JPH11293430A - Production of high toughness aluminum alloy casting and high toughness aluminum alloy casting obtained thereby - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a high toughness aluminum alloy casting by short time heat treatment and to provide a high toughness aluminum alloy casting obtd. thereby. SOLUTION: In the method for producing a high toughness aluminum alloy casting, an aluminum alloy casting after casting having a compsn. contg., by mass, 3.5 to 5.0% Si, 0.15 to 0.4% Mg, <=1.0% Cu, an improving treating agent, and the balance substantially Al with inevitable impurities in which the content of Fe is regulated to <=0.2% in particular is subjected to solution treatment in which it is held at >823K (550 deg.C) to <848K (575 deg.C) for 2 to 4 hr and is thereafter rapidly cooled, and subsequently, aging treatment is executed at 433K (160 deg.C) to 453K (180 deg.C) for 1 to 3 hr. The obtd. high toughness aluminum alloy casting is the one in which the area of eutectic Si grains in an aluminum matrix is regulated to <=6 μm<2> , furthermore, the roundness thereof is regulated to >=0.55, elongation to >=23% and impact value to >=23×10<4> J/m<2> . Moreover, the casting has >=290 MPa tensile strength and >=200 MPa proof stress.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-toughness aluminum alloy casting (hereinafter referred to as "aluminum casting") and an aluminum casting. The present invention relates to a method for producing an aluminum casting and an aluminum casting which can be applied to wheels and cross members of automobile suspension parts, impellers for high-speed rotating parts of compressors, etc., by imparting large elongation and high impact properties comparable to those of automobiles. .

[0002]

2. Description of the Related Art Some wheel suspension parts for automobiles are manufactured by processing a steel plate. However, aluminum castings (for example, (JIS) A) are used in view of weight reduction and design (design) properties.
(C4CH material). The cross members are also being manufactured from aluminum castings for the purpose of weight reduction. However, conventional aluminum castings are still low in toughness such as elongation and impact value and strength. For this reason, aluminum castings are applied only to relatively small vehicles such as wheels and cross members, and are used for aluminum alloy forgings (for example, (JIS) H400) for relatively large vehicles such as truck wheels. Alloy number 6061
(Chemical components are% by weight, Si: 0.40 to 0.8%, F
e: 0.7% or less, Cu: 0.15 to 0.40%, M
n: 0.15% or less, Mg: 0.8 to 1.2%, Cr:
0.04 to 0.35%, Zn: 0.25% or less, Ti:
0.15% or less, other: 0.15% or less, balance Al)
Etc.) have been used.

[0003] Aluminum alloy forgings have high reliability, such as high toughness and elongation, and excellent strength since there are few internal defects. However, there are problems such as high manufacturing cost and difficulty in obtaining a desired design. On the other hand, in order to produce relatively large parts such as truck wheels with aluminum castings and to give the same toughness and strength as aluminum forged products, the parts must be thickened,
The weight increases, and it is difficult to reduce the weight.

Japanese Patent Application Laid-Open No. H5-5148 discloses that an aluminum casting has a high strength and a high toughness comparable to that of an aluminum alloy forged product.
The melt containing 1.5 to 2.5%, Mg: 0.2 to 0.5%, or Sr: 0.005 to 0.2% and remaining Al is pressurized at 250 to 1500 kgf / mm2. There is a disclosure of casting into a mold and subjecting the obtained member to solution treatment.

On the other hand, the present inventors have previously described Japanese Patent Application Laid-Open No. 7-31
As disclosed in Japanese Patent Application Laid-Open No. 0150 and Japanese Patent Application Laid-Open No. Hei 7-310151, an aluminum casting cast with an Al-Si system such as (JIS) AC4CH is rapidly heated to reach a vicinity of a eutectic point (for example, 570 ° C.) and then rapidly cooled. Or quenching immediately after release, followed by aging treatment, especially by a high-temperature, short-time solution treatment, which is usually performed at 793K (520 ° C) to 82 ° C.
It proposes to economically obtain a tensile strength and impact value comparable to solution treatment at 3K (550 ° C.) for 4 to 6 hours.

