JP7768545B2 - Casting aluminum alloy and aluminum castings cast using the same - Google Patents

Description

The present invention relates to a casting aluminum alloy and an aluminum casting cast using the same.

Patent Document 1 (WO 2015/152133) discloses an Al-Si-Mg-based aluminum alloy for casting, which consists, by mass, of 12.0 to 14.0% Si, 1.5 to 4.0% Mg, 0.10% or less Mn, and the balance being Al and unavoidable impurities, and which has excellent specific rigidity, strength, and ductility, and a cast member made of the same.

International Publication No. 2015/152133

One aspect of the present invention is an aluminum alloy for casting, comprising 1.0 to 10.0 mass % of Ni, 8.01 to 18.0 mass % of Cu, and the balance being Al and unavoidable impurities.

According to this casting aluminum alloy, by adjusting the Ni content to 1.0 to 10.0 mass%, a Ni-based intermetallic compound phase, which is a flaky intermetallic compound phase resulting from Ni, can be dispersed and crystallized in the aluminum alloy. This improves the rigidity of the aluminum alloy. Furthermore, by adjusting the Cu content to 8.01 to 18.0 mass%, a Cu-based intermetallic compound phase, which is an intermetallic compound phase resulting from Cu, can be crystallized in a network-like pattern around the Ni-based intermetallic compound phase. Therefore, by allowing the Ni-based intermetallic compound phase and the Cu-based intermetallic compound phase to coexist in different crystallization regions, the rigidity of the aluminum alloy can be further improved. Furthermore, by allowing the Cu-based intermetallic compound phase to form a network-like pattern around the Ni-based intermetallic compound phase, the tensile strength of the aluminum alloy can be improved.

In the aluminum alloy for casting, the Ni content is preferably 3.0 to 10.0 mass%. By setting the lower limit of the Ni content to 3.0 mass%, the Ni-based intermetallic compound phase can be more dispersed and crystallized in the aluminum alloy. This can further improve the rigidity of the aluminum alloy.

In the aluminum alloy for casting, it is preferable that the Cu content [Cu] and the Ni content [Ni] satisfy the following condition (1).
10.0≦[Cu]+0.87[Ni]≦23.5...(1)

Preferably, the casting aluminum alloy further contains 5.0 to 20.0 mass% Si. By setting the Si content to 5.0 to 20.0 mass%, a Si phase can be dispersed and crystallized in the aluminum alloy. This improves the rigidity of the aluminum alloy. Furthermore, by setting the Ni content to 1.0 to 10.0 mass%, a Ni-based intermetallic compound phase can be crystallized around the Si phase. Furthermore, by setting the Cu content to 8.01 to 18.0 mass%, a Cu-based intermetallic compound phase can be crystallized in a network pattern around the Si phase and the Ni-based intermetallic compound phase. Therefore, by allowing the Si phase, Ni-based intermetallic compound phase, and Cu-based intermetallic compound phase to coexist in different crystallization regions, the rigidity of the aluminum alloy can be further improved.

In the aluminum alloy for casting, the Si content is preferably 5.0 to 14.5 mass%. By setting the upper limit of the Si content to 14.5 mass%, coarsening of the Si phase during the solidification process of the aluminum alloy is suppressed, and embrittlement of the aluminum alloy is easily suppressed. As a result, the tensile strength of the aluminum alloy is easily improved.

In the aluminum alloy for casting, it is preferable that the Si content [Si], the Cu content [Cu], and the Ni content [Ni] satisfy the following condition (2).
30.0≦[Si]+0.94[Cu]+2.02[Ni]≦42.5...(2)

Preferably, the casting aluminum alloy further contains 0.0001 to 0.1 mass% P. By adjusting the P content to 0.0001 to 0.1 mass%, AlP (aluminum phosphide) formed in the aluminum alloy acts as a heterogeneous nucleus for primary Si, thereby making it possible to refine the primary Si. This makes it easier to uniformly disperse and crystallize primary Si in the aluminum alloy. This makes it easier to suppress variations in rigidity and tensile strength in the aluminum alloy.

The casting aluminum alloy preferably further contains 0.01 to 3.0 mass% of Mg. By adjusting the Mg content to 0.01 to 3.0 mass%, an Mg-based intermetallic compound phase, which is an intermetallic compound phase originating from Mg, can be precipitated by aging treatment. This allows the tensile strength of the aluminum alloy to be further improved.

