JPH0751728B2 - Method for manufacturing sliding member made of high-strength sintered AL alloy - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sliding member made of a high-strength sintered Al alloy, which is used, for example, in a sliding portion of an internal combustion engine.

Conventional technology and its problems Conventionally used high Si content Al alloys have excellent wear resistance, but the wettability of lubricating oil is poor, and the Al alloys under severe sliding conditions. When sliding between the manufactured member and another member is started, there is a problem that the oil film is broken and seizure resistance is lowered. As a method to solve this problem, for example,
Lapping (finish polishing) of the sliding surface using alumina powder, etc., and by subjecting the sliding surface to special etching, etc., the primary crystal Si particles are lifted from the surrounding matrix layer, and between the primary crystal Si particles. There is a method of making the formed recesses into oil reservoirs, but it is not suitable as a method for treating mass-produced products because the surface treatment work that gives the optimum surface condition is difficult.

Further, the high Si content Al alloy is originally an alloy for casting, and according to the casting method, coarse primary crystal Si is crystallized and the required strength cannot be obtained. However, the effect was limited. On the other hand, by producing a hyper-eutectic Al alloy powder with a high Si content by an atomizing method, the grain size of primary crystal Si is suppressed to about several μm, and the compacted body is hot extruded to obtain high strength. Although a method of obtaining a sintered Al alloy member has been proposed, the problem of seizure resistance is a bottleneck. As a solution to this problem, there is a method of mixing lubricating powder such as molybdenum disulfide and graphite into the green compact, but cracks are likely to occur in the manufacturing process of sintered products, and it is extremely difficult to improve seizure resistance. Is. Moreover, a film of Al ₂ O ₃ .3H ₂ O is formed on the surface of the Al alloy powder at room temperature, and when the powder is pressurized, the adsorbed water is decomposed to generate hydrogen,
There is a problem that hydrogen remains in the sintered product, and in order to obtain structural members, it is necessary to control and suppress the amount of residual hydrogen by heating the green compact in an inert gas atmosphere. Has the disadvantage of complicating.

Means and Actions for Solving Problems The object of the present invention is to obtain a sliding member made of a high-strength sintered Al alloy having good seizure resistance without controlling or suppressing the content of hydrogen.

The purpose, in weight percent, is 10.0 ≦ Si ≦ 30.0, 2.0 ≦ Fe ≦ 10.
0, 0.5 ≤ Cu ≤ 7.5, 0.5 ≤ Mn ≤ 5.0 and 0.3 ≤ Mg ≤ 3.5, with the balance Al and Al alloy powder that is an unavoidable impurity, and a step of molding a green compact containing hydrogen. A step of subjecting the green compact to an extrusion process at an extrusion temperature of 300 to 450 ° C. to obtain an extruded product, and dehydrogenation of keeping the extruded product at a temperature of 450 to 520 ° C. for 0.5 to 7 hours in a vacuum. Forming a hole in the extruded product by performing a treatment.

In this sliding member, primary crystal Si is uniformly and finely distributed in the metal structure, and the porosity of at least the surface layer is 0.5 to 5.0.
It becomes volume%.

The Al alloy powder used in the present invention is effectively produced by an air atomizing method which is inexpensive to produce.
By setting the powder cooling rate at that time to 10 ² ° C / sec or more, it is possible to suppress the precipitation of coarse intermetallic compounds and prevent the elongation rate and impact value of the sintered product from decreasing.

If the manufactured Al alloy powder is compacted, then the compact is preheated in an inert gas atmosphere and hot extrusion is performed, the hydrogen content of the extruded sintered product 2
It can be up to 13cc / 100g (Al alloy), and can effectively prevent the occurrence of blisters (surface swelling) during heat treatment of the sintered product.

However, in the present invention, hot extrusion of the green compact (extrusion temperature 300
~ 450 ℃) was carried out, and a relatively large amount of hydrogen (13 to 25 cc / 100 g (Al alloy)) was left in the sintered product which was an extrusion molded product. In vacuum (atmospheric pressure 10 ^-2 to 10 ^-5
By performing a dehydrogenation treatment at a temperature of 450 to 520 ° C. for 0.5 to 7 hours, a matrix layer in which primary Si is uniformly distributed has pores with a size of several μm. , It functions as a lubricating oil reservoir in the sliding member. Thus, even if the sintered product from which the residual hydrogen is removed is subjected to the heat treatment, there is no fear of causing defects such as blisters and cracks, and a sound sliding member can be obtained.

