JPH0657864B2 - Heat resistant aluminum alloy with improved fatigue strength - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat-resistant aluminum alloy produced by a rapid solidification method, and particularly to a heat-resistant aluminum alloy that has been successfully improved in fatigue strength. .

[Prior Art] In the automobile industry and the aircraft industry, there is a strong demand for a heat-resistant material that is highly lightweight and can exhibit high strength (fatigue strength) even under high temperature conditions. At present, many studies have been conducted to meet such demands, and one of such research materials is an aluminum alloy, particularly an aluminum alloy produced by applying a rapid solidification method.

The rapidly solidified aluminum alloy is usually sprayed with a molten finely divided aluminum alloy having a high solute concentration onto, for example, a rotating cooling roll, and immediately rapidly solidified (high-speed cooling at 10 ³ ° C / sec or more).
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The rapidly solidified aluminum alloy thus obtained is in the form of powder, ribbon or flakes.
Since the above-mentioned solute elements are rapidly solidified from a supersaturated state, they have good solid solubility and generally have excellent heat resistance, strength, wear resistance and the like. For example, A in which the solute element is Cr
1-Cr alloys have excellent heat resistance (USP4033793-A,
The strength in the 100 to 350 ° C. range is excellent), and the Al-Si alloy having Si as a solute element is excellent in wear resistance (JP-A-59-13040).

[Problems to be Solved by the Invention] The inventors of the present invention have long been focusing on an Al--Cr heat resistant alloy among the rapidly solidified aluminum alloys and have been conducting studies to improve the fatigue strength of the alloy. . Al-C above
Although the r-type heat-resistant alloy substantially satisfies the required level of heat resistance, it is difficult to say that the fatigue strength of the r-type heat-resistant alloy is necessarily satisfied, and it was difficult to use it for parts such as connecting rods to which repeated stress is applied. .

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

The present invention has been made in consideration of such circumstances, and aims to provide a heat-resistant aluminum alloy capable of ensuring not only heat resistance but also excellent fatigue strength. is there.

[Means for Solving Problems] The heat-resistant aluminum alloy according to the present invention means Cr: 5
15% by weight (hereinafter simply referred to as%) and Si: 5 to 15%
And rare earth metal: 0.5 to 5%, Fe: 0.5 to 5
%, Ti: 0.1 to 5%, Zr: 0.1 to 5%, V: 0.1 to 5
%, Mn: 1 to 5%, Ni: 1 to 5%, one or more kinds selected from the group consisting of 5% or less in total, the balance being Al and inevitable impurities. is there.

[Operation] As apparent from the above description, the alloy of the present invention is based on the use of the rapid solidification method, because it is intended to utilize the following advantages of the rapid solidification method.

(A) The solid solubility limit of each alloy element can be expanded.

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

(C) As a result of the above (A) and (B), it can be 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 10 ² ° C / sec or more, preferably 10 ⁴ ° C / sec or more, and the alloy powder is not limited to atomized powder, and can be obtained by crushing a quenched thin piece or a quenched ribbon. Things can also be applied.

The inventors of the present invention have focused on the advantages of such a rapid solidification method in finding a solution to the above-mentioned problems, and have a tendency to obtain Al-C
The research was started by investigating the cause of the low fatigue strength of the r-based heat-resistant alloy. As a result, the present inventors have (1)
By cooling at high speed, Cr, Fe, Zr, V,
Since alloying elements such as REM are finely dispersed in Al in a solid solution state, there is no longer a relatively coarse dispersion layer which is a protective material against the propagation of fatigue cracks. (2) The rapidly solidified aluminum alloy powder Oxides are generally formed on the surface, but when the oxide-deposited aluminum alloy powder is solidified by powder metallurgy, the oxides are arranged along old powder grain boundaries (hereinafter sometimes referred to as PPB). Therefore, it is known that fatigue cracks are generated through the oxide when stress is applied and the propagation of the cracks is likely to occur, which causes the low fatigue strength.

Therefore, the present inventors focused their attention on the knowledge of the above (1) firstly, and conducted various studies from this direction to solve the above problems.
As a result, Si is selected as a basic alloying element that can be expected to improve fatigue strength, and this is blended with the Al-Cr heat resistant alloy described above, and other alloying elements are strictly specified to complete the present invention. Came to.

The types and blending amounts of alloying elements in the present invention will be described below while clarifying the reasons for defining them.

Cr: 5 to 15% Cr is an element that improves the heat resistance by combining with an Al matrix and other alloy elements to form a dispersed phase or a solid solution phase, but when the compounding ratio is less than 5% The volume ratio of the dispersed phase due to rapid solidification becomes small, and it becomes difficult to obtain desired heat resistance. On the other hand, if it exceeds 15%,
No matter how fast the cooling rate is increased, a coarse disperse phase is generated, and therefore the volume ratio of the disperse phase becomes extremely large, resulting in problems such as deterioration of toughness and deterioration of hot workability. .

