JPH0762199B2 - A1-based alloy - Google Patents

Description

TECHNICAL FIELD The present invention relates to an Al—Cr alloy produced by a powder metallurgy method, and more specifically, in an Al—Cr alloy, Cr is used.
In addition to defining the addition amount of Ti and Fe and further adding Ti and Fe in the required amounts, an alloy having a good balance of heat resistance, plastic workability, toughness and strength is provided.

[Prior Art] Al alloys have excellent characteristics such as light weight and good plastic workability, and are expanding their applications as materials that can replace Fe in industrial fields such as automobiles and aircraft where there is a strong demand for weight reduction. Is expected. For example, in the automobile industry, there is a movement to reduce the weight of parts such as connecting rods that move in a high temperature atmosphere to improve the performance of engines, and the emergence of lightweight and high-strength materials that can replace conventional iron. Long-awaited.

However, for parts that require a certain level of strength in a high temperature atmosphere, such as various engine parts, conventional fusion cast Al
It was difficult to apply an alloy (I / M alloy; ingot metallurgy). For example, in the case of the 2000 series alloy, which is said to have the highest heat resistance strength among conventional I / M alloys, its strength is mainly brought about by the precipitation phases of the main additive elements Cu and Mg, and the precipitation phase becomes coarse. In the temperature range of 150 ° C or higher, which causes heat generation, abrupt softening occurs and it is no longer possible to use it as a strength member.

Under these circumstances, various Al-based alloys to which the rapid solidification method has been applied have been developed in recent years to meet the demands of each industrial field. That is, molten A containing metallic elements such as Fe, Cr, Mn, Ni, Ti, Zr, V
If the alloy is rapidly solidified into fine particles such as powder and solidified into a lump by powder metallurgy, stable compounds containing the above metal elements even at high temperatures are finely dispersed in the Al matrix, resulting in high temperature strength. It is possible to expect a marked improvement in

As such a quenched powder metallurgy alloy, one mainly based on Al-Fe system has been extensively studied so far, and alloys having excellent heat resistance such as Al-Fe-Ce alloy have been developed. In addition, especially recently, for example, a report by L. Katgerman et al. (P / M Aerospace Materials 12
-14Nov.1984), the excellent heat resistance of Al-Cr based alloys has attracted attention.

[Problems to be Solved by the Invention] As an Al-Cr based alloy, US Pat.
Examples thereof include those disclosed in JP-A-59-116352 and JP-A-59-116352, each of which has excellent characteristics.

However, when considered as a practical material, it is important that the required properties are not only heat resistance but also good plastic workability and high toughness and strength. For example, if you try to apply these alloys to parts with complicated shapes such as connecting rods,
The fact that hot forging is possible is a necessary condition from the viewpoint of cost, and at the same time, a certain stress concentration is inevitably received, and the lower the notch sensitivity, the better.

The alloys that have been researched and developed so far have not yet possessed the characteristics that are indispensable for practical use at the same time, and it is extremely significant to develop an alloy with the above characteristics balanced. That is. Therefore, the present inventors have paid attention to the high heat resistance of the Al-Cr base alloy, and based on this system, studied the types and addition amounts of various additive elements, and completed the present invention.

[Means for Solving the Problems] Heat resistance, plastic workability, toughness and high strength according to the present invention are high.
Al-based alloy is an Al-based alloy manufactured by powder metallurgy, Cr: 5-10%, Ti: 0.5-3%, and Fe: more than 1% and 2.5
%, Including the balance Al and unavoidable impurities,
And conditional expression Cr + Fe + Ti ≦ 10.5% and Cr + 1.2Fe + 0.6Ti ≦
The gist is that where 10% is satisfied. Further, by satisfying the conditional expression Cr + 2.4Fe + 1.2Ti ≧ 10%, an Al-based alloy having higher strength can be obtained.

[Operation] The present invention basically focuses on the heat resistance imparting effect of Cr to Al and utilizes this. However, Ti and Fe are added to enhance these characteristics, and the compounding amount thereof is By properly adjusting, an Al-based alloy having good plastic workability and toughness is provided.

It should be noted that the Al-based alloy according to the present invention is premised on being manufactured by the powder metallurgy method as is clear from the above description, and exhibits a specific action and effect by adopting the powder metallurgy method. Is.

