JPH0788645A - Member made of aluminum alloy and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve joinability with a base material and improve thermal fatigue property by forming a high-strength layer by overlaying an Al-Cu based alloy by welding in a valve bridge part. CONSTITUTION:On the surface in a thermal stress concentration part (for example, a valve bridge part 4) in the base material (for example, a cylinder head 1) made of the aluminum alloy, the high-strength layer 5 composed by overlaying the Al-Cu based alloy whose solidus is higher than the base material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy member and its manufacturing method.

[0002]

2. Description of the Related Art Aluminum alloy castings are used as cylinder heads for automobile engines because of their heat conductivity, light weight and moldability.

By the way, as the engine becomes highly supercharged, the heat load on the cylinder head is increasing, and ensuring its reliability and durability has become an important issue. Especially in the highly supercharged diesel engine with severe heat load,
Thermal fatigue cracks in the valve bridge portion of the cylinder head (in other words, the intervalve portion between the intake hole and the exhaust hole) are becoming apparent, and effective measures are desired.

Among the various parts of the cylinder head, the valve bridge part has a large thermal stress due to the following reasons.
(Stress due to difference in thermal expansion) acts repeatedly.

(1) The highest temperature reached during operation.

(2) Rapid heating / cooling is repeated with operation / stop.

(3) Being restrained by the valve seat.

(4) It is easy to concentrate stress in terms of shape.

When the thermal stress as described above is repeated,
Thermal fatigue is likely to occur, which leads to penetration cracking in the worst case.

As a method for improving the thermal fatigue life,
Remelting processing (that is, remelting processing) using high-density energy such as laser and TIG arc is well known. This remelting treatment is a method of rapidly melting and solidifying the surface layer of the valve bridge portion by high-density energy and refining the metal structure to improve fatigue strength and characteristics, and is partially implemented.

According to this method, the thermal fatigue life can be improved to some extent simply by adding a remelting step to the conventional manufacturing step, but since the layer of the fine structure (that is, the modified layer) is as shallow as 2 to 3 mm, When the crack propagates beyond the modified layer, it rapidly expands. Therefore, it cannot be said that the fatigue life is improved sufficiently. Therefore, attempts have been made to make the modified layer deeper, but the deeper the remelt, the lower the solidification rate, the insufficient micronization of the metal structure, and the more easily defects such as bubble generation occur, and the fatigue life increases. There is a limit to the further improvement of.

As a method of improving the fatigue life of the valve bridge portion, a material having a higher thermal conductivity than the base material of the cylinder head with respect to the valve bridge portion (for example,
It is also proposed to form a thermal sprayed layer made of copper, copper alloy, silver, gold, etc. so as to quickly diffuse heat in the valve bridge portion (for example, JP-A-61-2242544). (See gazette).

[0013]

However, in the case of the sprayed layer in the above-mentioned known example, the sprayed layer is formed by spraying different metals such as copper and copper alloy onto the aluminum alloy constituting the base material of the cylinder head. Therefore, there may be a case where sufficient bonding strength cannot be obtained in both boundary layers, and since there is a difference in thermal expansion coefficient between the two, peeling in the boundary layer may become a problem.

The present invention has been made in view of the above points, and by forming a high-strength layer by depositing an Al-Cu alloy on the valve bridge portion to form a high-strength layer, the bondability with the base material is improved. In addition, the purpose is to improve thermal fatigue resistance.

[0015]

According to a first aspect of the present invention, as a means for solving the above-mentioned problems, the surface of the thermal stress concentration portion of the base material made of an aluminum alloy has a solidus line more than that of the base material. A high-strength layer is formed by overlay-bonding a high Al-Cu alloy.

In a second aspect of the present invention, as a means for solving the above-mentioned problems, in the aluminum alloy member according to the first aspect, the Al--Cu based alloy constituting the high strength layer is 2.0 to 7.0 wt% Cu and V, Zr, Ni
And at least one of the above.

According to a third aspect of the invention, as a means for solving the above-mentioned problems, in the aluminum alloy member according to the first or second aspect, the base material constitutes a cylinder head, and the heat treatment is performed. The stress concentration part is used as the valve bridge part.

In a fourth aspect of the present invention, as means for solving the above-mentioned problems, A having a solidus line higher than that of the base metal is formed on the surface of the thermal stress concentration portion of the base material made of an aluminum alloy.
The l-Cu alloy is welded by overlay welding, and then the base material is heat-treated to form a high-strength layer in the thermal stress concentrated portion.

In a fifth aspect of the present invention, as a means for solving the above-mentioned problems, in the method for producing an aluminum alloy member according to the fourth aspect, the Al--Cu based alloy constituting the high strength layer is replaced by 2 Cu of 0.0 to 7.0% by weight,
At least one of V, Zr, and Ni is contained.

In a sixth aspect of the present invention, as a means for solving the above-mentioned problems, in the method for producing an aluminum alloy member according to the fourth or fifth aspect, the base material constitutes a cylinder head, and The thermal stress concentration portion serves as a valve bridge portion.

