JP2024132243A - Eutectic Al-Si alloy for casting and eutectic Al-Si alloy casting - Google Patents

Abstract

[Problem] To provide a eutectic Al-Si alloy in which coarsening of Al-Fe-Si compounds is suppressed even when gravity casting or the like is used, which has a slower casting speed than die casting and is less likely to cause a supercooled state, and a eutectic Al-Si alloy casting in which coarsening of Al-Fe-Si compounds is suppressed. [Solution] A eutectic Al-Si alloy for casting, characterized in that it contains 11.0 to 13.0 wt% Si, more than 0.5 wt% and not more than 1.0 wt% Fe, and at least one of 0.005 to 0.05 wt% Sr, and 0.005 to 0.05 wt% Ca, with the total amount of Sr and Ca being 0.05 wt% or less. [Selected Figure] None

Description

The present invention relates to eutectic Al-Si alloys for casting and eutectic Al-Si alloy castings.

Al-Si alloys have excellent castability and mechanical properties, and are therefore widely used as casting alloys. However, Al is prone to being contaminated with Fe as an unavoidable impurity, and this effect becomes more pronounced when the proportion of scrap material in the raw material is high.

In particular, from the perspective of environmental protection, aluminum alloy castings made from recycled ingots have been increasing in recent years. However, Al-Si alloy castings made from recycled ingots are prone to being contaminated with Fe as an impurity, and the effect of Fe on the mechanical properties of Al-Si alloy castings has become an issue.

Fe has the effect of improving mechanical properties such as Young's modulus of Al alloys and preventing seizure of dies, but when it is contained in Al-Si alloys, it forms coarse, needle-like Al-Fe-Si compounds, which become the starting point of fracture.

In response to this, it is known that supercooling can be used as a method to prevent Al-Fe-Si compounds from coarsening, and casting methods with fast cooling rates, such as die casting, which are prone to causing a supercooled state, have been selected as casting methods for Al-Si alloys.

For example, Patent Document 1 (JP Patent Publication 8-134578) discloses "an aluminum alloy for die casting with excellent high-temperature strength and toughness, containing Cu: 1-7 wt%, Si: 10-16 wt%, Mg: 0.3-2 wt%, Fe: 0.5-2 wt%, Mn: 0.1-4 wt%, Ti: 0.01-0.3 wt%, P: 0.01 wt% or less, and Ca: 0.001-0.02 wt%, with the weight ratio of P/Ca adjusted to a range of 0.5 or less."

The aluminum alloy for die casting described in the above-mentioned Patent Document 1 is described as "The aluminum alloy for die casting according to the present invention is produced by casting a molten aluminum alloy having the above-mentioned composition at a cooling rate of 20°C/sec or more, and the average long diameter of the crystallized particles is controlled to 20 μm or less and the average long diameter of the eutectic Si is controlled to 10 μm or less."

Japanese Patent Application Publication No. 8-134578

Although the die casting method has a fast cooling rate, the molten metal is filled into the mold while applying high pressure, which can lead to casting defects such as air entrapment. In addition, there is also the problem that the die casting equipment itself is expensive.

In view of the problems in the conventional techniques described above, the object of the present invention is to provide a eutectic Al-Si alloy in which the coarsening of Al-Fe-Si compounds is suppressed, and a eutectic Al-Si alloy casting in which the coarsening of Al-Fe-Si compounds is suppressed, even when gravity casting or the like is used, which has a slower casting speed than the die casting method and is less likely to cause a supercooled state.

In order to achieve the above object, the inventors conducted extensive research into the composition of eutectic Al-Si alloys, and discovered that adding an appropriate amount of Sr and/or Ca to a eutectic Al-Si alloy creates a supercooled state, shortening the solidification time and suppressing the coarsening of Al-Fe-Si compounds, thus arriving at the present invention.

That is, the present invention provides:
Si: 11.0-13.0wt%,
Fe: more than 0.5 wt% and not more than 1.0 wt%;
Sr: 0.005-0.05wt%,
Ca: 0.005 to 0.05 wt%.
The total amount of the Sr and the Ca is 0.05 wt% or less;
The present invention provides a eutectic Al-Si alloy for casting, characterized in that

In the eutectic Al-Si alloy for casting of the present invention, by adding 0.005-0.05 wt% Sr and/or 0.005-0.05 wt% Ca, and making the total amount of Sr and Ca 0.05 wt% or less, a supercooled state can be created even when the cooling rate is slow, such as in gravity casting. As a result, the solidification time is shortened, and solidification can be completed before the Al-Fe-Si compounds become coarse.