That is, the Al alloy of the present invention needs to be one in which alloy elements are finely dispersed in an Al matrix, but it is difficult to form a finely dispersed structure in the melt casting method because the cooling rate is slow. On the other hand, the powder metallurgy method is a method of rapidly solidifying molten Al alloy to produce fine powder, foil pieces, flakes, ribbons, etc., and solidifying and forming them into a lumpy Al alloy having a desired shape by using these as a material. Since the method is adopted, a structure in which the intermetallic compound is finely dispersed in the matrix can be obtained.

However, if the alloying element has a high diffusibility under high temperature conditions, even if the rapid solidification method is used to form a powder material with a fine structure, the alloying element diffuses during sintering or under high temperature use environment. As a result, the microstructure is coarsened, and the high temperature strength and the like decrease. Therefore, it is necessary to select an alloy element having low diffusivity in a high temperature Al matrix, and Cr and Ti and Fe are also selected from this viewpoint. However, addition of a large amount of these alloy elements impairs workability and the like, so it is necessary to consider their negative aspects, and the selection of alloy elements and the design of their addition amounts are comprehensively determined from these viewpoints.

On the other hand, regarding the cooling rate at the time of rapid solidification, it is necessary to consider to prevent crystallization of coarse compounds, and it is desirable to set the cooling rate to 10 ³ K / sec or more. This is because the equilibrium solid solution limit of each of the above elements is extremely small, and when cooled at a rate lower than the above cooling rate, a remarkably coarse compound is crystallized and the desired finely dispersed metal structure cannot be obtained. 10 ³ K / sec
The means for obtaining the above cooling rate is not particularly limited, but in any case, it is necessary to solidify the Al alloy molten metal as a fine solid having a small heat capacity, and the method of powder metallurgy is used to make the fine solidified body into a solid mass. The present invention because it is necessary
Al-based alloys are required to be manufactured by powder metallurgy. A roll method and an atomizing method are exemplified as specific means for obtaining a cooling rate of 10 ³ K / sec or more. Also, in carrying out the atomizing method, there is no restriction on the type and conditions thereof, but since the moldability can be further improved by suppressing the oxidation of the surface of the atomized powder material, an inert gas is used as the fluid for atomizing. Recommended to use. However, it is of course possible to apply liquid atomization, air atomization, or the like.

The action of each element and the reason for the numerical limitation in the Al-based alloy of the present invention will be described below.

Cr; 5-10% Cr is an element having a low diffusion rate in Al. Therefore, Cr or a finely dispersed Al-Cr compound which is forcibly solid-solved in the Al matrix by the rapid solidification method does not easily aggregate or coarsen at high temperature as well as at room temperature, and therefore has strength at high temperature. The effect of preventing the deterioration is remarkable. In order to achieve this effect, it is necessary to add at least 5% or more, but if it is added in excess of 10%, it cannot prevent the formation of coarse crystallized matter, no matter how it depends on the rapid solidification. Not only the expected effect cannot be obtained, but rather the plastic workability and toughness are deteriorated.

Ti; 0.5-3% Ti, in the coexistence with Cr, has the effect of increasing the strength of the Al alloy at room temperature and high temperature. This effect is smaller than the effect of Fe described later, and becomes remarkable in the region where the Ti content exceeds 0.5%. At the same time, Ti has a gradual decrease in toughness of the alloy as the amount of Ti added increases, and it does not hinder the toughness more than the effect of improving heat resistance.

However, since Ti is a refractory metal, it has the effect of remarkably increasing the liquidus of the alloy, and if it is added in excess of 3%, the melting temperature will become extremely high and the oxidation of Al will be remarkable, and refractory materials such as crucibles and alloys It causes problems such as reaction and makes manufacturing difficult.

Fe; more than 1% and less than 2.5% Fe, in the coexistence with Cr, has the effect of significantly increasing the strength of the Al alloy at room temperature and high temperature. This effect is greater than the effect of Ti described above, but at the same time Fe has the effect of reducing the toughness of the alloy. Therefore, in the present invention,
Fe is contained in an amount of more than 1% and less than 2.5%, more preferably more than 1% and 2.0% or less.

Remainder; Al and unavoidable impurities The Al ingot used for the production of the alloy according to the present invention may be any commercially available Al ingot with a purity of 97% or more (including recycled ingot). It is preferable to use a primary metal having a purity of 99% or more.