In the aluminum alloy for casting, the Cu content is preferably 9.0 to 15.5 mass %.

Another aspect of the present invention is an aluminum casting produced using the above-described aluminum alloy for casting, which has high rigidity and excellent tensile strength.

FIG. 2 is a diagram showing the compositions, values of condition (1), values of condition (2), Young's modulus, and tensile strength of examples and comparative examples of casting aluminum alloys according to the embodiment. FIG. 2 is a view showing the observation results of the structure of a test piece of a casting aluminum alloy according to Comparative Example 1. FIG. 2 is a diagram showing the observation results of the structure of a test piece of the casting aluminum alloy according to Example 1. FIG. 10 is a diagram showing the observation results of the structure of a test piece of the casting aluminum alloy according to Example 2. FIG. 10 is a diagram showing the observation results of the structure of a test piece of the casting aluminum alloy according to Example 3. FIG. 10 is a view showing the observation results of the structure of a test piece of the casting aluminum alloy according to Example 8. FIG. 10 is a diagram showing the observation results of the structure of a test piece of the casting aluminum alloy according to Example 10. FIG. 10 is a diagram showing the observation results of the structure of a test piece of a casting aluminum alloy according to Comparative Example 2.

Hereinafter, embodiments of the casting aluminum alloy and aluminum castings cast using the same disclosed in the present application will be described with reference to the accompanying drawings. Note that the present invention is not limited to the following embodiments, and includes those defined in the claims.

First Embodiment
The aluminum alloy for casting according to the first embodiment contains 1.0 to 10.0 mass % of Ni, 8.01 to 18.0 mass % of Cu, and the balance being Al and inevitable impurities.

In this embodiment, "casting" includes casting by various casting methods such as sand casting, metal mold casting, and die casting. Furthermore, "aluminum alloy" refers to an alloy containing an aluminum phase as a primary phase. Accordingly, "cast aluminum alloy" refers to an aluminum alloy cast by various casting methods such as sand casting, metal mold casting, and die casting. The "mass %" of an element refers to the mass percentage of the element relative to the mass of the cast aluminum alloy. For example, the expression "A to B mass % of elements" means that the mass % of the element is A% or more and B% or less. The "balance" refers to components other than the listed elements that constitute the cast aluminum alloy. For example, the expression "a cast aluminum alloy containing ...Ni, ...Cu, with the balance being Al and unavoidable impurities" means that, of the components that constitute the cast aluminum alloy, the components other than Ni and Cu are Al and unavoidable impurities. This also applies to the following embodiments.

(Ni: Nickel)
The casting aluminum alloy of the first embodiment contains 1.0 to 10.0 mass% Ni. In the casting aluminum alloy of this embodiment, a Ni-based intermetallic compound phase, which is a long-flak intermetallic compound phase resulting from Ni, is dispersed and crystallized in the aluminum alloy, for example, as a primary crystal. Since the lower limit of the Ni content is 1.0 mass%, the amount of Ni-based intermetallic compound phase produced can be increased. This improves the rigidity of the aluminum alloy. Furthermore, since the upper limit of the Ni content is 10.0 mass%, coarsening of the Ni-based intermetallic compound phase during the solidification process of the aluminum alloy can be suppressed. This makes it easy to prevent, for example, cracks from propagating along the long-flak Ni-based intermetallic compound phase. This also makes it easy to prevent a decrease in the tensile strength of the aluminum alloy. The same applies to the following embodiments.

(Cu: Copper)
The casting aluminum alloy of the first embodiment contains 8.01 to 18.0 mass% Cu. In the casting aluminum alloy of this embodiment, a Cu-based intermetallic compound phase, which is an intermetallic compound phase resulting from Cu, crystallizes around the Ni-based intermetallic compound phase, for example, as a eutectic with Al, in a network pattern. Since the lower limit of the Cu content is 8.01 mass%, the amount of Cu-based intermetallic compound phase produced can be increased. This improves the rigidity of the aluminum alloy. Furthermore, since the upper limit of the Cu content is 18.0 mass%, excessive increase in the Cu-based intermetallic compound phase as a hard phase can be suppressed. This suppresses embrittlement of the aluminum alloy. This also suppresses a decrease in the tensile strength of the aluminum alloy. The same applies to the following embodiments.

