JPH066763B2 - Method for manufacturing high strength aluminum alloy sintered member - Google Patents

Description

TECHNICAL FIELD The present invention obtains a high-strength aluminum alloy member containing an alloying element which tends to precipitate a coarse intermetallic compound which impairs mechanical properties, by a powder metallurgy method. It is about the method.

2. Description of the Related Art In recent years, there has been a tendency for a high-strength aluminum alloy member containing an alloying element in an amount exceeding the melting limit of an α solid solution to be manufactured by powder metallurgy. In this method, an aluminum alloy powder obtained by an air injection method (atomization) or an inert gas injection method, which has good productivity, is often used.

However, when the aluminum alloy powder is obtained by the gas injection method, the cooling rate from the molten state is 10 ² ° C /
The aluminum alloy containing a large amount of the above alloying elements, which is small at more than 10 seconds and less than 10 ⁴ ° C./second and has different strength and rigidity, has a problem that a coarse intermetallic compound occurs. Therefore, the sintered product obtained from the powder has an insufficient elongation rate with respect to a tensile load, so that not only the characteristics required as a structural member cannot be obtained, but also secondary processing such as forging is difficult.

Conventionally, in order to deal with the problem, an aluminum alloy powder obtained by a gas injection method is compacted into a billet for extrusion, and the billet is hot extruded to crush coarse intermetallic compounds. At the same time, sintering and densification of the structure were carried out, thereby increasing the elongation of the fired crystal and improving the secondary workability. This hot extrusion process not only increases the number of steps, but also lowers the product yield and pushes up the product price.

Means and Actions for Solving Problems The object of the present invention is to provide a high-strength aluminum alloy sintered member containing a large amount of alloying elements that precipitate coarse intermetallic compounds that impair mechanical properties, by a hot working method. It's about getting at a low price.

The purpose of the first aluminum alloy powder containing a large amount of alloying elements that precipitates coarse intermetallic compounds that impair mechanical properties is that the cooling rate from the molten state is 10 ⁴ to 10 ⁶
C./sec. And other second alloy powders with a cooling rate from the molten state of 10 ² ° C / sec or more, 10 ⁴ ° C
/ Second is used, and the first aluminum alloy powder 5
By weight or more, less than 30 parts by weight, after mixing the second aluminum alloy powder 70 parts by weight or more, less than 95 parts by weight,
This is achieved by compacting and sintering to obtain a high strength aluminum alloy sintered member.

If an aluminum alloy powder containing a large amount of alloying elements that precipitates coarse intermetallic compounds that impair mechanical properties is produced at a cooling rate from the molten state of 10 ⁴ ° C / sec or more, It is possible to prevent coarsening of the compound. However, in order to obtain a powder at such a large cooling rate, it is necessary to use a spray roll method, a melt spuning method, a splat cool method, etc., and these powder manufacturing methods are complicated in process control, etc. However, it is not suitable for mass production and the powder manufacturing cost becomes high.

The present inventor, under such recognition, achieves the target alloy composition by mixing the first aluminum alloy powder containing a large amount of the alloy element in question with another second aluminum alloy powder. It was found that it is effective to produce only the first aluminum alloy powder by the high-speed cooling method, which is expensive to produce.

That is, by mixing a first aluminum alloy powder containing a large amount of alloying elements that precipitate a coarse intermetallic compound that impairs mechanical properties, and another second aluminum alloy powder, after compacting In the sintering process, it is possible to promote the diffusion by utilizing the concentration gradient between the powders, and improve the sinterability, and compared with the first aluminum alloy powder having poor compactability, By increasing the mixing amount of the second aluminum alloy powder having good compaction formability, the density of the compact is increased to improve the sinterability, and the forging after sintering is performed to achieve the target. The mechanical properties can be obtained. According to this method, not only the coarsening of intermetallic compounds in the sintered product can be prevented, but also the hot extrusion process is omitted, and a large amount of inexpensive second aluminum alloy powder is used, and the manufacturing cost is reduced. Can be achieved.

Specifically, the compounding ratio of the first aluminum alloy powder containing a large amount of alloying elements that precipitates coarse intermetallic compounds that impair mechanical properties is set to 5% by weight or more and less than 30% by weight, It is suitable that the blending amount of the aluminum alloy powder is 70% by weight or more and less than 95% by weight. The reason is,
If the compounding ratio of the first aluminum alloy powder is less than 5% by weight, the amount of alloying elements added to achieve the desired product strength will be insufficient, and if it exceeds 30% by weight, the powder compactability of the powder will decrease. This is not only due to the increase in manufacturing cost.