Si: 5 to 15% Si is a simple substance and is dispersed in the Al matrix to prevent fatigue crack propagation, so that it is effective in improving fatigue strength. However, if the blending ratio is less than 5%, the Si particles in the Al matrix become extremely fine and the desired effect cannot be obtained. On the other hand, if it exceeds 15%, there arises a problem that the Si particles in the Al matrix become coarse and the toughness decreases.

Rare earth element (REM): 0.5-5%, Fe: 0.5-5
%, Ti: 0.1 to 5%, Zr: 0.1 to 5%, V: 0.1 to 5
%, Mn: 1 to 5%, Ni: 1 to 5%, and a total of 5% or less of one or more selected from the group consisting of 5% or less. Although it has the effect of further improving it, 0.5% or more was necessary in the case of REM alone, for example, in order to effectively exhibit such an effect. However, if it exceeds 5%, problems with the material such as coarsening of the dispersed phase and reduction of toughness occur. The basis for setting the upper and lower limits is the same for elements other than REM.

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

Although the present invention is configured as described above, the present inventors also consider the knowledge of the above (2), that is, the knowledge that the oxide causes crack generation after solidification, The study was conducted from the direction of controlling the above oxides. As a result, an oxide of 1% or less was obtained. This point will be described below.

Oxide: 1.5% or less The air atomization method is generally used as a method for making the molten Al alloy powder into a powder form, but the Al alloy powder manufactured by this method has an oxide (mainly 1.5% or more) Al
₂ O ₃ ) is inevitably included.

It has been conventionally considered that these oxides disperse in the Al matrix at the time of solidification of the powder and improve the heat resistance. However, according to a detailed study by the present inventors, when it exceeds 1.5%, the effect of improving the heat resistance is small, and rather, the result that the fatigue strength is lowered as described in (2) above was obtained. . Even more preferably, it is recommended to suppress it to 1.0% or less. Therefore, the inventors of the present application have found that the effect of further improving fatigue strength can be exhibited by adding this requirement to the above items. In producing such an aluminum alloy, it is preferable to use an atmosphere gas for spraying having an oxygen concentration of 10% or less.

[Examples] Various Al alloy melts having the compositions shown in Table 1 below were prepared, and alloy powders were obtained by rapid solidification using a gas atomization method.

As the atomizing gas, nitrogen mixed with 5% oxygen was used for Material Nos. 11 and 12, and air was used for other samples. The cooling rate of the powder thus obtained was 10 ³ ° C / scc or more.

The above powder was cold preformed and then degassed in a can.
A sound solidified material was obtained by directly extruding at 0 ° C.

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

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

Fatigue Test parallel portion length 15 mm, a test piece having a diameter of 8 mm ^phi used to implement Ono Shikikai dry bending fatigue test at room temperature, to create the S-N curve, thereby seeking fatigue strength at 10 ⁷ cycles,
The results also shown in Table 1 were obtained.

Tensile test at room temperature and high temperature Tensile test was conducted at room temperature, 100 ° C, 200 ° C and 300 ° C using a test piece with a parallel part diameter of 6 ^mmφ and gauge length of 30 mm. Got
Regarding the toughness value, the ratio of the tensile strength (σNTS) of the notched test piece to the 0.2% proof stress (σ0.2) at room temperature (σNTS / σ0.
It was evaluated from 2).

Regarding the effect of Si, No. 1, 2, 3, 4, 5, 6
(Inventive material) and No. 13, 14, 15, 16, 17, 1
It is clear from the comparison with 8. That is, the fatigue strength can be significantly improved by adding Si without impairing the heat resistance. However, as is clear from the comparison between Nos. 7 and 8 and Nos. 19 and 20, addition of Si in excess of the upper limit results in lower toughness, and addition of less than the lower limit leads to improvement in fatigue strength. Little improvement was observed. As shown in Nos. 9 and 10 and Nos. 21 and 22, S
Even when the addition amount of i is appropriate, when the addition amount of Cr exceeds the upper limit value, toughness is deteriorated, and when it is less than the lower limit value, sufficient heat resistance can be imparted. There wasn't.

REM (Y, Ce), Fe, Mo, Zr, V, Mn, N
With regard to i, as is clear from the comparison between No. 1 to 6 and No. 26, there is a remarkable effect in improving heat resistance, but No. 2
As shown in 3 and 24, when an amount exceeding the upper limit was added, coarsening of the dispersed phase was caused and toughness was significantly reduced. Also
As shown in No. 25, when the total amount exceeds 5%, the toughness was decreased.

EFFECTS OF THE INVENTION Since the present invention is configured as described above, it is possible to provide an aluminum alloy having excellent heat resistance and significantly improved fatigue strength.

Claims (1)

[Claims] 1. Cr: 5 to 15% by weight (hereinafter simply referred to as "%") and Si: 5 to 15%, and rare earth metal: 0.1.
5-5%, Fe: 0.5-5%, Ti: 0.1-5%, Zr:
0.1-5%, V: 0.1-5%, Mn: 1-5%, Ni: 1
10 or more selected from the group consisting of 10% in total 5
% Or less, with the balance being Al and inevitable impurities, a heat-resistant aluminum alloy with improved fatigue strength.