[0021]

According to the invention of claim 1, 3, 4 or 6, the following effects can be obtained by the above means.

That is, the high-strength layer formed on the surface of the stress concentrating portion (for example, the valve bridge portion) in the base material (for example, cylinder head) made of aluminum alloy is the same kind of metal as the base material (for example, cylinder head). However, since it is assumed that the Al-Cu alloy having a higher solidus line than the base material (for example, the cylinder head) is welded by overlay welding, the metal structure becomes finer to the deep part and both A sufficient bonding strength can be obtained.

According to the invention of claim 2 or 5, the following effects can be obtained by the above means.

That is, since V, Zr, and Ni are substances that form a stable compound even at high temperature by adding a trace amount and improve the strength characteristics at high temperature, Al- which forms the high-strength layer.
By including it in the Cu-based alloy, the strength can be further enhanced at high temperatures. The content of Cu in the aluminum alloy constituting the base metal is set to 2.0 to 7.0% by weight because the content of 2.0% by weight or less deteriorates the build-up property and causes defects such as welding cracks. This is because it was taken into consideration that when the content exceeds 7.0% by weight, the strength is saturated and a coarse compound crystallizes to adversely affect the thermal fatigue strength.

[0025]

According to the invention of claim 1, 3, 4 or 6, the stress concentrating portion (eg valve bridge portion) in the base material (eg cylinder head) made of aluminum alloy.
A high-strength layer formed by overlay welding an Al-Cu-based alloy that is the same metal as the base material (for example, a cylinder head) and has a higher solidus line than the base material (for example, a cylinder head) on the surface of As a result, compared with the remelting process used conventionally, the metal structure becomes finer to a deeper part, and the bonding strength to the base material can be sufficiently obtained.
There is an excellent effect that the thermal fatigue resistance can be improved, the bond strength can be maintained high, and the durability against peeling and the like can be improved.

According to the invention of claim 2 or 5, V,
Since at least one of Zr and Ni is contained in the Al-Cu alloy forming the high strength layer, V,
Due to the strength-enhancing property of Zr and Ni possessed by high temperature, there is an excellent effect that the strength can be further enhanced at high temperature.

[0027]

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples.

In the following examples, FIGS.
As shown in FIG. 2, the valve bridge portion 4 (that is, between the intake hole 2 and the exhaust hole 3), which is a thermal stress concentration portion in the cylinder head 1 made of an aluminum alloy member, is made of an aluminum alloy that is a base material. An example is shown in which the high-strength layer 5 is formed by overlay welding an Al-Cu based alloy having a high phase line (in other words, a high freezing point). Reference numeral 6 is a valve seat of the intake hole 2, 7 is a valve seat of the exhaust hole 3, and 8
Is a cooling water passage.

The formation of the high-strength layer 5 will be specifically described. First, as shown in FIG. 3 (a), the recess 9 is formed in the valve bridge portion 4 by machining during or after casting. Then, as shown in FIG.
On the other hand, after overlay welding of an Al-Cu based alloy by TIG welding to form the overlay portion 5 ', the base material (that is, the cylinder head 1) is subjected to heat treatment (that is, quenching and tempering). After that, as shown in FIG. 3C, the raised portion of the built-up portion 5 ′ is cut to form the high-strength layer 5 on the valve bridge portion 4.

Next, the composition and solidus-liquidus (° C) of the base material and the overlay material used in Examples and Comparative Examples.
Is shown in Table 1.

[0031]

[Table 1]

Embodiment 1 This embodiment corresponds to the invention of claims 1 to 6.

An aluminum alloy having a composition of NO1 in Table 1 is used as a base material constituting the cylinder head 1, and an alloy having a composition of NO1 in Table 1 is used as a build-up material.
An l-Cu based alloy is used. The heat treatment condition at this time is 530
℃ × 4h → water quenching → 180 ℃ × 6h.

The high-strength layer 5 formed on the valve bridge portion 4 of the cylinder head 1 obtained as described above has a finer metallographic structure down to the deeper portion as compared with the conventionally used remelt treatment. At the same time, sufficient bonding strength to the base material can be obtained, so that thermal fatigue resistance can be improved, the bonding strength can be maintained high, and durability against peeling and the like can be improved. Moreover, in the case of the present embodiment, the Al--Cu based alloy forming the high-strength layer 5 has a grain size of 0.
Since 1% by weight of V and 0.15% by weight of Zr are contained, the strength improvement properties at high temperatures possessed by these substances can further enhance the strength at high temperatures.

Embodiment 2 This embodiment corresponds to the inventions of claims 1 to 6.

An aluminum alloy having a composition of NO1 in Table 1 is used as a base material constituting the cylinder head 1, and an alloy having a composition of NO2 in Table 1 is used as a build-up material.
An l-Cu based alloy is used. The heat treatment condition at this time is 530
℃ × 4h → water quenching → 180 ℃ × 6h.