[0006] However, in the above-mentioned Japanese Patent Application Laid-Open No. 5-5148, the tensile strength is improved by increasing the elongation to 10 to 12% by pressure casting into a mold with Si: 2.5 to 4.4% by weight. However, on the other hand, if Cu is contained in such a large amount, the corrosion resistance may be deteriorated. In the case of parts that are frequently exposed to rainwater, such as a truck wheel, the Cu content should be small as long as the tensile strength is not impaired. Further, in Japanese Patent Application Laid-Open No. 5-5148, a pressure casting method is used to produce a metal by forging. However, for a large component such as a truck wheel, a pressure casting apparatus becomes large-scale and the cost increases. Difficult to manufacture economically. Further, when Cu is contained in an amount of 1.5 to 2.5% by weight, segregation of eutectic Si is likely to occur, and mechanical properties may be varied.

For parts such as wheels and cross members of suspension parts for automobiles, impellers of high-speed rotating parts of refrigerators and compressors, in particular, elongation, impact value, tensile strength,
Mechanical properties such as proof stress are important. JP-A-5-5
148, JP-A-7-310150 and JP-A-7-310151, the elongation is 7-1.
About 2%, impact value is about 8-13 × 10 ⁴ J / m ² , and tensile strength is about 260-330 MPa. It is necessary to further improve the mechanical properties.

The present inventors have disclosed the above-mentioned JP-A-5-5148, JP-A-7-310150 and JP-A-7-310150.
In order to further improve the characteristics disclosed in Japanese Patent Application Laid-Open No. 310151, Japanese Patent Application Laid-Open No. Hei 9-272942 discloses, as weight ratios, Si: 1.65 to 5.0%, and Mg: 0.2 to 0.4.
%, Fe: 0.2% or less, the balance being substantially the composition of Al and inevitable impurities,
After reaching a temperature of 848 K (575 ° C.) exceeding 23 K (550 ° C.), a solution treatment of rapid cooling is performed.
8 to 5 at a temperature of K (140 ° C) to 473K (200 ° C)
A technique is disclosed in which a heat treatment for aging treatment for 5 hours is performed to secure tensile strength and proof stress in addition to toughness such as elongation and impact value with an aluminum casting having a low Si content.

[0009]

However, in Japanese Patent Application Laid-Open No. 9-272942, the time required for the aging treatment in the heat treatment is as long as 8 to 55 hours, which is not economical. For this reason, there has been a demand for a more economical development of a manufacturing method capable of securing tensile strength and proof stress in addition to toughness such as elongation and impact value. An object of the present invention is to provide a method of manufacturing an aluminum casting and an aluminum casting having economical properties, that is, toughness such as elongation and impact value, as well as tensile strength and proof stress.

[0010]

Means for Solving the Problems The present inventors have found that in order to obtain the above-mentioned characteristics, to secure the toughness by suppressing the amount of Si, and to reduce the corrosion resistance by reducing the amount of Cu in order to obtain the above characteristics. The obtained aluminum alloy composition was used, and solution treatment and aging treatment were combined with this composition, and intensive research was continuously conducted. Then, the content of Si was kept low at 3.5 to 4.5%, and the aluminum casting after casting exceeded 823K (550 ° C.) and 848
A solution treatment in which the temperature is kept at a temperature lower than K (575 ° C.) for 2 to 4 hours and then quenched, and then 433 K (160 ° C.)
By performing aging treatment at a temperature of 180 to 453 K (180 ° C.) for 1 to 3 hours, the heat treatment time including the aging treatment time is shortened, and furthermore, an aluminum casting having significantly superior toughness such as elongation and impact value is obtained. The present inventors have found out that they can be obtained, and reached the present invention.

That is, the method for producing a high toughness aluminum casting of the first invention is as follows: Si: 3.5-4.5%, M
g: 0.15 to 0.4%, Cu: 1.0% or less, improving treatment agent, balance substantially after Al containing a composition of not more than 0.2% or less of Al and inevitable impurities. Over 823K (550 ° C) and 848K (575
C.) for 2 to 4 hours, followed by a solution treatment of quenching, followed by 433 K (160 ° C.) to 453 K.
The aging treatment is performed at a temperature of K (180 ° C.) for 1 to 3 hours.

