JPH0931581A - Aluminum alloy casting and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an aluminum alloy casting minimal in casting cavities and precipitates, excellent in ductility, and capable of artificial aging treatment in a short time. SOLUTION: This aluminum alloy casting is produced by casting a molten aluminum alloy, having a composition consisting of, by weight, 4.5-5.5% Si, 1.0-1.5% Cu, 0.4-0.6% Mg, 0.002-0.010% Na, 0.01-0.02% Ti, 0.002-0.004% B, <=0.2% Fe, and the balance essentially Al, in a mold of 350-400 deg.C at 740-780 deg.C and subjecting the resultant casting to T6 treatment (consisting of solution heat treatment and successive artificial aging treatment).

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 used in, for example, a cylinder head of an automobile engine and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, JIS H 5202 has been used for a cylinder head of an aluminum alloy engine as described above.
AC2A and AC2B (both are Al-Cu
-Si system), AC4B (Al-Si-Cu system) and other aluminum alloys, or alloys in which Na is added to these alloys for the purpose of refining Si are applied, and after casting, T6 treatment (solution treatment). It was used by increasing its strength by post-artificial aging treatment).

Further, in recent years, in a diesel engine, TIG (Tungsten Inert G
As) The mechanical properties such as strength and toughness of the aluminum alloy are improved by the remelting treatment.

[0004]

However, among the above cylinder heads, AC2A, AC2B, A
In the case of using the C4B alloy, porosity, coarse eutectic Si, needle-like Fe compounds and other precipitates are easily generated,
There is a problem that ductility is poor.

Further, with respect to the alloy using the alloy obtained by subjecting Si to the refinement treatment by adding Na, the age hardening is slow and the artificial aging treatment requires a long time, so that it is not practical in terms of cycle time and cost. There is a problem.

Further, although the TIG remelting treatment has good material characteristics, there is a problem that a large increase in cost is unavoidable when there are many treated portions. It has been a problem in terms of materials and manufacturing in the cylinder head of the conventional aluminum alloy engine.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems in the cylinder head of a conventional aluminum alloy engine, and has a small amount of cavities and precipitates, excellent ductility, and a short time. It is an object of the present invention to provide an aluminum alloy casting that can be artificially aged and a manufacturing method for obtaining such an aluminum alloy casting.

[0008]

In order to achieve the above-mentioned object, the present inventor has studied the precipitation of eutectic Si, Fe compounds and the like,
As a result of extensive studies on alloying elements and casting conditions that affect the hardening time of artificial aging, the Fe content in the alloy is reduced and the ductility is reduced by minimizing the content of Si, Cu, Mg, etc. It has been found that harmful precipitates can be reduced, the crystal grains can be made finer by the combined addition of Ti and B, and the delay of age hardening due to the addition of Na can be eliminated.

The present invention is based on the above findings, and the aluminum alloy casting according to claim 1 of the present invention has Si: 4.5 to 5.5% and Cu: 1.0% by weight.
~ 1.5%, Mg: 0.4 to 0.6%, Na: 0.00
2 to 0.010%, Ti: 0.01 to 0.02%, B:
It is characterized in that the composition contains 0.002 to 0.004%, Fe: 0.2% or less, and the balance substantially consists of Al. As a means to solve

As the method for producing an aluminum alloy casting according to claim 2 of the present invention, the method for producing an aluminum alloy casting according to the second aspect of the present invention is such that the temperature of 740 to 780.degree. In the manufacturing method according to claim 3, which is an embodiment of the method for manufacturing an aluminum alloy casting according to the present invention, the obtained casting is subjected to T6 treatment (artificial aging treatment after solution treatment). In the manufacturing method according to claim 4, which is the same as the embodiment, the solution treatment is performed at 515
The structure is performed at a temperature of up to 525 ° C., and is characterized in that the structure of such a method for manufacturing an aluminum alloy casting is used as a means for solving the above-mentioned conventional problems.

[0011]

The reasons for limiting numerical values such as the chemical composition range of the aluminum alloy casting according to the present invention, the casting temperature and the mold temperature in the method for producing the aluminum alloy casting according to the present invention will be explained together with the respective operations.

Si: 4.5 to 5.5% Si forms a coarse eutectic, and a less element is preferable from the viewpoint of improving ductility, but it imparts fluidity to the molten metal.
Since it is an element having the effect of improving the castability of the alloy, it is added in the range of 4.5 to 5.5% as a necessary minimum.

Cu: 1.0 to 1.5% Cu is an element that contributes to increasing hardness by heat treatment, and for this purpose, addition of 1.0% or more is necessary. However, if the added amount exceeds 1.5%, Cu ₂ A
l precipitates and becomes too hard and the ductility deteriorates.
The upper limit value is 5%.

Mg: 0.4 to 0.6% Since Mg contributes to improving the strength of the casting by solid solution strengthening and age hardening, it is necessary to add 0.4% or more. However, when added in excess, Mg ₂ S
Therefore, the upper limit value is set to 0.6%, since it becomes i and precipitates and reduces the ductility.

