JPS62250147A - Heat-resisting aluminum alloy improved in fatigue strength - Google Patents

Abstract

PURPOSE:To obtain an Al alloy excellent in heat resistance and improved in fatigue strength, by limiting the composition of an Fe-Al alloy consisting of Fe, Si, rare earth metal, Cr, Mo, Zr, V, and Al. CONSTITUTION:The heat-resisting Al alloy improved in fatigue strength has a composition consisting of, by weight, 5-15% Fe, 10-20% Si, <=5%, in total, of one or more kinds among 1-5% rare earth metal, 1-5% Cr, 0.1-5% Mo, 0.1-5% Zr, and 0.1-5% V, and the balance Al with inevitable impurities. The above Al alloy can be obtained by subjecting the molten Al alloy with the above limited composition to solidification by rapid cooling at a cooling rate of >=about 10<2> deg.C/sec, preferably >=about 10<4> deg.C/sec, to form into an atomized powder, etc. Moreover, it is desirable to improve fatigue strength to a greater extent by using, in the above process of solidification by rapid cooling, an atmospheric gas of <=10% O2 content as the one for atomization so as to form the above Al alloy into the one containing oxides by <=about 1.5%, preferably <=about 1.0%.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a heat-resistant aluminum alloy manufactured by a rapid solidification method, and in particular to a heat-resistant aluminum alloy that has been successfully improved in fatigue strength. .

[Prior Art] In the automobile and aircraft industries, there is a strong demand for heat-resistant materials that are lightweight and can exhibit high strength (fatigue strength) even under high-temperature conditions.

Currently, a lot of research is being carried out to meet these demands, and one such research material is aluminum alloys, particularly aluminum alloys manufactured by applying the rapid solidification method.

The rapidly solidified aluminum alloy is usually produced by spraying a molten pulverized aluminum alloy with a high solute concentration onto, for example, a rotating cooling roll and immediately rapidly solidifying it (high-speed cooling at 103° C./sec or more).

The rapidly solidified aluminum alloy thus obtained is in the form of a powder, a ribbon, or a flake.
Since the solute element is rapidly solidified from a supersaturated state, it has good solid solubility and generally has excellent heat resistance, strength, abrasion resistance, etc.

For example, the Al-Fe alloy in which the solute element is Fe has excellent heat resistance (US P437919-A, 1
(Excellent strength in the 00 to 350° C. range), and Al-3i alloys whose solute element is Si have excellent wear resistance (Japanese Patent Application Laid-open No. 13040/1983).

[Problems to be Solved by the Invention] The present inventors have been focusing on Al-Fe heat-resistant alloys among the above-mentioned rapidly solidified aluminum alloys, and have been conducting studies to improve the fatigue strength of these alloys. Ta. The above Al-
Although Fe-based heat-resistant alloys meet the required level of heat resistance in roadways and grooves, they cannot necessarily be said to satisfy fatigue strength, making it difficult to use them in parts such as connecting rods that are subject to repeated stress. there were.

Therefore, improving the fatigue strength is extremely significant in ensuring the material reliability of the Al-Fe-based heat-resistant alloy, and this point will be highlighted as a problem to be solved in the future.

The present invention has been made in consideration of these circumstances, and aims to provide a heat-resistant aluminum alloy that not only guarantees heat resistance but also has excellent fatigue strength. be.

[Means for solving the problem] The heat-resistant aluminum alloy according to the present invention has Fe: 5 to
15ffEffi% (hereinafter simply referred to as %) and Si:1
Contains 0-20%, and rare earth metal scrap: 1-5%, cr:
t~s%, Mo: 0.1~5%.

Zr: 0.1 to 5%, V:O, 1 to 5%, and the gist is that it contains 5% or less in total, and the remainder consists of AI and unavoidable impurities. It is something to do.

[Function] As is clear from the above description, the alloy of the present invention is based on the use of the rapid +a solidification method, and this is because it attempts to utilize the following advantages of the rapid solidification method. .

(^) The solid solubility limit of each alloying element can be expanded.

(It) Metal particles and various intermetallic compounds can be finely and uniformly dispersed.

(C) As a result of the above compensation) and (8), it is expected that various properties such as strength, heat resistance, hot workability, and machinability can be improved.

Here, the cooling rate of the rapid solidification method is 102° C./sec or more, preferably 104° C./sec or more, and the alloy powder is not limited to atomized powder, but also those obtained by crushing rapidly cooled flakes or ribbons. Can be applied.

In finding a solution to the above-mentioned problem, the present inventors focused on the advantages of such a rapid solidification method, and the above-mentioned Al
We started our research by investigating the cause of the low fatigue strength of -Fe-based heat-resistant alloys. As a result, the inventors
(1) By cooling at high speed, Fe, Cr, Zr
, V, REM, and other alloying elements are finely dispersed in solid solution in AI, so there is no longer a relatively coarse dispersed layer that acts as a hindrance to fatigue crack propagation; (2) rapid solidification; Generally, oxides are formed on the surface of aluminum alloy powder, but when the oxide-adhered aluminum alloy powder is solidified by powder metallurgy, old powder grain boundaries (hereinafter referred to as PP)
Because the above oxides are arranged along the oxides (sometimes referred to as B), fatigue cracks occur through the oxides when stress is applied, and propagation of the cracks is likely to occur, which is the cause of the low fatigue strength. I learned.

Therefore, the present inventors focused on the above finding (1) in No. 341, and conducted various studies from this direction in order to solve the above problem. As a result, Si was selected as a basic alloying element that can be expected to improve fatigue strength, and in addition to blending it into the above Al-Fe heat-resistant alloy, other alloying elements were also strictly specified to complete the present invention. reached.

