JPH09157809A - Production of aluminum wheel disk casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a thin and lightweight automobile- use two piece aluminum wheel disk inexpensively. SOLUTION: The molten metal of an Al-Si-Mg base aluminum alloy contg., by weight, 5 to 12% Si, 0.2 to 0.8% Mg, and the balance Al with inevitable impurities is charged to a mold, which is rapidly cooled to 250 to 550 deg.C under the high rolling reduction of 500 to 1200kgf/cm<2> , and after that, the mold is opened. Immediately, it is subjected to preliminary aging treatment at 80 to 250 deg.C for >=5min and is subsequently subjected to artificial aging treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle wheel.
More specifically, the present invention relates to a method for manufacturing a disc, and in more detail, in a two-piece wheel or a three-piece wheel in which a rim and a disc are combined and bolted or welded, an aluminum wheel disc that is thinner and lighter than a conventional aluminum alloy casting. The present invention relates to a method for manufacturing a low cost.

[0002]

2. Description of the Related Art Wheels for automobiles are important safety parts, and their reliability such as strength and impact resistance is required to be high. Recently, aluminum alloy wheels have been widely used from the viewpoints of vehicle running stability and vehicle weight reduction.

The aluminum alloy wheel has a structure of 1
It can be roughly classified into a piece wheel and a 2 piece or 3 piece wheel. The one-piece wheel is made by integrally casting a rim portion on which a tire is mounted and a disc to be mounted on an axle, and finishing by machining. 1-piece wheel has high rigidity and has the advantage that the number of parts can be reduced, but it is difficult to change the design of the disk surface,
In order to prevent casting defects that cause air leakage during tire mounting, there are drawbacks such as strict control of casting conditions and a certain minimum thickness of the rim portion. Therefore, there is a limit to the reduction in wall thickness, and it is not possible to achieve sufficient weight reduction.

On the other hand, two-piece wheels and three-piece wheels
As shown in FIG. 1, the stool is a rim part (1) formed by expanding a rolled plate, and a separately manufactured disc part (2) assembled by welding or bolting, and has almost no internal defects. Since the aluminum alloy strip, which is highly ductile, is used as the material, it is possible to form rims with high dimensional accuracy.
For this reason, the reliability of the airtightness when the tires are mounted is high, and even if it collides with a sidewalk while running, it will only deform and will not cause a major accident such as loss. There is.

As described above, the two-piece wheel and the three-piece
The structure of the wheel has the advantage that the rim thickness can be made thinner than the one-piece wheel because of its structure, so it is possible to reduce the weight even with the same disc design, but from the viewpoint of rim formability, the rim material. Since there is a limit to the thinning of
In order to meet the demand for further weight reduction, it is necessary to reduce the weight of the disk portion at the same time.

Generally, disks can be classified into forged wheel disks and cast wheel disks depending on the manufacturing method. Forged wheel disks are usually Al-Mg-Si based alloys with good corrosion resistance and excellent workability, especially J
It is manufactured by forging a continuous cast rod or extruded material of IS6061, 6N01 alloy, and has high strength and high reliability, but it is difficult to reduce the wall thickness due to the restrictions of the molding method and the degree of freedom in shape is low. Since many steps such as pre-forming, roughing and finishing are performed, there are disadvantages that the yield is low and the manufacturing cost is high.

On the other hand, since the cast wheel disc can make a certain thickness difference as compared with the forged wheel disc, it has a high degree of freedom in shape and can be easily thinned. Although it has advantages such as low cost, it is necessary to pay close attention to its material and manufacturing method in order to obtain high strength and high reliability.

Conventionally, from the viewpoint of strength, toughness, and corrosion resistance, as an aluminum alloy for a cast wheel disk, an Al-Si alloy having good castability is used as a base for a small amount of M.
Al-Si-Mg-based JIS AC4C and AC4CH, in which g is added to give a heat treatment effect and mechanical properties are improved.
Alloys are widely used.

The manufacturing method is as follows: the mold is sufficiently preheated to ensure the hot water turning property, and then the molten metal is filled at a low speed.
Low-pressure casting is mainly adopted in which the riser is heated at a low pressure of about 1 to 0.5 atm. However, in a casting method having a slow solidification rate such as low pressure casting, the solidification structure (dendritic cell size) becomes coarse, so that the strength and toughness are deteriorated.

Therefore, by performing a solution treatment of keeping the temperature at a high temperature for a long time after casting, the eutectic Si forming the dendrite cells is spherically divided, and the strength-imparting element Mg is used.
Was completely solid-solved and then subjected to artificial aging treatment to obtain the strength and toughness required as a load wheel, but the solution treatment and aging treatment described above took a lot of time. Therefore, there have been problems such as an increase in manufacturing cost.

