JPH0699772B2 - High strength aluminum alloy for machine structural members - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Purpose of the Invention (1) Field of Industrial Application The present invention relates to a high-strength aluminum alloy for machine structural members.

(2) Conventional Technology Conventionally, as this type of aluminum alloy, there is known one produced by applying a so-called powder direct molding method in which a green compact having a high-pressure powder density is directly subjected to forging and the like.

(3) Problem to be Solved by the Invention When hydrogen gas is contained in an aluminum alloy, its fatigue strength is impaired, so conventionally, the green compact is subjected to degassing treatment at high temperature. Performing this treatment not only lowers the production efficiency of the aluminum alloy, but also may impair its strength.

In view of the above, it is an object of the present invention to provide the aluminum alloy that contains a hydride-forming component and can exhibit high fatigue strength without degassing.

B. Structure of the Invention (1) Means for Solving the Problems A high-strength aluminum alloy for machine structural members according to the present invention has Si 12.0 wt% or more and 28.0 wt% or less; Cu 0.8 wt% or more and 5.0 wt% or less. ; Mg 0.3 wt% or more, 3.5 wt%
Below; Fe 2.0 wt% or more and 10.0 wt% or less; Mn 0.5 wt% or more, 2.9 wt% or less; and at least one hydride-forming component selected from Co and Pd 0.2 wt%
The first characteristic is that the above content is 4% by weight or less.

Further, the high-strength aluminum alloy for machine structural members according to the present invention has Si 12.0 wt% or more and 28.0 wt% or less; Cu 0.8
Weight% or more, 5.0 weight% or less; Mg 0.3 weight% or more, 3.5 weight% or less; Fe 2.0 weight% or more, 10.0 weight% or less; Mn 0.5
% Or more and 2.9% or less; and at least one selected from Co and Pd, and at least one selected from Ti, Zr and Ni.
The second feature is that the content is 2% by weight or more and 4% by weight or less.

(2) Action In the first and second characteristics, when the content of the hydride-forming component is specified as described above, the hydrogen gas in the aluminum alloy is fixed as a hydride, so that the fatigue strength of the alloy. Is improved.

However, if the content of the hydride-forming component is less than 0.2% by weight, the hydride-forming action is reduced, and if it exceeds 4% by weight, problems such as elongation and toughness of the aluminum alloy are reduced.

In addition, if the contents of various alloy components are specified as described above,
In an aluminum alloy, high temperature strength, wear resistance, hot forgeability and Young's modulus are improved, the coefficient of thermal expansion is decreased, and stress corrosion cracking resistance at high temperature is improved.

The reason for containing each alloy component and the reason for limiting the content are as follows.

(A) About Si Si has the effects of improving wear resistance, Young's modulus and thermal conductivity and lowering the coefficient of thermal expansion. However, if it is less than 12.0% by weight, the above effects cannot be obtained. , On the other hand, 2
If it exceeds 8.0% by weight, the formability is deteriorated during extrusion and forging, and cracks are likely to occur.

(B) Cu Cu has the effect of strengthening the aluminum alloy during heat treatment. However, if it is less than 0.8% by weight, the above effect cannot be obtained, while if it exceeds 5.0% by weight, the stress corrosion cracking resistance property is deteriorated and the hot forgeability is deteriorated.

(C) About Mg Like Mg, Mg has the effect of strengthening an aluminum alloy in a heat treatment. However, if it is less than 0.3% by weight, the above effect cannot be obtained, while if it exceeds 3.5% by weight, the stress corrosion cracking resistance property is deteriorated and the hot forgeability is deteriorated.

(D) About Fe Fe has the effect of improving high temperature strength and Young's modulus. However, if it is less than 2.0% by weight, improvement in high temperature strength cannot be expected, while if it exceeds 10.0% by weight, high speed hot forging becomes practically impossible.

(E) About Mn Mn has the effect of improving high temperature strength and stress corrosion cracking resistance, and also improving hot forgeability, particularly in the range of Fe ≧ 4 wt%. On the other hand, if it is less than 0.5% by weight, the above effect cannot be obtained, while if it exceeds 2.9% by weight, adverse effects such as deterioration of hot forgeability are exhibited.

(3) Example Production of a high-strength aluminum alloy is carried out in the order of powder preparation, green compact formation and hot forging.

The atomization method is applied to the preparation of the powder. The prepared powder is subjected to a sieving treatment, and a powder having a diameter smaller than 100 mesh is used.

At least one hydride-forming component selected from Co and Pd, or at least one selected from Co and Pd and at least one selected from Ti, Zr, and Ni is used for powder preparation. It is added to the molten metal or to the powder after preparation. The latter is better for facilitating the formation of hydrides.

The powder may include Al ₂ O ₃ particles, SiC particles, Si ₃ N as necessary.
_At least one kind of hard particles selected from ₄ particles, ZrO ₂ particles, TiO ₂ particles and metallic Si particles is added. The addition amount of the hard particles is set to 0.5% by weight or more and 15.0% by weight or less with respect to the powder, and thus the aluminum alloy matrix.

