JPH0849035A - Shift fork made of wear resistant aluminum alloy having excellent fatigue strength - Google Patents

Abstract

PURPOSE:To impart excellent wear resistance and fatigue strength to a shift fork by subjecting an aluminum alloy added with Si and Cu to high pressure casting and subjecting the arm part of a shift fork having a structure in which fine primary crystal Si is dispersedly distributed into the matrix to shot peening treatment. CONSTITUTION:The compsn. of an alloy is constituted of the one contg., by weight, 13 to 17% Si, 2 to 6% Cu, and the balance Al with inevitable impurities, which is subjected to high pressure casting to form a shift fork. Moreover, this fork is the one having a structure in which primary crystal Si having 10 to 40mum average grain size is dispersedly distributed into the matrix, and in which compressive residual stress of >=5kg/mm<2> is present at least on the arm surface part. In the case of the production, it is subjected to high pressure casting under 1000kgf/cm<2> pressurizing force, is soaked at 500 deg.C for 4hr, is subjected to solution treatment for executing rapid cooling in warm water of 50 C and is subjected to aging treatment for executing heating at 170 deg.C for 8hr, and after that, the surface of the arm part is subjected to shot peening for 2 to 7min by using steel balls of 0.6mm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wear-resistant Al alloy shift fork which is a structural member of a transmission such as an automobile.

[0002]

2. Description of the Related Art Generally, as shown in a schematic plan view and a schematic side view of FIG. 1, a shift fork of a transmission generally has an arm portion curved from a central portion to both sides,
Moreover, it is known that a pad surface is formed on the inner side of the tips of both arms, which is manufactured by casting an Al-Si alloy melt containing high Si by a die-casing method.

[0003]

On the other hand, in recent years, automobiles have been tending toward higher output and higher speed, and there is also a strong demand for weight reduction, and along with this, operating conditions of the transmission incorporated in the automobile. However, the conventional Al alloy shift fork described above has a structure in which the primary crystal Si in which the die-cast castings constituting the conventional Al fork are dispersed and distributed in the matrix is refined, resulting in excellent wear resistance. However, under severe operating conditions, cracks are likely to occur particularly in the arm portion due to insufficient fatigue strength, and there is a problem in terms of reliability.

[0004]

Therefore, the present inventors have
From the above viewpoint, as a result of research to develop a wear-resistant Al alloy shift fork having excellent fatigue strength, as a result, the composition of the molten Al alloy was expressed in weight% (hereinafter,%
%), Si: 13 to 17%, Cu: 2 to 6%, and the rest is composed of Al and unavoidable impurities. When formed into a fork, the high-pressure casting casting forming this shift fork has a structure in which the primary crystal Si refined in the base material, that is, the primary crystal Si having an average grain size of 10 to 40 μm is dispersed and distributed. Shot peening is applied to the surface of the arm that requires particularly high fatigue strength,
When this is performed until the residual compressive stress of 5 kgf / mm ² or more exists on the surface of the arm portion, the resulting shift fork has excellent wear resistance due to the fine primary crystal Si, and The research result was obtained that the fatigue strength of at least the arm portion is remarkably improved by the residual compressive stress.

The present invention has been made on the basis of the above-mentioned research results, and has a composition containing Si: 13 to 17%, Cu: 2 to 6%, the balance being Al and inevitable impurities, and Primary crystal S having an average grain size of 10 to 40 μm in the matrix
It consists of a high pressure casting with a structure in which i is dispersed and distributed,
Further, the present invention is characterized by a wear-resistant Al alloy shift fork having excellent fatigue strength, in which at least a residual compressive stress of 5 kgf / mm ² or more is present on the arm surface.

In the shift fork of the present invention, the Si content of the high-pressure casting which constitutes the shift fork is 13 to 13.
The content of 17% is that the primary crystal S is contained when the content is less than 13%.
This is because the ratio of i is insufficient and the desired excellent wear resistance cannot be ensured. On the other hand, when the content exceeds 17%, the toughness decreases, and the Cu content also increases. 2-6% means that the content is 2%
If it is less than the above range, the strength and hardness cannot be sufficiently improved by the age hardening brought about by the Cu component. On the other hand, if the content exceeds 6%, the toughness is deteriorated. . Furthermore, the average grain size of primary crystal Si is set to 10 to 40 μm.
If the average particle size is less than 10 μm, the desired excellent wear resistance cannot be secured, while the average particle size is 40 μm.
It is based on the reason that the toughness and the machinability are deteriorated when it exceeds m. Furthermore, the lower limit of the residual compressive stress: 5 kgf / mm ² is empirically determined, and the residual compressive stress is 5 kgf / When it is more than mm ² , the fatigue strength is rapidly improved.

