JPH10251790A - Aluminum alloy casting excellent in thermal fatigue strength - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain Al alloy casting excellent in thermal fatigue characteristics and castability by specifying the microstructure and the average size equivalent to a circle in an Al alloy in which the contents of Si, Cu and Mg are specified and furthermore allowing it to contain eutectic Si in which the average roundness is specified. SOLUTION: The compsn. of Al alloy casting is composed of, by weight, 4 to 10% Si, 0 to 5% Cu. 0 to 1.0% Mg, and the balance Al with inevitable impurities. In the microstructure of this Al alloy casting, secondary dendrite arm spacing measured by a intersection method is regulated to 45μm, and the average size equivalent to a circle is regulated to <=10μm, Also, it is allowed to contains eutectic Si having >=70% average roundness. Furthermore, it is preferable that the area ratio of crystallized products other than eutectic Si in the microstructure is regulated to <=3% and the average roundness of the crystallized products is regulated to >=50%. Moreover, the porosity in the part to be applied with the heat loads of the Al alloy casting is preferably regulated to <=0.3%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy casting having excellent thermal fatigue strength, and more particularly to a cylinder head of a vehicle, particularly an automobile engine, which is required to have particularly high heat resistance.
The present invention relates to an integrally cast cylinder head made of an aluminum alloy casting.

[0002]

2. Description of the Related Art Cylinder heads made of aluminum alloy are often used in automobile engines, particularly gasoline engines, from the viewpoints of weight reduction, improvement of cooling performance, easiness of processing, and the like. Aluminum alloys for heads are generally JIS AC2A, AC2B, AC4B, A
C4C alloy or the like is used. Also, JP-A-49-5
No. 5515 discloses that 0.8 to 0.8 mm is used to improve thermal fatigue.
There is an example in which Mo, V, and Cr are added to an aluminum alloy containing 1.6% of Si and 3 to 4.8% of Mg.
However, the aluminum alloy disclosed in Japanese Patent Application Laid-Open No. 49-55515 has low castability (flowability) due to low Si content, and requires a large feeder depending on the product shape, resulting in poor casting yield. It is not practical.

In order to improve the thermal fatigue characteristics as one of the improvements in heat resistance, there is a technique for refining the microstructure by performing post-treatments such as re-melting and building up of different materials.
For example, JP-A-59-28049 discloses that the AC
High temperature exhaust valve in 4B alloy casting
A technique is disclosed in which a high toughness Al alloy is overlaid on a sheet portion to partially strengthen the sheet portion.

As another means for improving heat resistance, there is a technique of casting a heat-resistant material into a desired portion of an aluminum cylinder head. On the other hand, it is said that reducing casting defects also has the effect of improving heat resistance. In order to prevent casting defects, as disclosed in Japanese Patent Publication No. Hei 6-73740, a sodium element supply layer is formed in a portion of a mold where casting defects are likely to occur, and molten metal flowing into the mold is formed. There is a technology for efficiently adding sodium to a steel to prevent defects.

Japanese Patent Application Laid-Open No. 2-121766 discloses an aluminum cylinder head and a method for manufacturing the same. That is, "the entire aluminum cylinder head is formed of a hardened portion subjected to T5 or T6 heat treatment, and only the portion of the hardened portion where low cycle thermal fatigue is likely to occur has reduced the magnesium amount to less than 0.1% by weight. The aluminum cylinder head is formed by softening the aluminum cylinder head. The aluminum cylinder head is formed by "casting an aluminum alloy in a cylinder head-shaped mold and subjecting the entire molded article to T5 or T6 heat treatment. Before or after the T5 or T6 heat treatment, only the portion where low cycle thermal fatigue is likely to occur is re-melted in a vacuum atmosphere to reduce the magnesium content to less than 0.1% by weight. "
Here, "the part where low cycle thermal fatigue is likely to occur"
This is a substantially triangular portion connecting the hot plug 21, the intake port 22, and the exhaust port 23 of the ignition surface 20 of the aluminum cylinder head 26 indicated by oblique lines in FIG. 3. Reference numeral 25 denotes a hardened portion, reference numeral 27 denotes a softened portion, and reference numeral 24 denotes an intake port 22.
And the seat insert of the exhaust port 23.

