JP2005336569A - HIGH TOUGHNESS Al ALLOY CASTING - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high toughness Al alloy casting in which tensile strength, 0.2% proof stress and elongation can be obtained at high levels in a well balance. <P>SOLUTION: The high toughness Al alloy casting has a composition comprising, by mass, 2 to 5% Si, 0.2 to 0.5% Mg, 0.4 to 0.8% Cu, 0.05 to 0.3% Ge, and the balance Al with inevitable impurities. The casting has the tensile strength of ≥280 MPa, the 0.2% proof stress of ≥220 MPa, and the elongation of ≥12%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a high toughness Al alloy casting, and more particularly to an Al alloy casting excellent in various mechanical properties.

  Al alloy castings are suitable for use in chassis components such as vehicle bodies, suspension members, subframe members, various joint members, and aluminum wheels, and various techniques are disclosed for such alloys.

Such an Al alloy casting has a mass ratio of Si: 1.65 to 4.0% and Mg: 0.2 for the purpose of improving elongation, impact value, tensile strength, yield strength, and corrosion resistance. -0.4%, Fe: 0.2% or less, the balance is substantially composed of Al and inevitable impurities, the area ratio of eutectic Si in the Al base is 15% or less, and the elongation is 15%. As described above, a high toughness Al casting having an impact value of 30 to 40 × 10 ⁴ J / m ² or more has been proposed (see Patent Document 1). This high toughness Al casting has a composition with a low Si content, and after casting it is subjected to a high temperature solution treatment that is rapidly cooled to a high temperature close to the eutectic temperature, and then an aging treatment is appropriately applied to achieve excellent elongation. And impact values can be realized. In addition, this Al casting can be similarly subjected to a high-temperature solution treatment, and then an aging treatment for a long time, thereby realizing excellent tensile strength, yield strength, and corrosion resistance. According to such a technique, it is possible to reduce the weight accompanying the thinning of the parts, and to apply low-pressure casting or gravity casting, so that productivity can be improved.

  Further, for the purpose of realizing excellent toughness and preventing the occurrence of seizure on the mold, the mass ratio is 2% ≦ Si ≦ 4%, 0.2% ≦ Mg ≦ 0.5%, 0 .4% ≦ Cu ≦ 0.8%, 0.2% ≦ Fe ≦ 0.5%, 0.1% ≦ Ti ≦ 0.3%, and unavoidable impurities, the balance being Al, There has been proposed a high toughness Al alloy casting in which the particle size d of the α phase is 50 μm or less (see Patent Document 2). In this technique, the composition of the high toughness Al casting is made the same composition as that of the above-mentioned Patent Document 1, and the excellent toughness is achieved by making the content of Fe more than epoch-making 0.2% by mass. Both prevention of seizing on the mold can be realized. In addition, in the high toughness Al alloy casting described in Patent Document 2, the molten aluminum alloy having the above composition is filled into the mold cavity under pressure, and then the cooling rate is controlled to 5 ° C./S until the solidification of the molten metal is completed. The physical properties such as toughness are equivalent to those of the casting described in Patent Document 1, but the productivity is further improved.

Japanese Laid-Open Patent Publication No. 9-272942 (Abstract) Japanese Patent Application No. 2003-420405

However, in the techniques described in Patent Documents 1 and 2, it is difficult to say that sufficient values are obtained for toughness such as elongation and impact strength among mechanical properties of the obtained casting. For example, in the casting according to claim 4 of Patent Document 1, the tensile strength is 240 MPa or more and the 0.2% proof stress is 140 MPa or more, but the impact value is as low as 19 × 10 ⁴ . Therefore, in recent years, there has been a demand for the technical development of Al alloy castings in which all of tensile strength, 0.2% proof stress and elongation can be obtained at a high level with good balance.

  This invention is made | formed in view of the said request | requirement, and aims at providing the high toughness Al alloy casting from which all of a tensile strength, 0.2% yield strength, and elongation are obtained with a high level with sufficient balance.

  As described above, the present inventors diligently researched a high toughness Al alloy casting in which tensile strength, 0.2% proof stress and elongation can be obtained at a high level in a balanced manner. As a result, as shown in Patent Document 2, instead of limiting the Fe and Ti contents in the alloy components, the inventors have found that the above problem can be solved by limiting the Ge content. The present invention has been made in view of such knowledge.