Further, the high toughness aluminum casting of the second invention has a mass ratio of Si: 3.5 to 4.5% and Mg: 0.15 to
0.4%, Cu: 1.0% or less, improving agent, balance substantially Al and in particular unavoidable impurities, Fe: 0.2
% Of the cast aluminum alloy casting having a composition of not more than 823K (550 ° C) and 848K (575 ° C).
After the solution is kept at a temperature of less than 2 to 4 hours, a solution treatment of quenching is performed, and then 433 K (160 ° C.) to 453 K
By performing the aging treatment at a temperature of (180 ° C.) for 1 to 3 hours, the area of the eutectic Si particles in the aluminum matrix becomes 6
μm ² or less, circularity of 0.55 or more, elongation of 23% or more, and impact value of 23 × 10 ⁴ J / m ² or more.

The high toughness aluminum casting according to the third invention has a mass ratio of Si: 3.5 to 4.5% and Mg: 0.15 to
0.4%, Cu: 1.0% or less, improving agent, balance substantially Al and in particular unavoidable impurities, Fe: 0.2
% Of the cast aluminum alloy casting having a composition of not more than 823K (550 ° C) and 848K (575 ° C).
After the solution is kept at a temperature of less than 2 to 4 hours, a solution treatment of quenching is performed, and then 433 K (160 ° C.) to 453 K
By performing the aging treatment at a temperature of (180 ° C.) for 1 to 3 hours, the area of the eutectic Si particles in the aluminum matrix becomes 6
μm ² or less, circularity of 0.55 or more, elongation of 23% or more, impact value of 23 × 10 ⁴ J / m ² or more, tensile strength of 290 MPa or more, and proof stress of 200 MPa or more. It is characterized by. In addition, as an improvement processing agent in 1st invention-3rd invention, Sr: 0.0004-0.00
2% and / or Ti: 0.25% or less.

The reasons for limiting the chemical composition (% by mass) and the heat treatment conditions in the present invention will be described below. (1) Si: 3.5 to 4.5% Si affects toughness such as elongation and impact value, and castability such as fluidity. If the content of Si is less than 3.5%, the flowability of the molten metal becomes poor. On the other hand, if Si exceeds 4.5%, the area of the eutectic Si particles in the aluminum matrix increases, and the eutectic Si becomes network-like, lowering toughness such as elongation and impact value. Therefore, Si is set to 3.5 to 4.5%. Most preferably, Si: 4.0-4.5%.

(2) Mg: 0.15 to 0.4% Mg is effectively contributed to the improvement of strength by precipitating Mg ₂ Si by heat treatment for solution treatment and aging treatment. If Mg is less than 0.15%, the effect of improving strength is small. On the other hand, when Mg exceeds 0.4%, precipitation of Mg ₂ Si tends to be excessive, and the toughness is reduced. Therefore, Mg: 0.15 to 0.4%. Most preferably, Mg: 0.15 to 0.2%.

(3) Cu: 1.0% or less Cu is effective for improving strength, but deteriorates corrosion resistance. In the case of parts that are frequently exposed to rainwater, such as truck wheels, it is better that Cu is small as long as the strength is not impaired. Therefore, Cu is set to 1.0% or less. Preferably, Cu: 0.3% or less.

(4) Fe: 0.2% or less Fe as an inevitable impurity forms needle-like crystals when present in a large amount, and when it exceeds 0.2%, toughness is reduced. Therefore, Fe is set to 0.2% or less.

(5) Sr: 0.0004% to 0.002% Sr is an element effective for improving the eutectic Si by refinement and spheroidization. Both strength and toughness are improved by the refinement of eutectic Si. If Sr is less than 0.0004%, the effect of improving toughness and strength is small. On the other hand, when Sr is 0.
If it exceeds 002%, the influence on shrinkage is large, and the occurrence of casting defects such as pinholes is promoted. Therefore,
Sr: 0.0004 to 0.002%. Preferably, Sr: 0.0008 to 0.010%.

(6) Ti: 0.25% or less Ti is an element effective for refining crystal grains and improving toughness. However, even if it is contained in excess of 0.25%, the effect is not improved. Undesirably, Al-Ti-based compounds are crystallized and the toughness is reduced. Therefore, Ti: 0.25% or less. Preferably, the content of Ti is set to 0.2% or less.

