JPH0681710A - Local reinforcing method for cylinder head made of aluminum - Google Patents

Abstract

PURPOSE:To provide a local reinforcing method by which thermal cracking of an aluminum made cylinder head can be prevented from occurrence by sufficiently improving heat resistance easily and inexpensively at a part where an occurrence of thermal cracking may be expected. CONSTITUTION:After a part 11, where an occurrence of thermal cracking may foreseen in a cylinder head 10 made of aluminum when a buildup is not made, is reinforced by a buildup 12 of a heat resistant constituent, heat expansion buffer material 18 is built up again 19 in the middle position 17 between the part 11, where a cracking is foreseen before the reinforcement, and the part 16, where the cracking is foreseen after the reinforcement, following the elimination of a heat resistant constituent buildup part 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for locally strengthening an aluminum cylinder head of an internal combustion engine or the like, and more particularly to a method for locally strengthening an aluminum cylinder head by means of reinforced overlay.

[0002]

2. Description of the Related Art In recent years, with the increase in engine output, there has been a problem that an increase in heat load due to a temperature rise on an aluminum cylinder head and an increase in mechanical load.

That is, as shown in FIG. 6, due to this increase in load, the lower surface of the aluminum cylinder head 1, especially between the intake port 2 and the exhaust port 3 which is a relatively thinner portion than other portions (intervalve). Portion) and a portion between these ports 2 and 3 and the hot plug hole 4 will have thermal cracks 5.

The local strengthening method conventionally adopted as a measure to prevent this thermal cracking has the following techniques. First, the first means is a local strengthening method by alloying, in which an appropriate amount of heat resistant components (Cr, Mo, Cu, Ni, etc.) is added to improve heat resistant strength.

The second means is a local strengthening method by casting, in which a steel material or a refractory metal material is cast in a thermal cracking site.

Further, the third means is a local strengthening method by an improved treatment, in which an appropriate amount of strontium or titanium is added,
The crystal grains to be precipitated were made finer, the tensile strength was increased, and at the same time, the elongation property was improved and the heat crack resistance was improved.

And, the fourth means is a local strengthening method by a hard alumite treatment.
The heat resistance was improved by forming it to a thickness of about 00 μm.

In addition, the fifth means is a local strengthening method by remelting treatment, in which the aluminum base material is melted and rapidly cooled and solidified by a high-density energy source such as laser, electron beam, TIG, etc., whereby the crystal grains are miniaturized. It was intended to improve heat resistance.

[0009]

The conventional local strengthening method for an aluminum cylinder head has the following problems.

First, the local strengthening method by alloying as the first means increases the cost and deteriorates the castability due to the addition of the alloy, and causes casting defects such as "shrinkage cavities".
There was a problem that productivity and yield were deteriorated. In addition, there is a problem that due to the deterioration of the castability, the amount of micro-shrinkage that has a great influence on the heat resistance increases, and the alloying rather deteriorates the heat resistance.

In addition, the local strengthening method by casting as a second means requires aluminizing treatment as a pretreatment of the cast-in steel material in order to secure the cast-in property, as well as the oxidation prevention and the casting temperature. Thorough management and non-destructive inspection after casting have been required, resulting in a significant increase in man-hours.

Further, the local strengthening method by the improving process as the third means is a simple improving method, but there is a problem that the strengthening effect is small.

The local strengthening method by the hard alumite treatment as the fourth means has a larger heat resistance improving effect than the above alloying or improving treatment, but in order to treat only the cracked portion, the other portion is treated. There has been a problem that an alumite removing process by masking is required, which is a laborious and expensive process.

In addition, the local strengthening method by remelting treatment as the fifth means is a treatment having a simple treatment method and a large effect of improving heat resistance, but it is insufficient for the heat resistance improvement target currently required. There was a problem that was.

In view of the above-mentioned problems, an object of the present invention is to simply and inexpensively sufficiently improve the heat resistance of a portion where cracks are expected to occur and prevent the occurrence of thermal cracks. To provide.

[0016]

In order to achieve the above-mentioned object, a method for locally strengthening an aluminum cylinder head according to the present invention comprises:
After strengthening the predicted crack occurrence part of the aluminum cylinder head during non-build-up with a heat resistant component, it is located at an intermediate position between this predicted crack occurrence part during non-build-up and the crack occurrence predicted part after the above-mentioned strengthened build-up. After removing the heat-resistant component build-up portion, the thermal expansion cushioning material is built up again.

Preferably, the thermal expansion cushioning material is made of an aluminum-based alloy that is more resistant to thermal cracking than an aluminum casting as a base material of the cylinder head and has a thermal expansion coefficient equivalent to that of the base material.

