JPH0478698B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for obtaining an Al-based powder alloy from aluminum (Al)-based powder. <Conventional technology> So-called sintering of Al alloy from powder containing Al-based powder
The method of producing Al alloys has been studied for a long time, but the surface of Al powder is hard alumina (oxidized coating).
Therefore, sufficient strength could not be obtained by the conventional method of simply molding the powder and then sintering it at a temperature below the melting point. Therefore, a method has been devised in which powder is solidified by extrusion. However, gases (adsorbed gases) such as H ₂ O, O ₂ and N ₂ are adsorbed on the surface of Al powder, and gases such as H 2 O, O 2 and N 2 are adsorbed in the material during extrusion or during the heat treatment of the solidified Al alloy. or when Al alloy is used at high temperatures, the adsorbed gas, especially H _{2 O, expands at high temperatures as H 2 O} gas or H ₂ gas (3H ₂ O + 2Al→Al ₂ O ₃ + 3H ₂ ), and generally forms blisters. This results in the generation of material defects called (bubbles). Therefore, when extruding powder, H ₂ O
Conventionally, H ₂ O was degassed by heating in a vacuum. or,
It was thought that sufficient H ₂ O degassing could not be achieved without heating in a vacuum (for example, in Advances in
Powder Technology P.194). The conventional degassing method involves degassing in a heated vacuum. The molded powder or powder is put into a hot press as it is, and the powder is degassed and pressure-molded under a high-temperature vacuum.
Either make it into a billet for extrusion, or directly put the powder compact or powder into a can, heat the can, evacuate it to degas it, and then vacuum seal it after finishing to make it into a billet for extrusion. there was. <Problems to be solved by the invention> As described above, Al
The method of obtaining powder alloys does not pose much of a problem for research purposes, but when it comes to production, there are manufacturing and economic problems such as the process being too complicated and the cost being too high. The present invention was made in view of the above-mentioned conventional situation, and an object of the present invention is to make it possible to easily and economically obtain a blister-free Al-based powder alloy. <Means and effects for solving the problems> The structure of the present invention for achieving the above object is such that the aluminum powder has an apparent density of 65 to 65 as a true density ratio.
94%, and the powder compact is 300%
Heating in the atmosphere at a temperature of ℃ to 550℃,
It is characterized by degassing and plastic working. Each requirement of the above configuration is determined from the following considerations. (1) Density of powder compact Al-based powder adsorbs adsorbed gas, especially H ₂ O, on its surface. If this H ₂ O gas is not sufficiently separated from the powder particles, material defects such as blisters will occur after solidification. Therefore, in order to prevent material defects such as blisters, it is necessary to degas the powder compact.
For this purpose, it is necessary to adjust the apparent density of the powder compact to a true density ratio in the range of 65% to 94%. When the density is lower than 65%, the strength of the powder compact is low and cracks occur during handling such as transportation, resulting in poor yield and difficulty in handling. density is
In the case of 95% or more, the voids in the powder compact are closed from the outside, and if heating is continued during extrusion, the H ₂ O gas in the closed space expands and destroys the powder compact. The limit at which such a closed space occurs is a density of 95% or more, so the density of the powder compact must be 94% or less. More preferably, the density is preferably 70% to 90% to prevent cracking of the molded product or insufficient degassing. (2) Degassing conditions for powder compacts Conventionally, degassing of gases adsorbed in powder has been done from a thermodynamic point of view by predicting the degassing process by finding the equilibrium gas pressure that is balanced with the degree of vacuum and temperature. was common (LEYBOLDHERAEUS
GMBH，Vacuum Degassing of Metal
Powders, by P. Flecher and R. Ruthardt). Furthermore, since oxidation generally progresses in the atmosphere, degassing in the atmosphere has not been considered in the past. However, the actual degassing process is a time-related kinetic process, and it also contains water, which cannot be predicted thermodynamically like adsorbed gas, and Al powder has a strong oxide film. is difficult to reduce. However, the increase in the oxide film formed by actually performing heating in the atmosphere is slight. From the above points, it is thought that dehydration (gas) is possible in the atmosphere. At the temperature T (K) of various powders, the equilibrium partial pressure (mbar) required to reach a water vapor content of 1 ppm, which is considered to be sufficient degassing, is P=2981√T ₃ /exp(9562/T) (1 ) is given by On the other hand, the saturated water vapor pressure in the atmosphere is as shown in FIG. In other words, from this figure, during the rainy season, the hottest and humid season in Japan, if the temperature is 30°C and the relative humidity is 100%, the saturated water vapor pressure is 42 mbar.Even in this case, according to equation (1), if it is 408°C or higher, the water vapor in the powder is It can be seen that the amount can be reduced to 1 ppm or less. Also, at a temperature of 5℃ in winter, the relative humidity is 30℃.
%, the water vapor pressure in the atmosphere is about 3 mbar, and from equation (1), if heated above about 320°C, the amount of water vapor in the powder can be reduced to 1 ppm.
It can be seen that the following can be done. Therefore, the degassing temperature needs to be 300°C or higher. At temperatures above 550°C, moisture or other gases adsorbed on the powder are almost completely separated from the powder particles, so there is no need to increase the temperature above this temperature. (3) Heating atmosphere Conventionally, it was thought that heating Al powder in the atmosphere would cause an oxide film to grow, so heating in the atmosphere was not possible, but when we actually measured the amount of oxygen, we found that
The oxygen content of Al powder before heating in the atmosphere is 0.15-0.25wt%
Although it was only about 0.17~0.25wt after heating
It was found that there is almost no difference between % and Therefore, even if heating and degassing are performed in the atmosphere, the influence of oxidation will not be a problem. However, since the atmosphere contains water vapor, there is some partial pressure of H ₂ O, but when degassing is performed in an atmosphere of inert gas such as N ₂ , Ar, He, etc., this partial pressure becomes even smaller. This makes degassing easier. (4) Plastic processing method Powder plastic processing is a method for turning powder into an alloy lump with 100% density, and extrusion is generally used most often, but forging, rolling, etc. can also be used. (5) Raw material powder The Al-based powder targeted by the present invention includes all powders containing Al powder, that is, Al powder, Al alloy powder, mixed powder of Al powder and Al alloy powder, or
It is a mixed powder of Al powder, Al alloy powder, or a mixed powder of these and other metal powder or nonmetallic powder. <Example> Al-20wt%Si-5wt%Fe-4wt%Cu-1wt%
Approximately 70% Mg Al alloy powder (-100 mesh)
After molding at densities of 90% and 96%, the resulting powder compacts were heated in the air at temperatures of 300°C, 400°C, and 500°C for 7 hours, and then the extrusion ratio was 10:
Extrusion processing was performed in step 1. The obtained extruded material was heated at 500°C, and the presence or absence of blisters generated at this time was investigated. The results are shown in Table 1.