[0011]

Recently, in order to solve this problem, attempts have been made to overcome the problems in casting by the high pressure casting method, and some parts have been put to practical use by using casting alloys. There is. The high-pressure casting method is characterized by filling the molten metal at a low speed and pressurizing until the solidification is completed.
The occurrence of internal defects can be considerably prevented, and the dendrite cell size is reduced because the solidification rate is considerably increased. Therefore, it is known that spheroidization of eutectic Si is accelerated when the solution treatment temperature is kept at the subsequent solution treatment, and as a result, the solution treatment time can be shortened. But,
In order to obtain sufficient strength as a load wheel, it is necessary to dissolve a strength-imparting element (eg, Mg) into a matrix during solution treatment and precipitate an intermediate phase that contributes to strength during subsequent artificial aging treatment. Therefore, the solution treatment itself cannot be omitted, and as a result, the cost cannot be reduced.

Further, when a casting having a shape in which a thick hub portion and a thin spoke portion or a rim portion are integrated, such as a wheel disc, is water-quenched after the solution treatment, a difference in wall thickness results. However, if the difference in wall thickness is large, warpage deformation will occur and the accuracy of the product itself will deteriorate.Therefore, measures have been taken to reduce quenching distortion by quenching in warm water. However, since the product thickness is limited, improvement of the solution-water quenching process has been strongly demanded from the viewpoint of both the degree of freedom in product design and cost reduction.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a thin wall,
It is an object of the present invention to provide a method for manufacturing a lightweight two-piece automobile or three-piece wheel disk at low cost.

In order to solve the above-mentioned object, the inventors of the present invention have used solution-quenching behavior by using various Al-Si-Mg-based aluminum alloys which have been widely used as materials for wheel disks. As a result of examining
The following findings were obtained.

That is, according to the present invention, Si 5 to 12% by weight, M
g 0.2-0.8 wt%, the balance Al, and Al-Si-Mg-based aluminum alloy molten metal consisting of unavoidable impurities is filled in a mold, and under high pressure of 500-1000 kgf / cm ² , An aluminum wheel disk characterized by being rapidly cooled to a temperature of 250 to 550 ° C., then opened, immediately subjected to a preliminary aging treatment at a temperature of 80 ° C. to 250 ° C. for 5 minutes or more, and then an artificial aging treatment. It is a method of manufacturing a casting.

The Al-Si-Mg-based aluminum alloy is an aging-type alloy, and the precipitation-hardening phase is generated during the aging treatment, so that the strength of the alloy increases. Al-Si-M
The g-based aluminum alloy has the following aging precipitation process. Supersaturated solid solution → GP zone → intermediate phase → stable phase After solution treatment and quenching treatment of the alloy, natural aging treatment (T4 treatment) at room temperature causes Mg and Si of solute atoms and excess vacancy generated by quenching. A GP zone is formed in which the alloys are bonded, and the alloy strength is slightly increased. It is said that by performing artificial aging treatment thereafter, an intermediate phase, which is a precipitation hardening phase that contributes most to the strength of the alloy, precipitates, and sufficient strength can be obtained as a product.

However, during the natural aging treatment (that is, when the solution is left at room temperature after the solution treatment), most of the pores are G
Since it is contained in the P zone, precipitation of the intermediate phase is prevented even if artificial aging treatment is performed thereafter, and the highest strength of the alloy cannot be obtained. Therefore, it was found that by performing a pre-aging treatment immediately after solution treatment or after aging at room temperature, formation of GP zone can be prevented, and as a result, the strength after artificial aging treatment can be improved.

As a result of observing the solution-quenching behavior of a high-pressure casting having a high cooling rate in more detail, the inventors of the present invention have found that when the cooling rate from the start of solidification to room temperature is considerably high, as in high-pressure casting, the casting is continued. It has been found that the solute atom has a high degree of supersaturation in the material stage to some extent, and exhibits precipitation hardening behavior during the subsequent artificial aging treatment even without performing solution treatment again. Furthermore, by performing a pre-aging treatment at a constant temperature and time before reaching room temperature during cooling after solidification, aging precipitation is promoted during the subsequent artificial aging treatment, which is sufficient for use as a load wheel. It was found that various strengths can be obtained.

Further, by performing the above-mentioned preliminary aging treatment immediately after opening the mold, it is possible to simultaneously alleviate the quenching strain, which has been a problem in the conventional solution heat treatment and water quenching method, and it is thin and the difference in wall thickness is small. It has been found that a large wheel disk can be produced without any problem, and the present invention has been completed based on the result.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION A method for manufacturing a lightweight wheel disk casting according to the present invention will be described in detail below. First, the reasons for limiting the alloy components will be described below. The alloy casting of the present invention contains 5 to 12% by weight of Si and 0.2 to 0.8% by weight of Mg, and is composed of the balance aluminum and unavoidable impurities A.
It is characterized by being an l-Si-Mg-based aluminum alloy.

