JP4145242B2 - Aluminum alloy for casting, casting made of aluminum alloy and method for producing casting made of aluminum alloy - Google Patents

Description

  The present invention relates to an aluminum alloy for castings and a method for producing an aluminum alloy casting. More particularly, the present invention relates to an aluminum alloy for casting that exhibits high castability suitable for production of a thin-walled casting and the like, and high strength and excellent ductility even in an as-cast state, and a method for producing a casting made of the aluminum alloy. .

  In recent years, there has been a demand for weight reduction of various products, and there is a rapid shift from conventional cast iron products to lightweight aluminum alloy products. For example, in the case of an automobile, improvement in fuel efficiency can be expected by reducing the weight, and the reduction in weight is also effective for improving the environment.

  By the way, high strength and high ductility have been demanded even for thin-walled castings (especially die-cast products), which conventionally have been relatively demanding for strength and ductility. As a method of producing a thin casting having high strength and high ductility, for example, after casting the mold by evacuating, or conversely, filling the mold with oxygen and casting, the resulting casting is heat treated. A method for performing the above has been proposed. However, such a method requires heat treatment and causes an increase in manufacturing cost. In addition, the thinner and larger castings are distorted (blurred, deformed, etc.) by the heat treatment, and the correction is more costly.

  Therefore, in order to solve such problems, aluminum alloys that exhibit high strength and high ductility even in an as-cast state have been actively developed. For example, (a) JP-A-9-3582, (b) JP-A-11-293375, (c) JP-A-11-193434, (d) JP-A-9-268340, JP-A-9- Japanese Patent No. 316581, Japanese Patent Application Laid-Open No. 11-80872, etc. disclose such aluminum alloys. Hereinafter, the aluminum alloy described in each publication will be specifically described.

(a) In JP-A-9-3582, Mg: 3.0 to 5.5% (mass%: the same applies hereinafter), Zn: 1.0 to 2.0% (Mg / Zn: 1.5 to 5.5). 5) An aluminum alloy casting containing Mn: 0.05 to 1.0%, Cu: 0.05 to 0.8%, and Fe: 0.1 to 0.8% is disclosed. This Al—Mg—Mn—Zn—Cu-based alloy has a predetermined range of Zn and Cu as essential elements.

When the present inventor conducted a test study on this alloy casting, an intermediate phase such as MgZn ₂ or Mg ₃₂ (Al, Zn) ₄₉ was precipitated in the casting, resulting in changes in strength characteristics due to natural aging and stress corrosion cracking. It was. It has also been found that this alloy is prone to casting cracks and is not suitable for casting thin-walled members.

(b) In JP-A-11-293375, Mg: 2.5-7.0, Mn: 0.2-1.0%, Ti: 0.05-0.2% and Fe less than 0.3% , Si is 0.5% or less, the porosity of the 1-5 mm thick portion is 0.5% or less, the average equivalent circle diameter of the crystallized material is 1.1 μm or less, and the crystallized material area ratio is 5% A highly ductile aluminum alloy die casting characterized by the following is disclosed. This Al—Mg—Mn—Ti alloy handles Fe as an inevitable impurity, and its content is limited to less than 0.3%.

  As a result of a test study by the present inventor, a thin-walled mold casting using this alloy was prone to casting cracks. Further, when the amount of Mg increased, shrinkage cavities were easily generated in the central portion of the thickness. The occurrence of casting cracks and shrinkage cavities is undesirable because it increases the variation in strength characteristics and elongation.

(c) Japanese Patent Application Laid-Open No. 11-193434 discloses an aluminum alloy for high toughness die-casting with Mg: 3.0 to 5.5, Mn: 1.5 to 2.0%, and Ni: 0.5 to 0.9. Is disclosed.
In this Al—Mg—Mn—Ni-based alloy, Ni is an essential element, and the toughness of the die casting is improved by appropriately adjusting the content thereof. Moreover, since there is much content of Mn, the amount of crystallization of a compound increases, and as the Example shows, elongation is about 10%.

