JP2000192180A - Scroll made of die casting excellent in fatigue strength and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a scroll made of die casting free from the generation of blistering even if being subjected to heat treatment and high in fatigue strength. SOLUTION: This scroll made of die casting is made of an aluminum alloy having a compsn. contg. 9.5 to 11.0% Si, 3.5 to 6.0% Cu, 0.2 to 0.8% Mg, 0.4 to 1.4% Fe, 0.2 to 0.8% Mn, <=0.004% Ca and 0.001 to 0.05% P, contg., at need, 0.5 to 2.0% Ni, and in which the total content of impurities is controlled to <=0.2% and a casting structure in which eutectic Si having 3 to 5 μm average length is crystallized out, and, the amt. of the gas to be occluded in the product is controlled to <=1 cc/100 g-Al, and he average number of inclusions to <=0.01 pieces/cm2 by K10 value. Since the gaseous components in mold cavities are removed by atmospheric control executing oxygen blowing after evacuation, the amt. of the gas to be occluded in the die cast product is made low, and blistering is not generated even by heat treatment of T5, T6 or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scroll used for air conditioners for automobiles, homes, and the like, and a method for manufacturing the scroll.

[0002]

2. Description of the Related Art As one of the gas compression members of air conditioners,
Aluminum scrolls are used on the movable and fixed sides to reduce the weight of the rotating part. Although the operating atmosphere does not become as high as that of an internal combustion engine, it is continuously operated for a long time, so that reliability, especially high room temperature fatigue strength, is required. The scroll has spiral blades along various heights and thicknesses according to the type and capacity of the compressor as a main body. When forging a scroll having such a complicated shape, it is difficult to form a spiral blade having a uniform height and thickness. Therefore, the present inventors have found that by using a forging die provided with an air vent, it is possible to obtain a scroll having excellent normal-temperature fatigue strength and good shape accuracy without inviting complication of the die. This is introduced in Japanese Patent Application Laid-Open No. Hei 10-118734.

In the forging method, the productivity is low, and the cost of the scroll increases due to the production cost. As a method for increasing productivity, there is a die casting method. However, a gas component in a mold cavity is involved, and a casting defect such as a blow hole tends to occur in a die casting product. As the gas component, there is water vapor derived from a release agent applied to the inner surface of the mold, a lubricant applied to the plunger, and the like, in addition to the residual air. Gas components in the cavity that cause casting defects can be reduced by evacuating the mold cavity prior to casting. However, in a mold for casting a product having a complicated shape such as a scroll, the cavity is also complicated, the gas component is not completely removed even by evacuation, and air may enter from the joint of the mold, Still casting defects due to residual gas still occur.

As a solution to the disadvantages of the vacuum die-casting method, an oxygen die-casting method has been known (Japanese Patent Laid-Open No. Sho 50-1979).
No. 21143). In the oxygen die casting method, oxygen is filled in the cavity at a pressure higher than the atmospheric pressure in order to replace the gas in the cavity with oxygen. Since the oxygen fed into the cavity is blown out from the joints and the inlet of the mold, outside air is prevented from entering the cavity from the joints and the inlet of the mold. The fed oxygen reacts with the molten metal to form fine Al ₂ O ₃ and is dispersed in the product, and does not adversely affect the die cast product.

[0005]

It is also difficult to completely remove gas from the cavity by sending oxygen into the cavity at atmospheric pressure or higher. The residual gas is
This tends to occur when the cavity has a complicated shape.
That is, since the mold for scroll casting is designed in a cavity having a complicated shape, a bottleneck in which oxygen is not supplied is likely to occur. In the bottleneck, gases such as air and water vapor remain without being replaced by oxygen, and the residual gas is taken into the die-cast product to cause casting defects. Further, if the mechanical properties are improved by performing a heat treatment such as T5 treatment or T6 treatment on the die-cast product, the product after the heat treatment swells due to gas taken into the product.
Due to blistering, most die cast products are used as non-heat treated materials.