In the eutectic Al-Si alloy for casting of the present invention, it is preferable that the crystallization temperature of the iron-based compounds is lower than the eutectic point. The eutectic Al-Si alloy for casting of the present invention increases the supercooling during eutectic solidification by adding an appropriate amount of Sr and/or Ca, and shortens the solidification time, thereby suppressing the coarsening of the iron-based compounds (Al-Fe-Si compounds). Based on this mechanism, the effect of refining compounds that crystallize at a temperature higher than the eutectic solidification is reduced, but eutectic solidification occurring at a temperature higher than the crystallization temperature of the iron-based compounds allows the iron-based compounds to be significantly refined.

In the eutectic Al-Si alloy for casting of the present invention, it is preferable that the Fe content (M _Fe ) and the Si content (M _Si ) satisfy formula (1) or formula (2).
When M _Si is 11.0 wt% or more and less than 12.6 wt%:
_MFe ≦0.07× _MSi (1)
When M _Si is 12.6 wt% or more and 13.0 wt% or less:
M _Fe ≦1.01-0.01×M _Si (2)

When M _Si is 11.0 wt % or more and less than 12.6 wt %, the crystallization temperature of the iron-based compound (Al-Fe-Si compound) can be made lower than the eutectic temperature by satisfying M _Fe ≦0.07×M _Si . On the other hand, when M _Si is 12.6 wt % or more and 13.0 wt % or less, the crystallization temperature of the iron-based compound (Al- _Fe -Si compound) can be made lower than the eutectic temperature by satisfying _M Fe ≦1.01-0.01×M Si.

Furthermore, in the eutectic Al-Si alloy for casting of the present invention,
Mn: more than 0.0 wt% and not more than 0.3 wt%;
It is preferable that the balance consists of Al and inevitable impurities.
Adding an appropriate amount of Mn can improve the mechanical properties of eutectic Al-Si alloy castings.

The present invention also provides a eutectic Al-Si alloy casting made of the eutectic Al-Si alloy of the present invention, characterized in that the average major axis of the iron-based compounds is 50 μm or less.

The eutectic Al-Si alloy casting of the present invention is made of the eutectic Al-Si alloy for casting of the present invention, and the addition of an appropriate amount of Sr and/or Ca suppresses the coarsening of the iron-based compounds (Al-Fe-Si compounds), so that the average major axis of the iron-based compounds is 50 μm or less. The average major axis of the iron-based compounds is preferably 30 μm or less, and more preferably 20 μm or less.

The eutectic Al-Si alloy casting of the present invention preferably has a conductivity of 35.0% IACS or more. The eutectic Al-Si alloy casting of the present invention has a high conductivity due to the addition of Sr and/or Ca. It is more preferable that the conductivity is 38.0% IACS or more. The high conductivity of the eutectic Al-Si alloy casting makes it suitable for use as a conductive material.

According to the present invention, even when gravity casting or the like is used, which has a slower casting speed than the die casting method and is less likely to cause a supercooled state, it is possible to provide a eutectic Al-Si alloy in which the coarsening of Al-Fe-Si compounds is suppressed, and a eutectic Al-Si alloy casting in which the coarsening of Al-Fe-Si compounds is suppressed.