Japanese Patent Application Laid-Open No. Sho 62-248555 discloses that "a eutectic Si is finely divided by casting a molten aluminum alloy for casting containing a relatively large amount of Si using a mold and performing high-speed cooling. Aluminum alloy cylinder head ".

[0007]

However, the remelting, overlaying of dissimilar materials, and cast-in techniques have a problem that the production cost is high, and a low-cost microstructure control method that can be performed at the time of casting is required. I was Further, the addition of sodium has the effect of dispersing the shrinkage cavities that are concentrated, but even in such a case, since minute defects remain, the combination is often combined with degassing. However, it is difficult to perform degassing in the mold, and it is impossible to completely prevent minute defects. For this reason, the heat resistance was insufficient for use in a part where a large heat load was applied.

As disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2-121766, when only a portion of the hardened portion where low cycle thermal fatigue is likely to occur is formed in the softened portion, there is a possibility that settling may occur during combustion. There is a problem of lack of dimensional stability.
After all, it is considered that hardness and rigidity are necessary. Further, as disclosed in the above-mentioned JP-A-62-248555, eutectic S
There is a problem that it is difficult to improve the fatigue strength only by miniaturization of i. In order to improve the fatigue strength, eutectic S
In addition to miniaturization of i, it is necessary to introduce a concept of making the shape of eutectic Si as round as possible.

[0009] The present invention has been made in view of the above problems,
An object of the present invention is to provide an aluminum alloy casting and a cylinder head which are required to have heat resistance due to an aluminum alloy having excellent heat fatigue properties and excellent castability.

[0010]

That is, the aluminum alloy casting excellent in thermal fatigue strength according to the present invention has a weight ratio of Si:
4 to 10%, Cu: 0 to 5%, Mg: 0 to 1.0%, the balance of Al and the composition of unavoidable impurities, and the microstructure of the aluminum alloy casting is obtained by a crossing method. It is characterized by having eutectic Si having a measured secondary dendrite arm spacing of 45 μm or less, an average equivalent circle diameter of 10 μm or less, and an average circularity of 70% or more.

[0011] The area ratio of crystallized substances other than eutectic Si in the microstructure of the aluminum alloy casting is 3% or less;
The crystallized product has an average circularity of 50% or more. Further, the porosity of the portion of the aluminum alloy casting that receives the thermal load is 0.3% or less. Also, as an improver of eutectic Si, N
a: 0.002 to 0.030%, Sr: 0.002 to
It is made of an aluminum alloy containing at least one element of 0.030% and Sb: 0.02 to 0.20%. The aluminum alloy casting is a cylinder head.

Since the aluminum alloy casting of the present invention has the above-mentioned microstructure characteristics, the aluminum alloy casting cylinder head has excellent thermal fatigue characteristics in a portion in a combustion chamber which is repeatedly subjected to a thermal load. Hereinafter, the present invention will be described in more detail. The smaller the secondary dendrite arm spacing (hereinafter referred to as DAS2) measured by the intersection method in the microstructure of the aluminum alloy casting, the smaller the strength and strength.
It is known that toughness is improved.

In particular, the thermal fatigue strength is greatly improved by setting DAS2 to 45 μm or less. When applied to an engine having a large heat load, DAS2 is desirably 30 μm or less. Even if DAS2 of the microstructure is 45 μm or less, if the average circle-equivalent diameter of eutectic Si is larger than 10 μm and the average circularity is less than 70%, when a repeated heat load is applied. In addition, the interface between the aluminum matrix and the eutectic Si promotes the generation and propagation of cracks and lowers the thermal fatigue characteristics. Reduction of DAS2 was achieved by improving the cooling rate of the casting by local cooling of the mold during casting.
The reduction of the average equivalent circle diameter of i and the improvement of the average circularity are as follows:
The eutectic Si is refined by adding a eutectic Si improving element such as Sr, and the solution treatment conditions in the heat treatment are optimized. Therefore, in the aluminum alloy casting and the aluminum alloy casting cylinder head of the present invention,
It is necessary to satisfy the values of these three factors that DAS2 has a eutectic Si of 45 μm or less, an average equivalent circle diameter of 10 μm or less, and an average circularity of 70% or more.

