JP3355673B2 - Heat-resistant aluminum alloy and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength heat-resistant aluminum alloy used at a high temperature, such as an automobile engine part represented by a connecting rod, and a method for producing the same.

[0002]

2. Description of the Related Art The addition of silicon (Si) to aluminum (Al) has a remarkable effect on lowering the coefficient of thermal expansion, improving rigidity, and improving wear resistance. As a Si-based alloy, for example, JP-A-59-1304
No. 1, JP-A-61-29530, JP-A-63-29530
Japanese Patent Application Laid-Open No. 192838 and the like.

[0003] These Al-Si based alloys are at least 1
The main purpose of the alloy is to provide high rigidity and low thermal expansion by containing a large amount of Si of 0% by weight.
In order to further impart heat resistance, a small amount of Fe, Ni, Mn,
It is one to which a transition metal element such as Cu or Mg is added.
In addition, since the raw material powders of these Al-Si alloys contain Si having a eutectic composition or more and a transition metal element such as Fe as a third alloy component, they are manufactured by a rapid solidification powder manufacturing method. Since the raw material powder is difficult to sinter, it is usually solidified by an extrusion process capable of giving a large shear deformation to the powder to obtain a strong powder bond.

Some heat-resistant Al alloys in which Si does not exceed 10% by weight have been proposed. For example, JP-A-2-5
Japanese Patent No. 02836 discloses that the atomic percentage of Fe is 0.5 to 7.5%.
(1.0-14.4% by weight), X (where X = Mn, V, C
r, Mo, etc.) 0.25 to 4.55%, S
i 0.75 to 9% (1.3 to 9.8% by weight) and the balance A
and (Fe + X) / Si in an atomic ratio of 2.01 to 1
A rapidly solidified aluminum-based alloy is disclosed.
The above composition is described as a composition in which a metastable intermetallic compound precipitate generally represented by Al ₁₅ (Fe ₁ X) ₂ Si ₂ is stabilized. This alloy has at least 10
^The raw material alloy powder produced by rapid cooling at ⁵ to 10 ⁷ K / sec is heated to 300 to 500 ° C. in a vacuum and subjected to compression molding.

[0005] Further, Japanese Patent Application Laid-Open No. 1-319644 discloses that 5.5 to 15% of Fe and 0.5 to 2.5% of Si by weight ratio.
%, And at least one of Ni, Co, Zr, Cu, Mg and the like, wherein the total amount of these additional elements is 25% or less and the balance is Al. In this Al alloy, it is described that Fe improves heat resistance and Si has an effect of miniaturizing Fe-based intermetallic compounds. However, Cu and Mg etc. improve the strength by forming a solid solution. It is stated to be effective. Incidentally, the invention described in this publication is an inexpensive heat-resistant Al
The purpose is to provide an alloy with a cooling rate of 10 ² to 1
A raw material alloy powder is produced by a gas atomizing method of about 0 ⁵ K / sec, and this is subjected to hot compression molding such as extrusion to produce an alloy.

[0006]

The above-mentioned aluminum alloys are all aimed at improving properties such as heat resistance at high temperatures, high rigidity, and low thermal expansion. Particularly, aluminum alloys are used for automobile engine parts. It has been developed for connecting rods and the like in response to a demand for lighter weight.

However, at present, connecting rods and the like made of an aluminum alloy have not yet been put to practical use. This is because the conventional aluminum alloys proposed in the above publications and the like have insufficient high-temperature characteristics, and in particular, the fatigue strength at high temperatures of 150 ° C. or higher is still incomplete.

The present invention has been made in view of the above circumstances, and has as its object to provide a heat-resistant aluminum alloy having excellent strength at a high temperature economically and inexpensively.

[0009]

Means for Solving the Problems To achieve the above object, the heat-resistant aluminum alloy proposed by the present invention is composed of Fe 3 to 9.5% by weight and at least one of Mn, Ni, Mo and Cr 3. ~ 15%, Si 0.5 ~ 10%, Mg
0.3 to 5% and the balance of Al, containing no Cu as an alloying component, and having a tensile strength at 200 ° C. of 45 kg /
mm ² or more.

