JPS61130404A - Sintering method of aluminum powder - Google Patents

Abstract

PURPOSE:To obtain a sintered alloy having excellent wear resistance by forming a chemical conversion-treated layer consisting of K2AlF5 on the surface of Al powder which is sintering base body then mixing the powder with brazing filler metal powder and subjecting the powder mixture to compaction molding and sintering. CONSTITUTION:The chemical conversion-treated layer consisting of potassium pentafluoroaluminate (K2AlF5) is formed on at least one surface of the Al or Al alloy powder which is the sintering base body or the low melting Al alloy powder which is a brazing filler metal. Al-Si eutectic alloy powder contg., for example, about 7-12% Si is preferable for the low melting Al alloy powder as the brazing filler metal. About 99.5-97wt% Al powder and 0.5-3wt% low melting Al alloy powder are then mixed and after the powder mixture composed thereof is subjected to compaction molding, the molding is sintered in an atmosphere of an inert gas or reducing gas at the temp. above the m.p. of the brazing filler metal and below the m.p. of the Al powder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for sintering aluminum-based powder.

[Conventional technology]

In addition to exhibiting alloying properties that cannot be obtained with ingot alloys, sintered alloys are porous, so when used as friction members, the pores become oil pools, exhibiting good lubrication properties. ＠ Sintered bodies of aluminum or aluminum alloy have traditionally been desired as friction members, but aluminum is easily oxidized, and their surfaces are coated with aluminum oxide (A40m).
), it was difficult to sinter aluminum powder or aluminum alloy powder.◎ When aluminum-based powder KMt- is added, a sintered alloy can be obtained, but copper cannot be coated with oil such as lubricating oil. Aluminum-based sintered alloys containing copper are not desirable because they deteriorate and cause corrosion.

Therefore, there has been a demand for a porous aluminum-based sintered alloy that does not contain copper.

Aluminum alloy containing silicon (cst)v is widely used as a friction member due to its high wear resistance.
When powder of this alloy is instantaneously solidified at high temperature, Si grains grow and the properties deteriorate. Therefore, it is important to sinter at low temperatures!
! - Last but not least, sintering was impossible at low temperatures due to the aforementioned reasons such as the formation of an A403 film on the powder surface.

[Problem that the invention attempts to solve]

The present invention uses aluminum alloy powder as the main raw material, without using metal powder such as copper, which would limit the uses of the obtained sintered body, and without requiring special sintering conditions. It is an object of the present invention to provide a complete method for sintering aluminum-based powder.

[Means for solving problems]

In the method for sintering aluminum-based powder of the present invention, potassium pentafluoroaluminate is added to at least one surface of aluminum powder or aluminum alloy powder that is the base of the sintered body, or low melting point aluminum alloy powder that is the brazing material. CKtAtFs), and a step of completely mixing the powder for the sintered base with the brazing filler metal powder, compacting, and sintering.

In the present invention, the aluminum and aluminum alloy powder (hereinafter referred to as aluminum-based powder) is not particularly limited in its composition, and contains silicon (Si), copper (Cu), -r7, which is contained in ordinary aluminum alloys. Ga:' (Mn), zinc (Zn), titanium (Ti), chromium (Cr), zirconium (Zr), magnesium (
It may contain one or more types of additive elements such as Mg), and there are no particular restrictions on the content. However, it is preferable that Mg does not contain a large amount of gold.

As the low melting point aluminum alloy powder used as a brazing material (binding material) during sintering, At-8t eutectic alloy powder, which has a slightly lower melting point than aluminum powder, is mainly used. More specifically, the melting point is 10 to 100°C lower than that of aluminum powder, and the melting point of Ks htFs (
(approximately 540°C) or higher, such as Si? A powder of an ht-st eutectic alloy containing 7 to 12 units (by weight, the same hereinafter) is preferable. Note that the above-mentioned low melting point At alloy is usually used as its own powder, but in some cases it may be used in the form of being coated on the surface of aluminum powder. As the low melting point At alloy, one used as a brazing material when brazing aluminum-based materials can be used.