The value of DAS2 in the present invention is measured by the intersection method specified by the Japan Light Metal Institute. Materials of the Japan Light Metal Association [Light Metals (1988), Document 3, page 54-
60], the value of DAS2 measured by the intersection method is about 1.5 times the value measured by the secondary branch method. Also, DAS
In the case of a cellular structure in which the value of 2 cannot be measured, it may be replaced with a dendrite cell size (DCS).

The average equivalent circle diameter (μm) is a value expressed by the following equation (1) and indicates the degree of microstructure refinement. For example, the smaller the value of the average equivalent circle diameter (μm), the finer the microstructure. The average circularity (%) is a value represented by Expression 2, and 100 (%) in a perfect circle.
And indicates the degree of the eutectic Si to a circle. Therefore,
The larger the value of the average circularity (%) is, the closer the shape of the eutectic Si is to a perfect circle and rounded.

[0016]

(Equation 1)

[0017]

(Equation 2)

Next, crystallized substances other than eutectic Si will be described. Crystallized substances other than eutectic Si are Mg-Si based, A
Compounds such as l-Cu, Al-Si-Fe, etc., most of which are coarse and irregular in shape, such as needles, blocks, or kanji, and these crystals promote the growth of thermal cracks. I do. Therefore, it is necessary to reduce the amount of crystallization. Desirably, if the area ratio of the crystallized product is 3% or less and the average circularity is 50% or more, the heat crack resistance is remarkably improved. Reduction of the area ratio of the crystallized substances other than eutectic Si and improvement of the average circularity are performed by reducing impurities such as Fe and optimizing the solution treatment conditions in the heat treatment. Next, regarding the porosity in the microstructure, the strength, toughness, and thermal fatigue strength decrease when the porosity is present. If the porosity rate exceeds 0.3%, the effect is large, so 0.3%
It was as follows. The porosity rate (%) is a value obtained from the apparent density and the true density measured by the Archimedes method. The porosity rate is reduced by reducing hydrogen gas in the molten metal by degassing.

Hereinafter, the reasons for limiting the alloy elements constituting the present invention will be described. (1) Si: 4 to 10% The reason for setting Si to 4 to 10% is that the shape of the cylinder head is complicated and good castability is required. When the Si content is less than 4% or more than 10%, the shrinkage is large, and it is difficult to produce a sound casting by a general casting method such as gravity casting and low pressure casting. In addition, a large hot water is required, and the injection yield decreases. For this reason, the lower limit of the Si content is set to 4% and the upper limit is set to 10%.

(2) Cu: 0 to 5% The strength is improved by adding Cu. However, if the Cu content exceeds 5%, the castability is poor and the toughness is reduced. It was as follows. In the present invention, the lower limit of the Cu content is indicated as 0 (zero) because the case where Cu may not be contained is included.

(3) Mg: 0 to 1.0% The strength is improved by adding Mg. However, if the content exceeds 1%, the toughness is remarkably reduced, so 1% or less is desirable. In the present invention, the lower limit of the Mg content is indicated as 0 (zero), because the case where Mg may not be contained is included.

(4) Rest: Al and inevitable impurities Includes inevitable impurities such as Fe and Zn, and is based on aluminum.

(5) Eutectic Si improving agent: Na, S
r or Sb In addition to the composition comprising the above (1) to (4), as an improving agent for eutectic Si, Na: 0.002 to 0.002
0.030%, Sr: 0.002 to 0.030%, S
b: It is more desirable to contain at least one element of 0.02 to 0.20%. The alloy of the present invention exhibits high strength and toughness by performing the optimal heat treatment, and it is the eutectic Si improvement treatment that contributes to the improvement of toughness. S
The desired eutectic Si is obtained by adding 0.002 to 0.030% for r and Na and 0.02 to 0.20% for Sb.
The shape is obtained.

