JPH05117826A - Manufacture of high strength aluminum alloy-made rim - Google Patents

Abstract

PURPOSE:To provide a manufacturing method for rim used to a wheel for automobile, particulaly an aluminum alloy-made wheel. CONSTITUTION:After solution heat treatment is applied to the aluminum alloy plate material composed of by wt.%, 0.6-1.5% Si and 0.5-1.5% Mg, satisfying (Si>0.578Mg+0.4) or further <1.0% Cu, 0.15-O.45% Mn, <0.3% Cr and the balance Al with the inevitable impurities, this material is bent and flash but welding is applied to the bent end part, and after this material is finished to the rim-shape by roll-forming, heat treatment is executed at 170-200 deg.C. The weldability of the Al alloy having low Mg content is improved and the Al alloy-made rim having high strength and excellent stress corrosion crack resistance can be manufactured, and by thinning the thickness of the rim, lightening of the car is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a rim used for an automobile wheel, particularly an aluminum alloy wheel.

[0002]

2. Description of the Related Art A wheel made of an aluminum alloy is manufactured by separately manufacturing a rim and a disk and then joining them together. For the rim, a method is used in which a rolled material is formed into a cylindrical shape, both ends thereof are butted, joined by flash butt welding, and processed into a rim by spinning or ring roll processing.

That is, a non-heat treatment type 5000 series aluminum alloy material is used because it is welded. Various methods have been proposed as a method for improving the strength of the welded portion of an aluminum alloy rim. For example, by forming the welded portion into a spiral shape, peening processing is performed on the welded portion while preventing stress concentration during rolling processing. Has been proposed (Japanese Patent Laid-Open No. 62-107832) to improve the strength of the welded portion and prevent cracking during rolling.

As an aluminum alloy material for rims, from the viewpoint of stress corrosion cracking resistance, Al containing 3% or less of Mg is used.
A Mg-based aluminum alloy (AA5052, 5454-based aluminum alloy material) is used.

Recently, a high-strength material is required for weight reduction, and it is considered to increase the Mg content. However, when the Mg content is increased, the stress corrosion cracking resistance is deteriorated. Therefore, an alloy containing Cu to improve the corrosion resistance (Japanese Patent Publication No. 60-47899), and further increasing the Mg and Cu contents, A material in which the glitter of the welded portion after anodizing treatment is improved by adjusting the trace amounts of Si, Fe, Ti and B and controlling the crystal grains (Japanese Patent Laid-Open No. 2-834).
2, No. 2-11401) and the like have been proposed.

[0006]

As described above, Al-
It is a Mg-based 5000 series non-heat treatment type aluminum alloy,
In order to obtain high strength, it is necessary to increase Mg,
However, Cu is added to improve the stress corrosion cracking resistance. However, Cu is not preferable because it is an element that impairs workability and deteriorates corrosion resistance.

However, Al-Mg-S having a low Mg content
The i-aluminum alloy can be increased in strength by heat treatment, but since the heat-affected zone becomes equivalent in strength to the annealed material (O material) by welding, it has not been used for welded structures.

Therefore, an object of the present invention is to use a 6000 series heat-treatable aluminum alloy which has not been used for welding in the past, with a small amount of Mg, and to perform flash butt welding as a welding method. It is another object of the present invention to provide a method for producing an aluminum alloy rim having high strength and excellent stress corrosion cracking resistance by subsequent heat treatment by improving the subsequent formability.

[0009]

In order to solve the above problems, a heat treatment type aluminum alloy (JIS 6000, which has not been conventionally used for flash butt welding, is used.
System)), as a result of diligent research, after adjusting excess Si and performing solution treatment, the mold workability is improved by performing flash butt welding, and then by heat treatment,
The present invention has been completed by finding that a joint having excellent strength and stress corrosion cracking resistance can be obtained.

That is, the gist of the present invention is Si: 0.6 to
1.5%, Mg: 0.3 to 1.5%, and
Satisfies (Si> 0.578Mg + 0.4), or Cu: 1.0% or less, Mn: 0.15 to 0.45
%, Cr: 0.3% or less, and solution treatment of an aluminum alloy plate material composed of the balance Al and unavoidable impurities (cooling at a cooling rate of 300 ° C./min or more if necessary)
After that, it is bent into a cylindrical shape, the bent end portion is flash butt welded, and the rim shape is finished by roll forming, followed by heat treatment at 170 to 200 ° C. to manufacture a high-strength aluminum alloy rim. Is the way to do.

[0011]

The reason for defining the component composition of the aluminum alloy plate used in the present invention will be explained. Si: Si can be solution-treated, and then bent and heat-treated to form Mg ₂ Si to obtain high strength. However, if less than 0.6%, this effect cannot be obtained, and if more than 1.5%, the solution treatment state (T4 treatment)
The yield strength becomes high and the formability after flash butt welding deteriorates. In addition, the excess Si is (0.
578Mg + 0.4) or less, the moldability is deteriorated,
Strength is reduced.