Cr + Fe + Ti total; 10.5 (preferably 10) or less When the total of the above formula exceeds 10.5 in the alloy of the present invention, elongation and drawing, which are important for plastic working, are significantly reduced. Therefore, when plastic workability is required, the sum of the above equation is 10.5.
It is necessary to set the composition within the range not exceeding. Further, when the sum of the above formula is 10.5, the elongation and the drawing value vary, so in order to prevent this, the sum of the above formula is preferably 10 or less.

Cr + 1.2Fe + 0.6Ti total; 10 or less In the alloy of the present invention, when the above total exceeds 10, the toughness of the alloy is significantly reduced. Therefore, when toughness is required, it is necessary to set the composition within the range where the sum of the above formulas does not exceed 10.

The Al-based alloy according to the present invention, by satisfying the above-mentioned constitutional requirements, exhibits excellent heat resistance, plastic workability, and toughness, and has strength at room temperature strength equal to or higher than that of conventional structural alloys, specifically Although shows a 30 Kg / mm ² or more, further cold strength conventional high-strength alloys parallel above (specifically 40 Kg / m
m ² or more), the Cr, Fe, and Ti contents should be set so that Cr + 2.4Fe + 1.2Ti ≧ 10% is satisfied.

[Examples] The Al-based alloy according to the present invention will be described in more detail based on the following examples.

Alloys having the respective compositions (remaining Al and unavoidable impurities) listed in Table 1 were melted in an atmospheric furnace, and the melt was atomized in a nitrogen atmosphere to obtain fine alloy powder. The alloys shown in Nos. 15 and 16 are conventional I / M materials. After recovering these alloy powders, they were classified into 200 mesh under (74 μm or less) by a sieving method to adjust the particle size distribution. The average particle size of the powder at this time is 30
Was about 40 μm.

Next, the powder of which particle size was adjusted was made into a can made of 5052 alloy (outer diameter 70 mm;
The length of the can was 200 mm), and the inside of the can was sucked and degassed with a vacuum pump from a degassing hole provided at one end of the can and heated in an atmosphere of 350 ° C. for about 2 hours. The ultimate vacuum at the end of this degassing process was about 1 × 10 ⁻³ Torr.

The degassed powder is heated with the can for 2 hours in an atmosphere of 480 ° C and is subjected to hot extrusion at an extrusion ratio of about 20 by a hydrostatic extrusion method to obtain a substantially dense extruded round bar (external diameter 15.5). mm)
Got

Various tensile tests shown below were carried out on the round bar thus obtained.

1) Normal temperature tensile test Specimen shape …… Parallel part diameter 6 mm × parallel part length 36 mm (gage length 30 mm) Test method …… by ASTM B557M 2) Notch tensile test Specimen shape …… Test part length 30 mm, barrel diameter 12.7mm Notch valley diameter 8.96mm Notch angle 60 ° Notch tip R0.018mm or less Test method and conditions …… ASTM E602 3) High temperature tensile test Specimen shape …… Parallel diameter 6mm × flat diameter 36mm Test method… ... Test temperature 300 ° C Holding time 20 minutes Other conditions According to ASTM E21, the results of various tensile tests obtained by the above methods and conditions are also shown in Table 1.

In the table, σ _0.2 is proof stress, σ _B is tensile strength, δ is elongation, and ψ is drawing. Further, σ _NTS / σ _0.2 is the ratio of notch tensile strength and room temperature proof stress, and the σ _NTS / σ _0.2 value indicates the degree of notch sensitivity to tensile load (the smaller the value, the higher the notch sensitivity), and at the same time, the toughness Evaluation parameter 1
It is often used as a standard and is usually σ _NTS / σ _0.2
A value of 1 or more is required.

Nos. 1 to 6 are examples satisfying all the conditions of the present invention, exhibiting excellent properties as compared with the conventional I / M materials (Nos. 15 and 16), heat resistance, plastic workability, and toughness. It can be seen that both the strength and the strength are excellent.

