JPH0210842B2 - - Google Patents

Description

[Detailed description of the invention]

<Object of the invention> Industrial application field The present invention relates to a porous Al-based sintered sound absorbing material that has excellent corrosion resistance, and more specifically, a porous Al-based sintered sound absorbing material that contains Cu and has excellent mechanical properties as well as excellent corrosion resistance. Pertains to sintered sound absorbing materials. Conventional technology Among porous materials, Al-based sintered materials have (1) a lower specific gravity than Cu- or Fe-based sintered materials; (2) Since it has good malleability, it is relatively easy to bend. (3) Since the sintering temperature is low, the sintering equipment can be downsized, and therefore it can be manufactured at a relatively low cost. It has the following advantages. However, in the early days, Tokuko No. 43-20884,
As shown in the publications No. 45-24206, No. 45-24007, and No. 47-32163, development is progressing mainly for the purpose of oil-impregnated bearings for mechanical parts. For this reason, as an Al-based porous sintered material, only strength is required, and as a sintered component, Cu has good sinterability and is easy to obtain strength.
Many use Al alloy powder containing . Also,
As for manufacturing technology, since the oxide film such as Al ₂ O ₃ that exists on the surface of Al-based powder inhibits sintering, this oxide film is removed by pressure destruction.
The common method is sintering, and with this method, the porosity of the resulting sintered material remains at about 10 to 20%. After that, Japanese Patent Application Publication No. 53-90113 and Japanese Patent Publication No. 56
As described in Publication No. 11373, a method has been developed in which Al-based powder is partially sintered in a liquid phase under no pressure and in a non-oxidizing atmosphere to obtain a porous sintered material with a porosity of 40 to 50%. It has come to be widely applied to sound-absorbing materials, etc. However, this porous sintered material tends to have low mechanical strength because almost no pressure is applied before sintering.
Al-Cu powder to which Cu is added is often used as a raw material. However, although this Cu-containing porous Al-based sintered material improves its mechanical strength by containing a large amount of Cu, intermetallic compounds of Al and Cu may precipitate at grain boundaries. Therefore, when used in applications that require corrosion resistance, corrosion may progress along the intermetallic compound, which limits its use. Problems to be Solved by the Invention The present invention aims to solve these problems, and specifically provides a porous Al-based sintered sound absorbing material that is highly corrosion resistant despite containing a large amount of Cu. The purpose is to <Structure of the Invention> Means for Solving the Problems and Their Effects That is, the present invention provides a sintered mixed powder containing Al as a main component and Cu as an additive component in an amount exceeding the solid solubility limit at room temperature. It is an Al-based sintered material,
It is characterized in that communicating pores are formed between adjacent powder particles so that the porosity is 30-60%, and Cu in an amount exceeding this solid solution limit is treated as a solid solution with Al. The present invention will be explained below with reference to the drawings. In addition, FIG. 1 is an explanatory diagram of an example of the manufacturing process for manufacturing the porous Al-based sintered sound absorbing material according to the present invention, and FIG. 2 is an Al-Cu-based phase diagram. First, as shown in FIG. 1, a raw material powder 1 containing Al as a main component is uniformly scattered to a predetermined thickness from a hopper 2 into a container 3 (for example, a graphite container) that does not react with Al. This powder 1 is either one in which Cu powder is added to Al powder for mechanical improvement, or a mixed powder of Al--Cu alloy powder containing Cu and Al powder. The thickness of the spray at this time is adjusted by the depth of the container. Containers 3 naturally filled with raw material powder are stacked and sintered in a sintering furnace 4 maintained in a non-oxidizing atmosphere such as NH ₃ decomposition gas or N ₂ gas, and then cooled in a cooling zone 6. , container 3
By removing the aluminum sintered material, an Al-based porous sintered material 7 is obtained. During this sintering, the oxide film of each Al powder particle is destroyed due to the difference in thermal expansion coefficient between the inside and the oxide film, and the internal Al content is exposed through this destroyed portion, and sintering progresses. Because of this, exposed
Since the Al content and the liquid phase portion generated by partial melting are easily oxidized, it is preferable to control the partial pressure of oxygen to a low level in the sintering atmosphere and sinter in an atmosphere with a dew point of −30° C. or lower. In addition, by using fine-grained Al-based powder and controlling the amount of liquid phase due to partial melting, it is possible to easily obtain a sintered material with a porosity of 60% or more, but this sintered material has poor strength. It is weak, and sintering tends to be incomplete, which is not preferable. Furthermore, if the porosity is less than 30%, the number of independent pores increases locally and the existence of communicating pores disappears, resulting in metallic sintering, making it unsuitable as a sound absorbing material.The porosity is preferably 30 to 60%. However, although the Al-Cu porous sintered material obtained in this way has excellent mechanical strength and sound absorption properties, it has poor corrosion resistance, and its use in applications and places where corrosion resistance is required is restricted. Ru. In particular, Cu
In order to achieve a certain degree of mechanical strength by adding Cu, it is necessary to add Cu at a level above the solid solubility limit with Al at room temperature, and CuAl ₂ will precipitate by adding Cu above the solid solubility limit. However, corrosion resistance is significantly reduced. From this point of view, although Cu is blended above the solid solution limit, it is treated as an Al-Cu solid solution without being precipitated as an intermetallic compound such as CuAl ₂ and improves corrosion resistance. In general, alloys consisting of two or more different phases are more susceptible to corrosion than single-phase alloys due to electrochemical action between the different phases. In particular, porous metal materials have a much larger surface area than normal metal materials, so the effects of corrosion are very large, and improving corrosion resistance is particularly important for sound absorbing materials. In addition, the electrode potential is an important factor when aiming for corrosion resistance, and among these, Cu
The electrode potential differs widely between a solid solution with Al and an intermetallic compound.
We focused on the potential approaching the electrode potential of Al. To explain in more detail, Table 1 shows the details of various metals.
It shows the electrode potential of a solid solution with Al and an intermetallic compound,