Each alloy element is added to the Al alloy powder for the following reasons.

Regarding Si (10.0 ≦ Si ≦ 30.0% by weight): Si contributes to improvement of wear resistance and Young's modulus, suppresses thermal expansion coefficient to a low level, and improves thermal conductivity. If it is less than 10.0% by weight, the wear resistance is insufficient, and it becomes a factor of lowering the strength especially in the member having pores having the porosity of 0.5% by volume or more. On the other hand, if it exceeds 30% by weight, the workability at the time of hot extrusion is deteriorated, resulting in a reduction in yield and a decrease in mass productivity.

Regarding Fe (2.0 ≦ Fe ≦ 10.0% by weight): Fe is necessary to improve high temperature strength and Young's modulus. However,
If it is less than 2.0% by weight, improvement in high temperature strength can be expected.
When it exceeds 0% by weight, moldability is deteriorated and hot extrusion is practically impossible.

Regarding Cu (0.5 ≦ Cu ≦ 7.5 wt%): Cu is effective for strengthening the Al matrix by heat treatment. However, if it is less than 0.5% by weight, there is no effect of addition, and if it exceeds 7.5% by weight, stress corrosion cracking resistance is deteriorated, which is not preferable.

Regarding Mn (0.5 ≦ Mn ≦ 5.0% by weight): Mn is an important component and contributes to improvement of high temperature strength, improvement of hot extrusion and improvement of stress corrosion cracking resistance. However, if it is less than 0.5% by weight, there is no effect of addition, and if it exceeds 5.0% by weight, the hot extrusion processability rather deteriorates and the notch property deteriorates, which becomes a factor of strength reduction.

Regarding Mg (0.3 ≦ Mg ≦ 3.5% by weight): Mg, like Cu, is effective in strengthening the Al matrix by heat treatment.
However, if it is less than 0.3% by weight, there is no effect of addition, and if it exceeds 3.5% by weight, the stress corrosion cracking resistance property is deteriorated and the hot extrudability is deteriorated.

Next, the manufacturing process of the sliding member made of the high-strength sintered Al alloy according to the present invention will be specifically described.

First, the Al alloy powder having the above composition produced by the air atomizing method which is recommended because of its low manufacturing cost is used, and this is subjected to cold isostatic pressing (CIP method) or die compression molding method. Thus, a green compact is obtained by compacting to a density ratio of about 75%.

This green compact is heated to an extrusion temperature of 300 to 450 ° C. in the atmosphere and extruded within that temperature range. Extrusion temperature is 30
When the temperature is lower than 0 ° C, the deformation resistance of the green compact is large and the formability is deteriorated. On the other hand, when the temperature is higher than 450 ° C, the structure is coarsened (particularly Si grains are coarsened) and the strength is lowered.

The content of hydrogen in the obtained extruded product, that is, the sintered product, is 13 to 25 cc / 100 g (Al alloy), and the sintered product is kept in vacuum at a temperature of 450 to 520 ° C. for 0.5 to 7 hours. When the dehydrogenation treatment is performed, pores are generated in the sintered product as the hydrogen gas is removed, and the porosity becomes 0.5 to 5.0% by volume. If this holding temperature is less than 450 ° C, it will be difficult for target holes to occur,
If the seizure resistance cannot be improved, and if the temperature exceeds 520 ° C., a liquid phase is likely to occur and the pore diameter becomes coarse, which causes a decrease in product strength. Also, if the holding time at a temperature of 450 to 520 ° C is less than 0.5 hours, it is difficult for pores to occur, and if it exceeds 7 hours, the structure becomes coarse (particularly Si grains become coarse) and the product strength decreases. To do. Furthermore, the porosity of the sintered product is 0.5.
If it is less than volume%, the product strength is secured to some extent, but the pore volume as a lubricating oil reservoir is insufficient and seizure resistance is poor, and if it exceeds 5.0 volume%, the product strength is reduced and durability is impaired. .

The primary crystal Si is present in the structure in a substantially uniform distribution, but if the grain size is less than 5 μm, the wear resistance is poor,
If it exceeds 20 μm, the product strength will decrease, so the particle size will be 5
A target of 20 μm is preferable.

