JPH04308008A - Manufacturing method of aluminum powder alloy parts - Google Patents

Abstract

PURPOSE:To obtain parts made of Al powder and having high dimensional accuracy by forming caked bodies of the powder having satisfactory strength in spite of the presence of residual pores, converting the residual open pores into closed pores and carrying out sizing. CONSTITUTION:Al alloy powder obtd. by solidification by rapid cooling or by mechanical alloying is subjected to cold powder molding, heating and hot forging (A), to warm powder molding, heating and hot forging (B) or to heating and hot powder molding (C). Cold sizing (X) or warm sizing (Y) is then carried out to produce parts made of the Al powder.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing aluminum powder alloy parts economically, such as mechanical structural parts with excellent dimensional accuracy, using aluminum powder alloy.

0002

[Prior art] Conventionally, when producing iron-based sintered parts,
Utilizing the 10 to 20% of pores existing in the sintered body, pressure is applied to partially collapse them and locally deform into a shape that conforms to the mold without causing large plastic deformation as a whole. A so-called sizing method that ensures high dimensional accuracy is generally employed.

On the other hand, when producing aluminum powder alloy parts, a so-called powder metallurgy method is used in which aluminum alloy powder obtained by a rapid solidification method or a mechanical alloying method is put into a mold, solidified, and then hot forged. .

0004

[Problems to be Solved by the Invention] By the way, the sintering operation performed with the above-mentioned iron-based powder is a method for sintering aluminum alloy powder. It is almost impossible to use it because it inhibits the
It's practically meaningless. Therefore, aluminum alloy powder is generally obtained by a rapid solidification method or a mechanical alloying method, and then shaped and solidified by hot extrusion or hot forging at a relatively low temperature in order to maintain a metastable alloy phase and a fine structure. I try to do that. However, in the hot forging method of aluminum alloy powder described above, dimensional changes occur in the forged body due to expansion and contraction of the mold and compacted body due to heat. There is a problem in that it is difficult to manufacture mechanical structural parts with high dimensional accuracy.

As mentioned above, the sizing process is a local plastic deformation method for compressible materials that utilizes residual pores, and is completely different from the plastic deformation of non-compressible materials such as true density forging, wire drawing, and swaging. Due to different principles. Therefore, it is essential to have sufficient solidification strength and an appropriate amount of residual pores. However, in the case of aluminum alloy powder, using the conventional powder metallurgy method and the general sizing method for iron-based sintering methods results in 10 to 20% of pores remaining in the forged body, resulting in significant strength loss. On the other hand, in the case of a true density forged body, re-forging is required instead of sizing, so it cannot be applied from the viewpoint of improving dimensional accuracy.

[0006] The present invention takes into consideration the current state of the conventional manufacturing method of aluminum powder alloy parts as described above, and incorporates a sizing method into the rapid solidification powder metallurgy method to optimize the residual pores in the powder forged body necessary for the sizing method. The objective is to realize a method for manufacturing aluminum powder alloy parts having high dimensional accuracy comparable to that of iron-based sintered parts by suppressing the resulting decrease in strength of powder forged bodies.

[0007]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention involves hot or cold pressure molding of aluminum alloy powder to obtain a powder compact having a relative density of 75 to 93%, and The method for manufacturing aluminum powder alloy parts is to form a powder solidified body with a relative density of 95 to 98% through processing, and then to cold or warm sizing treatment.

[0008] Instead of the above invention, aluminum alloy powder is heated as a powder, and this is hot pressed and solidified to form a solidified powder with a relative density of 95 to 98%, and then cold or warm sizing is performed. It may also be a method for producing aluminum powder alloy parts by processing.

[0009]

[Operation] In the manufacturing method according to the first invention, in the first step, the relative density is adjusted to a range having connected pores (75 to 93%).
), and then in the second step, the pores are isolated in a hot state where the yield strength of the material is low, and the powder particles are bonded together. In the subsequent third step, the isolated pores left behind are used to perform the sizing treatment. The causes of the decrease in strength due to residual pores include stress concentration in the pores due to the shape of the so-called connected pores, and deterioration of grain boundaries due to an oxidizing atmosphere containing moisture that enters through the connected pores. Therefore, it is preferable to make the remaining pores as spherical as possible and to eliminate connected pores, leaving only isolated pores.

In the case of ordinary powder metallurgy, residual pores change from connected pores to isolated pores at a relative density of about 94%, and in the case of connected pores, the surrounding atmosphere penetrates into the interior. , reactions often occur, but when isolated pores are formed, diffusion from the surface layer becomes rate-limiting for penetration into the interior, making the reaction extremely slow, and hydrostatic compression processing using a gas such as so-called HIP is possible. This is because the original powder is deformed and the old powder grain boundaries come into contact, causing the voids to become smaller, but voids inevitably remain at locations such as the triple points of the grain boundaries. Whether these voids are three-dimensionally connected is determined mostly by their relative density. Therefore, the foamed material with true density is 94.
% or less, it is possible for the powder to consist of only isolated pores, but generally such a phenomenon does not occur when powder is compacted. In the case of aluminum alloy powder, as in the case of general powder metallurgy powder, it is economically difficult to cold compression mold the powder to a relative density of 94% or more.