Hereinafter, the types and amounts of alloying elements in the present invention will be explained while clarifying the reasons for specifying them.

■Fe: 5-15% Fe is an element that improves heat resistance by combining with the AI matrix and other alloying elements to form a dispersed phase or solid solution phase, but if the blending ratio is less than 5% The volume ratio of the dispersed phase due to rapid solidification becomes small, making it difficult to obtain the desired heat resistance. On the other hand, if it exceeds 15%,
No matter how fast the cooling rate is, a coarse dispersed phase is generated, and the volume ratio of the dispersed phase becomes extremely large, resulting in material problems such as decreased toughness and hot workability. .

■Si: 10 to 20% Si is dispersed in the AI matrix alone and has the effect of preventing fatigue crack propagation, so it is effective in improving fatigue strength. However, if the blending ratio is less than 10%, the Si particles in the AI matrix become extremely fine and the desired effect cannot be obtained. On the other hand, if it exceeds 20%, problems arise in that the Si particles in the AI matrix become coarse and the toughness decreases.

■Rare earth elements (REM) = 1-5%, Cr: 1-5%,
Mo2 0.1-5%, Zr: 0.1-5%, V: 0.1
5% in total of one or more species selected from the group consisting of ~5%
All of these elements have the effect of further improving the heat resistance of aluminum alloys through interaction with Fe, but in order to effectively demonstrate this effect, it is necessary to use REM alone. In some cases, 1% or more was required.

However, if it exceeds 5%, material problems will occur, such as coarsening of the dispersed phase and reduction in toughness. These upper limits
The basis for setting the lower limit is the same for elements other than REV.

By the way, when the total amount of the above elements exceeds 5%, adverse effects such as the above-mentioned coarsening of the dispersed phase occur.

Although the present invention is roughly configured as described above, the inventors of the present invention also considered the knowledge in (2) above, that is, the knowledge that oxides cause cracks to occur after solidification. We conducted a study from the perspective of regulating the above oxides. As a result, the result was that the oxide content was 1% or less, and this point will be explained below.

■ Oxide = 1.5% or less The air injection method is a common method for turning molten Al alloy into powder, but the Al alloy powder produced using this method has a surface of 1.5% oxides (mainly Al
203) are inevitably included.

It has been conventionally believed that these oxides are dispersed in the AI matrix during powder solidification and thereby improve heat resistance. However, according to detailed research conducted by the present inventors, when the amount exceeds 1.5%, the effect of improving heat resistance is small, and in fact, as mentioned in (2) above, fatigue strength is significantly reduced. Obtained.

Even more preferably, it is recommended to suppress it to 140% or less.

Therefore, the inventors of the present application have found that by adding this requirement (1) to the above (1) to (4), a further effect of improving fatigue strength can be achieved. In manufacturing such aluminum alloys, the oxygen concentration in the sprayed atmospheric gas is 1.
It is preferable to use one with a content of 0% or less.

[Example] Molten Al alloys having various compositions were prepared according to Table 1 below, and alloy powders were obtained by rapid solidification using a gas atomization method.

As the frost gas, nitrogen mixed with 5% oxygen was used for samples No. 9 and 10, and air was used for the other samples. The cooling rate of the powder thus obtained was 103° C./scc or more.

After preforming the above powder in a cold state, it was degassed in a can.
A sound solidified material was obtained by direct extrusion at 0°C.

Next, the amount of oxides in each solidified material was measured by activation analysis, and the correlation between the amount of oxides and various material properties was investigated, and the results are also listed in Table 1.

The fatigue strength test and heat resistance test are as follows.

Fatigue Test Using a test piece with a parallel length of 15III11 and a diameter of 8IIffI, an Ono dry bending fatigue test was carried out at room temperature, an S-N The results shown in Table 1 were obtained.

Tensile test at room temperature and high temperature. Diameter of parallel part 6 m + gage distance l! A 1130 mm test piece was used at room temperature, 100°C, and 200°C.

A tensile test was conducted at various temperatures of 300° C., and the results shown in Table 1 were obtained. Regarding toughness values, the tensile strength of the notched test piece at room temperature (cjNTs) and the 0.2% proof stress (
Evaluation was made from the ratio (oNTs/QQ,2) of ao,2).

Regarding the effect of Si, No. 1. 2.3.4 (
This is clear from the results of No. 12.13 and 14.15 (comparative materials). That is, the addition of Si significantly improves the fatigue strength. Furthermore, comparing Nos. 5 and 6 with Nos. 16 and 17, when the Si addition exceeds the upper limit, the toughness value decreases extremely, and when there is no groove in the lower limit, there is no effect on fatigue strength improvement. It is clear that this will be insufficient. Also, No. 017 and 8 and No.
As shown in 18 and 19, even if Sii is appropriate, if the Fe content exceeds the upper limit, the toughness value decreases, and if it does not meet the lower limit, the toughness value will decrease. I have not been able to grant it.

REM (Ce, La), Mo, Cr,
The effect of adding Zr and V is No, 22 and N001-4.
As is clear from the comparison, the toughness is extremely reduced when the upper limit is exceeded (comparative material 19.20).

[Effects of the Invention] Since the present invention is configured as described above, it was possible to provide an aluminum alloy having excellent heat resistance and significantly improved fatigue strength.

Claims (1)

[Claims] Fe: 5 to 15% by weight (hereinafter simply referred to as %) and Si:
Contains 10-20%, and rare earth metal: 1-5%, Cr
:1~5%, Mo:0.1~5%, Zr:0.1~5%
, V: A heat-resistant aluminum alloy with improved fatigue strength, characterized in that it contains 5% or less in total of one or more selected from the group consisting of 0.1 to 5%, and the remainder consists of Al and unavoidable impurities. .