In this case, Al--Cu forming the high-strength layer 5
Only the difference from Example 1 in that the system alloy contains 1.0% by weight of Ni, the same effect as in Example 1 can be obtained.

Embodiment 3 This embodiment corresponds to the inventions of claims 1, 3, 4 and 6.

An aluminum alloy having a composition of NO1 in Table 1 is used as a base material constituting the cylinder head 1, and an alloy having a composition of NO3 in Table 1 is used as a build-up material.
An l-Cu based alloy is used. The heat treatment condition at this time is 530
℃ × 4h → water quenching → 180 ℃ × 6h.

In this case, Al--Cu forming the high-strength layer 5
Example 1 is that the system alloy does not contain V, Zr, and Ni.
2 and 2, the refinement of the metal structure of the high-strength layer 5 and the bondability with the base material are the same as those of Examples 1 and 2.

Then, in order to confirm the effect of each of the above-mentioned examples, a thermal fatigue test was carried out together with Comparative Examples 1 to 3.

As shown in FIG. 4, the test piece 11 used in the thermal fatigue test has a length of 70 mm and a width of 150 formed of a base material having the compositions of NO1 and NO2 shown in Table 1.
mm, 15 mm thick rectangular parallelepiped (collected from a low-pressure cast ingot) is formed with a pair of holes 12, 12 at an interval of 4 mm.
A simulated valve bridge portion 13 was provided between 2 and 12. Examples 1 to 1 for the test piece 11
A thermal fatigue test was carried out on the simulated valve bridge portion 13 which was welded to the simulated valve bridge portion 13 by the same method as in No. 3 and Comparative Examples 1 to 3 described later by using the test apparatus shown in FIG.

The test apparatus comprises a rotor 14 having the test piece 11 attached to the outer periphery thereof, an oxygen-propane burner 15 for heating the test piece 11, and a test piece 11.
The cooling water tank 16 contains the cooling water W for cooling the cooling water, and the cooling water tank 17 for supplying the cooling water W to the cooling water tank 16. The test piece 11 is heated and cooled by the oxygen-propane burner 15. The thermal fatigue strength is represented by the number of cycles when cracks are connected in the simulated valve bridge portion 13 by repeating cooling with water W.

Comparative example 1 is the unprocessed one using the NO1 base material in Table 1, Comparative example 2 is the unprocessed one using the NO2 base material in Table 1, and Comparative example 3 is the NO2 base material in the table 1. The simulated valve bridge portion 13 was used after being subjected to remelting treatment and then heat treatment. The heat treatment conditions after the remelt treatment are: 500 ° C x 4h → water quenching → 180 ° C
It was x6h.

The thickness of the high-strength layer 5 in Examples 1 to 3 and the thickness of the modified layer in Comparative Example 3 were about 3 mm.

The test results were as shown in Table 2.

[0047]

[Table 2]

From the above test results, it can be seen that Examples 1 to 3 are superior in thermal fatigue strength at all the highest attainable temperatures as compared with Comparative Examples 1 to 3. Particularly, those of Examples 1 and 2 are excellent.

[Brief description of drawings]

FIG. 1 is a plan view of a cylinder head that is an embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is an explanatory view showing a procedure of build-up welding in the embodiment of the present invention.

FIG. 4 is a plan view of a test piece used for a thermal fatigue test.

FIG. 5 is a schematic side view of a test apparatus used for a thermal fatigue test.

[Explanation of symbols]

1 cylinder head, 2 intake holes, 3 exhaust holes, 4 valve bridge part, 5 high strength layer.

Claims (6)

[Claims] 1. An Al-base having a solidus line higher than that of the base metal on the surface of the thermal stress concentration portion of the base material made of an aluminum alloy.
An aluminum alloy member having a high-strength layer formed by overlay-bonding a Cu-based alloy. 2. The Al—Cu-based alloy forming the high-strength layer contains 2.0 to 7.0% by weight of Cu and at least one of V, Zr, and Ni. The aluminum alloy member according to claim 1, wherein the member is made of aluminum alloy. 3. The aluminum alloy member according to claim 1 or 2, wherein the base material constitutes a cylinder head, and the thermal stress concentration portion is a valve bridge portion. 4. An Al- having a higher solidus line than the base metal on the surface of the thermal stress concentration portion of the base material made of an aluminum alloy.
A method for manufacturing an aluminum alloy member, characterized in that a Cu-based alloy is welded by overlay welding, and then the base material is heat-treated to form a high-strength layer in the thermal stress concentrated portion. 5. The Al—Cu alloy forming the high-strength layer contains 2.0 to 7.0% by weight of Cu and at least one of V, Zr, and Ni. The method for manufacturing an aluminum alloy member according to claim 4, wherein 6. The method for producing an aluminum alloy member according to claim 4, wherein the base material constitutes a cylinder head, and the thermal stress concentration portion is a valve bridge portion. .