The heat treatment is performed when Cu is contained (No. 1 of the alloy of the present invention shown in Table 1 described later in the embodiment).
1 to No. 4, no. No. 10 and No. 10 of the comparative alloy. 11
-No. 13) Although elongation is reduced, T7 heat treatment (for example, solution treatment: 50) is performed to impart strength and proof stress.
0 ° C × 6 hours, artificial aging treatment: 220-250 ° C ×
(2-4 hours). When Cu is not contained (Nos. 5 to 9 of the alloys of the present invention and Nos. 14 to N of the comparative alloys shown in Table 1 described later in the embodiment).
o. 16) In order to impart not only strength but also elongation, T
6 heat treatment (for example, solution treatment: 530 ° C. × 6 hours,
(Artificial aging treatment: 180 ° C. × 4 hours).

According to the present invention, the structure of the aluminum alloy for casting (for example, DAS2, eutectic Si, porosity, crystallization) can be controlled. Therefore, it is possible to manufacture an aluminum alloy casting that can withstand deformation due to repeated thermal loads, and the thermal fatigue characteristics are significantly improved as compared with conventional alloys.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to tables and photomicrographs. (Embodiment) FIG. 1 according to the present invention is a view showing the structure of one combustion chamber of a four-cylinder cylinder head. It has a structure having an intake port 15 (see FIG. 2), one exhaust port 4, and a fuel injection nozzle 8. This aluminum alloy cylinder head 1 was cast by a low-pressure casting method (injection temperature: 700 ° C.) using molten aluminum having the chemical components shown in Table 1. At this time, the structure surrounded by the intake / exhaust port and the fuel injection nozzle 8 was miniaturized using spot water cooling of a mold. In addition, No. of the comparative example shown in Table 1. 11-No. No. 16 did not perform water cooling. Table 2 shows the results. 1 and 2, reference numeral 2 denotes a cylinder head body, 3 denotes an ignition surface, 5 denotes an exhaust valve, 6 denotes an exhaust valve seat, 7 denotes a combustion chamber, 8a denotes a fuel injection nozzle mounting hole, 9 denotes a piston, Indicates a cylinder block, 11 and 12 indicate water cooling jackets, 13 indicates a gasket, and 14 indicates an intake valve seat. In addition, the test piece used for the example of the alloy of the present invention was collected from a portion including the igniting surface 3. The heat-treated and processed test pieces were subjected to a thermal fatigue test to evaluate the thermal fatigue life in cycles up to the occurrence of cracks. The test conditions for the thermal fatigue test are from 50 ° C to 250 ° C
Heat until: 5 minutes, hold at 250 ° C: 10 seconds, 250 °
Cooling from C to 50 ° C .: 5 minutes, restraint rate was 1.0.

[0027]

[Table 1]

[0028]

[Table 2]

Table 1 shows Example No. of the alloy of the present invention. 1 to
No. 10 and Comparative Example No. of the comparative alloy. 11-No. 16
Table 2 shows the thermal fatigue life, DAS, average equivalent circle diameter and average circularity of eutectic Si, and crystallized substances other than Si (hereinafter simply referred to as crystallization). The area ratio, the average circularity, and the porosity ratio are shown.

Comparative Example No. 11-No. In the case of Example No. 16 of the alloy of the present invention, the thermal fatigue life was 412 to 528 cycles. 1 to No. For 10, 7
A long thermal fatigue life of 32 to 1122 cycles was obtained.

Hereinafter, examples of the alloy of the present invention and comparative examples of comparative alloys will be compared and described in detail. 1) Example No. of the alloy of the present invention. 1 is Al-7.8% S
An improvement treatment was performed by adding 0.025% of Na to an i-3.2% Cu alloy, and a die was subjected to spot water cooling and T7 heat treatment was performed during casting. The Fe content was 0.36%, which is almost the same as usual, the solution treatment of the heat treatment was performed at the usual 500 ° C., and the degassing treatment was not performed. As a result, DAS3
9 μm, eutectic Si average circle equivalent diameter 5.2 μm, eutectic Si average circularity 79%, crystallized matter area ratio 3.5%, crystallized material average circularity 44%, porosity rate 0.35% (FIG. 4 and FIG. 5), Comparative Example No. of the same alloy-based comparative alloy. 1
DAS and eutectic Si mean circle equivalent diameter are smaller than
The eutectic Si average circularity is large. For this reason, the thermal fatigue life was no. 11-No. 13 412-
It showed 732 cycles better than 454 cycles.

