JP2003170263A - Method for casting vehicle wheel under low pressure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for casting a vehicle wheel under a low pressure, by which a flawless casting can be performed and thereby, the vehicle wheel best suited for meeting high strength and high tenacity requirements can be cast under a low pressure, in the method for casting the vehicle wheel using a low Si aluminum alloy under a low pressure. <P>SOLUTION: In the method for casting the vehicle wheel, the casting process is performed in a mold of such a shape as corresponding to the vehicle wheel having a rim and a disc, a center gate is provided in the center of a cavity for forming the disc, and a side gate is provided in a cavity for forming the rim. Further, a molten metal of the aluminum alloy to be used is composed of 1.0 wt.% or lower of Cu, 2.4 to 4.6% of Si, 0.25 to 0.5 wt.% of Mg, an unavoidable impurity element and the balance Al and injected from each of the gates. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-pressure casting method for a wheel for a vehicle having a high yield strength and a high toughness suitable for using an aluminum alloy having a high yield strength and a high toughness.

[0002]

2. Description of the Related Art Wheels for vehicles, which are manufactured by processing a steel plate, are inexpensive and often used, but in recent years, they have been manufactured by casting aluminum because of their light weight and design (design). . Also, cross members and suspension parts have begun to be made of aluminum for the purpose of weight reduction. For this reason, aluminum castings are mainly used for relatively small parts such as passenger car wheels, cross members and underbody parts, and forged aluminum parts (eg JIS6061) have been used for relatively large parts such as truck wheels. There is.
The aluminum casting alloy currently having the best performance for strength parts is the AC4CH material stipulated in JIS, but this material is an aluminum alloy casting material with well-balanced mechanical properties and castability. It is used as an aluminum wheel and an underbody member for automobiles that require high strength and high toughness. The requirements for weight reduction of these members are strict, and C
Not only the shape study by AE etc. but also the material itself had to use the low Si aluminum alloy having better mechanical properties. However, the castability is slightly inferior to the AC4CH material which is most commonly used as the current high-strength and high-toughness aluminum alloy casting material, and it is difficult to integrally cast a thin and complex vehicle wheel. .

[0003]

Therefore, good casting is possible even in the low-pressure casting method for a vehicle wheel using an aluminum alloy having a low Si, and thus a vehicle wheel suitable for having high strength and high toughness is obtained. A low pressure casting method is provided.

[0004]

In order to achieve the above object, it is judged that it is preferable to use an AC4CH material as a basic material, in which the Si content is particularly changed, and it is optimal to use those aluminum alloys. Adopted a casting bill. That is, the present invention is a low-pressure casting method for a vehicle wheel, which comprises casting in a mold having a shape corresponding to a vehicle wheel having a rim portion and a disc portion, in which a center gate is provided at the center of the cavity forming the disc portion. , A side gate is provided in the cavity that forms the rim, and Cu1.0wt%
The following is characterized in that an aluminum alloy molten metal composed of Si 2.4 to 4.6%, Mg 0.25 to 0.5 wt%, unavoidable impurity elements, and the balance Al is used, and the aluminum alloy molten metal is poured from each gate. . The molten aluminum alloy may contain 0.55 wt% or less of Fe, 0.3 wt% or less of Ti, and 0.2 wt% or less of one or more of Sr, Sb, and Na.

With respect to the amount of aluminum, Si significantly improves the castability depending on the amount added. However, the solid solution in aluminum is as small as less than 2%, and Si that cannot be solid-solved is crystallized into aluminum as eutectic Si. This eutectic Si is extremely hard and brittle, and causes mechanical properties to deteriorate. So this Si
It was found that the mechanical properties are improved by reducing the amount of Si crystallized in the aluminum material by decreasing the content. However, a decrease in the amount of Si added results in a decrease in castability, and it is difficult to manufacture a product by current casting. For example, in the case of the low-pressure casting method, good products can be obtained even if the molds used in the center gate casting method for pouring the molten metal from the disc cavity and the side gate casting method for pouring the molten metal from the rim cavity are used as they are. I can't.