  That is, the high toughness Al alloy casting of the present invention has a mass ratio of 2% ≦ Si ≦ 5%, 0.2% ≦ Mg ≦ 0.5%, 0.4% ≦ Cu ≦ 0.8%, 0.8%. 05% ≦ Ge ≦ 0.3% and containing inevitable impurities, the balance being Al, tensile strength is 280 MPa or more, 0.2% proof stress is 220 MPa or more, and elongation is 12% or more. .

  Further, in such a high toughness Al alloy casting, it is desirable that at least one of Zr, Ti, and B is contained. It should be noted that a eutectic refining agent such as Sr or Na may be added to the high toughness Al alloy casting of the present invention. The Fe content is preferably 0.2% by mass or less, but can be contained up to 0.5% by mass by controlling the particle size.

  According to the high toughness Al alloy casting of the present invention, by optimizing the Ge content in the alloy, the excellent tensile strength, 0.2% proof stress and elongation of the Al alloy casting are realized at a high level in a balanced manner. be able to.

The preferred embodiments of the present invention will be described below.
The high toughness Al alloy casting of the present invention has a mass ratio of 2% ≦ Si ≦ 5%, 0.2% ≦ Mg ≦ 0.5%, 0.4% ≦ Cu ≦ 0.8%, 0.05%. ≦ Ge ≦ 0.3%, and inevitable impurities are contained, the balance is Al, the tensile strength is 280 MPa or more, the 0.2% proof stress is 220 MPa or more, and the elongation is 12% or more. The reasons for the inclusion of each element in such an alloy and the reasons for limiting its content are as follows.

  Si has the effect of improving the fluidity of the molten metal and improving the mechanical properties of the Al alloy casting. However, when the Si content is less than 2% by mass, the fluidity of the molten metal is deteriorated, so that the occurrence of casting defects is remarkably increased in the Al alloy casting. On the other hand, when the Si content exceeds 5% by mass, the amount of Si crystals distributed at the grain boundaries of the α-Al phase increases, so that the toughness of the Al alloy casting decreases. Therefore, the content of Si is set to 2 to 5% by mass.

Mg has the effect of improving the strength of the Al alloy casting by finely dispersing and precipitating Mg ₂ Si by T6 treatment. However, when the Mg content is less than 0.2% by mass, the above effect is insufficient. On the other hand, when the Mg content exceeds 0.5% by mass, the amount of Mg ₂ Si precipitated becomes excessive, and the toughness of the Al alloy casting is lowered. Therefore, the content of Mg is set to 0.2 to 0.5% by mass.

  Cu has the effect of solid-solution strengthening the metal structure of the Al alloy casting based on the high solid solubility limit in Al, and also has the effect of dispersion strengthening the metal structure by dispersion precipitation by T6 treatment. However, when the Cu content is less than 0.4% by mass, the effect of improving the strength of the Al alloy casting is not sufficient. On the other hand, when the Cu content exceeds 0.8% by mass, not only the stress corrosion cracking resistance of the Al alloy casting is lowered but also the corrosion resistance is deteriorated. Therefore, the Cu content is set to 0.4 to 0.8 mass%.

Ge has a solid solubility limit of 0.5 atm% or more, and since Al, Si, Mg and Cu do not produce a compound during precipitation, it has the effect of improving toughness without deteriorating the fluidity of the molten metal. . However, when the Ge content is less than 0.05% by mass, the above effect is insufficient. On the other hand, when the content of Ge exceeds 0.3% by mass, a Ge—Si—Mg system or Mg ₂ Ge is generated, and the elongation and strength are lowered. Therefore, the content of Ge is set to 0.05 to 0.3% by mass. In addition, the effect similar to the said effect which Ge shows can be acquired by containing Zn, Ag, Li, Sc, and Ga other than Ge. This is because these elements have an atomic radius ratio with Al in the above range. Among these elements, it is particularly preferable to contain Li.

The above are the essential elements to be contained in the high toughness Al alloy casting of the present invention. The reasons for the inclusion of each element that is preferably contained in the Al alloy casting as a subsidiary will be described below.
Fe has the effect of preventing the molten metal from sticking to the mold. However, if it is excessively contained, α-FeAlSi crystallizes at a high temperature, which causes a decrease in the toughness of the Al alloy casting.

Zr, Ti and B have an effect of refining crystal grains. However, when Zr or Ti is excessively contained, Al ₃ Zr that is a ZrAl-based high-temperature crystallized product or Al ₃ Ti that is a TiAl-based high-temperature crystallized product is generated, so that the fluidity of the molten metal deteriorates. As a result, casting defects are likely to occur. Note that B is an element that should be used in combination with Zr or Ti in order to develop a composite fine particle effect in cooperation with Zr or Ti.