Test Example An Al alloy powder having a composition shown as Example Samples I and II in Table 1 was produced by an air atomizing method at a cooling rate of 10 ² to 10 ⁴ ° C./second, and the powder was used for cold isostatic pressing. A green compact having a density ratio of 75% was molded by the molding method (CIP method). In this cold isostatic pressing method, the alloy powder was put in a rubber tube and the molding was performed under hydrostatic pressure of about 1.5 to 3.0 ton / cm ² .

The green compact obtained in the previous step was used as an extrusion material in the atmosphere,
Hot extrusion was performed under the conditions of an extrusion temperature of 380 ° C. and an extrusion ratio of 20 or more. At this time, if the extrusion ratio is less than 5, the strength varies, which is not preferable in practice. On the other hand, if the extrusion ratio exceeds 35, the deformation resistance increases, the moldability deteriorates, and the mass productivity falls.

The content of hydrogen content of the obtained extrusion molded product, that is, the sintered product was analyzed, and the results are shown in Table 2. Table 2 also shows the amount of hydrogen contained in the high Si alloy cast product having the composition shown in Table 1 as the conventional sample a.

Next, the plurality of sintered products obtained in the item was subjected to dehydrogenation treatment. That is, each sintered product was separately charged into a vacuum furnace of 10 ^-2 to 10 ^-5 Torr, held under each condition (temperature, heating time) shown in Table 3, and then allowed to cool in the furnace. Then, the porosity of the dehydrogenated sintered product was examined, and the results are shown in Table 3. The pore diameter was several μm.

Further, each sample treated in the item was subjected to an artificial age hardening treatment (T ₆ treatment) after the solution treatment, but no crack occurred.

The strength test shown in Table 4 was performed on the sample treated at 470 ° C. for 4 hours and the sample a of the conventional example (implemented at room temperature).

Similarly, a seizure resistance test was conducted on the sample treated at 470 ° C. for 4 hours and the sample a of the conventional example, and the results are shown in Table 5.

The seizure resistance test is as follows. A disc-shaped test piece with a diameter of 70 mm is Cu-plated with a length of 5 mm, width of 5 mm, and thickness of 10
mm spheroidal graphite cast iron mating material is brought into contact, lubricating oil (engine oil) at 90 ° C is supplied to the sliding surface at 500 ml / min, and the test piece is rotated at a speed of 5 m / sec. Was gradually increased from 100 kg / cm ^{2 in} increments of 5 kg / cm ² , and the surface pressure at the time when seizure occurred was measured.

<Evaluation of Test Results> From Table 2, Example samples which are extrusion molded products (sintered products)
It can be seen that the hydrogen contents of I and II are extremely large as compared with the conventional sample a.

From FIG. 3, an example sample which is an extrusion molded product (sintered product)
It can be seen that when dehydrogenation treatment is performed on I and II, vacancies are generated with the removal of hydrogen gas contained in the sample, and the porosity increases as the time increases and the temperature increases.

The example samples I and II having pores have a sufficiently high tensile strength as compared with the conventional example sample a (Table 4), which shows that the formed pores are not harmful. There is.

From the comparison of seizure resistance between the sample samples I and II having pores and the conventional sample a (Table 5), it is clear that the presence of pores contributes to the improvement of seizure resistance.

EFFECTS OF THE INVENTION According to the present invention, a high-strength sintered Al alloy sliding member having excellent mechanical strength and seizure resistance can be obtained. Further, since the harmful hydrogen gas generated by the decomposition of the adsorbed water on the surface of the Al alloy powder was positively used without being removed in advance before the extrusion processing, it was possible to heat the green compact before the extrusion processing. There is no need to adjust the atmosphere (the adjustment with an inert gas or the like is troublesome), and thus the productivity of the member can be improved.

Claims (1)

[Claims] 1. In weight%, 10.0 ≦ Si ≦ 30.0, 2.0 ≦ Fe ≦ 10.
0, 0.5 ≤ Cu ≤ 7.5, 0.5 ≤ Mn ≤ 5.0 and 0.3 ≤ Mg ≤ 3.5, with the balance Al and Al alloy powder that is an unavoidable impurity, and a step of molding a green compact containing hydrogen. A step of subjecting the green compact to an extrusion process at an extrusion temperature of 300 to 450 ° C. to obtain an extruded product, and dehydrogenation of keeping the extruded product at a temperature of 450 to 520 ° C. for 0.5 to 7 hours in a vacuum. And a step of forming pores in the extruded product by performing a treatment, the method for producing a sliding member made of a high-strength sintered Al alloy.