Although Cu can be used without addition, if higher yield strength is required, addition of Cu in excess of 1% significantly lowers toughness, so Cu is used in the range of 1% or less.
Si is a very important element for improving the castability, but if it exceeds 4.6%, the required yield strength and elongation cannot be obtained, and if it is less than 2.4%, the castability is increased. Significantly decreases, and it becomes difficult to manufacture a good casting. Mg is M
After forming a compound of g ₂ Si and forming a solid solution in the heat treatment,
It is an element added to obtain the necessary strength by uniformly and finely precipitating, but if it exceeds 0.5%, it will decrease the toughness, and if it is less than 0.25%, the strength improvement during heat treatment is insufficient. Becomes When Fe is contained in aluminum, it forms a needle-shaped crystallized substance with Si or the like, and significantly reduces toughness. It is possible to suppress the growth of needle-like crystallized substances containing Fe by increasing the solidification rate,
In the casting method claimed this time, if the Fe content exceeds 0.55%, the toughness is significantly reduced. Sufficient yield strength and toughness can be obtained without adding Ti, but Ti can be added for the purpose of further improving mechanical properties. In this case Ti
If the addition amount of Al exceeds 0.3%, TiAl ₂ crystallizes in large amounts at the crystal grain boundaries, which becomes a factor that particularly reduces toughness. Sr, Sb or Na is an element necessary for promoting spheroidization of eutectic Si during heat treatment and is preferably added in an amount of 0.2 wt% or less.

As the heat treatment, T6 treatment (solution treatment + aging treatment) can be applied. 500 to 5 for solution treatment
Hold at 45 ° C for 3-12 hours. It is also possible to maintain the solution treatment conditions at 545 to 560 ° C. near the eutectic temperature and shorten the solution treatment time to 0.5 to 3 hours.
After the holding, quenching is carried out with water or hot water in both cases, and mainly Mg ₂ Si is supersaturated to form a solid solution in the aluminum matrix. Then, in consideration of the required strength and toughness, aging treatment is performed at 130 to 200 ° C. for about 1 to 24 hours, and Mg ₂ Si solid-solved by the solution treatment is finely and uniformly precipitated in the aluminum matrix to obtain strength and toughness. To improve.

According to the casting method of the present invention, since the roles of each gate can be clearly separated from the center gate for the disk portion and the side gate for the rim portion, it is possible to manufacture a low Si material without causing casting defects. is there. On the contrary, the low castability can improve the problems peculiar to the bill for injecting the molten metal from the center gate and the side gates. That is, when the molten metal is poured from both the center gate and the side gates, the molten metals come into contact with each other in the cavity of the disk portion.
Due to the low castability, the filling speed of the molten metal becomes slow, and the effect of alleviating the collision between the molten metals is produced. At that time, it is possible to suppress the occurrence of hot water and entrapment of gas. Since the casting defect in the portion which becomes the design surface immediately becomes defective, it is important to improve the yield brought about by the suppression effect.