[0011] The above manufacturing process differs from the conventional powder forging method in that isolated pores are left and solidified by hot working. For this purpose, it is essential to sufficiently decompose and remove moisture present on the surface layer of the powder during hot heating, and for this purpose, the relative density of the compact in the first stage is set in the range where connected pores exist (75~ 93%). Next, in order to have sufficient strength of the solidified body in the state where residual pores exist compared to the state of true density, 9
It is necessary to compact and solidify the material to a relative density of 5% or more, which can be achieved within the range of temperature and pressure conditions in conventional powder forging methods.

On the other hand, the sizing process using residual pores requires an appropriate absolute amount of pores, as described above.
The amount is 2 to 5% in the case of this process with aluminum alloy powder.
It turns out that it is possible. Of course, even if there is a larger amount of pores, sizing treatment is possible, but it is practically difficult to tolerate a larger amount of pores in terms of deterioration of strength characteristics. It has become clear that when the amount of pores is less than 2%, the sizing approaches that of forging, causing problems such as increased deformation resistance, increased residual strain, and occurrence of seizure, which deteriorates dimensional accuracy.

[0013] Since the purpose of the present invention is to manufacture mechanical structural parts of high performance aluminum alloy with high dimensional accuracy, it is important to be able to form complex shapes. For this purpose, complex powder preforms can be made by cold compression molding of powder, but in the case of rather simple shapes, powder preforms can be made more easily by warm compaction. You can make it. Furthermore, more complex shapes can be created from the powder preform during hot heating.

The method according to the second invention is a manufacturing method in which the first step of powder preforming in the first invention is omitted, and this method directly heats the powder and solidifies it under pressure at a high temperature. . Although the sizing process itself is the same as the method according to the first invention, it is possible to manufacture economically by using a simpler method. It is desirable to use a relatively coarse powder in carrying out the method. The reason for this is that powder flowability at high temperatures generally deteriorates significantly, and even fine aluminum powder with poor flowability is difficult to handle at high speeds. Furthermore, when handling fine powder, it is important to prevent the fallen powder from sticking to the clearance with the mold. Coarse powder is also desirable for this purpose.

[0015] For the sizing process, either a cold method, that is, a method in which the mold is used at room temperature without actively heating it, or a method, in which the mold is temperature controlled and used in a warm state, that is, at 300° C. or less, can be used. I can do it. The optimum combination of conditions is selected depending on the shape, dimensional accuracy in the second stage, material to be forged, etc. It is desirable to use a commonly used liquid or solid lubricant such as oil during sizing.

[0016]

EXAMPLES Examples will be described below with reference to the drawings and tables. As a manufacturing method for the aluminum powder alloy part of the example, six methods shown in FIG. 1 were carried out, and a ring-shaped aluminum powder alloy part of 40φ×27φ×5 mm was manufactured using each manufacturing method.

[0017] Process (A) Cold powder forming → heating → Hot forging (B) Warm powder forming → heating →
Hot forging (C)
Heating → Hot forming (X) Cold sizing (Y) Warm sizing Tables 1 and 2 show the properties of the aluminum powder alloy used in each of the above treatment steps.

[0018]

[Table 1]

[0019]

[Table 2]

[0020] Values for temperature, pressure, time, etc. in each of the above steps are summarized in Table 3.

[0021]

[Table 3]

Further, Table 4 summarizes the characteristics and dimensional accuracy of parts manufactured by each manufacturing method.

[0023]

[Table 4]

As can be seen from the results in Table 4, compared to data on roundness and thickness variations in conventional hot forging or equivalent processing methods, cold or temperature sizing processing It will be understood that the method according to the present invention, which includes additional steps, has significantly improved dimensional accuracy.

[0025]

[Effect] As explained in detail above, in both the first and second inventions, optimal temperature and pressure conditions are selected for each process, and the solidified material has sufficient strength in the presence of residual pores. to obtain a solidified powder with a density of 95 to 98%,
By adding cold or temperature sizing treatment to this, it has become possible to obtain aluminum powder alloy parts with extremely high dimensional accuracy due to the effect of sizing treatment, which could not be applied in the past.

[Brief explanation of drawings]

[Fig. 1] Diagram illustrating combinations of processing steps in Examples.

[Explanation of symbols]

A Process of cold powder forming, heating and hot forging B Process of warm powder forming, heating and hot forging C Process of heating and hot forming X Cold sizing Y Warm sizing

Claims (2)

[Claims] Claim 1: A powder compact having a relative density of 75 to 93% is obtained by hot or cold pressure molding of aluminum alloy powder, which is then hot worked into a powder solidified body having a relative density of 95 to 98%. A method for manufacturing aluminum powder alloy parts, which is then subjected to cold or warm sizing treatment. [Claim 2] Aluminum alloy powder is heated as a powder, and this is hot-press-molded and solidified to have a relative density of 95 to 9.
A method for manufacturing aluminum powder alloy parts by solidifying the powder into an 8% powder and then sizing it cold or warm.