(7) Solution treatment: 823K (550 ° C.)
Quenching with cold water after holding at a temperature of over 848K (575 ° C) for more than 2 to 4 hours, and immediately after reaching a temperature of over 550 ° C and less than 575 ° C, segregation generated in the solidification process by a solution treatment of quenching in water and quenching. Is dissolved in the aluminum matrix and uniformly dispersed. Similarly, Si and Mg are solid-dissolved and uniformly dispersed.
Then, Mg ₂ Si is precipitated by aging treatment performed thereafter, and mechanical properties such as toughness and tensile strength are improved in the cast aluminum casting. By performing the solution treatment at a temperature of 823 K (550 ° C.) or less, the roundness of eutectic Si particles can be improved,
The effect of miniaturizing and dispersing eutectic Si particles is small, and it takes a long time to impart these effects.
The solution treatment at a high temperature exceeding K (550 ° C.) for a short time improves the roundness of the eutectic Si particles, and causes the eutectic Si particles to be refined and dispersed. On the other hand, when the solution treatment temperature is 848 K (575 ° C.) or more, the eutectic material is melted.
The upper limit temperature is less than 848K (575 ° C). Therefore, the solution treatment temperature exceeds 823 K (550 ° C.) and 848 K
(575 ° C.). 823K (550 ° C)
The above-mentioned effect can be obtained by maintaining the temperature at a temperature exceeding 850 K (575 ° C.) for more than 2 to 4 hours.

(8) Aging treatment: aging treatment at high temperature for a short time after high-temperature solution treatment, following the above-mentioned high-temperature solution treatment, from 433 K (160 ° C.)
A short-time aging treatment at a high temperature of 1 to 3 hours at a temperature of 453 K (180 ° C.) is performed. Normal aging is 418
K (145 ° C.) × 6 hours, but in the present invention, maintaining the temperature at 433 K (160 ° C.) or more for 1 hour or more promotes an increase in the amount of Mg ₂ Si deposited to improve the strength. . On the other hand, the aging temperature is set to 453K (180
(° C.), the promotion of Mg ₂ Si saturates. If the temperature is higher than this, overaging occurs and Mg ₂ Si re-dissolves to lower the strength.

[0022]

Embodiments of the present invention will be described below. (Embodiment) Si: 3 to 4%, Mg: 0.3 to 0.4%, 0.3%,
Fe: 0.1%, Cu: 0.5%, Sr: 80-100
ppm, Ti: 0.15 to 0.2%, balance substantially Al
Further, the molten metal was adjusted so as to become an aluminum alloy of inevitable impurities, and was cast by a low-pressure casting device to manufacture a truck wheel. The low-pressure casting apparatus includes a cavity of a truck wheel formed in a mold, and a stalk connecting the cavity to a furnace for holding a molten metal. In the holding furnace, the molten metal was held and heated so that the temperature became 720 ° C., the inside of the holding furnace was pressurized to 2 MPa, and injected into the upper mold cavity via stalk. At this time, the mold temperature was controlled at 350 ° C. After the aluminum casting was solidified in the cavity, it was taken out of the low-pressure casting device and subjected to a heat treatment (T6 treatment).

Hereinafter, (1) the effect of solution treatment conditions on the morphology of eutectic Si particles, (2) the relationship between solution treatment conditions and mechanical properties, and (3) the relationship between aging treatment conditions and mechanical properties. The relationship will be described sequentially. (1) Influence of Solution Treatment Conditions on Morphology of Eutectic Si Particles The solution treatment was performed under the following six conditions of Table 1 to Table 6 to examine the form of the eutectic Si particles. The photographs of the metal structure observed with an optical microscope are shown in FIGS. 1 to 6 (the same magnification in FIGS. 1 to 6).

[0024]

Table 1 Solution treatment No. Temperature (K) (° C) Retention time Form of eutectic Si particles 1 854K (581 ° C) None Figure 1 2 848K (575 ° C) None Figure 2 3 848K (575 ° C) 3 hours 3 4 838K (565 ° C) None Fig. 4 5 838K (565 ° C) 3 hours Fig. 5 6 838K (565 ° C) 8 hours

No. 1 is high temperature 854K (581 ° C)
In spite of the solution treatment under the condition of no holding time, some dissolution was observed as shown in the metallographic micrograph of FIG. No. 2, the solution treatment at 848 K (575 ° C.) without holding time showed that the eutectic Si particles were fine, but the circularity was 0.55 as shown in FIG.
Less than about 0.52, which is bad. Note that the circularity 1 is a perfect circle. No. 3 was subjected to solution treatment by holding at 848 K (575 ° C.) for 3 hours. As shown in FIG.
The i-particles are agglomerated due to aggregation. No. 4, 8
As shown in FIG. 4, the eutectic Si particles subjected to the solution treatment at 38 K (565 ° C.) without the holding time are fine, but have a circularity of less than 0.55, that is, about 0.52, which is poor. N
o. When the solution treatment was performed at 838 K (565 ° C.) for 3 hours, the eutectic Si particles were fine, and the circularity was as good as 0.58, which was 0.52 or more. N
o. As shown in FIG. 6, eutectic Si particles were agglomerated due to aggregation of eutectic Si particles as shown in FIG.