(d) Japanese Patent Laid-Open No. 9-268340 discloses high ductility aluminum with Mg: 0.01 to 1.2%, Mn: 0.5 to 2.5%, and Fe: 0.1 to 1.5%. An alloy is disclosed.
In this Al—Mg—Mn—Fe alloy, the content of Mg is reduced to suppress the occurrence of defects such as casting cracks and shrinkage cavities, thereby improving castability and elongation. For this reason, as can be seen from the examples, the alloy has a tensile strength of less than 190 MPa and is not sufficient in strength. The aluminum alloys disclosed in JP-A-9-316581 and JP-A-11-80872 are the same as this alloy.

Japanese Patent Laid-Open No. 9-3582 JP 11-293375 A JP 11-193434 A Japanese Patent Laid-Open No. 9-268340 Japanese Patent Laid-Open No. 9-316581 Japanese Patent Laid-Open No. 11-80872

  The present invention has been made in view of such circumstances. That is, an object of the present invention is to provide an aluminum alloy for castings that has less cast cracking, microporosity, etc. and has excellent castability. In particular, an object of the present invention is to provide an aluminum alloy for castings that can obtain a casting having high strength and excellent ductility even in an as-cast state. Furthermore, it aims at providing the aluminum alloy for castings with a small temporal change, such as a mechanical characteristic of a casting. Moreover, it aims at providing the manufacturing method of the casting using this aluminum alloy.

  As a result of intensive studies to solve this problem and repeated various systematic experiments, the present inventor is excellent in castability by properly managing the composition ratio of Mg, Mn and Fe, and also in an as-cast state. The inventors have discovered an aluminum alloy capable of obtaining a high-strength and high-ductility casting, and have completed the present invention.

(Aluminum alloy for casting)
That is, the aluminum alloy for castings according to the present invention has 4.0 to 6.0% magnesium (Mg) and 0.3 to 0.6% manganese (Mn) when the total is 100% by mass. , and a from 0.5 to 0.9% of iron (Fe), the balance being made of aluminum (Al) and unavoidable impurities.

  The aluminum alloy (Al-Mg-Mn-Fe alloy) of the present invention contains Mg, Mn, and Fe in an appropriate composition ratio, so that castability is improved and high strength and high ductility are expressed. . Hereinafter, the reason that can be considered at present and the background of the above composition will be described.

  It is known that Mg and Mn are dissolved in an Al base to improve the strength of the aluminum alloy. However, when a thin-walled mold casting is produced with an Al-Mg-Mn alloy, casting accompanying solidification shrinkage. Cracking, porosity, etc. occur and castability is poor. In addition, the variation in growth also increases.

  Therefore, in order to obtain an aluminum alloy having excellent castability and high strength and high ductility, the present inventor has focused on the relationship between the crystallized form of the crystallized product and the castability and mechanical properties in the solidification process. It was found that casting cracks in aluminum alloy castings frequently occur in the fragile liquid phase portion remaining between the primary Al dendrites growing in the solidification process. This is because, in the process of forming a casting by the development and bonding of primary dendrites, if the casting is constrained by the mold in the temperature range (quasi-solidus temperature range) where the casting begins to form and has strength, At that time, shrinkage stress acts on the casting. This is because the stress concentrates on the fragile liquid phase remaining between the dendrites, causing frequent hot cracking.

  Therefore, the present inventor came up with the idea of adding Fe to the Al-Mg-Mn alloy, and changed the crystallization behavior in the solid-liquid coexistence region by adjusting the amount of Mn and Fe in accordance with the amount of Mg, which is excellent. We succeeded in obtaining anti-casting cracks. Specifically, the Al—Mn—Fe eutectic is crystallized between the network of primary Al after the crystallization is completed without narrowing the crystallization temperature range of primary Al and greatly growing the dendrites of primary Al. I made it come out. And since the connection between each solid phase advances rapidly in that state, it is thought that it was hard to generate | occur | produce a casting crack.