[Table] As shown in Table 1, when the true density ratio was 96%, the powder compact sometimes cracked during heating before extrusion. Furthermore, when heated at 300°C, none of the densities cracked during heating, but blisters occurred during extrusion or after heating at 500°C for a short time. However, in the case of heating over 400℃, 500℃, 5
No blisters were observed even after heating for hours. <Effects of the Invention> According to the method for producing an Al-based powder alloy according to the present invention, the Al-based powder is degassed in the air at atmospheric pressure or in N ₂ ,
Since it is carried out in an inert gas such as Ar or He, the number of steps is fewer than conventional degassing treatment in vacuum, etc., the equipment is simple, and it can be carried out with high efficiency. Furthermore, the Al-based powder alloy obtained in this way has almost the same quality as that obtained by conventional methods, and there is no increase in oxide film despite heat treatment in air, making it suitable for producing powdered Al alloy. Very suitable.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between temperature and saturated water vapor pressure in the atmosphere.

Claims (1)

[Scope of Claims] 1. Shaped so that the apparent density of aluminum-based powder is 65 to 94% of the true density ratio, and the powder compact is heated in the air at a temperature of 300°C or higher and 550°C or lower to degas it. A method for producing an aluminum-based powder alloy, which comprises performing plastic working. 2 The apparent density of the powder compact is 70 to 90 in terms of true density ratio.
% of the aluminum-based powder alloy according to claim 1. 3 _N2 gas or Ar, He as degassing atmosphere gas
A method for producing an aluminum-based powder alloy according to claim 1 or 2, using an inert gas such as 4 As the aluminum-based powder, use aluminum powder, aluminum alloy powder, mixed powder of aluminum powder and aluminum alloy powder, or mixed powder of aluminum powder or aluminum alloy powder, or mixed powder of these and other metal powder or non-metallic powder. A method for producing an aluminum-based powder alloy according to any one of claims 1 to 3. 5. The method for producing an aluminum-based powder alloy according to any one of claims 1 to 4, using extrusion, forging, and rolling as the plastic working method.