Therefore, the area and circularity of the eutectic Si particles were measured for FIGS. The degree of circularity = (particle area) / (area of circle having the same perimeter (I) as measured particles) = 4πS / I ² . 5 Si particles by image analysis
It measures about 00 to 1000 pieces, and then calculates by statistical processing. FIG. 7 shows the relationship between the area (μm ² ) of the eutectic Si particles and the solution treatment time, and FIG. 8 shows the relationship between the circularity of the eutectic Si particles and the solution treatment time. 7 and 8, “As Cast” indicated by a black square mark is “as cast”, and “854K ST” indicated by a white triangle mark is a solution at a temperature of 854K (581 ° C.). Conversion (Solu
and “848K ST” indicated by a white circle are “848K (575
C.), and “838K ST” indicated by a black diamond are “838K (565).
C) at a temperature of (° C).

In FIGS. 7 and 8, when the solution treatment temperature indicated by a white circle is 848 K (575 ° C.), the area of the eutectic Si particles increases as the solution treatment time increases, and the solution treatment temperature increases. When the time is 5 hours, the area is as large as 17.3 μm ² . On the other hand, the circularity of the eutectic Si particles decreases with an increase in the solution treatment time, and the circularity decreases to 0.52 when the solution treatment time is 5 hours. Solution treatment temperature is the highest 8
At 54 K (581 ° C.), as shown in FIG. 1, melting was observed in a part, so that the heat treatment for maintaining at 854 K (581 ° C.) for a predetermined time was omitted.

Solution treatment temperature 838K indicated by black diamonds
At (565 ° C.), the area of the eutectic Si particles also increases with the increase in the solution treatment time, and the increase is almost saturated in the solution treatment time of 3 to 5 hours, and the area is as small as about 6 μm ² . The change is small even when the processing time changes. on the other hand,
The degree of circularity reached a maximum of about 0.6 at a solution treatment time of 5 hours, and showed a higher value than those treated at other solution treatment temperatures. From the above, the solution treatment temperature was 838K (565).
° C) is preferred.

(2) Relationship between Solution Treatment Conditions and Mechanical Properties Next, the relationship between solution treatment conditions and mechanical properties will be described. 9 to 11 show solution treatment conditions and 0.2%
The relationship among proof stress, elongation at break and absorbed energy (impact value) is shown. Solution treatment temperature 848K (575
C), the 0.2% proof stress increases with increasing solution treatment time (FIG. 9), but the elongation at break and the absorbed energy (impact value) show a marked decrease (FIGS. 10 and 11). ). Solution treatment temperature indicated by black diamond is 838K
(565 ° C.), the solution heat treatment time was increased by 0.3%.
Although the 2% proof stress is not changed to about 140 MPa, the elongation at break and the absorbed energy (impact value) are as follows.
Above, the absorbed energy (impact value) is about 34 × 10 ⁴ J
/ M ² or more, and in this embodiment, the solution treatment is
Those maintained at a temperature of 838 K (565 ° C.) for 3 hours gave the best results.

(3) Relationship between Aging Condition and Mechanical Property Next, the relationship between the aging condition and mechanical property will be described. The aging treatment was performed at 443 K (170 ° C.) on the high temperature side and at 418 K (145 ° C.) on the low temperature side, and mechanical properties such as tensile strength, 0.2% proof stress, and elongation at break with respect to the aging treatment conditions were examined. The results are shown in FIGS. In FIGS. 12 to 15, the aging process time indicated on the horizontal axis is represented by logarithmic scale of ks (kilosecond). From the figure showing the relationship between the aging treatment time and the tensile strength in FIG. 12, the tensile strength is improved (increased) as the aging treatment time increases. In the case of 443K (170 ° C) on the high temperature side indicated by the white triangle mark, about 1
0 tensile strength ⁴ seconds (about 2.8 hours) is saturated and the maximum value is about 320 MPa. On the other hand, the low-temperature side 4
In the case of 18K (145 ° C.), about 7 × 10 ² kiloseconds (about 1
The tensile strength saturates for a long time of 90 hours (ie, about 8 days), and is equal to or slightly higher than the tensile strength of about 320 MPa obtained by aging at 443 K (170 ° C.) on the high temperature side for about 2.8 hours. Is shown. From the diagram showing the relationship between the aging treatment time and the 0.2% proof stress in FIG. 13, the 0.2% proof stress increases with the increase in the aging treatment time, similarly to the relationship between the aging treatment time and the tensile strength in FIG. It has improved (increased).