(Al: aluminum, inevitable impurities)
The balance in the casting aluminum alloy of the first embodiment is Al and inevitable impurities. Examples of the inevitable impurities contained in the balance include elements such as Zn (zinc), Fe (iron), Mn (manganese), Cr (chromium), Sn (tin), Pb (lead), V (vanadium), and Ti (titanium). The content of the inevitable impurities is preferably 7.5% by mass or less in total, more preferably 5.0% by mass or less in total, 4.0% by mass or less in total, or 3.0% by mass or less in total. The same applies to the following embodiments.

According to the casting aluminum alloy of this embodiment, by adjusting the Ni content to 1.0 to 10.0 mass%, a Ni-based intermetallic compound phase can be dispersed and crystallized in the aluminum alloy. This improves the rigidity of the aluminum alloy. Furthermore, by adjusting the Cu content to 8.01 to 18.0 mass%, a Cu-based intermetallic compound phase can be crystallized in a network-like manner around the Ni-based intermetallic compound phase. Therefore, by allowing the Ni-based intermetallic compound phase and the Cu-based intermetallic compound phase to coexist in different crystallization regions, the rigidity of the aluminum alloy can be further improved. Furthermore, by allowing the Cu-based intermetallic compound phase to form a network-like structure around the Ni-based intermetallic compound phase, the tensile strength of the aluminum alloy can be improved.

In the casting aluminum alloy of this embodiment, the lower limit of the Ni content is preferably 1.5% by mass, and more preferably 2.0%, 2.1%, 3.0%, 3.5%, or 4.0% by mass. The upper limit of the Ni content is preferably 8.0% by mass, and more preferably 7.0%, 6.5%, or 6.1% by mass. Setting the lower and upper limits of the Ni content in this manner facilitates improving both the rigidity and tensile strength of the aluminum alloy. Alternatively, it is possible to prevent an extreme decrease in either the rigidity or the tensile strength, and facilitate the development of a balanced combination of both rigidity and tensile strength. In particular, setting the lower limit of the Ni content to 3.0% by mass allows the Ni-based intermetallic compound phase to be more dispersed and crystallized in the aluminum alloy. This further improves the rigidity of the aluminum alloy. The same applies to the following embodiments.

In the casting aluminum alloy of this embodiment, the lower limit of the Cu content is preferably 8.2 mass%, more preferably 9.0 mass%, 9.5 mass%, 10.0 mass%, 10.1 mass%, 10.5 mass%, 11.0 mass%, 11.5 mass%, or 11.9 mass%. The upper limit of the Cu content is preferably 17.5 mass%, more preferably 17.0 mass%, 16.5 mass%, 16.0 mass%, 15.5 mass%, 15.0 mass%, or 14.7 mass%. Setting the lower and upper limits of the Cu content in this manner makes it easy to improve both the rigidity and tensile strength of the aluminum alloy. Alternatively, it is easy to suppress a situation in which either the rigidity or the tensile strength is extremely reduced, and to achieve a balanced expression of both rigidity and tensile strength. The same applies to the following embodiments.

In the aluminum alloy for casting of this embodiment, the Cu content [Cu] and the Ni content [Ni] are blended so as to satisfy the following condition (1).
10.0≦[Cu]+0.87[Ni]≦23.5...(1)

In this embodiment, satisfying condition (1) makes it easy to improve both the rigidity and tensile strength of the aluminum alloy. Alternatively, it makes it easy to suppress an extreme decrease in either the rigidity or the tensile strength, and to exhibit both rigidity and tensile strength in a balanced manner. The lower limit of condition (1) is preferably 11.0, and more preferably 12.0 or 13.0. The upper limit of condition (1) is preferably 23.0, and more preferably 22.5. The same applies to the following embodiments.

Second Embodiment
The casting aluminum alloy of the second embodiment contains 5.0 to 20.0 mass % Si, 1.0 to 10.0 mass % Ni, 8.01 to 18.0 mass % Cu, and the balance being Al and inevitable impurities.

