JP2006022385A - HIGH TOUGHNESS Al ALLOY CASTING AND ITS PRODUCTION METHOD - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high toughness Al alloy casting capable of obtaining tensile strength, 0.2% proof stress and elongation at a high level in a well balance. <P>SOLUTION: The high toughness Al alloy casting has a composition containing, by mass, 2 to 4% Si, 0.2 to 0.5% Mg, 0.4 to 0.8% Cu and 0.05 to 0.3% Ni, and the balance Al with inevitable impurities, and has a tensile strength of ≥300 MPa, a 0.2% proof stress of ≥210 MPa and an elongation of ≥10%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a high toughness Al alloy casting and a method for producing the same, and more particularly to a technique for producing an Al alloy casting having various mechanical characteristics.

  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, the techniques described in Patent Documents 1 and 2 do not provide sufficient values for toughness such as elongation and impact strength among the mechanical properties of the resulting 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 technological development of Al alloy castings that can obtain tensile strength, 0.2% proof stress and elongation at a high level with good balance.

  This invention is made | formed in view of the said request | requirement, and aims at providing the toughness Al alloy casting and its manufacturing method in which a tensile strength, 0.2% yield strength, and elongation are obtained with a high level with good 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, when an Al alloy casting is manufactured using the techniques described in Patent Documents 1 and 2, excellent castability, in particular, excellent fluidity of the molten metal cannot be obtained. The knowledge that the property was not realized with good balance was obtained. Therefore, the inventors have made use of the fact that Ni improves the fluidity of the molten metal under such knowledge, instead of limiting the Fe and Ti contents in the alloy components as shown in Patent Document 2 above. An attempt was made to limit the Ni content. As a result, the inventors have obtained knowledge that the above-mentioned problems can be solved. That is, it is generally known that when Ni is contained in an aluminum alloy, the fluidity at the time of melting is improved. However, when Ni is contained, the elongation is reduced among the mechanical properties. For this reason, it is necessary to provide a suitable upper limit for the Ni content. However, as a result of various studies, it has been found that the elongation is hardly lowered if the content is up to 0.3% by mass. 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 ≦ 4%, 0.2% ≦ Mg ≦ 0.5%, 0.4% ≦ Cu ≦ 0.8%, 0.8%. 05% ≦ Ni ≦ 0.3% and inevitable impurities are contained, the balance is Al, the tensile strength is 300 MPa or more, the 0.2% proof stress is 210 MPa or more, and the elongation is 10% or more. . The high toughness Al alloy casting of the present invention can contain an α-Al phase refining agent such as Zr, Ti, Ti—B or the like.

  Moreover, the manufacturing method of the high toughness Al alloy casting of this invention is 2% <= Si <= 4%, 0.2% <= Mg <= 0.5%, 0.4% <= Cu <= 0.8% by mass ratio. 0.05% ≦ Ni ≦ 0.3%, and inevitable impurities, the balance being Al, the tensile strength is 300 MPa or more, the 0.2% proof stress is 210 MPa or more, and the elongation is 10% or more. In producing an Al alloy casting, an alloy having the above composition is cast, subjected to high-temperature heat treatment at 515 to 540 ° C., then subjected to rapid cooling treatment, and then subjected to aging treatment at a temperature of 165 to 185 ° C. . In such a method for producing a high toughness Al alloy casting, the solidification rate at the time of casting is set to 5 ° C./second or more, whereby the Ni content is increased to 6% by mass, and the fluidity is further improved. As a result, the tensile strength, 0.2% yield strength and elongation of the Al alloy casting can be realized at a higher level in a balanced manner.

  According to the high toughness Al alloy casting of the present invention, by optimizing the Ni content in the alloy, the flowability at the time of melting of the Al alloy casting is improved, and excellent tensile strength, 0.2% proof stress and Elongation can be achieved at a high level with good balance. In addition, below, the effect of this invention is demonstrated in detail.