[0006]

SUMMARY OF THE INVENTION The present invention has been devised in order to solve such a problem. The present invention is directed to an atmosphere in which a gas component is completely removed from a cavity of a mold prior to press-in of a molten aluminum alloy. It is intended to obtain a die-cast scroll excellent in fatigue strength by pressing a molten aluminum alloy having a predetermined composition, which has been subjected to a holding treatment, to prevent a gas-induced casting defect serving as a starting point of fatigue fracture. . In order to achieve the object, the die-cast scroll of the present invention has a composition of Si: 9.5 to 11.0% by weight, Cu:
3.5 to 6.0% by weight, Mg: 0.2 to 0.8% by weight,
Fe: 0.4 to 1.4% by weight, Mn: 0.2 to 0.8% by weight, Ca: 0.004% by weight or less, P: 0.001 to
Cast structure containing 0.05% by weight, the balance being substantially Al and other impurities controlled to a total amount of 0.2% by weight or less and eutectic Si having an average length of 3 to 5 μm. Made of an aluminum alloy with a carbon content of 1c
c / 100 g-Al or less, the average number of inclusions is characterized in that 0.01 pieces / cm ² or less at K ₁₀ value. The aluminum alloy may further contain 0.5 to 2.0% by weight of Ni.

This die-cast scroll has a vacuum degree of 1.
An aluminum alloy having a predetermined composition, which has been degassed and degassed and held at 740 to 760 ° C. in a mold cavity whose atmosphere has been adjusted by blowing oxygen at a pressure higher than the atmospheric pressure after reducing the pressure to 00 mbar or less. Melt 67
It is manufactured by press-fitting at a casting temperature of 0 to 700 ° C. After casting, T5 treatment at 160-220 ° C x 2-6 hours or solution treatment (480-500 ° C x 1-6 hours) → water quenching → T of aging treatment (160-220 ° C x 2-6 hours)
The strength can be improved by the six treatments.

[0008]

After the cavity of the mold is depressurized to a degree of vacuum of 100 mbar or less, oxygen is blown at a pressure higher than the atmospheric pressure, and the blown oxygen flows at a much higher flow rate than the conventional oxygen die casting method. It flows, and even a cavity with a complicated shape can fully reach every corner of the cavity. Therefore, water vapor and the like derived from the release agent and the lubricant attached to the inner surface of the mold are sufficiently washed out by the oxygen flow. Since the molten aluminum alloy is press-fitted into the cavity in which the interior of the mold has been cleaned, the amount of gas involved in the molten alloy filling the cavity is significantly reduced.

The obtained die-cast product has no casting defects such as blow holes and porosity caused by gas entrainment, and exhibits excellent fatigue strength. Further, since the size of the eutectic Si is regulated by adjusting the alloy components, the wear resistance is also improved. Furthermore, since there is no blistering during heat treatment,
The required strength can be imparted by precipitating Mg ₂ Si, CuAl ₂ or the like by T6 treatment. The gas content in aluminum products generally varies according to the manufacturing method.
For example, in the forging method using the wrought material, 0.3 cc / 10
0 g-Al or less, which is not a problem, but is usually 2-3 cc / 100 g-Al or more for die-cast products, 2-6 cc / 100 g-Al for sand castings, and 0.2-2.0 cc for die castings. / 100 g-Al gas content. If the gas content exceeds 1 cc / 100 g-Al, it cannot be used as a product for scrolls and the like that require fatigue strength. In view of this, the present invention has made it possible to manufacture a scroll by the die casting method with excellent productivity by suppressing the gas content to 1 cc / 100 g-Al or less irrespective of the die casting method.

Hereinafter, the components, contents, production conditions and the like of the aluminum alloy used in the present invention will be described. Si: 9.5 to 11.0% by weight An alloy component that improves the flow of molten metal, improves castability, and improves wear resistance as eutectic Si. Further, it also precipitates as Mg ₂ Si by the aging treatment, and has an effect of improving the strength. However, excess Si over 11.0% by weight
Is contained, primary crystal Si, which is a starting point of fatigue fracture, starts to crystallize, thereby lowering fatigue strength. Conversely, when the Si content is less than 9.5% by weight, a sufficient amount of eutectic S necessary for wear resistance is obtained.
i cannot be secured, and the molten metal flow during casting also deteriorates. Cu: 3.5-6.0% by weight Solid solution in the matrix and Al-Cu, Al-
Fine crystallized substances such as Cu-Mg are crystallized in the form of a network at grain boundaries, and are alloy components for improving the strength of the aluminum alloy. Further, the strength is also improved by precipitating as CuAl ₂ during the aging treatment. Such an effect becomes remarkable at a content of 3.5% by weight or more. However, when an excessive amount of Cu exceeding 6.0% by weight is included, coarse CuAl ₂ precipitates during the aging treatment, which causes a reduction in elongation.