[Table] As shown in Table 1, the electrode potential of the Al-Cu solid solution is -0.69V, and it is an intermetallic compound.
Compared to the CuAl ₂ electrode potential of -0.53V, it is close to -0.85V for pure Al. Therefore, even if the amount of Cu added exceeds the solid solubility limit at room temperature, _CuAl2 , which has a large difference from pure Al, will not precipitate, and Al will show an electrode potential close to that of pure Al.
- When fixed as a Cu-based solid solution, corrosion resistance can be significantly reduced. Note that this fixation can also be achieved by solution treatment, and the conditions are as follows:
In relation to the amount added, as shown in FIG. 2, it can be obtained by raising the temperature to the α phase of the Cu phase diagram (for example, 500° C.) and then rapidly cooling it. Example First, Al powder and Al-Cu powder were mixed, and this mixed raw material was sintered into a plate shape without pressure to obtain a porous sintered plate with a porosity of approximately 40% by volume. This sintered plate contains 3% Cu and the remainder is Al,
After holding this at a temperature of 580℃ for 1 hour, the water temperature is 18℃.
It is rapidly cooled in water at ℃ to convert the Cu contained in it to Al.
-Fixed as a Cu-based solid solution. That is, when we measured the microscopic structure and tensile strength before and after this treatment, we found that the CuAl ₂ phase completely disappeared at the grain boundaries of the structure after treatment, and the tensile strength was 195 kg/cm ² on average before treatment. However, after treatment, that is, by fixing Cu as an Al-Cu solid solution, it increased to an average of 285 Kg/cm ² . Next, the sintered plate of the present invention obtained as described above,
Regarding the above sintered plate before treatment for comparison,
A salt spray test specified in JIS Z 2371 was conducted. As a result, in the comparative example, an intermetallic compound of CuAl ₂ was precipitated at the grain boundaries, but white rust appeared on almost the entire surface after 48 hours of testing. On the other hand, even when tested for 144 hours, the product according to the present invention
White rust only appeared on 70% of the surface. <Effects of the invention> As explained above, the present invention has a porosity of 30 to 60%.
Although a relatively large amount of Cu is added to Al-Cu based porous sintered materials, Cu is treated and fixed as an Al-Cu based solid solution, so corrosion resistance, mechanical strength, sound absorption properties and A product with excellent corrosion resistance can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an example of the manufacturing process of the porous Al-based sintered sound absorbing material according to the present invention, and FIG. 2 is an Al-Cu-based phase diagram. Code 1...Raw material powder, 2...Hopper, 3...
Container, 4... Sintering furnace, 5... Sintering zone, 6...
Cooling zone, 7...Porous Al-based sintered material.

Claims (1)

[Claims] 1 An Al-based sintered material in which a mixed powder containing Al as a main component and Cu as an additive component in an amount exceeding the solid solubility limit at room temperature is sintered, and the porosity between adjacent powder particles is 30 to 60. A porous Al-based sintered sound absorbing material having excellent corrosion resistance, in which communicating pores are formed so that the Cu content exceeds the solid solution limit, and Cu is treated as a solid solution with Al.