The position of the side gate in the rim portion is preferably at least above the front surface of the design portion, and more preferably higher than the back surface of the design portion. The feature that appears in the cast product using the above-mentioned mold is the maximum DAS.
It is preferable that the position of the value is closer to the inside rim side than the back side of the disc surface. By doing so, it is possible to reduce the appearance of the molten metal poured from the center gate and the side gates in terms of design. Further, by providing the side gates high, even if the vicinity of the center gate is solidified early, the weight of the molten metal remaining on the rim portion can suppress the occurrence of defects due to the effect of the molten metal.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. Example 1 After melting pure aluminum using a 70 kg graphite crucible, each necessary element was added in the form of a metal or mother alloy (alloy with aluminum) to prepare an aluminum alloy melt having a target component. . Table 1 shows the added molten metal components (other than Al). In Table 1, No. 1 to 7 are Cu: Tr and Mg: about 0.35 wt%, and the Si content is changed in the range of about 2.0 to 5.0. No. 8 to 10 are Cu: Tr, Si
Is fixed to about 3.6 to 3.9, and the amount of Mg is set to about 0.2 to 0.
6 The alloy characteristics were measured by changing the amount of Mg. No. 1
1 to 15 have a Cu content of about 0 to 1.3 and Si of about 3.6.
It is fixed to ˜3.8, the amount of Mg is about 0.3, and the alloy characteristics are measured by the amount of Cu. In Table 1, No. 1,7,8,
Reference numerals 10 and 15 are comparative samples out of the composition range of the present invention.
As another comparison, No. AC4 commonly used for 16
The CH material is shown. Using this molten metal, a JIS No. 4 boat-shaped ingot case was cast (gravity casting), and a test material was prepared so that the riser was sufficiently effective and internal defects were suppressed as much as possible. The molten metal temperature during casting was 710 ± 10 ° C., and the boat temperature was 100 ± 10 ° C. After that, heat treatment (JIS T6) was performed under suitable conditions, and then a tensile test piece was processed and a tensile test was performed to confirm the situation. The results of the tensile test are the main components (Cu, Si,
It is shown in Table 2 together with Mg) and comprehensive judgment. The relationship between the Si content and the test piece No. Confirmed in 1-7. When the Si content exceeds 4.6%, it does not differ much from the mechanical properties of JIS AC4CH, which is the most commonly used current high strength and high toughness aluminum casting, so the upper limit of the Si content is 4.6%. did. In addition, in a casting test in which the number of gates was increased in the actual casting test to improve the castability, a good product could not be stably cast, so the lower limit of the Si content is set to 2.
It was 4%. Regarding the relationship of the Mg content, the test piece No. 8-10
Confirmed in. When the Mg content was 0.25% or less, the effect was not sufficient even if the heat treatment (JIS T6) was performed, and the required yield strength (including tensile strength and hardness) could not be obtained. Also M
If the g content exceeds 0.5%, sufficient toughness (elongation value) cannot be obtained. The relationship between the Cu content and the test piece No. 11-
Confirmed at 15. When the Cu content is added, the yield strength is improved, but the toughness (elongation value) is decreased. If the Cu content exceeds 1.0%, the required toughness cannot be obtained.

[0011]

[Table 1]

[0012]

[Table 2]

Further, after the casting with the target component, heat treatment (JIS T6) was carried out under each condition to determine the best value in the balance between yield strength and elongation value. Test piece No. The relationship between the heat treatment conditions (aging conditions) of 9, 10 and the proof stress and the elongation value are shown in FIGS. 1 and 2. As a result, the optimum aging time is 150 ° C.
It was defined as × 24h. A wheel was actually implemented using the aluminum alloy material, and a substantial strength test was performed. The component is the test piece No. 4 according to No. 4 boat shape. It is the same as the component of 5.

FIG. 4 is a sectional view showing a main part of a casting apparatus for carrying out the present invention, and FIG. 5 is a view taken along the line AA of FIG. 4 (however,
It is the figure which looked at the horizontal type and the lower type from the upper part). In FIG.
Reference numeral 1 denotes a mold, which is a lower mold 2 having various surface shapes corresponding to the wheel design, and an upper mold 3 located thereabove.
And horizontal molds 4 and 5 which are slidable left and right so as to form a cavity 6 by fitting with the lower mold 2 and the upper mold 3.
The lower die 2 is installed on a lower die base 8 fixed to a lower die platen 7. The upper mold 3 has a bolt 1 on the upper mold base 9.
It is fixed at 0. The cavity 6 includes a disc cavity 60 and a rim cavity 61, the disc cavity 60 includes a hub cavity 62 and a design cavity 63, and the rim cavity 61 includes a cross cavity 64 and a central cavity 65. . The center cavity 11a is provided in the hub cavity 62.
However, side gates 11b and 11c are formed in the cross cavities 64, 64, and
Stokes 13a, 13b through a, 12b and 12c
And 13c. Gates 11b and 11c
Is the center gate 11 when viewed from above as shown in FIG.
Symmetrical positions are arranged on both sides of a, that is, the centers of the respective gates are located on the same straight line. The lower end of these stalks has a closed container (not shown) containing molten metal.
Has been inserted into. The lower mold 2 has a lower mold cooling passage 14 at a position corresponding to the design cavity 63. Reference numeral 15 is a mold crack surface.