Mg: An alloy component that precipitates as Mg ₂ Si during aging treatment at 0.2 to 0.8% by weight and improves the strength of an aluminum alloy. Necessary Mg ₂ S
In order to secure the precipitation amount of i, in the present invention, the lower limit of the Mg content is set to 0.2% by weight. On the other hand, when an excessive amount of Mg exceeding 0.8% by weight is contained, coarse Mg ₂ Si is crystallized at the time of casting, and the fatigue strength is rather lowered. Fe: 0.4 to 1.4% by weight An alloy component effective for preventing the molten aluminum alloy from sticking to the mold during die casting. The effect of preventing seizure is an Fe content of 0.4% by weight or more. Becomes remarkable.
However, when the Fe content exceeds 1.4% by weight, coarse Al-Fe-based crystallization is likely to be generated, and the fatigue strength is deteriorated. Mn: 0.2 to 0.8% by weight An alloy component that becomes Al-Fe-Mn-Si-based crystallized substances, and at the same time, agglomerates acicular Al-Fe-based crystallized substances to improve fatigue strength. is there. 0.2% by weight
The above Mn content becomes remarkable. However, 0.8% by weight
When an excessive amount of Mn is contained, Al-Fe-Mn
-Si-based crystallization grows coarsely and the fatigue strength deteriorates.

Ca: 0.004% by weight or less It has an effect of refining eutectic Si. Eutectic S by Ca
If i is excessively miniaturized, the required wear resistance cannot be obtained. For example, when an excessive amount of Ca is contained, a large amount of fine eutectic Si having an average particle size of less than 3 μm, which is not effective for wear resistance, is crystallized. Therefore, in the present invention,
By regulating the upper limit of the Ca content to 0.004% by weight, the abrasion resistance required for the scroll is secured. P: 0.001 to 0.05% by weight An alloy component having an effect of increasing the size of eutectic Si. In the scroll material of the present invention, the average grain size of eutectic Si is adjusted to a range of 3 to 5 μm. Therefore, 0.001% by weight or more of P is added. In particular, in the die casting method in which the aluminum alloy is rapidly cooled, the eutectic Si is easily reduced to a size of less than 3 μm. Therefore, it is important to control the size of the eutectic Si by adding P. However, if the P content exceeds 0.05% by weight, the flow of the molten metal becomes poor, and defects such as insufficient meat easily occur in the die-cast product.

[0013]Ni: 0.5 to 2.0% by weight It is an alloy component added as necessary, and
A Y-shaped network is formed at the cast crystal grain boundaries as Ni-based crystals.
Form and strengthen the matrix. When using
High temperature strength for scrolls where the temperature reaches around 150 ° C
It is also an effective alloying component for imparting. Such an effect
The fruits become remarkable at a Ni content of 0.5% by weight or more,
Saturates at 2.0% by weight.
Invite to ascend. Other impurities: 0.2% by weight or less in total Aluminum used as scroll material in the present invention
Alloys are made of Na, S
r, Sn, Sb, Zn, Pb, Bi, etc. as impurities.
It is. If these impurities are contained in large amounts,
Crystallized in matrix as inclusions such as compounds and oxides
Or precipitates, deteriorating the fatigue strength of aluminum alloys
You. Therefore, the smaller the impurities, the better.
Defines the upper limit of the total amount of impurities to be 0.2% by weight. Book
The aluminum alloy to which the invention is directed further includes cast grains
Ti: 0.01 to 0.05% by weight
And B: may contain 0.0001 to 0.001% by weight
it can.

[0014] The ingot formulated in melting a predetermined composition of the melt was melted at seven hundred and forty to seven hundred and sixty ° C., held at the holding furnace 30 minutes or more. By this high-temperature smelting and holding treatment, the intermetallic compound already generated in the raw metal is sufficiently dissolved in the molten metal, and the cause of the fatigue crack is removed in advance. Furnace slag, which is the starting point of fatigue failure, is also floated and separated from the molten metal by high-temperature smelting and holding processing. At this time, it is preferable to separate the furnace slag by using the deslagging flux. Further, it is preferable to reduce the gas content in the molten metal as much as possible by performing a degassing process in which a gas such as N ₂ or Ar is blown into the molten metal while rotating the nozzle. The retained aluminum alloy melt is cooled to 670 to 70
When it reaches 0 ° C., it is used for casting. Die casting at a temperature exceeding 700 ° C. is not preferable because the life of the mold is shortened. Further, in controlling the casting structure, the mold is kept at a temperature of around 200 ° C., but when a high-temperature molten metal comes into contact with this mold, the mold temperature rises and causes a decrease in productivity. Become. Conversely, at a casting temperature of less than 670 ° C., the flow of the molten metal pressed into the mold becomes poor,
The reject rate increases. For the holding treatment, it is preferable to use a holding furnace provided separately from the casting furnace in order to increase productivity.