  Furthermore, according to the aluminum alloy of the present invention, since Al (Mn, Fe) compound is crystallized finely after fine Al is crystallized from the liquid phase as primary crystals, there is a coarse crystallized product that causes a decrease in ductility. It is thought that excellent ductility has been developed while maintaining high strength.

  By the way, the “aluminum alloy” referred to in the present invention includes not only an aluminum alloy (aluminum alloy for casting) as a casting material but also an aluminum alloy casting (product) after casting.

  Therefore, in the present invention, when the total is 100% by mass, 4.0 to 6.0% Mg, 0.3 to 0.5% Mn, and 0.5 to 0.9% Fe And 0.1 to 0.2% Ti, and the balance is made of Al and inevitable impurities, and is cooled and solidified at a cooling rate of 20 ° C./second or more to uniformly form fine primary aluminum and the compound. An aluminum alloy casting characterized by being dispersed may also be used.

  The aluminum alloy for castings according to the present invention is more preferable in terms of strength and ductility when the primary crystal aluminum having a dendrite cell size of 10 μm or less and the compound having a particle size of 5 μm or less are uniformly dispersed. . Furthermore, it is more preferable that the dendritic cell size of the primary crystal aluminum is 5 μm or less and the particle size of the compound is 3 μm or less.

  Here, the size of the dendrite cell (dendritic crystal) is a length when measured in the longitudinal direction, and is an average value of values obtained by measuring 100 cells. Moreover, the particle size of the compound was evaluated in the longitudinal direction (maximum length), and the average value of the values measured for 10 visual fields of a tissue photograph (visual field area 70 × 100 μm) photographed 1000 times using an image processing apparatus. It is.

  Thus, according to the aluminum alloy of the present invention, sufficient strength and excellent ductility can be obtained, for example, even in the case of producing a thin-walled mold casting, with almost no porosity such as casting cracks and shrinkage cavities. Can be obtained. For example, in an as-cast state in which heat treatment is not performed after casting, an aluminum alloy having a 0.2% proof stress of 130 MPa or more and a breaking elongation of 13% or more is obtained.

  Furthermore, the aluminum alloy solid-solution strengthened with Mg and Mn within the above composition range has the advantage that almost no change in hardness due to natural aging occurs and the change in mechanical properties over time is small.

(Production method of aluminum alloy castings)
The casting made of the above-described aluminum alloy of the present invention can be obtained, for example, by the following manufacturing method.

That is, in the method for producing an aluminum alloy casting according to the present invention, when the whole is 100% by mass, 4.0 to 6.0% Mg, 0.3 to 0.5% Mn, and 0.5 to 0.5%. An injection step of injecting a molten aluminum alloy containing 0.9% Fe and 0.1-0.2% Ti into the mold, the balance being Al and inevitable impurities; and after the injection step, and a solidifying step of the molten metal is cooling solidified, characterized in that the aluminum alloy casting can be obtained according to the present invention.

  When the solidification step is a step of cooling and solidifying at a cooling rate of 20 ° C./second or higher, an aluminum alloy casting in which the fine primary crystal aluminum and the compound described above are uniformly dispersed can be obtained with certainty. More preferably, the cooling rate is 50 ° C./second or more.

  In addition, “castability” in the present specification is a concept including not only the meltability and mold release property of the molten metal but also the occurrence rate of casting cracks and shrinkage cavities (porosity).

Next, the present invention will be described in more detail with reference to embodiments.
(1) Alloy composition
(a) Mg
Mg is an element that improves the mechanical strength (for example, tensile strength) of an aluminum alloy by being dissolved in an aluminum matrix. Mg is an element that affects the ductility and castability of an aluminum alloy.

  When Mg is less than 4.0% (mass percentage, the same applies hereinafter), the mechanical strength is not sufficiently improved, and in particular, it is difficult to ensure a yield strength of 130 MPa or more (0.2% yield strength, the same applies hereinafter). On the other hand, when Mg exceeds 6.0%, the molten metal is significantly oxidized. In addition, since the composition of Mn and Fe, where coarse crystals start to crystallize as primary crystals as the amount of Mg increases, moves to a lower concentration side. If it exceeds 1, ductility deteriorates due to crystallization of the coarse compound. Therefore, when the whole is taken as 100% by mass, Mg is preferably 4.0 to 6.0%, and more preferably 4.0 to 5.0%.