The method for producing a heat-resistant aluminum alloy according to the present invention is characterized in that Fe 3 to 9.5% by weight, Mn,
At least one of Ni, Mo and Cr 3 to 15%, S
i 0.5 to 10%, Mg 0.3 to 5%, and the balance of Al
And a raw material alloy powder containing no Cu as an alloy component is produced by a gas atomization method at a cooling rate of 10 ³ K / sec or more, and the raw material alloy powder is directly or embossed and heated to 1 ° C./sec or more. Rapid heating at speed 4
After powder forging at a temperature of 50 to 700 ° C, 10 ° C / sec
It is characterized by cooling at a cooling rate of c or more.

[0011]

According to the present invention, in order to obtain a heat-resistant Al alloy having an unprecedented strength at a high temperature, the heat history at the time of solidifying the raw material alloy powder is made as small as possible to obtain the alloy by rapid solidification. To prevent the fine structure of the raw material alloy powder from becoming coarse. For this purpose, powder forging is employed as a solidification method, and as an alloy composition for this purpose, the matrix is close to pure Al to maintain ductility, and at the same time, Mn and N are used together with Fe as elements for improving heat resistance.
i, Mo or Cr is added, and Mg is added to improve forgeability.

In the Al alloy of the present invention, of the alloy components added to Al, Fe is an element that is inexpensive and greatly improves the heat resistance while maintaining the ductility of Al. That is, Fe has a small impurity diffusion coefficient in Al, and
The alloy has the effect of greatly improving the heat resistance of the alloy and increasing the strength at high temperatures, and at the same time, hardly dissolves in Al in an equilibrium state, so that the matrix can be kept pure Al and excellent ductility can be maintained. However, when the Fe content is 3
If the amount is less than 9.5% by weight, the effect of improving the heat resistance is reduced. If the amount exceeds 9.5% by weight, large needle-like precipitates are formed and the alloy becomes brittle.

In addition to the improvement of heat resistance by Fe, M
n, Ni, Mo, Cr
Further improve the heat resistance of the alloy. Mn, Ni, Mo, C
r is relatively inexpensive and forms a solid solution in the Al matrix, but when added together with Fe, forms an intermetallic compound with Fe, so that the matrix can be kept close to pure Al and excellent ductility can be maintained. Yes, at the same time alone or by generating a fine intermetallic compound with Fe, significantly improving the heat resistance of the Al alloy and increasing the strength at high temperatures. However, if the content of these elements is less than 3% by weight, there is no effect of improving the heat resistance by the addition, and if it exceeds 15% by weight, coarse precipitates are formed to make the alloy brittle.

Si easily forms an intermetallic compound with Fe, Mn, Ni, Mo, and Cr, and has a function of spheroidizing and finely stabilizing the formed intermetallic compound, thereby increasing the strength at high temperatures. . At the same time, the excess Si has the effect of increasing the Young's modulus of the Al alloy and decreasing the coefficient of thermal expansion. When the amount of Si added is 0.5% by weight or more, it contributes to the spheroidization of the intermetallic compound for the first time. When only this effect is expected, it is sufficient to add at most 4% by weight.
If the effect of increasing the Young's modulus or decreasing the coefficient of thermal expansion is also aimed at, further addition is necessary. However, when the added amount of Si is 1
If the content exceeds 0% by weight, Si precipitates become coarse and the alloy becomes brittle, so it is necessary to keep the content to 10% by weight or less.

The reason why Mg is added to the Al alloy of the present invention is to improve the forgeability. In the present invention, in order to minimize the heat history during solidification of the raw material alloy powder,
It is solidified by forging. In general, it is known that the forging method has less plastic flow at the time of solidification than the extrusion solidification method, and it is difficult to break down a stable oxide (alumina) of the raw material alloy powder, so that it is difficult to achieve good bonding between the powders. This is the reason why the extrusion solidification method has been mainly used for the production of Al alloys. However, when Mg is added in an amount of 0.3% by weight or more, it is found that when the embossed body or the powder is heated, the Mg is diffused to the surface to reduce the alumina film, and good bonding between the powders can be obtained by the forging method. did. However,
If the added amount of Mg exceeds 5% by weight, the effect of improving the forgeability is saturated, so it is preferable that the amount is 5% by weight or less.