  In general high toughness cast Al alloy, the Si content is less than 5% by mass to achieve high toughness, and the effect of improving fluidity due to the latent heat action of Si cannot be sufficiently obtained. Poor fluidity. Further, the linear expansion coefficient is relatively large as compared with the Al alloy having a large Si content, and the hot shrinkage rate during casting is also relatively large. For this reason, in the Al alloy having a low Si content, the amount of cast holes in the thick wall portion is increased, and the hot solidification cracking property is also high.

  In order to improve the disadvantage of such an Al alloy having a low Si content, when a transition metal element (for example, Ni) is included in the Al alloy, the transition metal element is in the process of increasing the α-Al phase during casting. Then, a hard compound composed of Al and other constituent elements crystallizes. The latent heat when the hard compound is generated contributes to castability, particularly fluidity. Moreover, since the said hard compound generate | occur | produces in the grain boundary at the time of semi-melting, it can provide high temperature strength and can prevent a hot crack.

  The content of Ni in which the above effects are suitably achieved is as follows. That is, when the Ni content is 0.05% by mass or more, the fluidity and the solidification shrinkage are improved, while when it exceeds 0.3% by mass, the elongation, which is an evaluation standard for toughness, is lowered. Therefore, the limited range of the Ni content is set to 0.05 to 0.3% by mass. Moreover, the fall of the said elongation originates in generation | occurrence | production of a hard compound increasing. However, by increasing the solidification rate at the time of casting, the hard compound can be finely dispersed and crystallized, and a decrease in toughness can be suppressed. In addition, when acquiring this effect, content of Ni can be raised to 0.6 mass% by making a solidification rate into 5 degrees C / second or more. In addition, the cooling rate here is a cooling rate in a section in the initial stage of solidification, and is not an average speed in a section of the entire solidification.

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 ≦ 4%, 0.2% ≦ Mg ≦ 0.5%, 0.4% ≦ Cu ≦ 0.8%, 0.05%. ≦ Ni ≦ 0.3%, and inevitable impurities are contained, the balance is Al, the tensile strength is 300 MPa or more, the 0.2% proof stress is 210 MPa or more, and the elongation is 10% or more. The reason why each element is contained in such an alloy and the reason for limiting the content are as follows.

  Si has the effect of improving the mechanical properties of the Al alloy casting while improving the fluidity of the molten metal. However, when the Si content is less than 2% by mass, the fluidity of the molten metal is deteriorated, so that casting defects are significantly increased in the Al alloy casting. On the other hand, when the Si content exceeds 4% by mass, the amount of Si crystals distributed at the crystal 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 4% by mass.

Mg has an effect of improving the strength of the Al alloy casting by finely dispersing and precipitating Mg ₂ Si by T6 treatment (a treatment in which predetermined high-temperature heat treatment, rapid cooling treatment, and aging treatment are sequentially performed). 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 mass%, the strength improvement effect in 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%.

  Ni is as described above, and is an element that contributes to improving the fluidity of the molten metal. However, when the Ni content is less than 0.05% by mass, the effect of improving the fluidity of the molten metal is not sufficient, and excellent results on the solidification shrinkage cannot be obtained. On the other hand, when the Ni content exceeds 0.3% by mass, the elongation, which is the evaluation standard for toughness, is lowered. Therefore, the Ni content is set to 0.05 to 0.3% by mass.

Next, each limitation reason is demonstrated in detail about the manufacturing method of the high toughness Al alloy casting of this invention.
That is, when manufacturing the above-mentioned high toughness Al alloy casting, the mass ratio is 2% ≦ Si ≦ 4%, 0.2% ≦ Mg ≦ 0.5%, 0.4% ≦ Cu ≦ 0.8%. 0.05% ≦ Ni ≦ 0.3%, and inevitable impurities, the balance being Al, the tensile strength is 300 MPa or more, the 0.2% proof stress is 210 MPa or more, and the elongation is 10% or more. In producing an Al alloy casting, an alloy having the above composition is cast, subjected to high-temperature heat treatment at 515 to 540 ° C., then subjected to quenching treatment, and then subjected to aging treatment at a temperature of 165 to 185 ° C.