By dispersing the hard particles in the aluminum alloy matrix, crystal dislocations in the matrix can be fixed, the creep characteristics of the aluminum alloy can be improved, the thermal expansion coefficient can be lowered, and the Young's modulus and wear resistance can be improved. However, when the content of the hard particles in the aluminum alloy matrix is less than 0.5% by weight, the amount of wear of the aluminum alloy increases, the Young's modulus improves and the coefficient of thermal expansion decreases less, while 15.0% by weight is added. If it exceeds, fatigue strength, hot forgeability and machinability are remarkably deteriorated, and the amount of wear of the mating material is increased, which is not practical.

Molding of the green compact includes a primary molding step and a secondary molding step.

In the primary molding process, molding pressure is 1-10t / cm ² , powder temperature 300 ℃
The following is preferably 100 to 200 ° C. In this case, if the powder temperature falls below 100 ° C, the green compact density does not increase, while
If the temperature exceeds 00 ° C, powder agglomeration (bridging) may occur and work efficiency may decrease.

The green density is set to 75% or more. Below this value, the handleability of the green compact deteriorates.

In the secondary molding process, molding pressure is 3-10t / cm ² , green compact temperature 420
~ 480 ℃, mold temperature 300 ℃ or less, preferably 150 ~ 250 ℃
Is. In this case, if the mold temperature is lower than 150 ° C, the compact density does not increase, while if it exceeds 250 ° C, lubrication between the mold and the compact becomes difficult and seizure of the compact occurs. It may occur.

The green density is set to 95-100%. Below this value, cracking occurs in the aluminum alloy during hot forging.

In forming the green compact, only the primary forming step may be used.

The hot forging process is performed at a heating temperature of the green compact of 350 to 500 ° C. In this case, if the heating temperature is lower than 350 ° C., cracking occurs in the aluminum alloy, while if it exceeds 500 ° C., blister occurs in the aluminum alloy.

INDUSTRIAL APPLICABILITY The alloy of the present invention is most suitable as a constituent material of a sliding member for an internal combustion engine, and is applied to, for example, a bearing member such as a connecting rod cap and a crank journal bearing cap, and a spring retainer for intake and exhaust valves.

Hereinafter, a specific example will be described.

Using an aluminum alloy melt containing the chemical components shown in Table I, an atomizing method was applied to prepare a powder, and the powder was subjected to a sieving treatment to obtain a powder having a diameter smaller than 100 mesh.

Using the powder, a short cylindrical green compact having a diameter of 60 mm and a height of 40 mm was obtained. In this case, in the primary molding process, the molding pressure is 7t / cm ² ,
The powder temperature was 120 ° C. and the green density was 80%. In the secondary molding process, the molding pressure is 9t / cm ² and the green compact temperature.
The temperature was 460 ° C and the mold temperature was 240 ° C, and the green density was 99%.

The green compacts corresponding to the example alloys I and II and the comparative example alloy I were hot forged to obtain the alloys. Hot forging
It was performed under the conditions of heating temperature of the green compact of 480 ° C, mold temperature of 150 ° C, and free forging until the height reached 20 mm.

Further, a green compact corresponding to Comparative Example Alloy II was subjected to degassing and hot extrusion to obtain that alloy.

Example alloys I and II and comparative example alloys I and II from the parallel part diameter
A test piece having a length of 5 mm and a length of 20 mm was cut out, and a compression-tensile fatigue test was performed at a test temperature of 200 ° C. and a repetition number of 10 ⁷ times using the test pieces. The molten gas carrier method was applied to each test piece to measure the amount of hydrogen gas.

Table II shows the fatigue test results and hydrogen gas amount measurement results.

As is clear from Table II, the example alloys I and II have relatively large fatigue strengths despite the high hydrogen gas content. This is because the hydrogen gas in the alloy reacts with Co or Pd,
It is caused by being fixed as a hydride.

Since Comparative Example Alloy I does not contain a hydride-forming component, the fatigue strength decreases with the presence of hydrogen gas.

Since the comparative alloy II has been degassed, the amount of hydrogen gas is naturally reduced, and the fatigue strength is improved accordingly.

To carry out the various tests described below, comparative alloys III and IV having the aluminum alloy compositions shown in Table III are produced.
The manufacturing method is the same as that of the example alloys I and II. Comparative alloy II
The composition of I corresponds to JIS AC8C which is a casting material.

Table IV shows the coefficient of thermal expansion and Young's modulus of Example Alloys I and II and Comparative Example Alloy III.

As is clear from Table IV, the example alloys I and II are comparative example alloys.
The coefficient of thermal expansion is lower than that of III, and the Young's modulus is improved. This is mainly due to the Fe content.

Table V shows the results when a stress corrosion cracking test (JIS H8711) was performed on the example alloys I and II and the comparative example alloy Ir.

In the stress corrosion cracking test, a test piece with a length of 10 mm, a width of 20 mm, and a thickness of 3 mm was used as a load stress of σ _0.2 × 0.9 (where σ _0.2 is 0.2% proof stress of each alloy) at a liquid temperature of 30. ℃,
The test piece was immersed in a 3.5% NaCl solution for 28 days, and the superiority or inferiority of the stress corrosion cracking resistance was judged by the presence or absence of cracks in the test piece.