In addition, since the forging property of an Al alloy to which Mg is not added is extremely poor, a solidification method for adding a plastic flow such as extrusion must be employed. However, when the extrusion method is carried out industrially, the leading end portion and the trailing end portion of the extrusion become defective portions called discards, and it is necessary to use a large billet to increase the yield. However, it takes a lot of time to uniformly heat the entire large billet to the forging temperature. As a result, the fine structure of the powder becomes coarse during heating, resulting in deterioration of characteristics. That is, M
It can be said that it is almost impossible to heat and solidify Al alloy powder containing no g in a short time.

In addition, in the present invention, in order to maintain the ductility of the Al alloy, it is necessary to avoid adding an element which forms a solid solution in the matrix and causes a large precipitation hardening. For this reason,
Another major feature of the present invention is that Cu, which is a representative of such elements, is not added as an alloy component. However, elements other than the above-mentioned alloy components are allowed to be included as inevitable impurities including Cu.

Next, a method for producing an Al alloy according to the present invention will be described. First, a raw material alloy powder having the above-described alloy composition is produced by a gas atomizing method at a cooling rate of 10 ³ K / sec or more. The cooling rate is set to 10 ³ K / sec or more because the cooling rate of about 10 ² K / sec cannot exceed the characteristics of the conventional heat-resistant Al alloy. However, even if it is an inexpensive raw material alloy powder manufactured at a cooling rate lower than the technical and costly excessive quenching of 10 ⁵ to 10 ⁹ K / sec,
According to the method of the present invention described below, characteristics far exceeding those of the conventional heat-resistant Al alloy can be obtained.

The raw material alloy powder may be used as it is or after embossing for better handling,
Perform powder forging at a temperature of 0 ° C. However, the raw material alloy powder is rapidly heated to a temperature of 1 ° C./sec or more, preferably 15 ° C./sec or more, up to the powder forging temperature. 1 ° C / s
At a heating rate lower than ec , the heating time becomes longer and the heat history becomes larger, so that the fine structure of the raw material alloy powder obtained by the rapid cooling of the gas atomization method becomes coarse and its excellent properties are deteriorated. It is.

The rapid heating of the raw alloy powder before powder forging is performed by
It is preferable to perform the heating by any one of the induction heating method, the radiant heating method, and the direct current heating method. Among them, the induction heating method is the most economical and efficient method. The atmosphere for the rapid heating is not particularly limited. For example, the rapid heating can be performed in the air, in an inert gas, or in a vacuum, but is preferably performed economically in the air. In addition, even if rapid heating is performed in the atmosphere, oxidation due to the atmosphere is unlikely to occur because the heating time is short, and furthermore, harmful effects in the atmosphere are caused by hydrogen gas generated by the reaction of Al with water of crystallization separated from the powder surface during heating. There is an advantage that it is possible to cut off oxygen and water vapor.

It is desirable that the above-described forging process be performed only once. After performing powder forging, the obtained forged material is heated at 10 ° C /
Although cooling is performed at a cooling rate of at least sec, water cooling is a preferable means because the cooling rate is the fastest and economical. If the cooling rate is less than 10 ° C./sec, the heat history becomes large, so that the fine structure becomes coarse and the properties of the alloy deteriorate. Further, in order to reduce the heat history, it is preferable to perform cooling as soon as possible after forging.

[0022]

Example 1 A raw material alloy powder having the composition shown in Table 1 below was cooled at a cooling rate of 10 ^3.
It was manufactured by the K / sec air atomizing method.

[0023]

[Table 1]

Next, each of the raw material alloy powders having the compositions shown in Table 1
00g with a surface pressure of 4 ton / cm ² ,
mm embossed body (density 75%). This embossed body is placed in an induction heating furnace, and is rapidly heated in the atmosphere at an output of 50 kW, at a frequency of 3 kHz and at a heating rate of 16 ° C./sec.
It was heated to a forging temperature of 500 ° C. for 30 seconds. The heated embossed body was transferred from the induction heating furnace to the mold, and the surface pressure was 8 ton /
After forging in cm ² , the forged material was immediately cooled with water.

A test piece was cut out from each of the Al alloys thus obtained, and a tensile test was performed at 200 ° C. Table 2 shows the results obtained by the test. However, the criteria for the comprehensive judgment in this example are: ：: tensile strength ≧ 45 kg / mm ² and elongation at break ≧ 5% ×: tensile strength <45 kg / mm ² or elongation at break <5%,
And From the results shown in Table 2 below, it can be seen that the Al alloy according to the present invention exhibits an unprecedentedly excellent tensile strength at a high temperature and also has an excellent breaking elongation.