In general, in the aging treatment on the low temperature side, it takes a long time for the tensile strength and the 0.2% proof stress to reach the maximum value and saturate, and in the aging treatment on the high temperature side, the tensile strength and It takes a short time for the 0.2% proof stress to reach the maximum value and saturate. It is said that the maximum values of the tensile strength and the 0.2% proof stress are saturated at a lower value when the aging treatment is performed on the high temperature side than when the aging treatment is performed for a long time on the low temperature side. However, it is preferable to employ a high-temperature, short-time aging treatment because it is preferable that a satisfactory desired strength can be obtained in a short period of time in terms of improvement of work efficiency and energy reduction. Here, focusing on toughness and assuming that the desired tensile strength is 290 MPa or more, the aging time is 7200 seconds (2 hours) at 443 K (170 ° C.), and the 0.2% proof stress is 200 MPa or more. Aging time is 720 at 443K (170 ° C)
0 seconds (2 hours).

FIGS. 14 and 15 are diagrams showing the relationship between the aging temperature and the aging time, the elongation at break, and the absorbed energy (impact value). As the aging time increases, the elongation at break and the absorbed energy (impact value) decrease,
The tendency is opposite to that of the above-mentioned tensile strength and 0.2% proof stress. This indicates that the aging treatment resulted in the precipitation of Mg ₂ Si in the aluminum matrix and reduced the viscosity, while the greater the amount of Mg ₂ Si deposited, the higher the tensile strength and proof stress. ing. 14 and 15, the aging treatment time is 7200 seconds (2 hours) and the elongation is 23%.
Thus, the absorbed energy (impact value) becomes 23 × 10 ⁴ J / m ² , and a high-toughness aluminum casting can be manufactured.

That is, the most preferable form in the present invention is:
Si: 4 to 4.5%, Mg: 0.15 to 0.20%, T
i: 0.2%, Sr: 80 to 100 ppm, Cu: 0.
An aluminum casting of a tough material having a composition of 3% or less, the balance being substantially Al and inevitable impurities, particularly Fe: 0.2% or less, is kept at 838 K (565 ° C.) for 3 hours under a solution treatment condition, After quenching (quenching), the aging condition is 4
Heat treatment is performed at 43 K (170 ° C.) for 2 hours. And a high toughness aluminum casting obtained thereby. The aging treatment temperature on the high temperature side in the embodiment of the present invention is 443 K (1
Although the case of (70 ° C.) has been described, the effect of the high-temperature, short-time aging treatment of the present invention can be expected even when a temperature of 433 K (160 ° C.) or 453 K (180 ° C.), which is the temperature before and after that, is adopted. For example, at an aging temperature of 433 K (160 ° C.), the aging time is about 3 hours, and
At an aging temperature of K (180 ° C), the aging time is 1 to
Preferably, the time is about 2 hours.

(Comparative Example) (JIS) For aluminum casting equivalent to AC4CH, 793K (520 ° C) to 823K
After holding for 6 hours at (550 ° C.) and then quenching, an aging treatment for 4 to 6 hours at 418 K (145 ° C.) was performed. As a result, the elongation at break was about 7 to 12%, and the impact value was 8 to 10 × 10 ⁴ J / m ² , which were lower values than those of the present invention.

[0035]

As described above in detail, the method for manufacturing a high toughness aluminum casting of the present invention and the high toughness aluminum casting obtained by this manufacturing method, after casting with a composition in which the Si content is kept low, are 823K (550). ° C) and 848K (57
5 [deg.] C.) for 2 to 4 hours and then subjected to a high-temperature solution treatment of rapid cooling, followed by 433K (160 [deg.] C.) to 45 [deg.] C.
By performing the aging treatment at a temperature of 3 K (180 ° C.) for 1 to 3 hours, the toughness and the strength are excellent, and the required characteristics according to the application can be ensured. For this reason, for example, vehicle suspension parts such as wheels and cross members, and high-speed rotating parts such as refrigerators and compressor impellers can be made thinner and lighter, which is extremely useful in industry. In particular, the effect is extremely large industrially in that required characteristics can be ensured by a short-time aging treatment at a high temperature side, as compared with a conventional long-time aging treatment at a low temperature side.

