JPH11300476A - Aluminum alloy plate with superior weldability for wheel rim - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure welding strength and to prevent generation of weld crack at the time of rim forming by reducing the thickness of a surface oxide layer in a part containing the sides that form the end face of an alloy plate to be welded. SOLUTION: The thickness of an oxide layer 15 is adjusted to be 100 Åor less, desirably 10 Å or above and 100 Å or below, for the forming-required area 16a, 16b of an aluminum alloy plate 10 for wheel rims, the area including the end face 12a, 12b of the plate and having an width of at least about twice the thickness t of the plate from its side 13a, 13b. As a result, in the DC butt welding of the end face 12a, 12b, the oxide is reduced that flows into the weld zone, thereby preventing a weld crack caused by the oxide at the time of subsequent rim forming. The thickness of the oxide layer 15 is adjusted by acid cleaning of the base material in two steps using for example a sulfuric acid solution and a nitric acid solution. Incidentally the acid cleaning area is the entire surface, which is advantageous costwise in view of a means like masking, rather than the limited area of 16a, 16b for which forming is required.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy plate for a wheel rim excellent in weldability, for example, direct current butt weldability. For example, the present invention relates to a two-piece wheel for an automobile in which a disc and a wheel rim are formed of different members. The present invention relates to an aluminum alloy plate for a wheel rim having excellent weldability.

[0002]

2. Description of the Related Art Automobile wheels are one of the most important parts from the viewpoint of automobile safety. During traveling, the wheels are required to have sufficient strength to receive various loads and to have high dimensional accuracy, balance and the like to rotate at high speed. In addition, automobile wheels
High productivity and economic efficiency are also required for mass production.

FIG. 5 is a longitudinal sectional view showing an example of an automobile wheel 1. As shown in FIG. Conventionally, the wheel rim 2 is JIS G
Using "Hot rolled steel sheet and steel strip SAPH 32 for automobile structure" indicated by 3113 as a material, it is formed into an annular shape by material cutting → winding → flash butt welding → rim forming (flaring step and roll forming step). The vehicle wheel 1 has been manufactured by joining a disk 3 formed into a disk shape in a separate process to the wheel rim 2. Note that such an automobile wheel 1 is called a two-piece wheel because it is composed of two members, a wheel rim 2 and a disk 3.

[0004] In recent years, from the viewpoint of reducing the weight of the automobile and improving the running performance, the automobile wheel 1 is also required to be reduced in weight. Therefore, the wheel rim of the two-piece wheel has been manufactured from a high-tensile steel plate or an aluminum alloy plate.

[0005] Regarding the use of high-tensile steel plates for wheel rims,
There is already an example in which an 800 MPa class high-strength steel sheet has been actually adopted. However, there are still problems in terms of price, moldability and the like, and the application is limited to some types of vehicles.

On the other hand, the use of an aluminum alloy plate for the wheel rim has also been actively studied in order to meet the demand for improving the appearance quality of the wheel rim 2. Aluminum alloy wheel rims, like steel wheel rims,
A rectangular flat plate made of aluminum alloy (Al-Mg)
Wrap it in a cylindrical shape with a coiler in the longitudinal direction, align both ends and butt, make it into a cylindrical shape by flash butt welding using a flash butt welding machine, and perform rim forming by spinning processing or ring roll processing,
It is an annular wheel rim.

[0007] Incidentally, in order to increase the productivity of aluminum alloy wheel rims and to suppress the production cost, the efficiency and workability are both superior to flash butt welding. Therefore, they have already been adopted in the production process of steel wheel rims. DC butt welding (hereinafter, referred to as “DC butt welding” in this specification) has come to be used frequently. This DC butt welding is a method in which welding is performed by applying pressure while applying a direct current to a joint, and is performed by applying an alternating current and applying pressure while generating a flash for 5 to 10 seconds. Is a different welding method in principle.

[0008] However, in the DC butt welding of an aluminum alloy plate, unlike the case of a steel plate, when welding is performed under normal conditions, the thermal conductivity of the aluminum alloy is about three times that of iron and the specific resistance is about 2 times. Since the ratio is / 7 times, cracks in the welded portion easily occur in the rim forming performed after the DC butt welding.

In other words, aluminum alloy sheets are harder to heat and more easily escape heat than steel sheets.
It is difficult to obtain a healthy joint. For this reason, if the current density is slightly lower than the appropriate current density, a weld crack called “cold welding” is likely to occur in a flare processing step, a ring roll processing step, or a 180 ° bending test after welding. On the other hand, if the current density is slightly increased, cracks in the weld called “excessive heat input” tend to occur in the 180 ° bending test.

In order to prevent such weld cracking in the rim forming after welding, it is necessary to secure an upset allowance of at least four times the sheet thickness of the 5000 series aluminum alloy in view of safety. Did not. Therefore, (i) the yield of the raw material decreases, (ii) the amount of adhesion to the welding electrode tip increases with the increase in the amount of molten aluminum alloy extruded at the time of welding. The frequency of replacement and polishing of welding electrodes is not significantly increased when compared to steel wheel rims, because it induces sparks caused by aluminum alloy shards caught in between and makes it easier to generate welding defects. There was a problem of not obtaining.

By the way, various proposals have conventionally been made for manufacturing a wheel rim made of an aluminum alloy by DC butt welding. For example, Japanese Unexamined Patent Publication No. Hei 4-368531 discloses that an aluminum alloy wheel rim is formed by adopting a so-called two-stage pressing method in which an upset pressing force is further superimposed after a squeezing pressure is applied.
An invention that enables C-butt welding has been proposed.

Japanese Patent Application Laid-Open No. 6-142938 discloses that
Welding conditions are set based on the conductivity of the aluminum alloy plate of the 6000 series or 6000 series (Al-Mg-Si system) and the upslope time during welding. Has been proposed to make the DC butt weld part sound.