(b) Mn
Mn is an element that improves the mechanical strength of an aluminum alloy by forming a solid solution in an aluminum matrix, or forming a compound with aluminum to form a fine precipitate in the matrix, similarly to Mg. In addition, there is an effect of improving the seizure resistance with the mold.

  If Mn is less than 0.3%, the mechanical strength is not sufficiently improved, and if it exceeds 0.6%, a coarse crystallized product is crystallized, resulting in ductility degradation. Therefore, Mn is preferably 0.3 to 0.6% and more preferably 0.3 to 0.5% when the whole is 100% by mass.

(c) Fe
Fe is an element that changes the crystallization process during solidification and suppresses casting cracking due to solidification shrinkage. Fe also has an effect of improving seizure resistance with a mold when die casting is performed.

  If Fe is less than 0.5%, it is insufficient for greatly changing the crystallization process, and the effect of suppressing casting cracks is small. On the other hand, if the Fe content exceeds 0.9%, the coarse crystallized product is not preferable because the crystallization ductility is lowered. Therefore, when the whole is taken as 100% by mass, Fe is preferably 0.5 to 0.9%. Further research by the present inventors has revealed that Fe is more preferably 0.5 to 0.8% or 0.5 to 0.7%.

(d) Cr
Cr, like Mg and Mn, is an element that improves the mechanical strength by being dissolved in an aluminum matrix.

  When Cr is less than 0.1%, the mechanical strength is not sufficiently improved, and when it exceeds 0.7%, a coarse crystallized product is crystallized, resulting in a decrease in ductility. Therefore, when the whole is 100 mass%, Cr is preferably 0.1 to 0.7%, and more preferably 0.2 to 0.5%.

(e) Ti, B
Ti and B serve as nucleation sites for primary Al. Therefore, when these elements are added and increased, the crystal grain sizes of primary Al become smaller. As a result, it is considered that the solid-liquid flow state is maintained up to the high solid fraction rate side, the stress generation time due to solidification shrinkage shifts to the low temperature side, and the casting crack resistance is improved. Specifically, it is as follows.

  Ti becomes a nucleation site of α-Al, constitutes a fine structure, exhibits an effect of suppressing cast cracking and improving ductility, and can also improve the yield strength of an aluminum alloy.

Therefore, when the whole is 100% by mass, it is preferable that 0.01 to 0.3% of Ti is included. This is because when Ti is less than 0.01%, a fine structure cannot be obtained, and when Ti exceeds 0.3%, crystallization ductility of a coarse crystallized product (Al ₃ Ti or the like) decreases. It is more preferable that Ti is 0.1 to 0.2%.

B exhibits a great effect of refining crystal grains, particularly in the presence of Ti. If B is less than 0.01%, a fine structure cannot be obtained, and if it exceeds 0.05%, the change in crystal grain size is small and not economical. Accordingly, it is preferable that 0.01 to 0.05% of boron (B) is contained when the whole is 100% by mass in the presence of Ti. It is more preferable that it is 0.03 to 0.05%. B is economical when added as a titanium boride such as TiB ₂ in addition to the case where B is added alone.

(f) Be
Be alone exerts an effect on oxidation resistance and suppresses oxidative consumption of Mg during dissolution. Accordingly, it is preferable that 0.001 to 0.01% of beryllium (Be) be contained alone (without coexisting with Ti or the like) when the total is 100% by mass. It is more suitable in it being 0.005-0.01%. Needless to say, Be may coexist with Ti or the like.