Before adjusting the atmosphere of the mold cavity to press the molten aluminum alloy into the mold, the cavity is evacuated, and then oxygen is blown in at a pressure higher than the atmospheric pressure. When the pressure in the cavity is reduced to a degree of vacuum of 100 mbar or less, gas components such as N ₂ in the cavity are reduced. In order to reduce the pressure to a degree of vacuum of 100 mbar, it is preferable to fill the joints of the mold with a sealing material to prevent the invasion of outside air. Next, when oxygen is blown in at a pressure higher than the atmospheric pressure, the blown oxygen flows at high speed to reach every corner of the cavity, a release agent applied to the inner surface of the mold, a lubricant applied to the plunger, and the like. The water vapor derived from the water is completely washed out by the oxygen flow, and the atmosphere becomes free of air, water vapor and the like even in the cavity having a complicated system. At this time, since the cavity is maintained at a pressure higher than the atmospheric pressure, intrusion of outside air is suppressed. Since the molten aluminum alloy is press-fitted into the cavity whose atmosphere has been adjusted, no harmful gas components such as air and water vapor are trapped in the aluminum alloy when the molten aluminum alloy cools and solidifies in the cavity. Oxygen in the cavity reacts with the molten aluminum alloy, and the reaction product A
Since l ₂ O ₃ is dispersed as fine particles in the matrix, it does not adversely affect the obtained die cast product.

Gas content in product: 1 cc / 100 g
Al or less By such atmosphere adjustment, the amount of occluded gas contained in the die-cast product can be reduced to 1 cc / 100 g-Al or less. Since the obtained die-cast product has a significantly reduced occluded gas amount, no swelling that has occurred on the product surface when the conventional die-cast product is heat-treated is detected, and the die-cast product is subjected to heat treatment such as T5 treatment or T6 treatment. Target strength can be improved. Also, because there is little porosity,
The mechanical properties are also stable. Further, an extremely small amount of occluded gas means that there is no blowhole, porosity, etc., which is a starting point of high temperature fatigue failure, and in this respect, it can be said that the material is suitable for a scroll which is continuously operated for a long time.

With the aluminum alloy pressed into the cavity whose atmosphere of the casting structure is adjusted, a die-cast scroll having an extremely small occluded gas amount can be obtained. In addition, since the average length of the eutectic Si is in the range of 3 to 5 μm by adjusting the components such as the addition of P, the scroll is required to be rotated for a long time while being in contact with other members in the rotating state. The friction characteristics are satisfied. Fine eutectic Si having a size of less than 3 μm has insufficient wear resistance, while large eutectic Si having an average length of more than 5 μm increases the possibility of causing fatigue cracks.

[0018] The average number of inclusions: 0.01 pieces in the K ₁₀ value /
The cast structure obtained in cm ² or less die casting, Al, Na, C
oxides and oxide films such as a, Sr and Mg, Al-Si-F
Inclusions derived from intermetallic compounds such as e-based, Al-Ti-based, Ti-B-based, and Mg-Sb-based, and foreign matter mixed in from furnace materials, tools, etc. are observed with the naked eye or a 10-fold loupe. You. In order to provide the fatigue strength required for a scroll, the number of coarse inclusions is 0.01 / cm ² in the observation visual field.
It is important to keep below. The average number of inclusions is
Observe the fracture surface of the cast alloy material with a 10x loupe,
It displayed the counted number in the K ₁₀ value in terms of per unit area. In the measurement of the average number, the two fractured surfaces on the left and right are evaluated as one piece, and 5 to 6 pieces are evaluated as one sample. In the present invention, the average number of inclusions was calculated as the average value of the data of one sample with the area of 25 cm ² as the data of one sample. In this way the K ₁₀ value obtained 0.01 cells /
When it is not more than cm ² , excellent elongation characteristics and fatigue strength are imparted to the alloy material. On the other hand, K ₁₀ value of 0.01 defects / cm
If it exceeds ² , the required fatigue strength cannot be obtained.