[0018]

According to the above-mentioned structure, the portion where cracks are expected to occur when the aluminum cylinder head is not overlaid is reinforced with the heat resistant component. Therefore, this reinforced overlay improves the heat resistance of the portion where cracks are expected to occur when the overlay is not built up, and prevents the occurrence of thermal cracks in that portion.

However, as a result of improving the heat resistance of the predicted cracking site during non-build-up by this reinforced build-up, the site where thermal cracking occurs after this reinforced build-up is located at a position other than the reinforced build-up part. Change. It is considered that the cause of the change of the site where the thermal crack occurs is due to the difference in the thermal expansion coefficient between the heat-resistant component as the overlay material and the aluminum casting as the base material.

Therefore, after removing the heat resistant component build-up portion, the thermal expansion cushioning material is re-build-up at an intermediate position between the site where the crack is expected to occur during the non-buildup and the site where the crack is expected to be produced after the reinforced buildup. It The thermal expansion cushioning material used for the re-buildup is an aluminum-based alloy that is more resistant to thermal cracking than the aluminum casting used as the base material of the cylinder head and has a thermal expansion coefficient equivalent to that of the base material. That is, the buildup is strengthened by the heat-resistant component only in the weakest part of the aluminum cylinder head, and the thermal stress due to the difference in thermal expansion is alleviated at the intermediate position. This intermediate position does not need to have the heat resistance as much as the predicted crack initiation site during non-buildup.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a method for locally strengthening an aluminum cylinder head according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic view showing a method of locally strengthening an aluminum cylinder head of this embodiment. As shown in the drawing, first, a heat-resistant component is overlaid 12 on the predicted crack occurrence site 11 when the aluminum cylinder head 10 is not overlaid to locally strengthen it. The crack occurrence predicted portion 11 at the time of non-buildup is the lower surface of the aluminum cylinder head 10, especially between the intake port 13 and the exhaust port 14 (interval valve portion), which is a portion relatively thinner than other portions, And these ports 1
It is a portion between 3, 14 and the hot plug hole 15. Specifically, as shown in FIG. 2, it is a portion surrounded by a triangle D-C-E, and in particular, the frequency of thermal cracks that occur is large, and the portion having a large size is a shaded portion X, This is the part indicated by Y. The heat-resistant component is, for example, Ni, Co, M
The overlay 12 is performed by composite welding of TIG welding and MIG welding using a welding wire made of o, Cu, W or the like and filled with a capsule powder formed of the heat resistant component.

Next, the heat-resistant component build-up portion 12 is located at an intermediate position 17 between the crack occurrence predicted portion 11 (shaded portions X and Y) during the non-buildup and the crack occurrence predicted portion 16 after the reinforced buildup. After removing, the thermal expansion cushioning material 18 is overlaid 19 again. As shown in FIG. 3, the predicted crack initiation site 16 after the reinforced overlay is a portion x, near the diagonal line portions X, Y, as shown in FIG.
It is y. Therefore, the center between the shaded portions X and Y and the neighboring portions x and y becomes the intermediate position 17, and the overlaying 19 is performed on the intermediate position 17 by TIG welding. When this overlay welding is performed, the heat-resistant component overlay 12 that has been formed in advance is machined into a V-shaped groove having a width of 3 to 5 mm and a depth of 3 to 5 mm, and the V-shaped groove is re-coated. Welding is performed. The thermal expansion cushioning material 18 as a material for the re-buildup 19 is made of an aluminum alloy having a higher thermal expansion coefficient than an aluminum casting as a base material of the cylinder head 10 and having a thermal expansion coefficient equivalent to that of the base material. Specifically, JISA1100 series pure aluminum welding wire and low alloy JISA500
Re-buildup 18 is performed using a No. 0 welding wire or the like.

Next, the operation of the above embodiment will be described.

As shown in FIG. 2, according to the bench acceleration durability test, the area where the thermal crack occurs in the aluminum cylinder head 10 is the area surrounded by the triangle D-C-E. Better known. It is also known that the frequency of thermal cracks that occur is large and that the size of the size is large as indicated by the shaded portions X and Y as described above. Therefore, the portion where the heat-resistant component reinforcement overlay 12 by welding is required is centered on the portion indicated by the shaded portions X and Y. When the shaded portions X and Y are hardened by a heat-resistant component, the shaded portions X and Y can be strengthened to prevent thermal cracks, but the strengthened welded portions 12 make the positions weak against heat cracks. It will change. The position is the vicinity x, y of the shaded portions X, Y. Therefore, the portion for strengthening the build-up is located in the vicinity x,
Need to extend to y.