Mg: Mg forms high-strength by forming Mg ₂ Si like Si. However, if it is less than 0.3%, this effect cannot be obtained, and if it exceeds 1.5%, the hardenability deteriorates, so that the range of the heat influence of the flash butt welded portion becomes wide.

Cu: Cu coexists with Mg to impart age hardening and improve strength and abrasion resistance. However, 0.
If it is less than 05%, this effect cannot be obtained, and if it exceeds 1.0%, the yield strength in the solution heat treated state (T4 treatment) increases, the formability after flash butt welding deteriorates, and the corrosion resistance also decreases.

Mn, Cr: Mn and Cr can uniformly refine the structure and enhance the strength. If it is less than 0.15%, this effect cannot be obtained, and if it exceeds 0.45%, large crystallized substances are crystallized during ingot formation, and the fatigue strength is lowered.

Next, a method of manufacturing the rim will be described.

The method for producing a rim from a rolled plate material is as follows. A rolled plate material cut into a predetermined size is bent into a cylindrical shape, both ends are butted, joined by flash butt welding, and the welding bead is removed. Finished as a rim by roll forming. After that, the strength is increased by an age hardening treatment such as heat treatment or paint baking to obtain the desired strength.

Solution treatment: The solution treatment is carried out in order to improve the bending process after flash butt welding, and solute atoms serving as hardening elements are completely dissolved inside the material. The solution treatment conditions are as follows: heating to 450 ° C. or more and 580 ° C. or less at a temperature rising rate of 100 ° C./min or more, holding in this temperature range for less than 10 minutes, and then 150 ° C. or less to 300 ° C.
Cool at a cooling rate of at least 1 minute. If the heating rate is less than 300 ° C./minute, the crystal grains become coarse and the formability deteriorates. Further, if the heating temperature is lower than 450 ° C., the solid solution of solute atoms becomes insufficient, so that sufficient strength cannot be obtained even by the heat treatment after bending, and if it exceeds 580 ° C., the formability deteriorates due to eutectic melting. Further, even if held for 10 minutes or more, the effect is saturated, which is not preferable. Further, if the cooling rate up to 150 ° C. after the holding is less than 300 ° C./min, a coarse intermetallic compound precipitates at the grain boundaries and the ductility decreases, so that the bendability deteriorates.

Heat treatment after bending: The heat treatment after bending has the effect of increasing the strength by precipitating solute atoms solid-solved in the solution treatment. Therefore, the heat treatment after bending is performed after roll-forming into the shape of the rim to obtain the required high strength. However, if the temperature is lower than 170 ° C., the holding time becomes long, and if the temperature is 200 ° C. or higher, overaging causes the strength to decrease, which is not preferable. The heat treatment after bending can also be performed by heat treatment during baking of the coating.

Welding method: Flash butt welding was applied because the strength of the welded portion does not decrease with respect to the base metal and the welding speed can be increased.

[0020]

EXAMPLES Five kinds of alloys as invention examples shown in Table 1, three kinds of alloys as comparative examples, and AA5454 series alloys used as a conventional rim material were melted. Then, a plate material having a plate thickness of 4 mm was obtained by a usual method.

Example 1 B alloy materials shown in Table 1 were subjected to a bending test by changing the holding time of solution treatment and the cooling rate (quenching condition) as shown in Table 2. In addition, those materials were subjected to a test of mechanical properties as they were (as-quenched) and at 170 ° C. for 8 hours.

[0022]

[Table 1]

The bending test is 160 mm wide and 200 m long.
m with a thickness of 4 mm and a bending radius of 4 mm
° Bent. The results of these bending tests are shown in Table 2 and the mechanical properties are shown in Table 3.

[0024]

[Table 2]

[0025]

[Table 3]

From these results, the temperature rising rate is 100 ° C./min or more, the holding temperature is 450 to 580 ° C., and the cooling rate is 300 ° C./min.
Those treated within the range of the invention of not less than a minute are all good because cracks and skin roughness cannot be detected in the bending test.

However, No. 5 of the comparative example has a heating rate of 50.
The temperature was as low as ° C / min, the crystal grain size was as large as 120 µm, and roughening occurred in the bending test.

No. 6 has a low holding temperature of 430 ° C.,
It has poor mechanical properties after heat treatment at 0 ° C. × 8 hr, and is inferior to the conventionally used AA5454 material.

No. 7 had a high holding temperature of 600 ° C. and could not be subjected to a bending test due to eutectic melting.

No. 8 had a low cooling rate of 150 ° C./min, and the compound was precipitated during cooling and cracking occurred in the bending test.

Example 2 Here, an aluminum alloy plate material having a thickness of 4 mm was prepared,
500 ° C. at a heating rate of 500 ° C./min as solution treatment
After heating for 3 minutes and cooling to 150 ° C. at a cooling rate of 500 ° C./minute, the sample was left to cool in the atmosphere to obtain a test material (as-quenched material).

Then, a test piece having a width of 160 mm and a length of 905 mm was cut out and subjected to heat treatment after flash butt welding and bending.

Flash butt welding was performed under the conditions shown in Table 4.