Here, Si improves the castability, and Mg
Coexisting with Mg during heat treatment after casting _TwoDeposit Si,
It is necessary to obtain the strength required as a wheel disc.
Yes, it is necessary to add 5 wt% or more, but Si is 12
If the content exceeds 50% by weight, hard and brittle primary crystal Si is produced to improve toughness.
It is not preferable because it significantly decreases.

Mg, together with Si, is effective in improving the strength after heat treatment. However, if the addition amount is 0.2% by weight or less, sufficient strength cannot be obtained, and if it exceeds 0.8% by weight, the strength is improved. However, elongation and toughness are deteriorated, which is not preferable.

Other unavoidable impurities do not interfere with the effects of the production method of the present invention as long as they are within the standard JIS. Further, improving agents such as Na, Sr, and Sb, which are often added for refining eutectic Si grains forming a dendrite cell, are also added according to a conventional method using a commercially available mother alloy or flux. However, the addition of an appropriate amount is preferable because it does not impair the effects of the present invention and rather makes the cast structure finer and particularly improves the toughness.

The aluminum alloy casting according to the present invention is 500-120 when the molten metal filled in the mold is solidified.
It is necessary to solidify under a high pressure of 0 kgf / cm ² . If the casting pressure is less than 500 kgf / cm ² , shrinkage cavities and casting cracks occur frequently,
It is not preferable because the mechanical performance, particularly the elongation value, remarkably decreases. On the other hand, if the casting pressure is 500 kgf / cm ² or more,
It is possible to prevent shrinkage cavities and casting cracks, and by applying pressure,
Solidification proceeds with almost no air-gap at the aluminum-mold interface, so heat transfer is good, and the solidification structure (especially dendrite cell size) can be made extremely fine, and it is used as a wheel disk. Sufficient toughness can be obtained. On the other hand, if the casting pressure exceeds 1200 kgf / cm ² , the thermal fatigue of the surface layer of the mold becomes severe, heat cracks are likely to occur, and the life of the mold is significantly shortened, which is not preferable.

The greatest feature of the present invention is that the aluminum casting is rapidly cooled in the mold to a temperature range of 250 to 500 ° C., then the mold is opened, and immediately preliminarily aged in the temperature range of 80 to 250 ° C. for 5 minutes or more. It is to give processing.

If the product temperature at the time of mold opening is less than 250 ° C., the effect of the subsequent pre-aging treatment is not sufficient, and sufficient strength as a product cannot be obtained. On the other hand, if the temperature exceeds 500 ° C., the product is thermally deformed when the mold is opened, causing galling on the mold, which is not preferable. If the preliminary aging temperature is less than 80 ° C., the effect of reducing pores by the preliminary aging treatment cannot be obtained, and the aging at room temperature is not achieved, so that the sufficient strength improving effect cannot be obtained during the subsequent artificial aging treatment. On the other hand, the preliminary aging temperature is 25
When it exceeds 0 ° C, a stable phase begins to precipitate, and a sufficient strength improving effect cannot be obtained during the subsequent artificial aging treatment.

Although no particular detailed conditions are specified for the method of performing the pre-aging treatment immediately after the mold is opened, for example, a water tank filled with boiling water of 80 to 100 ° C. or 100 to 250 ° C. below the molding surface. Of the method of the present invention by installing an oil bath filled with mineral oil, dropping the product immediately after opening the mold, or immediately after opening the mold, by placing the product in a heat treatment furnace maintaining a predetermined temperature atmosphere. Can be satisfied. If the pre-aging holding time is 5 minutes or more, sufficient strength as a wheel disk can be obtained, but if it is less than 5 minutes, precipitation of the intermediate phase during the subsequent artificial aging treatment is insufficient and the strength improving effect is unacceptable. The artificial aging conditions to be carried out subsequently are determined according to the required performance of the final product, and the aluminum alloy casting according to the present invention is subjected to the tempering conditions specified in JIS standard according to the alloy to be applied, thereby the strength, elongation, The toughness can be improved considerably.

[0028]

Embodiments will be described in detail below based on embodiments. (Example 1) First, the casting apparatus shown in FIG. 2 was used for casting. This casting apparatus includes a product part (4) (wheel disk shape) formed in a mold (3) and a molten metal supply path (5).
And an injection sleeve (6) into which a fixed amount of molten metal is poured, and a plunger tip (7) which moves inside the injection sleeve to fill and pressurize the molten metal in the cavity. Here, a water cooling pipe (8) was passed through the mold (3) at regular intervals along the product part (4), and injection cooling was performed together with water cooling.