(g) Mo
Mo has an effect of suppressing generation of noro accompanying oxidation of the Al—Mg alloy molten metal. If Mo is less than 0.05%, the effect of inhibiting oxidation is not sufficient, and if it exceeds 0.3%, a coarse crystal is crystallized and ductility is lowered, which is not preferable. Therefore, when the whole is 100% by weight, Mo is preferably 0.05 to 0.3%, and more preferably 0.1 to 0.2%.

(h) Inevitable impurities The inevitable impurities are not limited in type and content unless they adversely affect the properties of the aluminum alloy, but the present inventor has managed by controlling the contents of Si and Cu, which are inevitable impurities. The present inventors have found that the castability, strength or ductility of an aluminum alloy is improved.

  That is, when the whole is 100% by mass, it is preferable that Si, which is an inevitable impurity, is 0.5% or less and Cu is 0.3% or less.

Si is an unavoidable impurity contained in aluminum ingots and the like. If it exceeds 0.5%, Mg ₂ Si precipitates in the matrix by natural aging, and the mechanical properties of the aluminum alloy change over time. Therefore, it is not preferable.

  Cu is an element that promotes casting cracking and inhibits corrosion resistance. Therefore, when using the aluminum alloy which concerns on this invention as a structural member, it is preferable to set it as 0.3% or less especially.

(2) Applications The method for producing an aluminum alloy or casting according to the present invention can be used for various aluminum alloy castings.

  For example, in the field of automobiles and motorcycles, body structural members, chassis members, wheels, space frames, steering wheels (core bars), seat frames, suspension members, engine blocks, transmission cases, pulleys, oil pans, shift levers, By using the aluminum alloy of the present invention and its manufacturing method for instrument panels, door impact panels, intake surge tanks, pedal brackets, front shroud panels, etc., these members can be manufactured at low cost without heat treatment. .

  The aluminum alloy of the present invention has high strength and high ductility even in an as-cast state, but it is of course possible to perform cold working or heat treatment after casting.

Next, the present invention will be described in more detail with reference to examples according to the present invention.
(Production and testing of test pieces)
(1) First Example Sample No. 1 shown in Table 1 was used. 1-5 and sample no. Using aluminum alloys having an alloy composition of C1 to C7, test pieces having various restraint lengths were produced for each sample, and the cast cracking properties were evaluated. In Table 1, the main component Al is omitted (hereinafter the same).

  Specifically, as shown in FIG. 1, various test pieces are manufactured by a vertical die-casting machine having a die having a cavity having a cross section of 7 mm in thickness and a width of 10 mm, and the constraint length of which can be variously changed. The casting crack was evaluated.

  The casting conditions were a melting temperature of 750 ° C., a mold temperature of 50 to 100 ° C., a casting pressure of 63.7 MPa, and a plunger speed of 0.6 m / s. Each molten metal was pressurized and injected with a plunger (injection step), and then solidified at a cooling rate of about 100 ° C./second (solidification step).

  The cast cracking resistance was evaluated based on the restraint length when cracking occurred. It shows that it is an alloy which is hard to raise | generate a casting crack, so that the restraint length is long. The test results of the test pieces thus obtained are shown in FIG.

  In this test, a heat insulating sheet having a thickness of 0.5 mm × a height of 10 mm was attached to the three portions of the cavity in the central portion in the restraining length direction, and the position where the casting crack occurred was limited to that portion. . The state of the three-sided tension of the heat insulating sheet is shown in FIG. 2 which is a cross-sectional view taken along the line AA in FIG.

(2) Second Example Sample No. 2 shown in Table 1 was used. 6-14 and sample no. A plate-shaped casting having a thickness of 2 m, a width of 50 mm, and a length of 70 mm was produced by a vertical die casting machine using an aluminum alloy having an alloy composition of C8 to C10.

  The casting conditions were a melting temperature of 750 ° C., a mold temperature of 50 to 100 ° C., a casting pressure of 63.7 MPa, and a plunger speed of 1.4 m / s. Further, the molten metal was injected into the cavity under pressure (injection step) and then solidified at a cooling rate of about 100 ° C./second (solidification step).

