from the viewpoint of the mold life. Therefore, the molding pressure is preferably set to less than 800 MPa in consideration of mass productivity.

The formed green compact is sintered, for example, by heat treatment in a nitrogen atmosphere (sintering process). As the heat treatment furnace, a batch type furnace is preferable, and the green compact is heated in a state where the inside of the furnace is sufficiently replaced with nitrogen. The flow rate of nitrogen is preferably 1 L / min or more. In addition, the temperature pattern in the main sintering process is arbitrary in principle, but, for example, one having a temperature increase and a heat retention in one stage or two stages or more is used. Here, for example, when the temperature pattern shown in FIG. 1 is considered and the first heat treatment is degreasing, the temperature T1 and the holding time t1 are the temperature and holding time at which the lubricant adhering to the surface of the green compact can be degreased. (For example, 380 to 420 ° C., 50 to 70 min). When the second heating step is sintering, the temperature T2 and the holding time t2 are set to a temperature and holding time suitable for sintering of the green compact (preferably 560 to 640 ° C., holding time 30 min or more, Preferably, the temperature is set to 580 to 620 ° C. and the holding time is 60 minutes or more. The temperature T2 here corresponds to the maximum temperature during sintering. If the sintering temperature is lower than 560 ° C. at the maximum temperature, the sintering action is not sufficiently generated, and if it is higher than 640 ° C., there is a possibility that deformation that cannot be ignored occurs in the sintered body. For the above reasons, it is preferable to set the maximum temperature during sintering within the above range. Of course, the sintering step is not limited to a nitrogen atmosphere, and may be performed in other atmospheres as long as various conditions are satisfied.

The density of the obtained sintered aluminum alloy material is measured in accordance with, for example, the Archimedes method according to JIS Z 2501: 2000. Then, the relative density is calculated by dividing the density measured by the Archimedes method by the true density.

Further, the crushing strength of the obtained sintered aluminum alloy material is measured in accordance with, for example, a test method based on JIS Z 2507: 2000.

As described above, the sintered aluminum alloy material according to the present invention is obtained by compression-molding and sintering an aluminum alloy powder containing 1 to 30% by weight of magnesium and a pure aluminum powder. It is possible to generate a strong necking bond and increase the strength of the sintered body. Further, by allowing pure magnesium powder to be contained, the green compact can be molded at a high density even in the case of cold molding. In addition, since this sintered body (sintered aluminum alloy material) can be manufactured without performing processing that leads to cost increase such as warm forming or introduction of reducing gas, the manufacturing cost can be reduced. This enables mass production.

In particular, when heating in the sintering process, the maximum temperature (that is, the sintering temperature) is set in the range of 560 to 640 ° C., and the sintering (necking bonding) is sufficiently promoted without causing deformation. Thus, it becomes possible to stably manufacture a strong sintered body (sintered aluminum alloy material).

As mentioned above, although one Embodiment of this invention was described, the sintered aluminum alloy material and its manufacturing method which concern on this invention are not limited to the form of the said illustration, It can take arbitrary forms within the scope of the present invention. Of course.

Hereinafter, examples of the present invention will be described.

In each of Examples (Examples 1 to 10) and Comparative Examples (Comparative Examples 1 to 9), pure aluminum powder and any one of the aluminum alloy powders (alloy powders 1 to 3) shown in Table 1 were mixed in a V shape. The powder mixed by the machine was used as the raw material powder. Here, all of the alloy powders 1 to 3 are produced by a gas atomizing method.

As the green compact, the raw material powder having the above composition was formed into a predetermined cylindrical shape by cold forming. More specifically, a fatty acid amide-based lubricant was applied to the molding die, and compacting was performed in the mold lubrication state. After pressing at a molding pressure of 620 MPa and a holding time of 5 seconds, a green compact having an inner diameter of 8 mm, an outer diameter of 16 mm, and an axial dimension of 5 mm was obtained by taking out the green compact from the molding die.

After obtaining the green compact as described above, a predetermined heat treatment was performed on the green compact in a desktop vacuum gas replacement furnace (Yamada Electric Co., Ltd .: VFN-1220). Specifically, after the green compact was placed in the furnace, the gauge pressure was evacuated to -0.1 MPa, and nitrogen gas was introduced into the furnace. After introducing nitrogen gas until the pressure in the furnace became equal to atmospheric pressure, the exhaust valve was opened and the discharge flow rate of nitrogen gas was set to 2 L / min. The temperature pattern at this time is set as shown in FIG. 1, and the fatty acid amide-based lubricant adhering to the surface of the green compact is degreased by holding t1 = 400 ° C. and t1 = 30 min. Was sintered by holding t2 = 60 min at T2 = 560-640 ° C. (see Table 2 to Table 4 described later). For Comparative Examples 1 to 9, T2 was held at 550 to 650 ° C. and t2 was maintained for 60 minutes.

For the sintered bodies (Examples 1 to 9) obtained as described above, the density was measured in accordance with the Archimedes method based on JIS Z 2501: 2000. Furthermore, the crushing strength of the sintered body was measured in accordance with a test method based on JIS Z 2507: 2000. For Comparative Examples 1 to 9, the crushing strength was measured for only Comparative Example 1 and Comparative Example 3 in which the compacting and sintering processes could be performed without deformation or cracking. The results are shown in Tables 2 to 4. In each table, the value of the crushing strength in parentheses indicates the stress value when the strain amount is 1 mm when the fracture amount is not broken until the strain amount reaches 5 mm.