Na: 0.002-0.010% Na is an element that contributes to the refinement of Si, and for this purpose, addition of 0.002% or more is required. However, if added in excess of 0.010%, the casting becomes brittle, so its upper limit is made 0.010%.

Ti: 0.01 to 0.02% B: 0.002 to 0.004% Ti alone has no grain refining effect, but B
The compounded addition of Al contributes to the refinement of crystal grains and has the effect of eliminating the delay of age hardening which is an adverse effect of Na addition. Therefore, 0.01% or more for Ti and 0. 002% or more is added. However, even if added excessively, the effect is hardly improved. Therefore, the upper limit of each is 0.02% and 0.004%.
And

Fe: 0.2% or less Fe precipitates as a needle-shaped Fe compound and adversely affects the ductility, so its upper limit is made 0.2%.

Mold temperature: 350 to 400 ° C. Casting temperature: 740 to 780 ° C. The aluminum alloy casting according to the present invention has the above composition, but as described above, it suppresses the formation of precipitates and is ductile. From the viewpoint of preventing the deterioration of
Due to the low content of g, Fe, etc., the melting point is rather high,
It cannot be said that the porosity does not tend to increase because the fluidity of the molten metal decreases slightly. Therefore, when casting the aluminum alloy casting, it is necessary to preheat the mold and to raise the casting temperature in accordance with the increase in the melting point of the alloy. That is, the mold temperature is 3
If the temperature is less than 50 ° C, the number of casting cavities increases and the ductility of the product is impaired. On the contrary, if the temperature exceeds 400 ° C, cooling becomes too slow and crystal grain coarsening and other adverse effects occur.
Set to. Regarding the pouring temperature, if it is lower than 740 ° C, the fluidity of the molten metal is lowered to cause poor molten metal swirling, and if it is higher than 780 ° C, the cooling is slow, casting defects such as porosity and eutectic Si. Since it becomes easy to coarsen, the temperature is set to 740 to 780 ° C.

T6 Treatment By subjecting the aluminum alloy casting according to the present invention to T6 treatment (artificial aging treatment after solution treatment) as in the conventional case, for example, mechanical performance suitable for a cylinder head is obtained. To be At this time, in the so-called T5 treatment only with artificial aging treatment, it takes a long time to cure to a predetermined hardness (HRB50) and good ductility cannot be obtained. Therefore, for example, more preferably 515 to 525 ° C. Solution treatment at temperature is required. Also, so-called T7
In the treatment (stabilization treatment after solution treatment), overaging occurs and the ductility is impaired.

[0020]

EXAMPLES The present invention will be specifically described below based on examples.

Porosity Generation Rate First, among the aluminum alloys shown in Table 1, alloy No.
An aluminum alloy having the composition of 1 (corresponding to the aluminum alloy casting composition of the present invention) was melted in an electric furnace, and JIS H
Using the mold test piece mold established in 5202, 200
7 to the mold test piece mold preheated to each temperature of ˜430 ° C.
By pouring at a casting temperature of 60 ° C, JIS
A No. 4 tensile test piece established in Z 2201 was obtained.

[0022]

[Table 1]

Then, using the obtained tensile test pieces,
A tensile test was carried out based on the method defined in JIS Z 2241, and the ratio of the cavities appearing on the fracture surface to the entire fracture surface was defined as the rate of generation of the cavity (area%), and the relationship with the mold temperature was determined. I asked.

The results are shown in FIG. 1, and it was confirmed that the pre-heating of the mold to 350 to 400 ° C. can significantly reduce the porosity. In calculating the porosity generation rate, the fracture surface of each tensile test piece was observed by SEM (scanning electron microscope), and the percentage of the dendrite-shaped portion existing on the 40-fold screen with respect to the entire fracture surface was measured by an image analyzer. I asked.

Mechanical Properties Each aluminum alloy shown in Table 1 was melted by an electric furnace,
Under each casting condition shown in Table 2, JIS H5202
JISZ 22 using the mold test piece mold established in
No. 4 tensile test piece established in 01 is cast, and the obtained tensile test piece is subjected to heat treatment under the conditions shown in Table 3, and then a tensile test is performed based on the method established in JIS Z 2241. In addition, the hardness was measured using the hardness test piece collected from the gripped portion of the test piece after the tensile test. These results are also shown in Table 2. In addition, TI
Regarding G remelting treatment, TIG remelting treatment (arc current: 250 A, torch speed; 500 cm / min, shield gas: He + Ar) was applied to a test material cast in a flat plate shape.
And then solution treatment and artificial aging treatment,
A No. 14A tensile test piece established in IS Z 2201 was sampled, and the tensile strength and the elongation at break were determined using a strain gauge having a gauge length of 10 mm.

[0026]

[Table 2]

[0027]

[Table 3]

As a result, in the aluminum alloy castings of Examples in which the chemical composition of the material alloy, the casting conditions and the heat treatment conditions satisfy the requirements of the present invention, good results can be obtained for both tensile strength and elongation at break. Was confirmed.