As is clear from Table VI, the example alloys I and II are comparative example alloys.
The stress corrosion cracking resistance is superior to that of IV, which is mainly due to the addition of Mn.

Table VI shows the results when a sliding wear test was performed on Example Alloy I and Comparative Example Alloy III.

The sliding wear test is a JIS S50C with a diameter of 135 mm that rotates a 10 mm long, 10 mm wide, and 5 mm thick test piece at a speed of 2.5 m / sec.
Press the disk with a pressure of 200 kg / cm ² , and add 5 cc of lubricating oil.
The amount of wear was measured by determining the weight difference (g) before and after the test on the test piece, which was carried out over a sliding distance of 18 km under a condition of / min.

As is apparent from Table VI, Example Alloy I is Comparative Example Alloy II.
It has better wear resistance than I, which is due to the Si content.

Next, the alloys A ₁ and A ₂ containing hard particles will be described.

The chemical composition of the aluminum alloy matrix in the alloys A ₁ and A ₂ was the same as that of the example alloys I and II shown in Table I, and various hard particles were dispersed in these matrices as shown in Table VII. Further, alloys A ₁ and A ₂ are the alloys of Examples I and II.
Manufactured in the same way as.

Table VIII shows the fatigue test results and hydrogen gas amount measurement results for alloys A ₁ and A ₂ . The test method and measurement method are the same as above.

As is clear from Table VIII, the alloys A ₁ and A ₂ have improved fatigue strength as compared with the example alloys I and II in Table II with the addition of hard particles.

Table IX shows the thermal expansion coefficient and Young's modulus of alloys A ₁ and A ₂ .

As is clear from Table IX, alloys A ₁ and A ₂ have a lower coefficient of thermal expansion and a higher Young's modulus than those of the example alloys I and II in Table IV. This is because the particles are dispersed.

Further, when the same stress corrosion cracking test (JIS H8711) was performed on the alloys A ₁ and A ₂ , the occurrence of cracks was not recognized.

Table X shows the case where the same sliding wear test as described above was performed on the alloy A ₁ .

As is apparent from Table X, alloy A ₁ is the example alloy I of Table VI.
It has excellent wear resistance as compared with, which is due to the dispersion of hard particles in the aluminum alloy matrix.

Table XI shows the results when a creep test was performed on Alloy A ₁ and Comparative Example Alloy 1.

The creep test is performed by applying a compressive force of 12 kg / mm ² at 170 ° C for 100 hours to a test piece with a diameter of 6 mm and a length of 40 mm in the parallel portion. It was measured by determining the front-to-back length ratio (%).

As is clear from Table XI, alloy A ₁ has a reduced amount of creep shrinkage as compared to comparative example alloy I, which is due to the fact that the hard particles are dispersed in the aluminum alloy matrix and thus the crystals of the aluminum alloy matrix This is because dislocations are fixed.

The creep shrinkage of the comparative alloy II corresponding to the cast material is 0.04%, and that of the alloy A ₁ is almost equal to that of the cast material.

Table XII shows the chemical composition of Example Alloys III-XII, and Table XII
III shows the fatigue test results and hydrogen gas amount measurement results of these alloys III to XII. The production method of each alloy, the fatigue test and the hydrogen gas amount measurement method for those alloys are described in Example Alloys I and II.
Is the same as in.

C. Effects of the Invention According to the inventions described in (1) and (2), a high strength for mechanical structural members capable of avoiding adverse effects of hydrogen gas and exhibiting high fatigue strength without degassing treatment. A strong aluminum alloy can be provided. Also, since this alloy is not limited by the amount of hydrogen gas, it is not necessary to consider degassing treatment, and therefore, in the production of the alloy, it is possible to carry out the steps of conventional compaction, extrusion and forging in sequence. It is possible to apply the powder direct molding method in which the powder compacting process is directly transferred to the forging process, which simplifies the alloy production and improves the mass productivity.

Furthermore, this alloy has excellent high temperature strength, wear resistance, hot forgeability and Young's modulus, and has a low coefficient of thermal expansion.
Moreover, the stress corrosion cracking resistance property under high temperature is improved.

Claims (2)

[Claims] 1. Si 12.0% by weight or more and 28.0% by weight or less; Cu
0.8 wt% or more, 5.0 wt% or less; Mg 0.3 wt% or more,
3.5 wt% or less; Fe 2.0 wt% or more, 10.0 wt% or less; Mn
0.5 wt% to 2.9 wt%; Co and Pd
At least one hydride-forming component selected from 0.
2 wt% or more and 4 wt% or less; 2. Si 12.0% by weight or more and 28.0% by weight or less; Cu
0.8 wt% or more, 5.0 wt% or less; Mg 0.3 wt% or more,
3.5 wt% or less; Fe 2.0 wt% or more, 10.0 wt% or less; Mn
0.5 wt% to 2.9 wt%; Co and Pd
A hydride-forming component comprising at least one selected from the group consisting of Ti, Zr, and Ni
0.2 wt% or more and 4 wt% or less;