JPS60224705A - Manufacture of aluminum powder - Google Patents

Abstract

PURPOSE:To manufacture chemically stable Al powder by atomizing molten Al in an atmosphere of an inert gas mixed with oxygen. CONSTITUTION:Molten Al is atomized at <=-15 deg.C in an atmosphere formed by mixing an inert gas such as gaseous Ar with 0.5-30vol%, especially 1-10vol% oxygen to manufacture Al powder. Since the surface of the Al powder is uniformly coated with a dense oxide film, the powder occludes hardly moisture or various kinds of gases.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing aluminum powder used in powder metallurgy, and in particular to a method for producing aluminum atomized powder.

Throughout this specification, the term "inert gas" refers to Ar.

In addition to so-called inert gases such as Hθ, it also includes an inert gas against aluminum, typified by N2 gas. The term "aluminum" refers to pure aluminum, commercially available aluminum containing small amounts of impurities, and various aluminum alloys.

BACKGROUND ART Sprayed powder is generally used as aluminum powder for powder metallurgy, and conventionally, the method for obtaining this atomized powder is to mix molten aluminum with a spraying medium such as water, air, or inert gas. It is atomized.

However, if atomization is carried out in water or air, during powder production, and if atomization is carried out in inert gas, during storage, handling, and compression molding in the atmosphere after powder production. In both cases, a hydrated oxide film is formed on the surface of the aluminum spray powder, and this film causes defects in the final product as described below.

Therefore, recently, in order to prevent the occurrence of such defects and to improve the mechanical properties of the product by making the resulting spray powder more uniform and finely structured, the so-called spray roll method or rotating circle method has been developed. Ultra-quenching methods for sprayed droplets, such as the plate method, are also being considered.

However, in any of these methods, since aluminum is extremely chemically active, the formation of a hydrated oxide film on the surface of the aluminum spray powder is completely prevented in an environment containing moisture such as water or humidity. It cannot be avoided. That is, in the atomization process, the time required for the spray droplets to solidify and cool down to room temperature is 10
Although it is extremely short at 4 to 1050C/8eC, aluminum oxidizes immediately even in such a short period of time, and the hydration reaction also progresses at the same time, so a hydrated oxide film is formed on the surface of the sprayed powder. is generated.

This hydrated oxide film grows particularly rapidly in the high-temperature environment of powder metallurgy processes, and is generally known as boehmite (pseudo-boehmite).
Alternatively, it takes the form of vialite, etc., but it is extremely coarse and porous, the pores are complicated, and it is also thick.

For this reason, during storage, handling, or compression molding of aluminum spray powder, a hydrated oxide film with countless pores is formed on the surface of the spray powder, which grows over time, resulting in compression molding. This results in the storage of large amounts of harmful moisture and various gases.

In such a molded article, a phenomenon called "bulge" in which a part of the surface swells up is observed.

This blistering causes quality defects such as surface peeling in aluminum final products obtained through the subsequent sintering process and various heat treatment processes.

The storage, handling and compression molding of aluminum atomized powder produced under an atmosphere of inert gas are carried out in containers filled with inert gas. However, performing various treatments using inert gas in each step of powder metallurgy is extremely complicated, which not only lengthens the time it takes to obtain the desired product but also causes an increase in costs.

OBJECT OF THE INVENTION The purpose of the invention is to prevent oxidation and hydration reactions of aluminum powder during the production of aluminum spray powder.
A chemistry that can maintain the quality when stored or compression molded in the atmosphere without having to take the highly inefficient means of using inert gas during storage and compression molding. An object of the present invention is to provide a method for producing a physically stable aluminum powder.

Structure of the Invention The method for producing aluminum atomized powder according to the present invention is to atomize molten aluminum in an atmosphere containing an inert gas mixed with oxygen.

In this invention, commercially available industrial liquid oxygen with a purity of 99.5% or higher is usually used as the oxygen to be mixed with the inert gas, but if the oxygen is of a purity equivalent to or higher than this, the production method can be used. , it goes without saying that the purpose does not matter.

The mixed gas in this invention is oxygen 05 to 30 voF'
%, and the balance is preferably adjusted to be composed of inert gas. If the oxygen concentration exceeds 30 vOp%, there is a danger that the obtained aluminum powder will explode;
5vo7? This is because if it is less than %, it is difficult to form the desired chemically stable oxide film on the surface of the aluminum powder. A particularly preferable oxygen concentration range is 1 to 10 vol.
%.