Furthermore, the suitable manufacturing method of the high toughness Al alloy casting of this invention is demonstrated in detail.
That is, when manufacturing the above high toughness Al alloy casting, the mass ratio is 2% ≦ Si ≦ 5%, 0.2% ≦ Mg ≦ 0.5%, 0.4% ≦ Cu ≦ 0.8%, 0 .05% ≦ Ge ≦ 0.3%, containing inevitable impurities, balance is Al, tensile strength is 280 MPa or more, 0.2% proof stress is 220 MPa or more, and elongation is 12% or more In manufacturing a casting, after casting an alloy having the above composition, it is subjected to a high-temperature heat treatment at 490 to 540 ° C., followed by a rapid cooling treatment, and then an aging treatment at a temperature of 155 to 190 ° C.

  The reason for containing each alloy element and the reason for limiting its content are the same as in the above case. As the casting method, for example, die gravity casting or general die casting can be applied, the casting temperature is 720 to 730 ° C., the die temperature is 250 ° C. to 300 ° C. in die gravity casting, and 150 ° C. in die casting. It is preferable to set it to -250 degreeC.

  When the temperature of the high-temperature heat treatment (solution treatment) is less than 490 ° C., homogenization between the strengthening phase and the nucleus site atoms does not proceed sufficiently, whereas when it exceeds 540 ° C., partial burning occurs and the grain boundary strength Is not preferable because it significantly decreases. Therefore, the heat treatment temperature was set to 490 to 540 ° C. In addition, although this high temperature heat processing time is based on the dimension of a product, sufficient homogenization is generally implement | achieved in 4 to 10 hours.

  Further, when the aging treatment temperature is less than 155 ° C., not only the precipitation of the strengthening phase is not sufficiently obtained, but also the treatment time increases, so that it is not economical. This is not preferable because the effect of forming fine nucleation sites with Ge is lost because of excessive growth. Therefore, the aging treatment temperature was set to 155 to 190 ° C. In general, the aging treatment time is preferably 5 to 14 hours. Incidentally, the process of sequentially performing the solution treatment, the rapid cooling process, and the aging process is a so-called T6 process.

Hereinafter, the present invention will be described in more detail with reference to examples.
In the composition of Al-3Si-0.25Mg-0.6Cu, Ge was added at 0, 0.05, 0.1, 0.2, 0.3, and 0.4% by mass, respectively, and T6 treatment (525 The tensile strength, 0.2% proof stress and elongation of the Al alloy casting obtained by solution treatment at 4 ° C. for 4 hours followed by rapid cooling and then aging at 175 ° C. for 6 hours were measured. The results are shown in FIGS.

  As is clear from FIG. 1 and FIG. 2, excellent results were obtained for all of the tensile strength, 0.2% proof stress and elongation within the range of the present invention, that is, 0.05 ≦ Ge ≦ 0.3. . The reason for this is as follows.

That is, generally, a strengthening phase is precipitated in an Al alloy member subjected to T6 heat treatment, and excellent strength and proof stress can be obtained. However, when the precipitation of the strengthening phase is excessive or when there is segregation, the toughness decreases. When a small amount of Ge is contained, during casting or solution treatment, Ge is solid-solved in the grain boundary of the base α-Al phase, and similarly strengthening elements such as Cu, Si and Mg, It becomes a starting point of precipitation, that is, a nucleus during aging heat treatment. For this reason, the fine dispersibility of precipitation strengthening phases, such as A1 ₂ Cu and Mg ₂ Si, improves, and strength and elongation improve. Under such a phenomenon, as is clear from FIGS. 1 and 2, when the Ge content is 0.05% by mass or more, improvement in strength (tensile strength and 0.2% proof stress) and elongation are observed. When it exceeds 2% by mass, a compound peculiar to Ge starts to precipitate, so that the mechanical properties start to deteriorate, and when it exceeds 0.4% by mass, the strength and elongation decrease compared to the case where Ge is not contained. . The decrease in strength and the like is due to the fact that Ge / Si is co-deposited to produce a Si / Ge—Mg compound and the strengthening action of Mg ₂ Si is reduced. From the above, the effectiveness of the grounds for limitation of the Ge content of the present invention was demonstrated.