1 is a graph showing a composition range in which iron-based compounds can be refined by adding Sr and/or Ca. 1 shows the microstructure of an example eutectic Al-Si alloy casting 1 obtained using a boat mold (low magnification). 1 shows the microstructure of an example eutectic Al-Si alloy casting 1 obtained using a boat mold (high magnification). 1 shows the microstructure of an example eutectic Al-Si alloy casting 1 obtained using a shell cup (low magnification). 1 shows the microstructure of an example eutectic Al-Si alloy casting 1 obtained using a shell cup (high magnification). 1 shows the microstructure of an example eutectic Al-Si alloy casting 2 obtained using a boat mold (low magnification). 1 shows the microstructure of an example eutectic Al-Si alloy casting 2 obtained using a boat mold (high magnification). 1 shows the microstructure of comparative eutectic Al-Si alloy casting 1 obtained using a boat mold (low magnification). 1 shows the microstructure of comparative eutectic Al-Si alloy casting 1 obtained using a boat mold (high magnification). 1 shows the microstructure of comparative eutectic Al-Si alloy casting 1 obtained using a shell cup (low magnification). 1 shows the microstructure of comparative eutectic Al-Si alloy casting 1 obtained using a shell cup (high magnification). 1 is a microphotograph (low magnification) of a comparative eutectic Al-Si alloy casting 2 obtained using a boat mold. 1 is a microphotograph (high magnification) of a comparative eutectic Al-Si alloy casting 2 obtained using a boat mold. 1 is a microphotograph (low magnification) of a comparative eutectic Al-Si alloy casting 3 obtained using a boat mold. 1 is a microphotograph (high magnification) of a comparative eutectic Al-Si alloy casting 3 obtained using a boat mold. This is the cooling curve when a boat mold is used. This is a cooling curve when a shell cup is used.

The eutectic Al-Si alloy for casting and the eutectic Al-Si alloy casting of the present invention will be described in detail below, but the present invention is not limited to these.

1. Eutectic Al-Si alloy for casting The eutectic Al-Si alloy for casting of the present invention is characterized by containing an appropriate amount of Sr and/or Ca. Each component will be described in detail below.

(1) Additional elements (1-1) Essential additional elements Si: 11.0 to 13.0 wt%
Si is an element that improves castability, and also crystallizes as primary Si or eutectic Si, improving the mechanical properties of eutectic Al-Si alloy castings. If the content is less than the lower limit, castability becomes insufficient, and if the content exceeds the upper limit, coarse crystals that become the starting point of fracture are formed, adversely affecting elongation, so it is necessary to limit the content within the above range. Furthermore, if the content of Si exceeds 13.0 wt%, the crystallization of primary Si cannot be suppressed even with the addition of an appropriate amount of Sr and/or Ca, and coarse primary Si crystals are crystallized.

Fe: more than 0.5 wt% and 1.0 wt% or less Fe is an element that is easily mixed in as an impurity, but it has the effect of improving the Young's modulus of eutectic Al-Si alloy castings and also has the effect of preventing seizure to a mold. If the Fe content is too high, it becomes difficult to suppress the coarsening of Al-Fe-Si compounds even if Sr and/or Ca are added, so the Fe content must be 1.0 wt% or less. On the other hand, if the Fe content is 0.5 wt% or less, the amount of Al-Fe-Si compounds formed is small and coarsening is unlikely to occur, but the effect of improving the Young's modulus of eutectic Al-Si alloy castings and the effect of preventing seizure to a mold cannot be obtained.

In the eutectic Al-Si alloy for casting of the present invention, it is preferable that the crystallization temperature of the iron-based compound is lower than the eutectic point. The crystallization temperature and eutectic point (temperature of eutectic solidification) of the iron-based compound may be determined by obtaining a cooling curve during casting, or may be calculated using appropriate thermodynamic calculation software.

Figure 1 shows the range of Fe content at which Al-Fe-Si compounds crystallize after eutectic Si, derived from the ternary phase diagram of Al, Si, and Fe. Figure 1 shows that the boundary conditions are different at the Si content of 12.6 wt%.

Here, when the Si content (M _Si ) is less than 12.6 wt%, it is preferable that the Fe content (M _Fe ) and the Si content (M _Si ) satisfy the relationship M _Fe ≦ 0.07 × M _Si . When the Fe content (M _Fe ) and the Si content (M _Si ) satisfy this relationship, the crystallization temperature of the Al-Fe-Si compound becomes lower than the eutectic solidification temperature, and the effect of suppressing the coarsening of the Al-Fe-Si compound becomes remarkable.