(Si: silicon)
The casting aluminum alloy of the second embodiment contains 5.0 to 20.0 mass% Si. In the casting aluminum alloy of this embodiment, the Si phase is dispersed and crystallized, for example, as primary Si and as eutectic Si with Al. Since the lower limit of the Si content is 5.0 mass%, the amount of crystallized Si phase can be increased. This improves the rigidity of the aluminum alloy. Furthermore, since the upper limit of the Si content is 20.0 mass%, coarsening of the Si phase during the solidification process of the aluminum alloy can be suppressed. This suppresses embrittlement of the aluminum alloy. This suppresses a decrease in the tensile strength of the aluminum alloy. Furthermore, since the upper limit of the Si content is 20.0 mass%, this suppresses an increase in the buoyancy acting on the Si phase due to coarsening of the Si phase. This suppresses floating and/or separation of the Si phase in the aluminum alloy. This suppresses variations in the structure and tensile strength of the aluminum alloy. The same applies to the following embodiments.

According to the casting aluminum alloy of this embodiment, by adjusting the Si content to 5.0 to 20.0 mass%, primary and eutectic Si phases can be dispersed and crystallized in the aluminum alloy. This improves the rigidity of the aluminum alloy. Furthermore, by adjusting the Ni content to 1.0 to 10.0 mass%, a Ni-based intermetallic compound phase can be crystallized around the Si phase. Furthermore, by adjusting the Cu content to 8.01 to 18.0 mass%, a Cu-based intermetallic compound phase can be crystallized in a network pattern around the Si phase and the Ni-based intermetallic compound phase. Therefore, by allowing the Si phase, Ni-based intermetallic compound phase, and Cu-based intermetallic compound phase to coexist in different crystallization regions, the rigidity of the aluminum alloy can be further improved.

In the casting aluminum alloy of this embodiment, the lower limit of the Si content is preferably 5.5 mass%, more preferably 5.6 mass%, 6.0 mass%, 6.5 mass%, 7.0 mass%, 7.5 mass%, 8.0 mass%, or 8.5 mass%. The upper limit of the Si content is preferably 18.0 mass%, more preferably 17.0 mass%, 16.5 mass%, 16.4 mass%, 16.0 mass%, 15.5 mass%, 15.0 mass%, 14.5 mass%, 14.0 mass%, 13.8 mass%, or 13.5 mass%. By setting the lower and upper limits of the Si content in this manner, it is easy to improve both the rigidity and tensile strength of the aluminum alloy. Alternatively, it is easy to suppress a situation in which either the rigidity or the tensile strength is extremely reduced, and to easily achieve a balanced development of both rigidity and tensile strength. In particular, by setting the upper limit of the Si content to 14.5 mass %, coarsening of the Si phase during the solidification process of the aluminum alloy can be suppressed, and embrittlement of the aluminum alloy can be further suppressed. This makes it easier to improve the tensile strength of the aluminum alloy. The same applies to the following embodiments.

In the aluminum alloy for casting of this embodiment, the Si content [Si], the Cu content [Cu], and the Ni content [Ni] are blended so as to satisfy the following condition (2).
30.0≦[Si]+0.94[Cu]+2.02[Ni]≦42.5...(2)

In this embodiment, satisfying condition (2) makes it easy to improve both the rigidity and tensile strength of the aluminum alloy. Alternatively, it is easy to suppress a situation in which either the rigidity or the tensile strength is extremely reduced, and to exhibit both rigidity and tensile strength in a balanced manner. The lower limit of condition (2) is preferably 30.5, and more preferably 31.0 or 31.5. The upper limit of condition (2) is preferably 42.0, and more preferably 41.5. The same applies to the following embodiments.

Third Embodiment
The casting aluminum alloy of the third embodiment contains 5.0 to 20.0 mass% Si, 1.0 to 10.0 mass% Ni, 8.01 to 18.0 mass% Cu, 0.0001 to 0.1 mass% P, and the remainder being Al and inevitable impurities.

(P: Rin)
The casting aluminum alloy of the third embodiment contains 0.0001 to 0.1 mass% P. Since the lower limit of the P content is 0.0001 mass%, the effect of refining primary crystal Si can be improved. Therefore, primary crystal Si can be uniformly dispersed and crystallized in the aluminum alloy. Furthermore, since the upper limit of the P content is 0.1 mass%, a decrease in the fluidity of the aluminum alloy can be suppressed. Therefore, the castability of the aluminum alloy can be improved. The same applies to the following embodiments.