Depending on the engine model, the neighboring parts x and y, which are weak against thermal cracks, may come to the position of the z part shown in FIG. Therefore, every time a new engine is developed,
If the engine is subjected to an accelerated durability test after the reinforced overlay and the overlay reinforced portion is changed, it takes a long time for development and there is a problem that the cost required for the development becomes very large.

Then, as a result of analyzing the cause of the change in the crack generation position by the overlay strengthening depending on the engine type as described above, it was found that the thermal expansion coefficient was different between the heat resistant component as the overlay material and the aluminum casting as the base material. It has been found. That is, according to the present invention, the strengthening overlay 12 is performed only on the weakest portion of the aluminum cylinder head 10, and the above-mentioned neighboring portions x and y are provided.
Is to solve the problem in terms of the difference in the coefficient of thermal expansion, which is the main cause.

That is, the shaded portions X and Y and their neighboring portions x and
At the intermediate position 17 which is the center of y, the thermal expansion cushioning material 18
It is better to re-build 19 above. This is because the intermediate position 17 does not require heat resistance as much as the shaded portions X and Y. Therefore, in FIG. 1, the overlay 1 is formed in the range of the shaded portions X and Y.
2. At the intermediate position 17 between the shaded portions X and Y and the adjacent portions x and y in AB and CD, the aluminum casting as the base material is more resistant to thermal cracks and the coefficient of thermal expansion is different from that of the base material. It suffices to re-build 19 the thermal expansion cushioning material 18 that is substantially the same. In FIG.
The same applies to the portions D-E and F-G. As described above, the present invention is capable of sufficiently improving the heat resistance of the predicted crack initiation site 11 by the overlay welding, which is a simple and inexpensive local strengthening method, and prevents the occurrence of thermal cracks.

As shown in FIG. 5, it is possible to prevent thermal cracks based on the difference in thermal expansion by overlaying the heat-resistant component up to the range of V. However, in this method, it is necessary to widen the width of W in FIG. 4 at the time of welding, and there are problems that it is difficult to control the preheating temperature due to the long welding time, and the process time becomes long. . Further, it becomes difficult to control the preheating temperature, so that there is a problem that the molten metal is burned down.

[0030]

As described above, according to the method for locally strengthening the aluminum cylinder head according to the present invention, the heat resistance of the crack occurrence predicted portion can be sufficiently improved easily and inexpensively, and the occurrence of the heat crack can be prevented. The excellent effect of being able to do is exhibited.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a method for locally strengthening an aluminum cylinder head according to the present invention.

FIG. 2 is a schematic diagram showing a predicted site of thermal cracking when the aluminum cylinder head according to the present invention is not overlaid.

FIG. 3 is a schematic view showing a predicted site of occurrence of thermal cracks after the hardfacing of the aluminum cylinder head according to the present invention.

FIG. 4 is a schematic view showing a change in a thermal crack occurrence site due to a difference in model of an aluminum cylinder head.

FIG. 5 is a schematic view showing another example of a method for locally strengthening an aluminum cylinder head by overlaying.

FIG. 6 is a schematic view showing a site where a thermal crack occurs in a conventional aluminum cylinder head.

[Explanation of symbols]

 10 Cylinder head made of aluminum 11 Predicted site of crack generation when not built up 12 Reinforced buildup 16 Predicted site of crack generation after reinforced buildup 17 Intermediate position 18 Thermal expansion cushioning material 19 Rebuilding

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenji Hida 8 Tsutana, Fujisawa City Kanagawa Prefecture Isuzu Central Research Institute Co., Ltd. (72) Inventor Yuji Matsunami 8th Tsuna shelf, Fujisawa City Kanagawa Prefecture Isuzu Central Research Co., Ltd. In-house

Claims (2)

[Claims] 1. An aluminum cylinder head, which has a predicted crack generation portion during non-build-up, is strengthened with a heat-resistant component, and then a predicted crack generation area during non-build-up and a predicted crack generation area after the strengthened build-up. A method for locally strengthening an aluminum cylinder head, characterized in that the heat-expansion cushioning material is removed at the intermediate position, and then the thermal expansion cushioning material is re-laid up. 2. The aluminum-made alloy according to claim 1, wherein the thermal expansion buffer material is made of an aluminum-based alloy that is more resistant to thermal cracking than an aluminum casting as a base material of the cylinder head and has a thermal expansion coefficient equivalent to that of the base material. Local strengthening method of cylinder head.