[0019] 0.01 / cm ² or less of K ₁₀ value can be achieved in the following manner. Na and C mixed during alloying
a, Sr, Sb, Zn, Pb, Sn, Bi, etc. are suppressed as much as possible by selecting the compounding raw materials.
By maintaining at a high temperature of 0 to 760 ° C. for preferably 30 minutes or more, Na, Ca, Sr, Sb, Zn,
Pb, Sn, Bi, etc. are floated and separated from the molten metal as furnace slag such as oxide. When the slag that floated is removed from the molten metal, N
a, Ca, Sr, Sb, Zn, Pb, Sn, Bi, etc., very low aluminum alloy melt. Mg, Al and the like also float as oxide films on the surface of the molten metal, but these oxide films are separated from the molten metal at the time of scrap removal. When the molten metal is transferred from the holding furnace to the pool, a method is adopted in which oxides and oxide films are not entangled in the molten metal. Further, by shortening the low-temperature holding time during casting, Fe, Ti, S
It prevents other elements such as b from growing into coarse crystals. Inclusions derived from furnace materials and tools are 740-760 ° C
Is separated from the molten metal by the holding process.

The heat-treated die-cast scroll is made of M by T5 or T6 treatment.
By precipitating g ₂ Si, CuAl _2, etc., the strength is further improved. In the T5 treatment, the casting is
Heat to 2 ° C for 2-6 hours. In T6 processing, 480 to 50
After a solution treatment at 0 ° C. × 1 to 6 hours, water quenching is performed.
Aging treatment is performed at ２２０220 ° C. for 2 to 6 hours. At the time of quenching, water at normal temperature to 80 ° C is used. If the heat treatment conditions are not satisfied, a sufficient treatment effect cannot be obtained or the heat treatment cost increases. Since the amount of occluded gas in the casting to be heat-treated is kept very low by adjusting the atmosphere of the mold cavity, the gas component does not expand due to heating during the heat treatment and does not cause swelling. This is a point that is significantly different from conventional die-cast products. In addition, as long as the required design values are satisfied, the strength slightly decreases,
A dimensional stabilization process that raises the aging temperature to suppress dimensional distortion due to aging precipitation and reduces the amount of machining can also be employed. The aging condition in this case is 220 to 350 ° C. × 1 to 5
Set to time.

[0021]

[Example] N ₂ gas was ejected from a rotating rotor for 30 minutes.
The molten aluminum alloy whose components were adjusted was degassed.
Next, deslagging treatment is performed using a deslagging flux.
For 45 minutes, the inclusions were sufficiently floated and separated from the molten metal, and the slag floating on the surface of the molten metal was removed.
The prepared aluminum alloy melt contains Si: 10.1% by weight, Cu: 4.32% by weight, Mg: 0.56% by weight,
Fe: 0.58% by weight, Mn: 0.32% by weight, P:
0.01% by weight, Ca: 0.004% by weight, Cr: 0.
03% by weight, Zn: 0.04% by weight, Na: 0.000
3% by weight, Sr <0.0005% by weight, Sb <0.01
% By weight, Ti: 0.02% by weight, B: 0.0001% by weight, Ni: 0.01% by weight, and the remainder had an Al composition excluding impurities.

When the temperature of the molten aluminum alloy was lowered to 680 ° C., it was cast into a die casting mold to produce a scroll having the shape shown in FIG. 1 and having an outer diameter of 100 mm and a height of 70 mm. Prior to casting, a mold release agent was applied to the inner surface of the mold heated to 200 ° C., and the cavity was evacuated to a vacuum of 75 mbar at a suction rate of 700 mbar / sec. Then, the pressure was reduced to 4,000 mbar. The atmosphere was adjusted by blowing oxygen. Also, a lubricant was applied to a plunger for pressing the molten aluminum alloy into the cavity. After cooling and solidification of the aluminum alloy cast in the cavity whose atmosphere was adjusted, the scroll as a product was taken out of the mold. A test piece was cut out from the obtained product, the components were analyzed, the microstructure was observed, and the amount of occluded gas and the number of inclusions were measured. In addition, the cast product was subjected to T5 treatment of heating at 180 ° C. for 4 hours, and then its mechanical properties were investigated. The occluded gas amount was measured by the Lansley method.