The dew point when atomizing using this mixed gas is optimally adjusted depending on the gas mixture ratio, the gas injection speed, the alloy composition of the sample, the use of the final product, etc. Regarding this point, according to the results of experiments conducted by the present inventors by variously changing the alloy composition and the mixed gas composition, it was found that the generation and growth of the above-mentioned harmful hydrated oxide film can be prevented and defects can be prevented in the final product. In order to suppress this, it was found that it is particularly preferable to adjust the temperature to -15°C or lower.

Example Examples of this invention will be described below.

The samples include ZnlQwL%, Mg4wL%,
Fe.

After placing it in a crucible, high frequency melting is performed at 900°C to obtain a molten metal. Then, at the same time, this molten aluminum was allowed to flow down from the molten metal nozzle installed at the bottom of the melting crucible.
A mixed gas having the following composition, the gas pressure of which was adjusted to 8-8, is ejected through the spray nozzle of an atomizer arranged annularly around the tip of the molten metal nozzle. Through this series of operations, the molten aluminum turns into extremely fine mist droplets and scatters radially downward.

The mixed gas used here is 7 voj'% oxygen and the balance A.
After adjusting the dew point to -35°C, the atomizer was introduced through a conduit to the atomizer.

The above-mentioned high-frequency melting furnace, melting crucible with a molten metal nozzle, and atomizer with a spray nozzle are equipped with an external It is placed inside a cylindrical sealed container with a conical part connected to the cyclone device.

The aluminum atomized powder produced by atomizing the molten duck is instantaneously cooled to room temperature while descending at high speed in the cylindrical container.

The particle size of the aluminum spray powder obtained in this example is:
It was 350 meters.

Next, this atomized powder is filled into a stainless steel capsule with a diameter of 50 mm and a length of 10 mm, and degassed to 10 torr. After that, 1 at 450℃ and 2000 atm.
A hot isostatic press treatment was applied for 1 minute, and the obtained green compact was directly subjected to a 450° C.4 hot extrusion and then subjected to a hydrostatic treatment at 120° C. for 24 hours.

The round bar obtained through each of the above treatments has a tensile strength of 75 K.
g7m7/, cuff resistance 3K9/myf, and elongation 3%, and showed extremely poor mechanical properties compared to a similar treatment using conventional aluminum spray powder. The reason for this is that instead of the porous hydrated oxide film that was formed on the surface of conventional aluminum spray powder, a dense and thin oxide film was formed uniformly on the surface of the spray powder obtained by the method of this invention. This is because the generation of fine pores, which are considered to be caused by the presence of moisture or various gases, was suppressed on the surface and inside of the aged round bar.

This can be explained using a microscopic photograph of a cross section of an aluminum final product obtained through each process of powder metallurgy.
When aluminum spray powder obtained by the conventional method is used, as shown in Figure 2, fine pores are formed due to the influence of moisture or various gases adsorbed and contained in the porous layer of the hydrated oxide film. In contrast, when the sprayed powder of this example was used, it was clearly observed that there were no such voids and the cross section was sound.

Effects of the Invention Compared with the aluminum spray powder obtained by the conventional method, the aluminum spray powder obtained by the method of the present invention is superior in the following points.

(1) Conventionally, in order to prevent blistering of the final product, which is thought to be caused by the presence of a porous hydrated oxide film, a long degassing process was required after filling the capsule when compression molding the sprayed powder.

In some cases, dehydration treatment was also required to eliminate the effects of water occlusion.

On the other hand, the aluminum spray powder obtained by this invention has a surface uniformly covered with a dense oxide film, so it hardly absorbs moisture or various gases.
The degassing process after filling the capsule is completed within a very short time, and in most cases, the dehydration process is
Not necessary.

(2) Regarding the change in aluminum spray powder, the product obtained by this invention is chemically stable compared to conventional powder, so it can be stored in the atmosphere without special consideration. 01 can be handled.

(3) When using the aluminum powder obtained by the method of the present invention, it is possible to perform compression molding, sintering, or subsequent heat treatment without considering the influence of atmospheric moisture.
You can get high quality purpose products without any blisters.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 respectively show a compression molded and sintered iron using the aluminum spray powder and the aluminum spray powder obtained according to the embodiment of the present invention. that's all

Claims (1)

[Claims] A method for producing aluminum powder, which comprises atomizing molten aluminum in an atmosphere in which oxygen is mixed with an inert gas.