On the other hand, when the Si content (M _Si ) is 12.6 wt % or more and 13.0 wt % or less, it is preferable that the Fe content (M _Fe ) and the Si content (M _Si ) satisfy M _Fe ≦ 1.01 - 0.01 × M _Si . When the Fe content (M _Fe ) and the Si content (M _Si ) satisfy this relationship, the crystallization temperature of the Al-Fe-Si compound becomes lower than the eutectic solidification temperature, and the effect of suppressing the coarsening of the Al-Fe-Si compound becomes remarkable.

Sr: 0.005 to 0.05 wt% and/or Ca: 0.005 to 0.05 wt%
Sr and Ca have the effect of causing supercooling during casting of Al-Si alloys. It is believed that the addition of Sr and/or Ca decomposes the solidification nuclei of primary crystal Si and eutectic Si, and as a result, the degree of supercooling during eutectic solidification increases. The occurrence of supercooling shortens the solidification time, and solidification is completed before the Al-Fe-Si compounds become coarse, so that the coarsening of the Al-Fe-Si compounds can be suppressed. This effect becomes noticeable when Sr and/or Ca is added at 0.005 wt% or more. On the other hand, since no further effect can be expected even if more than 0.05 wt% is added, it is preferable to add Sr and/or Ca at 0.05 wt% or less. When both Sr and Ca are added, the total amount must be 0.05 wt% or less. Sr and Ca also have the effect of making eutectic Si finer.

(1-2) Optional Added Elements Mn may be added to the eutectic Al--Si alloy for casting of the present invention.

Mn: more than 0.0 wt% and 0.3 wt% or less Mn has the effect of improving Young's modulus and preventing seizure to a mold like Fe, and also has the effect of changing the shape of Al-Fe-Si compounds from needle-like to lumpy. By changing the shape of Al-Fe-Si compounds from needle-like to lumpy, stress concentration on the Al-Fe-Si compounds is alleviated, and the strength and reliability of eutectic Al-Si alloy castings can be improved. On the other hand, if added in an amount exceeding 0.3 wt%, coarse Al-Mn compounds are likely to be formed, which may reduce the mechanical properties of eutectic Al-Si alloy castings.

Other elements Cu is not an element that affects the coarsening of Al-Fe-Si compounds, primary Si and eutectic Si, but has the effect of improving the mechanical properties of eutectic Al-Si alloy castings by solid solution strengthening and precipitation strengthening (aging treatment), so its inclusion is permitted up to the upper limit of 5.0 wt% as an additive element in the JIS standard for aluminum alloys for casting and die casting. If the Cu content exceeds 5.0 wt%, coarse Al-Cu compounds are likely to be formed, and the corrosion resistance of eutectic Al-Si alloy castings is reduced. In order to improve the mechanical properties, the Cu content is preferably 0.05 to 5.0 wt%. A more preferable content is 0.1 to 3.5 wt%.

Mg is not an element that affects the coarsening of Al-Fe-Si compounds, primary Si, and eutectic Si, but rather has the effect of improving the mechanical properties of eutectic Al-Si alloy castings through solid solution strengthening and precipitation strengthening (aging treatment), so its inclusion is permitted up to the upper limit of 1.5 wt% as an additive element in the JIS standard for aluminum alloys for casting and die casting. If the Mg content exceeds 1.5 wt%, coarse Al-Mg compounds are likely to form. To improve mechanical properties, the Mg content is preferably 0.4 to 1.5 wt%. A more preferable content is 0.4 to 1.0 wt%.

Zn: more than 0.0 wt % but not more than 1.0 wt % Zn has the effect of improving the mechanical properties of eutectic Al-Si alloy castings, but if added in an amount exceeding 1.0 wt %, the corrosion resistance of the eutectic Al-Si alloy is liable to decrease.

When added alone or in combination, Ti and B have the effect of promoting the refinement of the cast structure of eutectic Al-Si alloy castings, and each may be added up to 0.5 wt%.

(1-3) Inevitable impurities Since recycled raw materials are often used for the eutectic Al-Si alloy for casting of the present invention, the inclusion of inevitable impurities is permitted within a range that does not impair the properties of the eutectic Al-Si alloy for casting of the present invention and the eutectic Al-Si alloy casting. An example of the inevitable impurities is P.

2. Eutectic Al-Si Alloy Casting The eutectic Al-Si alloy casting of the present invention is made of the eutectic Al-Si alloy for casting of the present invention.