  From this as-cast plate-like casting, a flat plate tensile test piece having a flat surface as cast surface was produced. Each specimen was examined for tensile strength, 0.2% yield strength and elongation at break. The results are shown in Table 2. In addition, the tensile test of each test piece was performed using the autograph tensile tester made from Shimadzu, and said each characteristic was calculated | required from the stress-strain diagram obtained about each test piece.

(3) Third Example Sample No. shown in Table 1 was used. 15 to 19 and sample no. Using an aluminum alloy having an alloy composition of C11 and C12, an as-cast plate-like casting was manufactured in the same manner as in the second example.

  Here, in order to investigate the influence of the time-dependent change (artificial aging) of the mechanical properties of each plate-like casting, the plate-like casting in an as-cast state, and the plate-like casting after heating it at 175 ° C. for 10 hours, Was prepared, and the hardness (Vickers hardness) of each plate casting was examined. The results are shown in Table 3.

  In addition, Vickers hardness calculated | required hardness converted into the size of the impression mark made by loading 5 kg of loads for 30 second using the Akashi Bickus hardness meter.

(4) Fourth Example Further, the relationship between the cast cracking resistance of the Al alloy casting and the amount of Fe was examined in detail. That is, the sample Nos. Test pieces having various restraint lengths having an alloy composition of 20 to 26 were produced in the same manner as in the first example. In each sample, the contents of Fe were mainly changed while the contents of Mg, Mn, and Ti were made similar. The point that the casting crack resistance is evaluated by the restraint length when a crack occurs is the same as in the case of the first embodiment. The test results of the test pieces thus obtained are shown in FIG.

(5) Fifth Example The influence of the alloy composition on the oxidation resistance of the Al alloy molten metal was examined. First, sample Nos. Shown in Table 5 were used. 27 and sample no. An Al alloy melt having an alloy composition of 28 was prepared. Each molten metal was measured in advance. These molten metals were put into an alumina crucible and held at 750 ° C. for 5 hours in an air atmosphere.

  After the molten metal was cooled, the weight of the solidified Al alloy was measured. And the oxidation increase of Al alloy was calculated | required from the weight difference before and behind the said heating holding. The results are also shown in Table 5. Table 5 shows the rate of increase in oxidation (oxidation increase rate) relative to the weight of the molten metal before the heating and holding.

(Evaluation)
(1) Castability Sample No. in the composition range of the present invention. The aluminum alloys 1 to 5 are sample Nos. It can be seen from FIG. 3 that the constraint length at which cracks occur is sufficiently long for C1 to C7. Specifically, Sample No. No. 1 has a restrained length of 50 mm, sample No. The restraint length of Nos. 2 and 3 is 70 mm. No cracking occurred until the restraint lengths of 4 and 5 were 80 mm.

  From these, it was found that the cast cracking resistance was greatly improved by adding an appropriate amount of Fe while suppressing the amount of Mn. It has also been found that casting crack resistance is further improved by adding Ti as a nucleation site while Mg, Mn and Fe are in the composition range according to the present invention.

  In particular, as is apparent from Table 4 and FIG. 4, sample No. 1 containing Mg, Mn and Ti within the preferred composition range of the present invention and containing 0.5 to 0.8% of Fe was used. The castings of 222 to 24 Al alloy were further improved in casting crack resistance.

(2) Strength and ductility
(a) Sample No. 6 to 14 are all aluminum alloys within the composition range of the present invention. As can be seen from Table 2, these aluminum alloys all have a tensile strength of 250 MPa or more, a 0.2% proof stress of 130 MPa or more, and an elongation of 15% or more. Therefore, it has been found that even in an as-cast state, the aluminum alloy according to the present invention exhibits excellent ductility while maintaining sufficient strength. In particular, there are those having a tensile strength of 300 MPa or more, a 0.2% proof stress of 150 MPa or more, and an elongation exceeding 20%.

  Sample No. Sample No. 6 containing Ti in the aluminum alloy No. 6 In No. 7, crystal grains were further refined and ductility was further improved.