The Kt AtFs chemical conversion treatment layer is formed according to the method described in Japanese Patent Application No. 191311/1983, which was previously proposed by the present inventors.

The chemical conversion treatment step in the present invention is carried out by bringing at least one of the aluminum-based powder serving as the base of the sintered body or the low-melting aluminum alloy powder serving as the brazing material into contact with a treatment solution containing potassium and fluorine.

The chemical conversion treatment liquid used in the process of forming the chemical conversion treatment layer of the present invention can be prepared by various methods, and for example, by the following method. One method is to dissolve potassium hydrogen fluoride (KHR) in t-water. The amount of potassium hydrogen fluoride dissolved is 1 to 80 g per 1 part of water, which is suitable for producing potassium pentafluoroaluminate. 6. Another preparation method is to prepare a mixed aqueous solution by dissolving potassium fluoride (KF) and hydrogen fluoride (HF) in water. Cough, potassium hydroxide (KOH)
) and hydrogen fluoride dissolved in water may also be used. These aqueous solutions have a fluorine to potassium molar ratio of 1 to 10.
Preferably, it contains 0.5 to 40 g/l of potassium.

Methods for bringing raw material powder such as aluminum powder into t-contact with the chemical conversion treatment solution include dipping, coating, and spraying, but the contact time is determined by the amount of potassium and fluorine in the chemical conversion treatment solution. Although it cannot be determined unconditionally depending on the concentration, temperature of the processing liquid, etc., for example, 0.5 seconds to 2 seconds.
A range of about 0 minutes is good. Due to this contact, the oxide film existing on the surface of the aluminum powder is destroyed, and aluminum, potassium, and fluorine react chemically, forming KshtFs.
is generated. The formation of this compound varies with temperature. Naturally, the chemical reaction proceeds sufficiently even at room temperature. However, when the temperature at the time of contact is raised to 40 to 70°C, the oxide film on the FF is completely and rapidly removed. Formed firmly on the surface of the body.

Since this chemical conversion treatment layer is firmly attached, it will not fall off from the powder during subsequent processes such as compaction. Sintering therefore takes place completely.

The above chemical conversion treatment layer may be formed on all of the raw material powders, only on the low melting point At powder to be mixed, or only on the aluminum powder. In principle, the chemical conversion treatment is applied to the raw material powder, but in some cases it may be applied to the coarse particles before being pulverized. The aluminum-based powder can be produced by various methods such as an atomized method and a mechanical pulverization method.

In the present invention, the particle size of the raw material powder is not particularly limited and may be any particle size commonly used in powder metallurgy, but is preferably about 100 to 325 mesh.

As a method for preparing the raw material powder, aluminum-based powder t-
99.5~97 weighed, low melting point aluminum alloy powder t
It is preferable to mix within the range of -0.5 to 3% by weight.

If the amount of low melting point aluminum powder increases, the aluminum powder may melt during sintering.

If the amount decreases, the bond between the aluminum powders becomes insufficient.

The entire mixed powder is placed in a mold having a cavity of the desired shape and compacted. The pressure during compaction may be at least as high as a pressure that does not break the obtained compact, and the appearance of the obtained sintered body is adjusted as appropriate with reference to the total density. Usually 3 tons/
A value around c- is appropriate.

When compacting the powder, a lubricant such as stearin and zinc, which is commonly used when forming the compact, may be used in combination. The sintering atmosphere is preferably an inert gas or a reducing gas. The sintering temperature is above the temperature point of the brazing material and below the temperature point of the aluminum powder.

When sintering the aluminum-based powder of the present invention, other metal powders or powders such as graphite that are normally added during sintering may be used. You can also do this in addition. Further, in order to further impart a low melting point At alloy or lubricating properties to the obtained sintered body, other metals such as copper and lead can be infiltrated.