The eutectic Al-Si alloy casting of the present invention has an average major axis of 50 μm or less because the addition of an appropriate amount of Sr and/or Ca suppresses the coarsening of the Al-Fe-Si compounds. The average major axis of the Al-Fe-Si compounds is preferably 30 μm or less, and more preferably 20 μm or less.

In addition, the eutectic Al-Si alloy casting of the present invention suppresses coarsening of the eutectic Si by adding an appropriate amount of Sr and/or Ca. The diameter of the eutectic Si is preferably 1 μm or less, more preferably 0.9 μm or less, and most preferably 0.8 μm or less.

The method for measuring the particle size of the Al-Fe-Si compound and eutectic Si is not particularly limited as long as it does not impair the effects of the present invention, and various conventionally known structural observation methods can be used, such as optical microscope observation or SEM observation.

The eutectic Al-Si alloy casting of the present invention has high electrical conductivity due to the addition of an appropriate amount of Sr and/or Ca. The electrical conductivity is preferably 35.0% IACS or more, and more preferably 38.0% IACS or more. There are no particular limitations on the method for measuring electrical conductivity as long as it does not impair the effects of the present invention, and any conventionally known measuring method may be used.

The eutectic Al-Si alloy casting of the present invention can be obtained by casting a molten aluminum alloy consisting of the eutectic Al-Si alloy for casting of the present invention. Here, by using the eutectic Al-Si alloy for casting of the present invention to which an appropriate amount of Sr and/or Ca has been added, there is no need to use a die casting method with a high cooling rate to refine the Al-Fe-Si compound, and gravity casting, etc., with a low cooling rate, can be suitably used.

By using gravity casting, etc., it is possible to easily and efficiently obtain eutectic Al-Si alloy castings in which the Al-Fe-Si compounds are refined while suppressing casting defects such as air entrapment. In addition, gravity casting does not require expensive equipment like die casting, and it is possible to reduce the introduction costs of manufacturing equipment.

Other casting conditions are not particularly limited as long as they do not impair the effects of the present invention, and various conventional casting methods and casting conditions can be used.

The above describes representative embodiments of the present invention, but the present invention is not limited to these, and various design modifications are possible, all of which are included in the technical scope of the present invention.

Example
Raw materials mixed to obtain the compositions shown in Example 1 and Example 2 in Table 1 were inserted into a graphite crucible, and the molten metal treatment conditions shown in Table 2 and the casting conditions shown in Table 3 were used to obtain the practical eutectic Al-Si alloy casting 1 and the practical eutectic Al-Si alloy casting 2 of the present invention. Specifically, the alloy was melted in air, deslag-removed, and degassed by a rotary degasser. Next, the practical eutectic Al-Si alloy casting of the present invention was obtained by gravity casting. A boat mold (JIS No. 4 mold) or a shell cup (sand mold) was used for gravity casting in Example 1, and the casting temperature was 750°C and the mold temperature was 156°C for the boat mold, and the casting temperature was 758°C and the mold temperature was room temperature for the shell cup. A boat mold (JIS No. 4 mold) was used for gravity casting in Example 2, and the casting temperature was 757°C and the mold temperature was 155°C.

Table 1 also shows the crystallization temperatures of primary Si, eutectic Si, and iron-based compounds (Al-Fe-Si compounds) in the compositions shown as examples, but the crystallization temperature of the iron-based compounds is lower than the eutectic solidification temperature. Here, each crystallization temperature was calculated using Thermo-Calc, a commercially available integrated thermodynamic calculation software.

Comparative Example
Comparative eutectic Al-Si alloy castings 1 to 3 were obtained in the same manner as in the Examples, except that the compositions shown as Comparative Examples 1 to 3 in Table 1 were used, and the molten metal treatment conditions and casting conditions shown in Tables 2 and 3 were used. P was intentionally added to Comparative Example 1 and Comparative Example 2, resulting in a high P content. Table 1 also shows the crystallization temperatures of primary crystal Si, eutectic Si, and iron-based compounds (Al-Fe-Si-based compounds) in each composition obtained in the same manner as in the Examples, but in Comparative Example 2 and Comparative Example 3, the crystallization temperature of the iron-based compounds is higher than the eutectic solidification temperature.