According to the casting aluminum alloy of this embodiment, by setting the P content to 0.0001 to 0.1 mass%, AlP (aluminum phosphide) formed in the aluminum alloy acts as a heterogeneous nucleus for primary Si, thereby making it possible to refine the primary Si. This makes it easy to crystallize primary Si uniformly dispersed in the aluminum alloy. This makes it easy to suppress variations in rigidity and tensile strength in the aluminum alloy.

In the casting aluminum alloy of this embodiment, the lower limit of the P content is preferably 0.0003 mass%, more preferably 0.0006 mass%. The upper limit of the P content is preferably 0.05 mass%, more preferably 0.04 mass% or 0.03 mass%. By setting the lower and upper limits of the P content as described above, it is easy to suppress variations in the rigidity and tensile strength of the aluminum alloy. This also applies to the following embodiments.

<Fourth embodiment>
The casting aluminum alloy of the fourth embodiment contains 1.0 to 10.0 mass % Ni, 8.01 to 18.0 mass % Cu, 0.01 to 3.0 mass % Mg, and the balance being Al and inevitable impurities.

(Mg: magnesium)
The casting aluminum alloy of the fourth embodiment contains 0.01 to 3.0 mass% Mg. Since the lower limit of the Mg content is 0.01 mass%, the effect of precipitating an Mg-based intermetallic compound phase, which is an intermetallic compound phase originating from Mg, by aging the aluminum alloy can be improved. This allows for precipitation strengthening of the aluminum alloy. Furthermore, since the upper limit of the Mg content is 3.0 mass%, excessive increase in the Mg-based intermetallic compound phase can be suppressed. This allows for suppression of a decrease in elongation of the aluminum alloy.

According to the casting aluminum alloy of this embodiment, by adjusting the Mg content to 0.01 to 3.0 mass%, it is possible to precipitate an Mg-based intermetallic compound phase, which is an intermetallic compound phase originating from Mg, by aging treatment, thereby further improving the tensile strength of the aluminum alloy.

In the casting aluminum alloy of this embodiment, the lower limit of the Mg content is preferably 0.05 mass%, more preferably 0.1 mass%, 0.2 mass%, or 0.3 mass%. The upper limit of the Mg content is preferably 2.0 mass%, more preferably 1.0 mass%, 0.8 mass%, or 0.6 mass%. By setting the lower and upper limits of the Mg content in these ranges, the tensile strength of the aluminum alloy is easily improved.

The casting aluminum alloy of this embodiment preferably further contains 5.0 to 20.0 mass% of Si and 0.0001 to 0.1 mass% of P.

By using the aluminum alloy for casting according to the above embodiment, it is possible to provide an aluminum casting having high rigidity and excellent tensile strength. Therefore, this aluminum casting is suitable for a wide variety of applications requiring high rigidity and high tensile strength. Examples of applications of this aluminum casting include components for machine tools, robots, automobiles, etc.

<Example>
FIG. 1 shows the composition (mass%), values for condition (1), value for condition (2), Young's modulus (GPa), and tensile strength (MPa) of examples and comparative examples of the casting aluminum alloy according to the above embodiment. The tensile strength (MPa) was measured for test pieces of the casting aluminum alloy according to the examples and comparative examples in accordance with JIS Z 2241 (Method of tensile testing for metallic materials). The test pieces used were No. 14A test pieces with a diameter of 6 mm and a parallel length of 36 mm, cast by a mold casting method. The Young's modulus was determined from the slope within the elastic range of the relationship between stress and strain in a tensile test. The strain was the average value of the measured values of two uniaxial strain gauges attached opposite each other to the parallel surface of the test piece.

(Comparison between Examples 1 to 10 and Comparative Example 1)
As shown in FIG. 1 , the Cu content in Examples 1 to 10 is 8.01% by mass or more, while the Cu content in Comparative Example 1 is less than 8.01% by mass. Here, the Young's modulus in Examples 1 to 10 is 95 to 108 GPa, while the Young's modulus in Comparative Example 1 is 95 GPa. Therefore, the rigidity of Examples 1 to 10 is improved by up to about 14% compared to Comparative Example 1. Furthermore, the tensile strength of Examples 1 to 10 is 170 to 261 MPa, while the tensile strength of Comparative Example 1 is 160 MPa. Therefore, the tensile strength of Examples 1 to 10 is improved by up to about 63% (at least about 6%) compared to Comparative Example 1. Thus, it was confirmed that the rigidity and tensile strength of a casting aluminum alloy can be improved by setting the lower limit of the Cu content to 8.01% by mass.