Suppose now that the target alloy composition is 12.0 ≦ Si ≦ 28.0%, 0.8 ≦
Cu ≦ 5.0%, 0.3 ≦ Mg ≦ 3.5%, 2.0 ≦ Fe ≦ 10.0%,
If 0.5 ≦ Mn ≦ 5.0% (both by weight), the composition of the first aluminum alloy powder is 5 ≦ Fe ≦
40% by weight, 3 ≦ Mn ≦ 25% by weight, balance Al, and the composition of the second aluminum alloy powder is 13 ≦ Si ≦ 29% by weight,
2 ≦ Cu ≦ 5% by weight, 0.5 ≦ Mg ≦ 2% by weight, balance Al
Is preferred. Here, the second aluminum alloy powder excludes Fe as an Al-Si-Cu-Mg alloy when the cooling rate from the molten metal is 10 ² ° C / sec or more and less than 10 ⁴ ° C / sec. In addition, if Si and Fe coexist, a coarse Al—Si—Fe intermetallic compound is likely to occur. In addition, the reason why the cooling rate from the molten metal at the time of producing the first aluminum alloy powder that is an Al-Fe-Mn alloy must be 10 ⁴ to 10 ⁶ ° C / sec is that the Al-Fe-Mn alloy solid This is because when the liquid coexistence temperature range (the temperature range from the start of solidification to the completion of solidification) is wide and the cooling rate is small, intermetallic compounds such as Al ₃ Fe coarsely precipitate and the elongation rate of the final product decreases. In addition, Fe,
Not only Mn but also transition elements such as Ni, Cr, V, Co, and Ti have a solid solution limit of 1.5% by weight or less with respect to Al, and in an aluminum alloy containing these elements,
Since the intermetallic compound containing the element is likely to coarsely precipitate, the cooling rate during the production of the aluminum alloy powder is preferably sufficiently large, and the aluminum alloy powder containing these alloy elements is Since it exhibits self-disintegrating property and can be efficiently pulverized for finely pulverizing powder, it has an advantage suitable for mass production.

The method of the present invention is carried out by the following procedure, for example.

Production of aluminum alloy powder: The first aluminum alloy powder is produced by the spray roll method, then finely divided by a pulverizer, and then classified so as to be finer than 100 mesh. Powders coarser than 100 mesh reduce the elongation of the final product and are not recommended for use.

The second aluminum alloy powder is manufactured by a gas injection method and then classified so as to be finer than 100 mesh.

Mixing of powders: The first and second aluminum alloy powders thus obtained are mixed with a double cone mixer.
Mix evenly with an eblender) or ball mill.

Compacting: heating the mixed powder to a temperature of 250-350 ° C,
Molding is performed at a pressure of 3 to 8 ton / cm ² by a mold heated to the same temperature without using wax. At this time, when the powder molding temperature is 250 ° C., the deformation resistance of the powder is large, and when it exceeds 350 ° C., a bridge phenomenon is apt to occur due to the mutual adhesion of the powders during pressurization, and the mold filling property And the resulting decrease in productivity.

Further, the molding may be carried out at a pressure of 3 to 8 ton / cm ² by a molding method such as cold isostatic pressing (CIP method).

In any of the molding methods, if the applied pressure is less than 3 ton / cm ² , sufficient sintering strength cannot be obtained, and 8 ton / cm ²
If it exceeds the above range, the manufacturing cost is increased due to the increase in the size of the device, and it is not industrially established.

The density ratio of the resulting green compact (the ratio of the green compact density (g / cc) to the true density (g / cc) of the metal having the same composition as the green compact expressed as a percentage) is 90. ~ 99.5
% Is desirable. The reason is that if the density ratio is less than 90%, the desired sintering strength cannot be obtained, and if the density ratio exceeds 99.5%, the removal of the contained gas during sintering is not complete and it is harmful to the inside of the sintered crystal. This is because the gas will remain.

Sintering: The green compact obtained in the preceding paragraph is placed in a sintering furnace and preferably heated and maintained at a temperature of 350 to 580 ° C. in an inert atmosphere such as vacuum, nitrogen gas or argon gas. Sintering temperature is 350
If it is less than ℃, the sintering does not proceed sufficiently, and if it exceeds 580 ° C, a large amount of liquid phase appears and the product strength decreases.