[Evaluation test]
(1) Microstructure From the obtained working eutectic Al-Si alloy castings and comparative eutectic Al-Si alloy castings, cubes measuring 1 cm on a side were cut out with their centers at a position 13 mm from the bottom surface, and the cross sections were buffed to prepare samples for microstructure observation under an optical microscope.

The microstructure of the practical eutectic Al-Si alloy casting 1 obtained using the boat mold is shown in Figures 2 and 3. As can be seen from Figures 2 and 3, there is almost no primary Si crystallization in the practical eutectic Al-Si alloy casting 1 obtained using the boat mold, and a fine eutectic Si structure is observed. In addition, the iron-based compounds (area surrounded by a solid line in Figure 3) are significantly refined, with an average major axis of approximately 20 μm.

The microstructure of the practical eutectic Al-Si alloy casting 1 obtained using a shell cup is shown in Figures 4 and 5. As can be seen from Figures 4 and 5, even when using a shell cup, which has a slower cooling rate than a boat mold, the practical eutectic Al-Si alloy casting 1 obtained has almost no primary Si crystallization, and a fine eutectic Si structure is observed. In addition, coarsening of the iron-based compounds (area surrounded by solid lines in Figure 5) is suppressed, with the average long diameter being approximately 30 μm.

The microstructure of the practical eutectic Al-Si alloy casting 2 obtained using the boat mold is shown in Figures 6 and 7. As can be seen from Figures 6 and 7, there is almost no primary Si crystallization in the practical eutectic Al-Si alloy casting 1 obtained using the boat mold, and a fine eutectic Si structure is observed. In addition, the iron-based compounds (area surrounded by a solid line in Figure 7) are significantly refined, with the average long diameter being approximately 20 μm.

The microstructure of comparative eutectic Al-Si alloy casting 1 obtained using the boat mold is shown in Figures 8 and 9. Because comparative eutectic Al-Si alloy casting 1 does not contain an appropriate amount of Sr and/or Ca, the iron-based compounds are significantly coarsened, with an average major axis of 100 μm or more. It can also be seen that a large amount of primary Si has crystallized, and the eutectic Si structure is coarsened.

The microstructure of comparative eutectic Al-Si alloy casting 1 obtained using a shell cup is shown in Figures 10 and 11. Comparative eutectic Al-Si alloy casting 1 does not contain an appropriate amount of Sr and/or Ca, and because a shell cup was used, which has a slower cooling rate than the boat-shaped casting, the iron-based compounds are more significantly coarsened. It can also be seen that a large amount of primary Si has crystallized, and the eutectic Si structure is coarsened.

The microstructure of comparative eutectic Al-Si alloy casting 2 obtained using the boat mold is shown in Figures 12 and 13. Comparative eutectic Al-Si alloy casting 2 does not contain appropriate amounts of Sr and/or Ca, and contains more than 1.0 wt% Fe and more than 13.0 wt% Si, as well as a large amount of P, so that the iron compounds are extremely coarse, with an average major axis of 200 μm or more. It can also be seen that a large amount of primary Si has crystallized, and the eutectic Si structure is coarse.

The microstructure of comparative eutectic Al-Si alloy casting 3 obtained using a boat mold is shown in Figures 14 and 15. Comparative eutectic Al-Si alloy casting 3 contains an appropriate amount of Sr and/or Ca, but contains more than 1.0 wt% Fe and more than 13.0 wt% Si, so the effect of refining the iron-based compounds is not sufficient, and the average major axis of the iron-based compounds is about 100 μm. Also, although the eutectic Si structure is refined, coarse primary Si crystals are crystallized.

The average grain size of eutectic Si in the practical eutectic Al-Si alloy casting 1, practical eutectic Al-Si alloy casting 2, and comparative eutectic Al-Si alloy casting 1 obtained using the boat mold was measured and found to be 0.74 μm, 0.84 μm, and 3.08 μm, respectively. It can be seen that the eutectic Si is significantly finer in the practical eutectic Al-Si alloy casting 1 and practical eutectic Al-Si alloy casting 2. The observation area used for measuring the average grain size of eutectic Si was 0.035 ^mm2 .