[0026]

[Table 2]

Example 2 With respect to the sample 9 having the highest strength obtained in Example 1, the heating rate of the embossed body and the cooling condition of the forged material were changed among the solidification conditions of the raw material alloy powder having the same composition. It carried out similarly to Example 1. The properties of the obtained Al alloy were tested in the same manner as in Example 1, and the results are shown in Table 3.

[0028]

[Table 3]

From the results shown in Table 3, it can be seen that the heat resistance of the Al alloy is affected by both the conditions of the alloy composition and the heat history during solidification. Although the solidification conditions of samples 9d and 9e are out of the range of the method of the present invention, since the alloy composition is appropriate for obtaining high strength, the tensile strength at 200 ° C. is determined in Example 1. A value of 45 kg / mm ² or more is obtained. The elongation at break of samples 9a, 9b and 9c is 5
%, It does not satisfy the criterion in Example 1. However, this is because the alloy composition sacrifices some of the elongation at break for high strength, and the solidification condition approaches the lower limit of the range determined by the method of the present invention. Because it is.

Example 3 Sample 9 was carried out in the same manner as in Example 1, except that the method for heating the embossed body and the heating atmosphere were changed among the conditions for solidifying the raw material alloy powder having the same composition. However, 3 for radiant heating
In a 0 kW gold image furnace, direct energization heating was performed by energizing the embossed body with a copper electrode at a maximum output of 30 kW. In an Ar atmosphere, the flow rate was set to 7 liters / minute, and in a vacuum atmosphere, the degree of vacuum was set to about 10 ^-5 torr using an oil rotary pump and a diffusion pump. The properties of each of the obtained Al alloys were tested in the same manner as in Example 1, and the results are shown in Table 4.

[0031]

[Table 4]

From the results shown in Table 4, it can be seen that almost the same alloy characteristics can be obtained by any of the heating methods, and that the heating atmosphere can be performed not only in a vacuum or in an inert gas but also in the atmosphere. It turns out that the atmosphere is better than the inside.

[0033]

According to the present invention, by reducing the heat history of the specific alloy composition and the raw material alloy powder of the composition during solidification, it has excellent strength not at high temperatures, and is represented by a connecting rod. It is possible to economically and inexpensively provide a heat-resistant aluminum alloy suitable as an automobile engine part or the like.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Katsuyoshi Kondo 1-1-1, Koyokita, Itami-shi, Itami-shi, Hyogo Sumitomo Electric Industries, Ltd. Itami Works (56) References JP-A-1-319644 (JP, A JP-A-59-157202 (JP, A) JP-A-47-26363 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 1/04 C22C 21/00-21 / 18 B22F 3/17

Claims (4)

(57) [Claims] 1. Fe 3 to 9.5% by weight, Mn, N
i, Mo and / or Cr at least one of 3 to 15%, Si
0.5 to 10%, 0.3 to 5% of Mg, and the balance of Al, do not contain Cu as an alloy component, and have a tensile strength at 200 ° C. of 45 kg / mm ² or more. Heat resistant aluminum alloy. 2. Fe 3 to 9.5% by weight, Mn, N
at least one of i, Mo and Cr 3 to 15%, Si
0.5-10%, Mg 0.3-5%, and the balance of Al
And a raw material alloy powder containing no Cu as an alloy component is produced by a gas atomization method at a cooling rate of 10 ³ K / sec or more, and the raw material alloy powder is directly or embossed and heated to 1 ° C./sec or more. Rapid heating at speed 4
After powder forging at a temperature of 50 to 700 ° C, 10 ° C / sec
A method for producing a heat-resistant aluminum alloy, comprising cooling at a cooling rate of not less than c. 3. The heat-resistant aluminum according to claim 2, wherein the rapid heating of the raw material alloy powder is performed in the atmosphere by any of an induction heating method, a radiation heating method, and a direct current heating method. Alloy manufacturing method. 4. The method for producing a heat-resistant aluminum alloy according to claim 2, wherein the forged material is water-cooled immediately after the powder forging.