2) Example No. of the alloy of the present invention 2 corresponds to Example No. 2. The same alloy system as in No. 1 was modified with Sr,
e content reduced to 0.12%, solution treatment 510 °
C and high temperature. As a result, Example No.
1, the Al-Si-Fe-based compound decreases,
Since the solid solution of the Cu-based compound advanced, Compared to No. 1, the eutectic Si average circularity increased to 81%, the crystallization area ratio decreased to 2.7%, and the crystallization average circularity also increased to 53%. Therefore, the thermal fatigue life increased up to 782 cycles.

3) Example No. of the alloy of the present invention. No. 3 is the same as that of Example No. 3. In the same alloy system as in No. 1, an improvement process was performed with Sb, and a degassing process was performed to reduce the amount of hydrogen gas. As a result, Example No. Compared to 1, the porosity rate was reduced to 0.24%, so the thermal fatigue life increased to 786 cycles.

4) Example No. of the alloy of the present invention No. 4 is Example No. 4. In the same alloy system as in Example 1, the Fe content was reduced to 0.12%, solution treatment was performed at a high temperature of 510 ° C., and degassing was performed. As a result, Example No. Compared to 1, the area ratio of the crystallized product was reduced to 2.7%, the average circularity of the crystallized product was increased to 53%, and the porosity was reduced to 0.24%. Therefore, the thermal fatigue life increased to 832 cycles.

5) Example No. of the alloy of the present invention. 5 is Al
0.03% Sb in -6.9% Si-0.32% Mg alloy
%, The mold was subjected to spot water cooling, and a T6 heat treatment was performed during casting. The Fe content is 0.34%, which is about the same as usual, and the solution heat treatment is usually 530%.
° C, and no degassing was performed. As a result, D
AS 41 μm, eutectic Si average circle equivalent diameter 5.3 μm, eutectic Si average circularity 73%, crystallization area ratio 0.4%, crystallization average circularity 47%, porosity rate 0.37%, same Comparative Example No. 14 compared to DA
The average circle equivalent diameter of S and eutectic Si is small, and the average circularity of eutectic Si is large. For this reason, the thermal fatigue life was no. 14-No. It showed 806 cycles better than 16 475-528 cycles.

6) Example No. of the alloy of the present invention. No. 6 is Example No. 6. The same alloy system as in No. 5 was modified with Na,
e content reduced to 0.12%, solution treatment 540 °
C and high temperature. As a result, Al-Si-
Fe-based compounds decrease, eutectic Si becomes spherical and Mg-S
Since the solid solution of the i-type compound advanced, 5 compared to DAS 41 μm and eutectic Si average circle equivalent diameter 4.9 μm
, The mean circularity of eutectic Si slightly increased to 78%, the area ratio of crystallized matter decreased to 0.2%, and the average circularity of crystallized matter increased to 55% (FIG. 6 and FIG. 7). Therefore, the thermal fatigue life increased to 853 cycles.

7) Example No. of the alloy of the present invention 7 is Example No. 7. In the same alloy system as in Example 5, the Fe content was reduced to 0.12%, solution treatment was performed at a high temperature of 540 ° C., and degassing was performed. As a result, Example No. Compared to No. 5, the average circularity of eutectic Si increased to 78%, the area ratio of crystallized matter decreased to 0.2%, the average circularity of crystallized matter increased to 55%, and the porosity was 0.22%. %. Therefore, the thermal fatigue life increased to 907 cycles.

8) Example No. of the alloy of the present invention No. 8 is Example No. 8. The same molten metal as in No. 7 was used, and the spot water cooling of the mold at the time of casting was further enhanced, and solution treatment was performed at 540 ° C. As a result, the DAS can be reduced to 30 μm (see FIGS. 8 and 9), so that the thermal fatigue life is 1
Increased to 122 cycles.