Forging: If necessary, the obtained sintered product is forged by using an ordinary press machine. Forging temperature is 350-4
80 ° C is desirable. If the temperature is lower than 350 ° C, the temperature of the sintered product will be lost to the mold, and the temperature will decrease, causing forging cracking.If it exceeds 480 ° C, the temperature of the sintered product will be affected by the deformation heat generated by forging. Excessively rises, a liquid phase appears and the product strength decreases.

Heat treatment, machining: For preceding obtained in forged product, if necessary, T 6 _(after solution treatment, artificial upon curing process), T 7 _(after solution treatment, stabilization), such as Heat-treated and then machined to obtain a finished product.

Test Example First stage: The first and second aluminum alloy powders having the compositions shown in Table 1 were produced by the method of the above-mentioned item, 10 parts by weight of the first aluminum alloy powder, and the second aluminum alloy powder.
90 parts by weight, with those uniformly mixed for 30 minutes by a double cone blender, which was charged into a mold having an inner diameter of 30 mm ^phi, perform powder compaction under the following conditions, 30 mm ^phi × 50 mm
A cylindrical green compact of was obtained.

Second step: heating the green compact to a temperature of 470 ° C. in the atmosphere,
Forging was performed using a die preheated to a temperature of 430 ° C, and a sintered member that was a forged product of 47 mm ^φ × 20 mm (Table 1,
Inventive Example Alloy A) was obtained.

The third step: from sintered member was cut parallel portion diameter 5 mm ^phi, tensile specimens parallel portion length 30 mm, was conducted a tensile test at room temperature. The results are shown in Table 2.

Comparative Example B: Air injection method for alloy B shown in Table 1 (cooling rate from molten metal 10 ₂ ° C / sec or more, less than 10 ₄ ° C / sec)
Using the powder obtained in the above, a forged product was formed by the same method as the first and second steps of the method of the present invention. The density ratio of the green compacts in this case is 95 because the powder compactability is poor.
Stayed at%.

Comparative Example C: With respect to the alloy C shown in Table 1, a green compact was molded, hot extruded, and then hot forged.

Then, the same tensile test pieces as those of the example of the present invention were cut out from the molded products obtained in Comparative Examples B and C, and the tensile test was carried out.
The results are shown in Table 2.

<Evaluation of Test Results> From the comparison between the invention alloy A and the comparative alloy B, the invention alloy A is superior in both tensile strength and proof stress to the comparative alloy B using powder by the conventional air injection method. You can see that

Further, from the comparison between Inventive Example Alloy A and Comparative Example Alloy C, there is no significant difference in static strength except for the elongation rate, and there is no need for a hot extrusion process. It can be seen that the member is obtained.

EFFECTS OF THE INVENTION As is clear from the above description, in the present invention, as the first aluminum alloy powder, the cooling rate from the molten state is 10
The second aluminum alloy powder has a cooling rate of 10 ² ° C from the molten state as well as ⁴ to 10 ⁶ ° C / sec.
/ Second or more and less than 10 ⁴ / second, and the first aluminum alloy powder 5 parts by weight or more and less than 30 parts by weight and the second aluminum alloy powder 70 parts by weight or more and less than 95 parts by weight. After mixing and compacting and sintering, it is possible to eliminate coarse intermetallic compounds in the product sintered parts even if the hot extrusion process that was required in the past is omitted, improving productivity. Therefore, the product price can be reduced.

Claims (1)

[Claims] 1. A first aluminum alloy powder containing a large amount of alloying elements for precipitating a coarse intermetallic compound that impairs mechanical properties, and another second aluminum alloy powder are mixed, and then pressed and fired. A method for producing a high-strength aluminum alloy member by binding, wherein, as the first aluminum alloy powder, a cooling rate from a molten state of 10 ⁴ to 10 ⁶ ° C / second is used,
As the second aluminum alloy powder, one having a cooling rate from a molten state of 10 ² ° C / sec or more and less than 10 ⁴ ° C / sec is used, and the first aluminum alloy powder is 5 parts by weight or more and less than 30 parts by weight. And a mixture of 70 parts by weight and less than 95 parts by weight of the second aluminum alloy powder, and then compacting and sintering the mixture.