No. 7 is an Al-6Cr-1Ti alloy that does not contain Fe, N
o.8 and 9 are alloys in which Fe is added to these alloys. Fig. 1 was obtained by comparing room temperature strength and high temperature strength. From this figure, the effect of improving the strength and heat resistance by adding Fe is clearly recognized. However, No. 8 and 9 are the parameters [Cr +
1.2Fe + 0.6Ti] amount exceeds 10, the value of σ _NTS / σ _0.2 is less than 1, and the toughness is low. In Nos. 10 to 14, the amount of [Cr + Fe + Ti] as a parameter is out of the range of the present invention, the values of elongation (δ) and reduction (ψ) are small, and plastic workability is poor. Fig. 2 shows the amount of [Cr + Fe + Ti] as a parameter and the elongation (δ) in the normal temperature tensile test based on the data in Table 1.
It is a plot of the relation of the diaphragm (ψ),
In the region where the amount of Fe + Ti] exceeds 10.5, the elongation and the reduction are extremely reduced, and it is clear that the amount of [Cr + Fe + Ti] should be set to 10.5 or less.

In addition, Fig. 3 is a graph plotting the amount of [Cr + 1.2Fe + 0.6Ti] and σ _NTS / σ _0.2 value of the parameter, σ _NTS /
The σ _0.2 value changes almost linearly with respect to the [Cr + 1.2 Fe + 0.6 Ti] amount, so that the σ _NTS / σ _0.2 value becomes 1 or more (that is, strength reduction almost occurs even under stress concentration due to notch). (Cr + 1.2Fe +0.6)
It turns out that the amount of Ti] should be 10 or less.

Furthermore, as a result of analyzing the data in Table 1, it was found that the room temperature and high temperature strengths change almost linearly with respect to the parameter [Cr + 2.4Fe + 1.2Ti] amount (see FIG. 4).
The room temperature strength of 5000 series alloys, which are often used as structural materials, is about
Although it is around 30 kg / mm ² , it can be seen that the alloys Nos. 1 to 6 of the present invention all have higher room temperature strength than the above 5000 diameter alloy. Considering that the normal temperature strength of the 2000 series alloy, which is often used as a heat resistant high strength material, is around 40 Kg / mm ^2, it is possible to set the [Cr + 2.4 Fe + 1.2 Ti] amount to 10 or more from Fig. 4. It can be said that it is preferable. In Table 1, comparing the strengths at 300 ° C., the alloys of the present invention are all 2000 series alloys.
It has more than twice the high temperature strength, and its superiority is confirmed.

The above relational expressions are summarized in Table 2.

[Effects of the Invention] The present invention is configured as described above, and the following effects can be obtained.

(1) It is possible to obtain an Al-based alloy having good plastic workability, toughness, and the like, and having excellent room temperature strength and high temperature strength.

(2) In the field of automobiles, weight reduction of engine parts is promoted, and effects such as improvement in fuel consumption and output can be obtained.

(3) In the field of aircraft, weight reduction of outer plates, legs (particularly wheels), engine parts, etc. is promoted, and effects such as improved fuel economy and improved output can be obtained.

(4) It is possible to reduce the weight and increase the strength of various mechanical parts used in a high temperature atmosphere, parts for electric appliances, and the like.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of addition of Fe on the room temperature strength and high temperature strength in the Al-6Cr-1Ti alloy, and FIG. 2 is a graph showing the correlation between the amount of Cr + Fe + Ti and elongation and drawing in the alloy of the present invention, FIG. Is Cr + 1.2Fe + 0.6 in the alloy of the present invention
FIG. 4 is a graph showing the correlation between the Ti amount and the toughness, and FIG. 4 is a graph showing the correlation between the Cr + 2.4Fe + 1.2Ti amount and the room temperature strength and the high temperature strength in the alloy of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-B 35-301 (JP, B1) JP-B 40-4129 (JP, B1)

Claims (2)

[Claims] 1. An Al-based alloy produced by a powder metallurgy method, wherein Cr: 5-10% (meaning weight%; the same applies hereinafter), Ti: 0.5
~ 3% and Fe: more than 1% and less than 2.5%, consisting of balance Al and unavoidable impurities, and conditional expression Cr + Fe + Ti ≤ 10.5
% (However, each element in the conditional expression shows a% value, the same applies hereinafter) and Cr + 1.2Fe + 0.6Ti ≦ 10%, which is a high-strength Al base with excellent heat resistance, plastic workability, and toughness. alloy. 2. The Al-based alloy according to claim 1, which satisfies the conditional expression Cr + 2.4Fe + 1.2Ti ≧ 10%.