  The reason for containing each alloy element and the reason for limiting its content are as described above. As the casting method, for example, a die gravity casting method or a general die casting method can be applied, the casting temperature is 715 to 735 ° C., the die temperature is 120 to 350 ° C. in the die gravity casting method, and the die casting method. Then, 90-250 degreeC is preferable.

  In addition, when the temperature of the high-temperature heat treatment (solution treatment) is less than 515 ° C., for example, when Zr is contained, homogenization between the strengthening phase and the nucleus site atoms does not proceed sufficiently, whereas , Partial burning occurs, and the grain boundary strength is remarkably lowered. Therefore, the heat treatment temperature was set to 515 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 6 hours.

  Furthermore, if the aging treatment temperature is less than 165 ° C., not only the precipitation of the strengthening phase is not sufficiently obtained, but also the treatment time increases, which is uneconomical. This is not preferable because the strengthening phase grows too much and lowers the toughness. Therefore, the aging treatment temperature was set to 165 to 185 ° C. In general, the aging treatment time is preferably 6 to 8 hours.

Hereinafter, the present invention will be described in more detail with reference to examples.
[Effect of each component element]
Al-3Si-0.6Cu-0.25Mg was prepared as a base material, and adjusted to alloys having the respective compositions shown in Table 1 using various contained elements. The resulting alloy was then cast as shown in Table 1 and further subjected to T6 treatment (high temperature heat treatment at 525 ° C. for 4 hours, rapid cooling treatment (70 ° C.), and aging treatment at 175 ° C. for 6 hours). Thus, Al alloy castings of Comparative Examples 1 to 12 and Invention Examples 1 to 13 were obtained. Regarding the type of casting, in the case of laminar flow DC (200 ton), the mold temperature is 90 to 250 ° C., the initial speed is 0.15 m / sec, the injection speed is 0.3 m / sec, and the pouring temperature. Was 730 ° C., and the casting pressure was 90 MPa. In the case of boat shape (GDC), the mold temperature was 120 to 350 ° C, and the pouring temperature was 730 ° C.

  The measurement results of tensile strength, 0.2% proof stress and elongation, and MIT flow length for the Al alloy castings of Comparative Examples 1 to 12 and Invention Examples 1 to 13 are also shown in Table 1, and the tensile strength, 0. The measurement results of 2% proof stress and elongation are shown in FIGS.

Hereinafter, it is confirmed that the scope of the present invention is suitable for each series shown in Table 1 for each demonstration purpose.
(Series 1, Series 5: Influence of Ni content)
According to Table 1 and FIGS. 1 and 2, for Invention Examples 1 to 3 in which the Ni content is within the scope of the present invention, the tensile strength, 0.2% proof stress and elongation are all obtained at a high level in a balanced manner. Yes. On the other hand, for Comparative Examples 1 to 4 in which the Ni content deviates from the scope of the present invention, when the Ni content is small, the tensile strength and 0.2% proof stress are not sufficient, and the Ni content is When it is excessive, the elongation is not sufficient. Therefore, it was demonstrated that the preferable range of Ni content is 0.05 to 0.3% by mass. Since the MIT flow length increases as the Ni content increases, the fluidity is proportional to the Ni content. However, if the Ni content is within the scope of the present invention, there is no problem with the fluidity. It was also demonstrated that if the Ni content is within the range of the present invention, all of the tensile strength, 0.2% proof stress and elongation can be obtained at a high level in a balanced manner regardless of the type of casting.