(2) Measurement of Cooling Curve A thermocouple was fixed so that its temperature measuring junction was located 13 mm from the bottom surface of the mold, and the cooling curve was measured while the thermocouple was cast-in during casting.

The cooling curves for Example 1 and Comparative Example 1 when a boat mold was used are shown in Figure 16. It can be seen that supercooling occurs in Example 1, which contains an appropriate amount of Sr. In addition, when the crystallization temperature is calculated from the inflection point in the cooling curve (the point where the cooling rate slows down due to crystallization), the crystallization temperature of primary Si is 574°C and the eutectic solidification temperature is 568°C in Example 1, while the initial appearance temperature of primary Si is 578°C and the eutectic solidification temperature is 577°C in Comparative Example 1. It was difficult to determine the crystallization temperature of iron-based compounds from the cooling curve.

The cooling curves for Example 1 and Comparative Example 1 when using a shell cup are shown in Figure 17. It can be seen that in Example 1, which contains an appropriate amount of Sr, supercooling occurs even when a shell cup with a slow cooling rate is used. In addition, when the crystallization temperature is calculated from the inflection point in the cooling curve (the point where the cooling rate slows down due to crystallization), the eutectic solidification temperature is 563°C in Example 1, and the initial temperature of primary Si is 578°C and the eutectic solidification temperature is 577°C in Comparative Example 1. It was difficult to determine the crystallization temperature of iron-based compounds and the crystallization temperature of primary Si in the examples from the cooling curve.

(3) Measurement of Electrical Conductivity The eutectic Al-Si alloy castings having each composition obtained using the boat mold were cut into a thickness of 15 mm, and the measurement surface was polished, and then the electrical conductivity was measured at room temperature using Auto Sigma 3000 from GE Sensing & Inspection Technology. The electrical conductivities of the practical eutectic Al-Si alloy casting 1, the practical eutectic Al-Si alloy casting 2, the comparative eutectic Al-Si alloy casting 1, the comparative eutectic Al-Si alloy casting 2, and the comparative eutectic Al-Si alloy casting 3 were 39.7% IACS, 37.3% IACS, 31.2% IACS, 28.2% IACS, and 34.9% IACS, respectively. It can be confirmed that the practical eutectic Al-Si alloy casting has a high electrical conductivity of 35.0% IACS or more.

The above results show that even in eutectic Al-Si alloys that contain a relatively large amount of Fe, by adding an appropriate amount of Sr and/or Ca, the Al-Fe-Si compounds can be significantly refined without using a die casting method with a high cooling rate. In addition, it can be confirmed that primary Si and eutectic Si are also refined by adding an appropriate amount of Sr and/or Ca. Furthermore, it can be seen that by adding an appropriate amount of Sr and/or Ca, high electrical conductivity can be imparted to eutectic Al-Si alloy castings.

Claims (6)

Si: 11.0-13.0wt%,
Fe: more than 0.5 wt% and not more than 1.0 wt%;
Sr: 0.005-0.05wt%,
Ca: 0.005 to 0.05 wt%.
The total amount of the Sr and the Ca is 0.05 wt% or less;
A eutectic Al-Si alloy for casting, characterized by: The crystallization temperature of the iron-based compound is lower than the eutectic point.
The eutectic Al-Si alloy for casting according to claim 1, the Fe content (M _Fe ) and the Si content (M _Si ) satisfy formula (1) or formula (2);
The eutectic Al-Si alloy for casting according to claim 1 or 2,
When M _Si is 11.0 wt% or more and less than 12.6 wt%:
_MFe ≦0.07× _MSi (1)
When M _Si is 12.6 wt% or more and 13.0 wt% or less:
M _Fe ≦1.01-0.01×M _Si (2) Mn: more than 0.0 wt% and not more than 0.3 wt%;
The balance is composed of Al and inevitable impurities.
The eutectic Al-Si alloy for casting according to claim 1 or 2, The casting eutectic Al-Si alloy according to claim 1 or 2 is made of the casting eutectic Al-Si alloy,
The average major axis of the iron-based compound is 50 μm or less;
The eutectic Al-Si alloy casting is characterized by the above. Having a conductivity of 35.0% IACS or more;
The eutectic Al-Si alloy casting according to claim 5,