Furthermore, the preferred range for Si, Mg, and Cu, which are constituent elements of the high toughness Al alloy casting of the present invention, will be demonstrated.
In the composition of Al-0.4Mg-0.6Cu, Si is contained in 1.5, 2, 3, 5, 6, and 7% by mass, respectively, and T6 treatment (after solution treatment at 525 ° C. for 4 hours) The tensile strength and Charpy impact value of the Al alloy castings obtained by quenching and then aging at 175 ° C. for 6 hours were measured. The result is shown in FIG. As is apparent from FIG. 3, when the Si content is less than 2% by mass, the fluidity of the molten metal is deteriorated, the defects are remarkably increased at the time of pressure casting, and excellent mechanical properties cannot be obtained. Moreover, when Si content exceeds 5 mass%, Si crystal | crystallization will increase and inertia will fall. The toughness at this time is equivalent to that of a 7 mass% Si alloy that is a general standard material. As described above, the effectiveness of the limitation basis of the Si content in the Al alloy casting of the present invention was proved.

In the composition of Al-3Si-0.6Cu, Mg was added in an amount of 0.15, 0.2, 0.3, 0.5, 0.6, and 0.7% by mass, respectively, and T6 treatment (525 ° C. After the solution treatment for 4 hours, the aluminum alloy casting obtained by quenching treatment and then aging treatment at 175 ° C. for 6 hours was measured for tensile strength and Charpy impact value. The result is shown in FIG. As is clear from FIG. 4, when the Mg content is less than 0.2% by mass, the effect of improving the strength due to precipitation of Mg ₂ Si during the T6 heat treatment is not obtained. Further, when the Mg content exceeds 0.5 wt%, it increases the amount of precipitation of _Mg 2 Si, the toughness is lowered. Thus, the effectiveness of the grounds for limiting the Mg content in the Al alloy casting of the present invention has been demonstrated.

  In the composition of Al-3Si-0.4Mg, 0.3, 0.4, 0.6, 0.8, 0.9, and 1.1% by mass of Cu were added, respectively, and T6 treatment (525 ° C. After the solution treatment for 4 hours, the aluminum alloy casting obtained by quenching treatment and then aging treatment at 175 ° C. for 6 hours was measured for tensile strength and Charpy impact value. The result is shown in FIG. Cu has a high solid solubility limit in Al and is an element that not only strengthens the structure by solid solution, but also strengthens it by dispersion precipitation by combining solution treatment and aging treatment. Further, Cu is an element that significantly contributes to the improvement of mechanical properties because it does not significantly reduce toughness up to a certain content. However, in general, it is an element that lowers corrosion resistance and is known to have low compatibility with undercarriage parts and the like. Based on such knowledge, as is clear from FIG. 5, when the Cu content is less than 0.4 mass%, the effect of improving the tensile strength and Charpy impact value cannot be sufficiently realized, On the other hand, if it exceeds 0.8 mass%, stress corrosion or the like occurs, which is not preferable. Thus, the effectiveness of the grounds for limiting the Cu content in the Al alloy casting of the present invention has been demonstrated.

  As described above, the high toughness Al alloy casting of the present invention balances the excellent tensile strength, 0.2% proof stress and elongation of the high toughness Al alloy casting, particularly by optimizing the Ge content. It can be realized at a high level. Therefore, the present invention is useful in that it can be applied to a vehicle body, a suspension member, and the like, which are expected to require more advanced mechanical properties in the future.

It is a graph which shows the relationship between the tensile strength and 0.2% yield strength of Al alloy casting, and Ge content. It is a graph which shows the relationship between elongation of Al alloy casting, and Ge content. It is a graph which shows the relationship between the tensile strength and Charpy impact value of Al alloy casting, and Si content. It is a graph which shows the relationship between the tensile strength and Charpy impact value of Al alloy casting, and Mg content. It is a graph which shows the relationship between the tensile strength and Charpy impact value of Al alloy casting, and Cu content.

Claims (2)

  In mass ratio, 2% ≦ Si ≦ 5%, 0.2% ≦ Mg ≦ 0.5%, 0.4% ≦ Cu ≦ 0.8%, 0.05% ≦ Ge ≦ 0.3%, and inevitable A high-toughness Al alloy casting characterized by containing a general impurity, the balance being Al, a tensile strength of 280 MPa or more, a 0.2% proof stress of 220 MPa or more, and an elongation of 12% or more.   The high toughness Al alloy casting according to claim 1, wherein at least one of Zr, Ti, and B is contained.

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