[Effect]

In the present invention, the chemical conversion treatment layer Fi formed on the surface of the aluminum powder and the A40s' formed on the aluminum surface
During sintering, the elements in the powder that are in contact with each other can easily diffuse into one another, resulting in a good sintered alloy. In particular, the fusion and diffusion of the low melting point At alloy powder becomes easy.The chemical conversion treatment layer of the present invention is free from moisture in the air,
Since it does not cause corrosion even if it comes into contact with water, there is no problem even if the chemical conversion layer remains in the sintered body.
This has an advantageous effect on the subsequent infiltration of aluminum alloys, etc. In addition, by appropriately forming the chemical conversion treatment layer, the powder compactability of the powder can be improved. ! iIN can also be adjusted.

〔Example〕

The present invention will be explained below with reference to Examples.

Example 1 At-12% 3i alloy powder (100 mesh 5) t- as a brazing material was immersed in a liquid containing H, F- ions to form a chemical conversion film on the entire surface of the powder. 30 g of this powder was mixed with aluminum powder (100 mesh) IKF to obtain a mixed powder. This was compacted into pellets with a diameter of 6 gourds and a height of 6 mm, and the compact density was 2.4 g/ex').
A sintered body was obtained by heating at 570° C. for 1 hour in a nitrogen gas atmosphere (wF final density: 26 g/eat').

The frictional properties of the sintered body thus obtained.

It was measured using a bottle-disk type friction test.

For measurement, attach the sintered body to the upper bottle side, and 5U to the disk.
S430? It was done using Friction test.

The test was carried out while dripping onto mineral oil, and the total seizure load had a friction coefficient μ of more than 1. Further, for comparison, similar measurements were performed on a cast (melted) At-12-Si alloy. Table 1 shows their mounting loads. As can be seen from the results in Table 1, by forming a sintered body, the furnace resistance is improved by about 50%.

Example 2 The chemically treated AL-Si alloy powder described in Example 1 was mixed with commercially available graphite powder for phosphorization at a weight ratio of 19:1. 8 g of said powder and aluminum powder IKe
and gold to obtain a mixed powder. This mixed powder was used in Example 1.
In the same manner as above, the powder was compacted into pellets with a diameter of 6 m, and the density of the compact was 2.4 g/6N.
It was sintered by heating at 0 tll: for 2 hours (sintered body density 2
．． 6 g 10n').

The resulting sintered body was tested using a bottle-disc friction tester.
A male friction test was conducted in the same manner as in Example 1, and the friction coefficient μ
and specific wear amount Ws f were measured. Note that in this example, oil was not used because the characteristics in dry friction were measured.

Load 1. I marked it as OKf. The results are shown in Table 2 above.

For comparison, Table 2 also shows the results of the At-12%81 alloy obtained by casting.

As can be seen from the results in Table 2 above, the sintered body produced according to this example is Graphai)? Because it contains graphite, the coefficient of friction is lower than that of a cast product that does not contain graphite, indicating that it has good lubricity.

〔Effect of the invention〕

The present invention forms a chemical conversion layer on the surface of aluminum or aluminum alloy powder, consisting of Ks ALF*, which has a low melting point and has a similar effect to the flux during brazing. A40. Good sintering can be achieved without any interference caused by especially,
According to the method of the present invention, sintering can be performed without adding copper or steel alloy powder, so the sintered alloy obtained by the present invention does not deteriorate oil or corrode other metal members. Therefore, it can be used as a base member in places where oil lubrication is required. Furthermore, according to the method of the present invention, it is possible to sinter aluminum alloy powder containing Si gold, which has good wear resistance. It has various excellent effects such as the ability to obtain sintered parts.

Claims (1)

[Claims] (1) Forming a chemical conversion layer made of potassium pentafluoroaluminate on at least one surface of aluminum or aluminum alloy powder that is the base of the sintered body or low melting point aluminum alloy powder that is the brazing material; A method for sintering aluminum-based powder, comprising the steps of mixing a powder for a base material and a powder for a brazing filler metal, compacting the powder, and sintering the powder.