In counting the number of inclusions, the cast
0.5cm high and 5cm long
Notch and break it with a naked eye and a 10x loupe
10 samples of 0.5 cm x 5 cm per sample (2
Surface), that is, 25 cm in total ^Two Observe the area of
And inclusion data as the average value of the data of 7 samples
Count the number of items and count the number to 1cm^Two Convert to
By K_TenValues were calculated. Inclusions are mostly oxides
System, the inclusions of about 0.1 to 3 mm were blackish
It had a color tone. Table 1 shows the survey results. Note that the comparison
For this reason, ordinary dieker without adjusting the atmosphere of the cavity
Sucrose manufactured under the same conditions except casting by the strike method
(Comparative Example 1), aluminum alloy melted at 760 ° C
Degassing and deslagging treatment without holding the molten metal, 68
Mold whose atmosphere is adjusted when the temperature drops to 0 ° C
Scrolls (Comparative Example 2) manufactured by casting
Investigated similarly.

Since both the present invention and Comparative Examples 1 and 2 had the same composition conditions and cooling conditions during casting, they had almost the same structure, and there was no problem in terms of structure. However, the amount of occluded gas was the largest in Comparative Example 1 usually manufactured by die casting,
The number of inclusions showed the largest value in Comparative Example 2 in which no holding treatment was performed. The effect of the large amount of occluded gas and the number of inclusions is T5
It appears as a low mechanical strength after the treatment. On the other hand, in the example of the present invention, both the amount of occluded gas and the number of inclusions are low, and the mechanical properties after T5 treatment are excellent. Generally, the mechanical properties required for scrolls are tensile strength at room temperature of 3
70N / mm ² or more, fatigue strength (× 10 ⁷ cycles) 1
Considering that it is 20 N / mm ² or more, it is understood that the die-cast scroll of the example of the present invention can sufficiently withstand use.

[0025]

[0026]

As described above, the die-casting scroll of the present invention has a very low occluded gas amount despite being manufactured by the die-casting method, and thus has a starting point of fatigue fracture. There is no casting defect such as blowhole or porosity, and the strength can be improved by heat treatment without swelling, and the number of inclusions can be reduced. In this way, an inexpensive scroll can be provided because it can be manufactured by the die casting method having excellent productivity.

[Brief description of the drawings]

FIG. 1 is a scroll manufactured in an embodiment.

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) // C22C 1/02 503 C22C 1/02 503J C22F 1/00 601 C22F 1/00 601 602 602 611 611 630 630G 631 631 681 681 691 691B 691C (72) Inventor Takaaki Inari 1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture F-term in Nippon Light Metal Co., Ltd. Group Technology Center 3H039 BB05 BB07 BB07 CC02 CC03 CC35

Claims (5)

[Claims] 1. Si: 9.5 to 11.0% by weight, Cu:
3.5 to 6.0% by weight, Mg: 0.2 to 0.8% by weight,
Fe: 0.4 to 1.4% by weight, Mn: 0.2 to 0.8% by weight, Ca: 0.004% by weight or less, P: 0.001 to
Cast structure containing 0.05% by weight, the balance being substantially Al and other impurities controlled to a total amount of 0.2% by weight or less and eutectic Si having an average length of 3 to 5 μm. Made of an aluminum alloy with a carbon content of 1c
c / 100 g-Al or less, die-cast scrolling average number of inclusions and excellent fatigue strength is 0.01 pieces / cm ² or less at K ₁₀ value. 2. The aluminum alloy further comprises Ni: 0.5 to
The die-cast scroll excellent in fatigue strength according to claim 1, which contains 2.0% by weight. 3. A degassing / deslagging treatment is applied to a mold cavity whose atmosphere has been adjusted by blowing oxygen at a pressure higher than the atmospheric pressure after reducing the pressure to a degree of vacuum of 100 mbar or less, and holding at 740 to 760 ° C. 3. A method for manufacturing a die-cast scroll having excellent fatigue strength, comprising press-fitting a molten aluminum alloy having the composition according to claim 1 or 2 at a casting temperature of 670 to 700 ° C. 4. The method for producing a die-cast scroll excellent in fatigue strength according to claim 3, wherein after casting, aging treatment is performed by heating at 160 to 220 ° C. for 2 to 6 hours. 5. After casting, solution treatment, heating to 480-500 ° C. for 1-6 hours, water quenching, and then 160-220.
4. The method for producing a die-cast scroll having excellent fatigue strength according to claim 3, wherein the aging treatment is performed by heating to 2 [deg.] C. for 2 to 6 hours.