[0007]

EXAMPLES Next, the shift fork of the present invention will be specifically described by way of examples. In the crucible furnace, the molten Al alloy having the composition shown in Table 1 was prepared, and the molten metal temperature: 78
High-pressure casting was performed under the conditions of 0 ° C. and molten metal pressurizing pressure: 1000 kgf / cm ² to obtain the above-mentioned Al alloy molten metal as a high-pressure casting, which was held at a temperature of 500 ° C. for 4 hours and then in hot water of 50 ° C. A solution treatment of quenching and a heat treatment of an age hardening treatment of maintaining the temperature at 170 ° C. for 8 hours are performed, and then in this state, a shot peening treatment is performed for 2 to 7 minutes on the surface using a steel ball having a diameter of 0.6 mmφ. The shift forks 1 to 7 of the present invention and the comparative shift forks 1 to 7 each having a dimension of a distance between the tips of the arm portions: 90 mm and a curvature of the inner side surface of the arm portion: 45 R are applied without applying a predetermined time within the range or shot peening. Manufactured.

Next, with respect to the various shift forks obtained as a result, the structure of an arbitrary portion on the inner surface of the arm portion was observed with a metallurgical microscope, and the primary crystal S dispersedly distributed in the base material was observed.
The average particle diameter of i was calculated, and the residual compressive stress at 12 arbitrary points in the arm was determined by X-ray diffraction to determine the direction dependence of the aluminum lattice constant. The average value (12 places) was determined. Further, the above various shift forks were subjected to a fatigue test and a wear test for the purpose of evaluating fatigue strength and wear resistance. In the fatigue test, the shift fork was horizontally fixed to the middle part of the vertical axis with a pin, and a one-sided upper surface of the tip part of the arm part (pad surface part) was subjected to a one-sided repeated compression load with a vibration frequency of 3 Hz, and the arm part was not broken. The number of repetitions until occurrence was measured, and the fatigue breaking load of 10 ⁶ times was calculated. In the wear test, the above shift fork was installed in the bench synch durability tester, shift gear: 3rd ← → 2nd, rotation speed: 8000r.pm (during downshift), shift time: 0.25 seconds, oil The maximum wear depth of the pad surface was measured under the conditions of temperature: 120 ° C., number of cycles: 100,000 times.
The results of these measurements are shown in Table 1.

[0009]

[Table 1]

[0010]

From the results shown in Table 1, the shift forks 1 to 7 of the present invention are all broken by the residual compressive stress of 5 kgf / mm ² or more on the surface portion of the high-pressure casting that constitutes the shift forks. It shows excellent fatigue strength without generation and excellent wear resistance due to fine primary crystal Si, while the residual compressive stress is 5 kgf / mm ² as seen in Comparative Shift Forks 1 to 3. It is clear that when the ratio is less than the above value, or when it does not exist at all, the arm portion is broken in a relatively short time. As described above, the wear-resistant Al alloy shift fork of the present invention has excellent fatigue strength and wear resistance, and therefore can sufficiently satisfy this even under severe operating conditions of the transmission and can be used for a long time. It exhibits excellent performance over a period of time.

[Brief description of drawings]

FIG. 1 is a schematic plan view and a schematic side view showing a shift fork of a transmission.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toru Kono 1-297 Kitabukuro-cho, Omiya-shi, Saitama Prefecture Central Research Laboratory, Mitsubishi Materialial Co., Ltd. (72) Masaaki Sakai, 3-1 Koganecho, Niigata-shi, Niigata Mitsubishi Materials Niigata Manufacturing Co., Ltd. (72) Inventor Kenichi Asano 5-3-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation (72) Hideo Inohara 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation Within the corporation

Claims (1)

[Claims] 1. A composition comprising, by weight, Si: 13 to 17%, Cu: 2 to 6%, the balance being Al and inevitable impurities, and having an average particle size of 10 to 40 μm in the matrix. Primary crystal S
It consists of a high pressure casting with a structure in which i is dispersed and distributed,
A shift fork made of wear-resistant Al alloy having excellent fatigue strength, characterized in that residual compressive stress of 5 kgf / mm ² or more is present at least on the arm surface.