9) Example No. of the alloy of the present invention 9 is Al
0.08% Sb in -9.5% Si-0.75% Mg alloy
%, The mold was subjected to spot water cooling, and a T6 heat treatment was performed during casting. The Fe content is 0.34%, which is about the same as usual, and the solution heat treatment is usually 530%.
° C, and no degassing was performed. As a result, D
AS 43 μm, eutectic Si average circle equivalent diameter 7.2 μm, eutectic Si average circularity 72%, crystallization area ratio 0.4%, crystallization average circularity 45%, porosity rate 0.35% The fatigue life was determined by the comparative example No. of the comparative alloy. 11-No. It showed 806 cycles better than 16 412-528 cycles.

10) Example No. of the alloy of the present invention 10 is
Al-4.4% Si-4.3% Cu alloy is improved with Na, and during casting, the mold is spot-water-cooled.
7 heat treatments were performed. Fe content is 0.3
5%, solution treatment by heat treatment was performed at ordinary 500 ° C., and degassing treatment was not performed. As a result, DAS 42 μm, eutectic Si average circle equivalent diameter 5.4 μm, eutectic Si average circularity 7
3%, crystallized matter area ratio 3.5%, crystallized matter average circularity 46
% And a porosity ratio of 0.34%. 11-No. 16 of 412-528
It showed 754 cycles better than the cycle.

11) Comparative Example No. of Comparative Alloy 11 is A
The T7 heat treatment was performed without performing the improvement treatment with the 1-7.8% Si-3.2% Cu alloy, and without performing spot water cooling of the mold during casting. Fe content is 0.36%, which is about the same as usual,
Solution treatment in heat treatment was performed at a normal temperature of 500 ° C., and degassing was not performed. As a result, the DAS was as large as 54 μm, the eutectic Si average circle equivalent diameter was as large as 12.3 μm, and the eutectic Si average circularity was as small as 61% (see FIG. 10). And short.

12) Comparative Example No. of Comparative Alloy 12 is Comparative Example No. 12. 11 by reducing the Fe content to 0.12%,
When the solution temperature was increased to 510 ° C., the area ratio of the crystallized product was reduced to 2.7%, and the average circularity of the crystallized product was increased to 53%. However, DAS is as large as 54 μm and eutectic S
i The average circle equivalent diameter is as large as 12.3 μm and the eutectic S
Since the i-average circularity is as small as 61%, the thermal fatigue life is as short as 454 cycles.

13) Comparative Example No. of Comparative Alloy No. 13 is Comparative Example No. 13. The porosity rate was reduced to 0.24% by adding degassing treatment to Comparative Example No. 11. 12
In the same manner as described above, the DAS is as large as 54 μm, the eutectic Si average circle equivalent diameter is as large as 12.3 μm, and the eutectic Si average circularity is as small as 61%.
It is as short as 51 cycles.

14) Comparative Example No. of Comparative Alloy 14 is A
The T6 heat treatment was performed without performing the improvement treatment and the spot water cooling of the mold at the time of casting with a 1-6.9% Si-0.32% Mg alloy. The Fe content was 0.34%, which is almost the same as usual, the solution treatment by heat treatment was performed at usual 530 ° C, and the degassing treatment was not performed. As a result, the DAS is as large as 50 μm, the eutectic Si average circle equivalent diameter is as large as 10.9 μm, and the eutectic Si average circularity is as small as 57%.
The thermal fatigue life is as short as 475 cycles.

15) Comparative Example No. of Comparative Alloy 15 is Comparative Example No. 15. 14, the improved treatment by the addition of Na was added, the eutectic Si average circle equivalent diameter was reduced to 5.0 μm, and the eutectic Si average circularity was increased to 73% (see FIGS. 11 and 12). However, due to the large DAS of 50 μm, the thermal fatigue life is as short as 528 cycles.

16) Comparative Example No. of Comparative Alloy No. 16 is Comparative Example No. 14 was obtained by adding spot water cooling of the mold at the time of casting, and DAS was reduced to 42 μm (FIGS. 13 and 14), but the eutectic Si average circle equivalent diameter was as large as 10.5 μm and the eutectic Si average Due to the small circularity of 58%, the thermal fatigue life is as short as 524 cycles.