[Brief description of the drawings]

FIG. 1 is a view showing a metallographic micrograph of a solution treatment performed at 854K (581 ° C.) and no holding time.

FIG. 2 is a view showing a metallographic micrograph of a solution treatment performed at 848 K (575 ° C.) without a holding time.

FIG. 3 is a view showing a metallographic micrograph of a solution treated by holding at 848 K (575 ° C.) for 3 hours.

FIG. 4 is a micrograph of a metallographic structure subjected to a solution treatment at 838 K (565 ° C.) without a holding time.

FIG. 5 is a diagram showing a metallographic micrograph of a solution treatment performed at 838 K (565 ° C.) for 3 hours.

FIG. 6 is a view showing a metallographic micrograph of a solution treatment performed by holding at 838 K (565 ° C.) for 8 hours.

FIG. 7 is a diagram showing the relationship between solution treatment time and the area of eutectic Si particles.

FIG. 8 is a diagram showing a relationship between solution treatment time and circularity.

FIG. 9 is a diagram showing the relationship between solution treatment time and 0.2% proof stress.

FIG. 10 is a view showing the relationship between solution treatment time and elongation at break.

FIG. 11: Solution heat treatment time and absorbed energy (impact value)
FIG.

FIG. 12 is a diagram showing a relationship between aging treatment time and tensile strength.

FIG. 13 is a diagram showing the relationship between aging treatment time and 0.2% proof stress.

FIG. 14 is a diagram showing a relationship between aging treatment time and elongation at break.

FIG. 15 is a diagram showing the relationship between aging treatment time and absorbed energy (impact value).

[Explanation of symbols]

 (None).

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22F 1/00 630 C22F 1/00 630B 691 691B 691C

Claims (4)

[Claims] 1. A mass ratio of Si: 3.5 to 4.5%,
Mg: 0.15 to 0.4%, Cu: 1.0% or less, improved treating agent, balance substantially after Al and, among the unavoidable impurities, particularly Fe: 0.2% or less. A solution treatment in which the aluminum alloy casting is kept at a temperature of more than 823K and less than 848K for 2 to 4 hours and then quenched,
A method for producing a high-toughness aluminum alloy casting, which comprises subjecting to an aging treatment at a temperature of 433 K to 453 K for 1 to 3 hours. 2. Si: 3.5 to 4.5% by mass ratio,
Mg: 0.15 to 0.4%, Cu: 1.0% or less, improved
Treatment agent, the balance substantially of Al and inevitable impurities
In particular, Al after casting containing a composition of Fe: 0.2% or less.
The minium alloy casting is heated to a temperature of more than 823K and less than 848K.
After the solution is kept for 2 to 4 hours and then quenched,
After that, at a temperature of 433K to 453K for 1 to 3 hours
Eutectic S in the aluminum matrix
i-particle area is 6 μm^TwoLess than or equal to 0.60
Having an elongation of 23% or more and an impact value of 23 × 10
^FourJ / m^TwoHigh toughness aluminum characterized by having above
Alloy castings. 3. Si: 3.5-4.5% by mass ratio,
Mg: 0.15 to 0.4%, Cu: 1.0% or less, improved treating agent, balance substantially after Al and, among the unavoidable impurities, particularly Fe: 0.2% or less. A solution treatment in which the aluminum alloy casting is kept at a temperature of more than 823K and less than 848K for 2 to 4 hours and then quenched,
Then, after aging treatment at a temperature of 433 K to 453 K for 1 to 3 hours, the eutectic S
i particles have an area of 6 μm ² or less, a circularity of 0.55 or more, an elongation of 23% or more, and an impact value of 23 × 1
0 ⁴ J / m ² or more, a tensile strength of at least 290 MPa, high-toughness aluminum alloy castings proof stress and having a least 200 MPa. 4. The improvement treatment agent according to claim 1, wherein the Sr content is 0.0004 to 0.002%.
And / or Ti: 0.25% or less of a high toughness aluminum alloy casting.