As shown in Table 2, when alloy powder 1 having the composition Al-10Mg-1Si is used and heat treatment is performed at a maximum temperature of 560-640 ° C. with a pure aluminum powder content of 70-95 wt% (Examples 1 to 6) The crushing strength of the obtained sintered bodies was 120 MPa or more. On the other hand, when the amount of pure aluminum powder was less than 70% by weight (Comparative Examples 4 and 5), cracks occurred during compacting or sintering, and a sintered body could not be obtained. . Even when the amount of pure aluminum powder is 70 to 95% by weight, if the maximum temperature during sintering exceeds 640 ° C. (Comparative Example 2), deformation occurs during heat treatment, and the sintered body Could not get. For Comparative Examples 1 and 3, sintered bodies could be obtained, but for Comparative Example 1, the maximum temperature during sintering was less than 560 ° C., and for Comparative Example 3, the blending amount of alloy powder 1 The crushing strength was 100 MPa or less.

Further, as shown in Table 3, when alloy powder 2 having the composition Al-30Mg was used and the blending amount of pure aluminum powder was 95 wt% (Example 7) and 70 wt% (Example 8), it was obtained. The crushing strength of the obtained sintered bodies was 120 MPa or more. On the other hand, when the amount of pure aluminum powder was less than 70% by weight (Comparative Examples 6 and 7), cracks occurred during compacting or sintering, and a sintered body could not be obtained. .

Further, as shown in Table 4, when alloy powder 3 of composition Al-5Mg was used and the blending amount of pure aluminum powder was 95 wt% (Example 9) and 70 wt% (Example 10), it was obtained. The crushing strength of the obtained sintered bodies was 120 MPa or more. On the other hand, when the amount of pure aluminum powder was less than 70% by weight (Comparative Examples 8 and 9), cracks occurred during compacting or sintering, and a sintered body could not be obtained. .

Moreover, about the cross section of the sintered compact produced in Example 4, surface layer part (area | region within 0.3 mm in depth from the surface) and deep layer part (depth from surface to 0.3 mm) by X-ray photoelectron spectroscopy (XPS). A deeper region was analyzed. The results for magnesium and aluminum are shown in Table 5. The numerical values in the table are atomic%, and the total of Mg and Al is described to be 100 atomic%. In Table 5, “−” indicates that the value was below the detection limit.

As shown in Table 5, it can be seen that magnesium exists as a compound regardless of the surface layer portion and the deep layer portion. Moreover, regarding the magnesium concentration, the surface layer portion had a higher concentration than the deep layer portion. In this case, as shown in Table 2, the crushing strength showed a very large value (200 MPa or more). The reason why the surface layer portion and the deep layer portion are different from the average composition of the entire sintered aluminum alloy material (sintered body) is that the cross section of the sintered body is the old powder grain boundary and the old powder surface. .

As described above, since the sintered aluminum alloy material according to the present invention is dense and has high strength, for example, machine parts having sliding parts (sliding parts) and machine parts for various applications. Widely applicable to.

Claims (8)

1. A sintered aluminum alloy obtained by compression molding a raw powder containing aluminum alloy powder containing 1 to 30% by weight of magnesium and pure aluminum powder to form a green compact and sintering the green compact Material,
   A sintered aluminum alloy material in which the ratio of the pure aluminum powder to the raw material powder is set to 70 to 95% by weight, and the ratio of the aluminum alloy powder to 5 to 30% by weight.
2. 2. The sintered aluminum alloy material according to claim 1, wherein a magnesium concentration in a region within a depth of 0.3 mm from the surface is higher than a magnesium concentration in a region deeper than a depth of 0.3 mm from the surface.
3. The sintered aluminum alloy material according to claim 1 or 2, wherein the relative density is 90% or more by weight.
4. The sintered aluminum alloy material according to any one of claims 1 to 3, wherein the crushing strength is 120 MPa or more.
5. A mixing step of preparing a raw material powder containing the aluminum alloy powder and the pure aluminum powder by mixing aluminum alloy powder containing 1 to 30% by weight of magnesium and pure aluminum powder;
   A compacting step of compacting the raw material powder to form a compact,
   A method for producing a sintered aluminum alloy material comprising a sintering step of obtaining a sintered body by sintering the green compact,
   In the mixing step, the aluminum alloy powder and the pure aluminum powder are adjusted so that the proportion of the pure aluminum powder in the raw material powder is 70 to 95% by weight and the proportion of the aluminum alloy powder is 5 to 30% by weight. A method for producing a sintered aluminum alloy material.
6. The method for producing a sintered aluminum alloy material according to claim 5, wherein, in the compacting step, the compact is formed from the raw material powder by cold forming.
7. The method for producing a sintered aluminum alloy material according to claim 5 or 6, wherein the green compact is sintered at a maximum temperature of 560 to 640 ° C in the sintering step.
8. The method for producing a sintered aluminum alloy material according to any one of claims 5 to 7, wherein the green compact is sintered in a nitrogen atmosphere in the sintering step.

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