(Series 2: Influence of Si content)
According to Table 1 and FIGS. 3 and 4, for Invention Examples 4 to 6 in which the Si content is within the scope of the present invention, the tensile strength, 0.2% proof stress and elongation are all obtained at a high level in a balanced manner. Yes. On the other hand, for Comparative Examples 5 and 6 in which the Si content departs from the scope of the present invention, when the Si content is small, the tensile strength and the 0.2% proof stress are not sufficient, and the Si content is low. When it is excessive, the elongation is not sufficient. Therefore, it was demonstrated that the preferable range of the Si content is 2 to 4% by mass.

(Series 3: Effect of Mg content)
According to Table 1 and FIGS. 5 and 6, all of the tensile strength, 0.2% proof stress and elongation are obtained at a high level with good balance for the inventive examples 7 to 10 whose Mg content is within the scope of the present invention. Yes. On the other hand, for Comparative Examples 7 and 8 in which the Mg content deviates from the scope of the present invention, when the Mg content is small, the tensile strength and the 0.2% yield strength are not sufficient, and the Mg content is When it is excessive, the elongation is not sufficient. Therefore, it was demonstrated that the preferable range of the Mg content is 0.2 to 0.5% by mass.

(Series 4: Influence of Cu content)
According to Table 1 and FIGS. 7 and 8, for Invention Examples 11 and 12 whose Cu content is within the scope of the present invention, all of the tensile strength, 0.2% proof stress and elongation are obtained at a high level in a balanced manner. Yes. On the other hand, for Comparative Examples 9 and 10 in which the Cu content deviates from the scope of the present invention, when the Cu content is small, the tensile strength and the 0.2% yield strength are not sufficient, and the Cu content is When it is excessive, the elongation is not sufficient. Therefore, it was demonstrated that the preferable range of the Cu content is 0.4 to 0.8% by mass.

  As described above, in the high toughness Al alloy casting of the present invention, in particular, by optimizing the Ni content in the alloy, the flowability of the Al alloy casting is improved, and excellent tensile strength, 0.2% proof stress and elongation can be realized at a high level with good balance. 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 a balanced manner in the future.

5 is a graph showing measurement results of tensile strength and 0.2% proof stress for each of Al alloys of series 1 and 5 shown in Table 1. 5 is a graph showing the measurement results of elongation for each of the series 1 and 5 Al alloys shown in Table 1. It is a graph which shows the measurement result of a tensile strength and 0.2% yield strength about each Al alloy of the series 2 shown in Table 1. FIG. 4 is a graph showing the measurement results of elongation for each Al alloy of series 2 shown in Table 1. It is a graph which shows the measurement result of a tensile strength and 0.2% yield strength about each Al alloy of the series 3 shown in Table 1. FIG. 5 is a graph showing the measurement results of elongation for each Al alloy of Series 3 shown in Table 1. It is a graph which shows the measurement result of tensile strength and 0.2% yield strength about each Al alloy of the series 4 shown in Table 1. FIG. 5 is a graph showing the measurement results of elongation for each Al alloy of series 4 shown in Table 1.

Claims (2)

  In mass ratio, 2% ≦ Si ≦ 4%, 0.2% ≦ Mg ≦ 0.5%, 0.4% ≦ Cu ≦ 0.8%, 0.05% ≦ Ni ≦ 0.3%, and inevitable A high-toughness Al alloy casting characterized by including a general impurity, the balance being Al, a tensile strength of 300 MPa or more, a 0.2% proof stress of 210 MPa or more, and an elongation of 10% or more.   In mass ratio, 2% ≦ Si ≦ 4%, 0.2% ≦ Mg ≦ 0.5%, 0.4% ≦ Cu ≦ 0.8%, 0.05% ≦ Ni ≦ 0.3%, and inevitable In producing a high-toughness Al alloy casting containing a general impurity, the balance being Al, a tensile strength of 300 MPa or more, a 0.2% proof stress of 210 MPa or more, and an elongation of 10% or more, an alloy having the above composition is cast. , A high temperature heat treatment at 515 to 540 ° C., followed by a rapid cooling treatment and then an aging treatment at a temperature of 165 to 185 ° C.

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