On the other hand, although the material alloy components satisfy the requirements of the present invention, the aluminum alloy casting of Comparative Example 8 which has not been heat-treated can obtain a relatively good elongation at break, but the desired elongation is expected. The tensile strength could not be obtained, and only the artificial aging treatment (T5
In the aluminum alloy casting of Comparative Example 9 subjected to the (treatment), the tensile strength was slightly improved, but the breaking elongation was reduced. Further, in the aluminum alloy casting of Comparative Example 1 which was subjected to the high temperature artificial aging treatment (T7-1 treatment) after the solution treatment, the ductility (elongation at break) was obtained although the tensile strength showed a good value. In the case of Comparative Example 2 which was not subjected to the artificial aging treatment (T7-2 treatment) at a higher temperature, the ductility was slightly improved, but the tensile strength was confirmed to be reduced.

Further, in the aluminum alloy castings of Comparative Examples 3 to 6 containing a large amount of Si, Cu and Fe, although good results were obtained with respect to tensile strength, all had low elongation at break and expected ductility. Couldn't get

The aluminum alloy casting of Comparative Example 7, which had been subjected to T6 treatment after TIG remelting treatment, was made of Si, Cu, F.
It was confirmed that good strength and ductility were obtained despite the large e content, but the cost of this TIG remelting treatment is high, as described above.

FIG. 2 is a plot of the relationship between the tensile strength and the elongation at break for the tensile test results shown in Table 2, in which the aluminum alloy castings according to the examples of the present invention indicated by ◯, and □. Except for the aluminum alloy castings that have been subjected to the TIG remelting treatment indicated by the mark, the tensile strength tends to decrease as the breaking elongation increases, and it is understood that it is extremely difficult to satisfy both of these. .

Thermal Deformation Characteristics From the No. 4 tensile test pieces obtained in Examples and Comparative Examples 3 and 4 shown in Table 2, 5 mmφ × 20 mmL thermal deformation test pieces were sampled and a thermal expansion coefficient measuring device was used. The thermal deformation characteristics of each aluminum alloy casting were investigated.

The results are shown in Table 4,
In the aluminum alloy casting according to the present invention, Cu ₂
Due to the decrease of precipitates such as Al and Mg ₂ Si,
It was confirmed that the aluminum alloy casting according to the present invention is less likely to be thermally deformed and is suitable for an engine cylinder head or the like.

[0035]

[Table 4]

[0036]

As described above, according to the first aspect of the present invention.
The aluminum alloy casting according to
4.5-5.5%, Cu: 1.0-1.5%, Mg:
0.4-0.6%, Na: 0.002-0.010%,
Ti: 0.01 to 0.02%, B: 0.002 to 0.0
04%, Fe: 0.2% or less, with the balance being substantially A
Since it is composed of 1 and the content of Si, Cu, Mg, Fe, etc. is suppressed, it is possible to reduce precipitates, and since Ti and B are added in combination, the delay of age hardening due to addition of Na is eliminated. As a result, it is possible to obtain an extremely excellent effect that an aluminum alloy casting having good strength and ductility can be obtained by artificial aging treatment for a short time.

In the method for producing an aluminum alloy casting according to claim 2 of the present invention as the method for producing an aluminum alloy casting, the temperature of 740 to 780 ° C. in a mold preheated to a temperature of 350 to 400 ° C. Since the molten metal is cast, the formation of voids can be effectively prevented and the ductility of the aluminum alloy casting can be improved. As an embodiment of the method for producing the aluminum alloy casting, the method according to claim 3 or 4 is provided. In the manufacturing method concerned,
Since the obtained casting is subjected to solution treatment at a temperature of 515 to 525 ° C. and then to artificial aging treatment, for example, it has extremely good mechanical properties suitable for a cylinder head of an aluminum alloy engine. The extremely excellent effect that an aluminum alloy casting having the above can be produced is brought about.

[Brief description of drawings]

FIG. 1 is a graph showing an example of the results of examining the effect of mold temperature on the rate of formation of cavities during casting of an aluminum alloy casting according to the present invention.

FIG. 2 is a graph showing an example of the relationship between tensile strength and elongation at break in aluminum alloy castings that have been subjected to various heat treatments.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Yuichi Sugawara 1-21, Fujimi-cho, Gyoda-shi, Saitama, Ltd. Inside Tokyo Light Alloy Manufacturing Co., Ltd. (72) Inventor, Hideaki Kuratomi, Kanagawa-ku, Yokohama 2 Takaramachi Nissan Motor Co., Ltd.

Claims (4)

[Claims] 1. Si: 4.5-5.5%, C by weight
u: 1.0 to 1.5%, Mg: 0.4 to 0.6%, N
a: 0.002-0.010%, Ti: 0.01-0.
02%, B: 0.002-0.004%, Fe: 0.2
% Or less, and the balance substantially consisting of Al, an aluminum alloy casting. 2. The method for producing an aluminum alloy casting according to claim 1, wherein the molten metal having a temperature of 740 to 780 ° C. is cast into a mold having a temperature of 350 to 400 ° C. 3. The method for producing an aluminum alloy casting according to claim 2, wherein the obtained casting is subjected to T6 treatment (artificial aging treatment after solution treatment). 4. The method for producing an aluminum alloy casting according to claim 3, wherein the solution treatment is performed at a temperature of 515 to 525 ° C.