(Comparison between Examples 1 to 10 and Comparative Example 2)
As shown in FIG. 1 , the Cu content in Examples 1 to 10 is 18.0 mass% or less, while the Cu content in Comparative Example 2 exceeds 18.0 mass%. Here, the Young's modulus in Examples 1 to 10 is 95 to 108 GPa, while the Young's modulus in Comparative Example 2 is 104 GPa. Therefore, in Examples 1 to 10, the fluctuation range of rigidity is within a range of 4 to 9% compared to Comparative Example 2. Furthermore, the tensile strength in Examples 1 to 10 is 170 to 261 MPa, while the tensile strength in Comparative Example 2 is 119 MPa. Therefore, in Examples 1 to 10, the tensile strength is improved by a maximum of approximately 120% (at a minimum, approximately 43%) compared to Comparative Example 2. Thus, it was confirmed that by setting the upper limit of the Cu content to 18.0 mass%, it is possible to suppress the variation in rigidity of the casting aluminum alloy, stably exhibit rigidity, and significantly improve tensile strength.

(Comparison of Examples 2 to 9 with Example 1)
As shown in FIG. 1 , the Cu content in Examples 2 to 9 is 9.0 mass% or more, while the Cu content in Example 1 is less than 9.0 mass%. Here, the Young's modulus in Examples 2 to 9 is 95 to 108 GPa, while the Young's modulus in Example 1 is 99 GPa. Therefore, in Examples 2 to 9, the fluctuation range of rigidity is within a range of 4 to 9% compared to Example 1. Furthermore, the tensile strength in Examples 2 to 9 is 181 to 261 MPa, while the tensile strength in Example 1 is 172 MPa. Therefore, in Examples 2 to 9, the tensile strength is improved by a maximum of about 52% (at a minimum, about 5%) compared to Example 1. Thus, it was confirmed that by setting the lower limit of the Cu content to 9.0 mass%, it is possible to suppress the variation in rigidity of the casting aluminum alloy, stably exhibit rigidity, and improve tensile strength.

(Comparison of Examples 2 to 9 with Example 10)
As shown in FIG. 1 , the Cu content in Examples 2 to 9 is 15.5 mass% or less, while the Cu content in Example 10 exceeds 15.5 mass%. Here, the Young's modulus in Examples 2 to 9 is 95 to 108 GPa, while the Young's modulus in Example 10 is 104 GPa. Therefore, in Examples 2 to 9, the fluctuation range of rigidity is within a range of 4 to 9% compared to Example 10. Furthermore, the tensile strength in Examples 2 to 9 is 181 to 261 MPa, while the tensile strength in Example 10 is 170 MPa. Therefore, in Examples 2 to 9, the tensile strength is improved by a maximum of about 54% (at a minimum of about 6%) compared to Example 10. Thus, it was confirmed that by setting the upper limit of the Cu content to 15.5 mass%, it is possible to suppress the variation in rigidity of the casting aluminum alloy, stably exhibit rigidity, and improve tensile strength.

(Casting aluminum alloy structure)
Observation results of the structures of test pieces of the cast aluminum alloys are shown in Figures 2 to 8. Figure 2 shows the results of observation of the microstructures of Comparative Example 1, Figure 3 shows Example 1, Figure 4 shows Example 2, Figure 5 shows Example 3, Figure 6 shows Example 8, Figure 7 shows Example 10, and Figure 8 shows Comparative Example 2, observed by a scanning electron microscope (SEM).