Here, the aluminum alloy having the composition shown in Table 1 was melted by a usual method, degassed by Ar gas bubbling for about 20 minutes at a molten metal temperature of 720 ° C., and then under the casting conditions shown in Table 2. 350m diameter by pressure casting
A wheel disk having a wall thickness of 5 to 60 mm was produced.

[0030]

[Table 1]

The temperature of the product portion immediately after casting was measured by a thermocouple (9) installed in the product portion (4). After these disks were pre-aged under the conditions shown in Table 2, 1
An artificial aging treatment was performed at 50 ° C. for 6 hours, and a tensile test piece and a Charpy test piece were sampled from the rim portion of the disc, and the Charpy impact value, which is an index value of tensile strength, proof stress, elongation value, and toughness, was obtained. It was measured.

Further, these discs were welded to a rim made of 5454 alloy by MIG welding (a filler material 4043), and then subjected to a rotary bending durability test and an impact test based on the Japanese automobile standard (JASO) to obtain a road wheel. I checked the performance. In the rotating bending endurance test, the wheel was set on the rotating disk, the rotating shaft attached to the wheel was rotated 100,000 times while applying a certain amount of bending moment, and the wheel was removed after the test. It was done by checking for cracks or deformation. In the impact test, the table with sufficient rigidity and strength is tilted from the horizontal at a certain angle, a wheel with tires is mounted on the table, and the weight is dropped freely from a predetermined height. Impact through the tire against, remove the wheel after the test,
It was performed by examining the presence or absence of cracks or deformation. The results are summarized in Table 2.

[0033]

[Table 2]

As is clear from Table 2, the wheel disk produced by the method of the present invention shows performance comparable to that of a conventional low-pressure cast JISAC4CH alloy (solution-> water quenching-> T6 temper). It was confirmed that the required strength and toughness level of the dough wheel were secured. On the other hand, when the alloy composition and manufacturing conditions were not within the scope of the claims of the present application, sufficient strength could not be obtained, and it was confirmed that cracks were likely to occur during the rotary bending durability test and the impact test.

Example 2 An aluminum alloy having the composition of alloy No. 2 shown in Table 1 was melted by a usual method and degassed by Ar gas bubbling for about 20 minutes at a melt temperature of 720 ° C. Then, pressure casting was performed under the casting conditions shown in Table 3 to produce a disc having a diameter of 350 mm.

The wall thickness of this disc depends on the hub portion (1
The thickness of 2) is constant (18 mm), and the spoke part (1
The wall thickness of 3) was changed to 3 to 7 mm to obtain wheel disks having different ratios of maximum wall thickness / minimum wall thickness. Here, as the thickness of the spoke portion (13) becomes thinner, the wheel disk becomes lighter, but the difference in thermal expansion during cooling after mold opening or after solution heat treatment becomes large and thermal deformation easily occurs. become. After heat-treating these wheel discs under the conditions shown in Table 3, the warp deformation of the disc seat surface was measured.
The results are also summarized in Table 3.

[0037]

[Table 3]

As is apparent from Table 3, even if a thin-walled disc is manufactured by high pressure casting, simply by subjecting it to conventional heat treatment (that is, water quenching, T6 temper after solution heat treatment),
It was confirmed that, although the strain after quenching was large, the method of the present invention hardly caused the quenching strain, and the warp deformation amount was smaller than that of the thick low-pressure cast product.

[0039]

As described above in detail, the aluminum wheel disk casting produced by the manufacturing method of the present invention does not need to be subjected to solution heat treatment and has sufficient performance as a wheel disk for two-piece or three-piece wheels. In addition, since it can be obtained and the quenching strain at the time of heat treatment can be prevented, the thickness can be reduced, and the manufacturing cost of the material can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal section of a two-piece aluminum wheel.

FIG. 2 is a cross-sectional view of a main part of a pressure casting device in an example.

[Explanation of symbols]

 1 rim part 2 disk part 3 mold 4 product part (wheel disk) 5 molten metal replenishment path 6 plunger sleeve 7 plunger tip 8 water cooling pipe 9 thermocouple for measuring product temperature 10 gas venting part 11 spout part 12 hub part 13 spokes

Claims (1)

[Claims] 1. Si 5 to 12% by weight, Mg 0.2 to 0.8
The mold is filled with an Al-Si-Mg-based aluminum alloy melt containing 50% by weight and the balance Al and unavoidable impurities, and is heated at a high pressure of 500 to 1200 kgf / cm ^{2 to} 250 to
After quenching to a temperature of 500 ° C, the mold is opened and immediately 80
After pre-aging treatment for 5 minutes or more at a temperature of ℃ ~ 250 ℃,
A method for producing an aluminum wheel disk casting, which is characterized by performing an artificial aging treatment thereafter.