[0047]

As described above, according to the present invention, it is possible to manufacture an aluminum alloy casting and a cylinder head made of an aluminum alloy having better thermal fatigue characteristics than conventional alloys without performing the conventional steps such as remelting and overlaying. As a result, it is easy to reduce the number of manufacturing steps and the manufacturing cost of the aluminum alloy cylinder head. Therefore, it is possible to reduce the weight of diesel engines that are often mounted on trucks and the like. In addition to the cylinder head, it is also possible to apply an aluminum cast part to a part that receives a severe heat load.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an aluminum cylinder head according to the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a plan view of a main part of a conventional aluminum cylinder head.

FIG. 4 shows an example of the alloy of the present invention. 1 is a microstructure photograph (magnification: 100 times).

FIG. 5 is an example of the alloy of the present invention. 1 is a microstructure photograph (magnification: 400 times).

FIG. 6 is an example of the alloy of the present invention. 6 is a microstructure photograph (magnification: 100 times).

FIG. 7 shows an example of the alloy of the present invention. 6 is a microstructure photograph (magnification: 400 times).

FIG. 8 shows an example of the alloy of the present invention. 8 is a microstructure photograph (magnification: 100 times).

FIG. 9 shows an example of the alloy of the present invention. 8 is a microstructure photograph (magnification: 400 times).

FIG. 10 shows a comparative example of a comparative example alloy. 11 is a microstructure photograph (magnification: 100 times).

FIG. 11 shows Comparative Example No. of the comparative example alloy. 15 is a microstructure photograph (magnification: 100 times).

FIG. 12 shows Comparative Example No. of Comparative Example Alloy. 15 is a microstructure photograph (magnification: 400 times).

FIG. 13 shows Comparative Example No. of the comparative example alloy. It is a microstructure photograph of 16 (magnification: 100 times).

FIG. 14 shows a comparative example of a comparative example alloy. It is a microstructure photograph of 16 (magnification: 400 times).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Aluminum alloy cylinder head 2 Cylinder head main body 3 Fire surface 4 Exhaust port 5 Exhaust valve 6 Exhaust valve seat 7 Combustion chamber 8 Combustion injection nozzle 8a Combustion injection nozzle mounting hole 9 Piston 10 Cylinder block 11, 12 Water cooling jacket 13 Gasket 14 Intake valve seat 15 Intake port 20 Tactile surface 21 Hot plug 22 Intake port 23 Exhaust port 24 Between seat inserts 25 Hardened part 26 Aluminum cylinder head 27 Softened part

Claims (5)

[Claims] 1. A weight ratio of Si: 4 to 10%, Cu:
An aluminum alloy having a composition of 0 to 5%, Mg: 0 to 1.0%, the balance of Al and unavoidable impurities, wherein the microstructure of the aluminum alloy casting has a secondary dendrite arm spacing measured by a crossing method. 45 μm or less,
Average circular equivalent diameter is 10 μm or less and average circularity is 70%
An aluminum alloy casting having excellent thermal fatigue strength, comprising the above eutectic Si. 2. The microstructure of an aluminum alloy casting, wherein the area ratio of a crystallized substance other than eutectic Si is 3% or less, and the average circularity of the crystallized substance is 50% or more. An aluminum alloy casting having excellent thermal fatigue strength according to claim 1. 3. The aluminum alloy casting having excellent thermal fatigue strength according to claim 1, wherein the porosity of the portion of the aluminum alloy casting that receives the thermal load is 0.3% or less. 4. As a modifier for eutectic Si, a weight ratio of:
Na: 0.002 to 0.030%, Sr: 0.002 to
The thermal fatigue strength according to any one of claims 1 to 3, comprising an aluminum alloy containing at least one element of 0.030% and Sb: 0.02 to 0.20%. Excellent aluminum alloy casting. 5. The aluminum alloy casting having excellent thermal fatigue strength according to claim 1, wherein the aluminum alloy casting is a cylinder head.