[0034]

[Table 4]

In the evaluation test, the formability was evaluated by a bending test after flash butt welding, and the solution treated material was subjected to a bending test and a mechanical property test after flash butt welding. Also, after flash butt welding, 170 × 8h
After heat treatment at r of 200 ° C. for 30 minutes, the mechanical properties were tested and the strength of the rim product was evaluated.

The bending test piece has a width of 160 mm and a length of 200 m.
m, thickness 4 mm, and a sample having a welded portion in the width direction was sampled. Bending test is 180 ° bending, minimum bending radius 4m
m (equivalent to the plate thickness). The bendability was evaluated by visually observing cracks generated in the welded portion. The mechanical property test piece is a JIS No. 5 tensile test piece (width: 25 mm, test length: 20 mm).
0 mm) and a welded portion was provided in the width direction of the test piece. Table 5 shows the results of the bending test and mechanical properties of the as-quenched material. Table 6 shows the results of mechanical properties after heat treatment after flash butt welding.

[0037]

[Table 5]

[0038]

[Table 6]

From these results, the inventive materials A to E are
In both cases, no bending occurred in the bending test as it was quenched,
With heat treatment at 200 ℃ for 30 minutes, yield strength is 256M
A yield strength of Pa or more was obtained, and I material (A
The strength is 2.44 times higher than that of A5454).

On the other hand, the F material of the comparative example had a high Mg content of 1.6% and cracked in the bending test. The G material had a high Si content of 1.6% and cracked in the bending test. Material H had a low Si content of 0.6% and a small excess Si content calculated from the relational expression with Mg, and cracking occurred in the bending test.

Table 7 shows the mechanical properties of the base material as it is solution-treated (as-quenched) and after it is heat-treated.
From these results, it is understood that the yield strength can be increased 2.6 times or more as compared with the conventionally used material I.

[0042]

[Table 7]

[0043]

[Table 8]

Also, as-welded B material and after welding 1
The hardness distribution of the cross section including the welded portion of the heat-treated product of 70 ° C. × 8 hr and the as-welded product of I material were determined at 2 mm intervals and are shown in FIG.

From these results, the material B obtained by subjecting the aluminum alloy of the present invention to the solution treatment (quenching) has a higher hardness level in the welded portion as shown in FIG. 1 as compared with the conventionally used material I. However, the hardness distribution hardly changed, and the elongation value in the tensile test including the welded portion was also the same. Further, there is no occurrence of cracks in the bending test, and even after flash butt welding, roll forming processing equivalent to that of the conventionally used aluminum alloy I material can be performed. Further, it can be seen that the strength higher than that of the conventionally used aluminum alloy I material can be obtained by performing heat treatment after flash butt welding.

[0046]

INDUSTRIAL APPLICABILITY The present invention uses a heat treatment type aluminum alloy of the 6000 series which has a small amount of Mg and which has not been used for conventional welding. After solution treatment, flash butt welding is performed. By performing heat treatment after roll forming, it is possible to manufacture an aluminum alloy rim with high strength and excellent resistance to stress corrosion cracking, and the rim thickness can be reduced, leading to a lighter automobile. ,
It is industrially useful.

[Brief description of drawings]

FIG. 1 is a graph showing a hardness distribution of a cross section including a welded portion of an example and a comparative example.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location B60B 21/00 7146-3D C22C 21/02 8928-4K (72) Inventor Hidetoshi Uchida Minato-ku, Tokyo 5-11-3 Shimbashi Sumitomo Light Metal Industry Co., Ltd. (72) Inventor Takao Taka 5-4-33 Kitahama, Chuo-ku, Osaka City Sumitomo Metal Industry Co., Ltd.

Claims (3)

[Claims] 1. Si: 0.6 to 1.5% (weight%, the same shall apply hereinafter), Mg: 0.3 to 1.5%, and (Si
> 0.578Mg + 0.4), the solution treatment is performed on the aluminum alloy sheet material containing the balance Al and unavoidable impurities, and then bent into a cylindrical shape, and the bent end is flash-butt welded and roll-formed. A rim-shaped rim made of a high-strength aluminum alloy, which is heat-treated at 170 to 200 ° C. 2. Si: 0.6 to 1.5%, Mg: 0.3
.About.1.5%, Cu: 1.0% or less, Mn: 0.
An aluminum alloy plate material containing 15 to 0.45%, one or two kinds of Cr: 0.3% or less, further satisfying (Si> 0.578Mg + 0.4), and the balance Al and unavoidable impurities. After the solution treatment, it is bent into a cylindrical shape, the bent end is flash butt welded, and the rim shape is finished by roll forming, and then 170 to 200 ° C.
A method for manufacturing a rim made of a high-strength aluminum alloy, which comprises heat-treating. 3. The solution heat treatment is carried out by heating to 450 ° C. to 580 ° C. at a temperature rising rate of 100 ° C./min or more, holding this temperature range for less than 10 minutes, and then 300 ° C./150° C. or less.
The method for producing a high-strength aluminum alloy rim according to claim 1 or 2, which is performed by cooling at a cooling rate of not less than a minute.