As shown in Fig. 1, Comparative Example 1 has a Cu content of 4.7 mass%. As shown in Fig. 2, in Comparative Example 1, thin needle-like Cu-based intermetallic compound phases 30 are sparsely crystallized around Si phase 10 and Ni-based intermetallic compound phase 20 crystallized in the aluminum alloy. Furthermore, in Comparative Example 1, there are many portions in the aluminum alloy where Cu-based intermetallic compound phase 30 is not crystallized, and even in portions where Cu-based intermetallic compound phase 30 is crystallized, adjacent Cu-based intermetallic compound phases 30 are distributed discontinuously with no connection between them. As a result, as shown in Fig. 1, it is difficult to improve the tensile strength of the casting aluminum alloy in Comparative Example 1.

As shown in Fig. 1 , Example 1 contains 8.2 mass% Cu, Example 2 contains 10.1 mass% Cu, Example 3 contains 11.9 mass% Cu, Example 8 contains 15.0 mass% Cu, and Example 10 contains 17.0 mass% Cu. As shown in Figs. 3 to 7 , in Examples 1, 2, 3, 8, and 10, Cu-based intermetallic compound phases 30 are crystallized almost uniformly throughout almost the entire aluminum alloy. Furthermore, in Examples 1, 2, 3, 8, and 10, adjacent Cu-based intermetallic compound phases 30 are continuously distributed in a state of being connected to each other, and a mesh-like network is formed between some of the Cu-based intermetallic compound phases 30. As a result, as shown in Fig. 1 , the tensile strength of the casting aluminum alloys of Examples 1, 2, 3, 8, and 10 is improved. 4 to 6, the Cu-based intermetallic compound phase 30 that constitutes the mesh itself grows thicker, and the mesh-like network expands to be distributed over almost the entire area of the aluminum alloy in Examples 2, 3, and 8. As a result, as shown in FIG. 1, the tensile strength of the aluminum alloy for casting in Examples 2, 3, and 8 can be further improved.

As shown in Fig. 1, the Cu content of Comparative Example 2 is 18.5 mass%. As shown in Fig. 8, in Comparative Example 2, the Cu-based intermetallic compound phase 30 that constitutes the network is coarsened into granular (lumpy) shapes, and the network is broken and/or destroyed. As a result, as shown in Fig. 1, it is difficult to improve the tensile strength of the casting aluminum alloy in Comparative Example 1.

As a result of observing the structure of the test specimens of the cast aluminum alloy, it was confirmed that the Si phase 10, the Ni-based intermetallic compound phase 20, and the Cu-based intermetallic compound phase 30, which are crystallized in different regions, can coexist. It was also confirmed that by adjusting the Cu content to 8.01 to 18.0 mass%, the Cu-based intermetallic compound phase 30 can be continuously crystallized in a mesh-like pattern around the Si phase 10 and the Ni-based intermetallic compound phase 20. It was also confirmed that by adjusting the Cu content to 9.0 to 15.5 mass%, a mesh-like network of the Cu-based intermetallic compound phase 30 can be formed throughout almost the entire aluminum alloy. As a result, as shown in FIG. 1 , in Examples 1 to 10, the rigidity of the cast aluminum alloys was improved, or the rigidity was stably expressed with a small fluctuation range, and the tensile strength was also improved, compared to Comparative Examples 1 and 2.

10 Si phase 20 Ni-based intermetallic compound phase 30 Cu-based intermetallic compound phase

Claims (7)

3. A casting aluminum alloy containing 0 to 10.0 mass% Ni, 8.01 to 18.0 mass% Cu, 5.0 to 20.0 mass% Si, 0.01 to 3.0 mass% Mg, and the remainder being Al and unavoidable impurities. 2. The aluminum alloy for casting according to claim 1 , wherein the Cu content [Cu] and the Ni content [Ni] satisfy the following condition (1):
10.0≦[Cu]+0.87[Ni]≦23.5...(1) 3. The casting aluminum alloy according to claim 1, wherein the Si content is 5.0 to 14.5 mass%. 4. The aluminum alloy for casting according to claim 1 , wherein the Si content [Si], the Cu content [Cu], and the Ni content [Ni] satisfy the following condition (2):
30.0≦[Si]+0.94[Cu]+2.02[Ni]≦42.5...(2) The casting aluminum alloy according to any one of claims 1 to 4 , further comprising 0.0001 to 0.1 mass% of P. The casting aluminum alloy according to any one of claims 1 to 5 , wherein the Cu content is 9.0 to 15.5 mass%. An aluminum casting cast using the aluminum alloy for casting according to any one of claims 1 to 6 .