(b) On the other hand, Sample No. deviating from the composition range according to the present invention. C8-C10 aluminum alloys were unable to achieve both strength and ductility. For example, sample No. C8 had a tensile strength and a 0.2% proof stress high because the amount of Mn exceeded 0.6% by mass, but had an elongation of less than 10% and low ductility. On the contrary, sample No. with Mn of less than 0.3% by mass was obtained. Sample No. C9 or Mg containing less than 4.0% by mass. Although C10 was highly ductile, its strength was insufficient.

(3) Effect of aging Sample No. 15 to 19 are all aluminum alloys within the composition range of the present invention. As can be seen from Table 3, these aluminum alloys had little change in hardness between the as-cast state and after heating at 175 ° C. for 10 hours.

  On the other hand, sample No. Since the C11 and C12 aluminum alloys contain a large amount of Si beyond the inevitable impurities, the change in hardness between the as-cast state and after heating at 175 ° C. for 10 hours was large. In other words, age hardening occurs, and there is a concern that the aluminum alloy having such a composition may change characteristics due to natural aging.

(4) Oxidation resistance Sample No. in Table 5 27, 28, while Mg, Mn, Ti and Fe are each within the preferred composition range of the present invention, and further containing 0.1 to 0.2% of Mo, It was also revealed that it exhibits excellent oxidation resistance.

It is sectional drawing which shows the vertical die-casting machine provided with the metal mold | die for casting crack evaluation which can change restraint length. It is AA sectional drawing in FIG. It is the bar graph which showed the relationship between restraint length and castability about each test piece. It is a graph which shows the relationship between casting cracking property and Fe amount.

Claims (12)

When the whole is 100 mass% (mass percentage), 4.0-6.0% magnesium (Mg), 0.3-0.5% manganese (Mn), 0.5-0. and 9% of iron (Fe), 0.1 to 0.2 percent of titanium (Ti) and a, foundry aluminum alloy balance being made of aluminum (Al) and unavoidable impurities.   Furthermore, the aluminum alloy for castings of Claim 1 containing 0.1-0.7% of chromium (Cr) when the whole is 100 mass%.   Furthermore, the aluminum alloy for castings of Claim 1 containing 0.01-0.05% boron (B) when the whole is 100 mass%.   Furthermore, the aluminum alloy for castings of Claim 1 containing 0.001-0.01% of beryllium (Be) when the whole is 100 mass%.   Furthermore, the aluminum alloy for castings of Claim 1 containing 0.05-0.3% molybdenum (Mo) when the whole is 100 mass%.   2. The aluminum alloy for casting according to claim 1, wherein the inevitable impurities are 0.5% or less of silicon (Si) and 0.3% or less of copper (Cu) when the total is 100 mass%.   The aluminum alloy for casting according to claim 1, wherein the Fe is 0.5 to 0.8 mass%. When the whole is 100 mass%, 4.0 to 6.0% Mg, 0.3 to 0.5% Mn, 0.5 to 0.9% Fe, 0.1 to and a 0.2% Ti, aluminum alloy casting the balance being made of Al and unavoidable impurities.   The aluminum alloy casting according to claim 8, wherein the tensile strength is 250 MPa or more in an as-cast state in which heat treatment is not performed after casting.   The aluminum alloy casting according to claim 8, wherein the 0.2% proof stress is 130 MPa or more in an as-cast state in which heat treatment is not performed after casting.   The aluminum alloy casting according to claim 8, wherein the elongation at break is 13% or more in an as-cast state in which heat treatment is not performed after casting. When the whole is 100 mass%, 4.0 to 6.0% Mg, 0.3 to 0.5% Mn, 0.5 to 0.9% Fe and 0.1 to 0.2 An injection process for injecting a molten aluminum alloy containing Al and unavoidable impurities into the mold.
After infusion step and a solidifying step of the molten metal of the aluminum alloy is cooling solidified,
A method for producing an aluminum alloy casting, wherein the aluminum alloy casting according to any one of claims 8 to 11 is obtained.

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