The operation of the above configuration will be described. First, the molten metal in the closed container is pressurized to stoke 1
3a, 13b and 13c to runners 12a, 12b and 1
The cavity 6 is filled from the gates 11a, 11b and 11c through 2c. Center gate 11a
Since there is a difference in height between the side gates 11b and 11c, the molten metal passing through the center gate 11a fills the design portion cavity 63 and the side gates 11b and 1c.
The molten metal passing through 1c fills the rim cavity 61. That is, the molten metal merges in the rim cavity 61. When the pressurization is released after a lapse of a predetermined time, the molten metal in each stalk returns to the closed container, and the molten metal in the cavity 6 is solidified to obtain a wheel.

The solidification process of the molten metal in the above casting process will be described in detail below. Side gates 11b, 1
The molten metal injected from 1c into the cavity 6 solidifies from the upper end of the rim cavity 65 toward its lower end. On the other hand, the molten metal injected from the center gate 11a into the disc cavity 60 is
Solidification proceeds from 3 toward the hub cavity 62.
Therefore, it is possible to reduce the thickness of the wheel design portion in terms of the casting plan without providing the design portion cavity 63 with the molten metal flow function and the molten metal supply function. Further, since the coagulation starts from the design section, the structure of the design section becomes fine and high strength can be maintained. Further, the aluminum wheel manufactured according to the present invention has different DAS values along the circumferential direction of the rim, and the DAS value is large near the side gate.
The DAS value in the degree direction was small. As the test method, a limit test was carried out using the physical impact tester shown in FIG. 3 in accordance with the measurement method of the Ministry of Transport's "Technical Standards for Disc Wheels Made of Light Cars for Passenger Cars" (1992 Jiju No. 41). As the method of the limit test, U = mgh, so the limit value was determined by increasing the height and weight of the falling weight. The limit condition of the aluminum wheel manufactured according to the present invention is 460 m.
m, 750 kgf, showing a high strength limit strength contrast. This value was 230 mm and 850 kgf for the conventional AC4CH manufactured in the same manner, which was 1.8 times as high as the limiting strength compared with AC4CH, which was a good result.

(Comparative Example) A vehicle wheel was manufactured by a center gate casting method and a side gate casting method. Except for this, the vehicle wheel was subjected to low pressure casting in the same manner as in Example 1. However, in both cases, casting defects occur frequently and the yield is very poor. This is a casting defect due to the use of a low Si material. In the center gate method in which only the hub portion of the disk portion is poured, the effect of feeding is insufficient near the inner flange portion of the rim, which is the final reaching portion of the molten metal. Many shrinkage cavities occurred. On the contrary, in the side gate method in which the molten metal is injected only from the rim portion, the molten metal did not enter the thin-walled and complicated-shaped disk portion, and casting failure occurred.

[0018]

As described above, by investigating the casting method, even if compared with the AC4CH material which is currently generally used as a high strength / high toughness material, a high yield strength, high toughness aluminum alloy casting is obtained. Obtainable. As a result, it is possible to further promote the change of the iron-based member used for the strength and toughness to the aluminum alloy casting, and the member already using the aluminum casting alloy can be further reduced in weight.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between aging time and proof stress.

FIG. 2 is a graph showing aging time and elongation value.

FIG. 3 is a diagram showing an impact test device used for measurement in the present invention.

FIG. 4 is a diagram of a mold used in the present invention.

5 is a cross-sectional view taken along the line AA of FIG.

[Explanation of symbols]

1 mold, 2 lower mold, 3 upper mold, 4, 5 horizontal mold, 6 cavities 11a, 11b, 11c gate, 30 wheels

Claims (2)

[Claims] 1. A low-pressure casting method for a vehicle wheel, which comprises casting in a mold having a shape corresponding to a vehicle wheel having a rim portion and a disc portion, wherein a center gate is provided at the center of a cavity forming the disc portion. , A side gate is provided in the cavity forming the rim, and Cu
An aluminum alloy molten metal containing 1.0 wt% or less, Si 2.4 to 4.6%, Mg 0.25 to 0.5 wt%, unavoidable impurity elements, and the balance Al is used, and the molten metal is poured from each gate. Low-pressure casting method for vehicle wheels. 2. A low pressure casting method for a vehicle wheel, wherein the molten aluminum alloy contains 0.55 wt% or less of Fe, 0.3 wt% or less of Ti, and 0.2 wt% or less of one or more of Sr, Sb or Na.