Furthermore, Japanese Patent Application Laid-Open No. 6-136493 proposes an invention in which an aging Al-Mg-Si alloy plate capable of obtaining high weld joint strength is used as a material for a wheel rim. The present invention proposes a material that replaces the currently mainstream 5000 series aluminum alloy.

[0014]

However, according to the inventions according to these proposals, it is not possible to simply and reliably eliminate a weld crack in a rim forming after welding.

That is, the inventions proposed in JP-A-4-368531 or JP-A-6-142938 all specify a part of the welding conditions. Requires management. But,
Normally, wheel rims are manufactured on a production line unique to each automobile manufacturer, and even if welding conditions are specified, it is difficult to implement and manage them side by side, so it is hard to say that this is a realistic invention. In consideration of the mass productivity of the wheel rim, it is desirable that DC butt welding can be performed without changing the welding conditions so far as much as possible.

In the invention proposed in Japanese Patent Application Laid-Open No. 6-136493, Mg ₂ Si is precipitated by solution treatment / quenching treatment and artificial aging treatment of T6 to obtain high strength. For this reason, it is necessary to perform an artificial aging treatment at, for example, 180 ° C. for 8 hours after forming the wheel rim in order to control the size and density of Mg ₂ Si. It is hard to say that this is a realistic invention in view of the production line.

Here, an object of the present invention is to secure a high welding strength without causing any change in the conventional welding conditions, in particular, the welding conditions of DC butt welding, and to generate a weld crack in a rim forming after welding. It is possible to obtain a sound joint without defects, thereby reducing the upset allowance (for example, 3 times or less of the plate thickness), improving the yield, and reducing the welding electrode replacement / polishing frequency. To provide an aluminum alloy plate for a wheel rim.

[0018]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, cracks in the welded portion in rim forming are caused by oxides present in the welded portion during welding. The inventors have found that the above problem can be completely solved by performing welding while reducing the amount of the oxide, and further studied and completed the present invention.

Here, the gist of the present invention is characterized in that an oxide layer having a reduced thickness is provided on at least a part of a surface including a side forming an end face to be welded. Aluminum alloy plate for wheel rims with excellent weldability.

In the present invention, the oxide layer has a thickness of 100
It is desirable that the thickness be 10 mm or less, more preferably 10 mm or more and 100 mm or less, in order to eliminate weld cracks in rim forming.

Further, in the above-mentioned present invention, said part is
Similarly, it is desirable that the length be in the range of (sheet thickness × 2) times from the above side in order to eliminate the weld crack. In another aspect, the present invention provides that the thickness of the oxide layer on the surface of the aluminum alloy strip is 100 mm or less, preferably
This is a method for manufacturing an aluminum alloy plate for a wheel rim excellent in weldability, characterized in that the aluminum alloy strip is cut into a predetermined length after adjusting the length to 10 mm or more and 100 mm or less.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an aluminum alloy plate for a wheel rim according to the present invention will be described in detail with reference to the accompanying drawings. In the following embodiments, an application to a wheel rim of a two-piece wheel for an automobile will be described as an example, and a case where DC butt welding is performed will be described as an example.

FIG. 1 is a perspective view showing an example of an aluminum alloy plate 10 for a wheel rim according to the embodiment. As the base material 11 constituting the aluminum alloy plate 10 for a wheel rim, a conventionally known 5000-type (Al-Mg-based) aluminum alloy for a wheel rim was used.

The base material 11 is wound into a cylindrical shape in the longitudinal direction, and is subjected to DC butt welding in a state where both end surfaces 12a and 12b are aligned and butted to be processed into a cylindrical shape. On both surfaces 14 and 14 including sides 13a and 13b forming the end surfaces 12a and 12b, oxide layers 15 and 15 having reduced thickness are provided.

The surface of an aluminum alloy plate, which is a wheel rim material produced by hot rolling, is usually provided with an aluminum-based and magnesium-based oxide layer of 500 mm.
Although present in a thickness of about, the oxide layer 15 of the present embodiment,
This thickness is reduced to 100 mm or less by appropriate means. The technical significance of providing this oxide layer 15 will be described below.

In the DC butt welding used for joining the end faces 12a and 12b of the base material 11 constituting the aluminum alloy plate 10 for a wheel rim, as described above, the end faces 12a and 12b are brought into contact with each other and energized to contact the end faces 12a and 12b. This is a welding method in which the end faces 12a and 12b are heated and melted by utilizing the resistance, and the welding strength is sufficiently ensured by upset pressing. Conventionally, in order to join the base material 11 soundly by DC butt welding, the upset allowance is set to four times or more the sheet thickness in consideration of safety. That is, an oxide layer composed of an aluminum-based oxide and a magnesium-based oxide that is stable at room temperature has end faces 12a and 12b and end faces 12a and 12b.
b is present in the vicinity of the surface including the sides 13a and 13b forming the end face 12a,
The oxide originally present on 12b and the oxide that flows in along with the upset from near the surface including the sides 13a and 13b exist, and the oxide originally present on the end faces 12a and 12b is completely discharged. To the extent that the effect is eliminated by the impact (about 4 times)
An upset allowance was necessary to reliably discharge oxides, expose a new surface, and perform sound welding.

However, according to the results of the study by the present inventors,
Reducing the amount of oxide flowing from near the surface including the sides 13a and 13b with the upset is also effective in improving the joining strength of DC butt welding. That is, in the present embodiment, attention is paid to the oxide that is present near the end surfaces 12a and 12b of the surface of the base material 11 and flows into the joint portion with the upset, and the DC butt welding is performed while reducing the amount of the oxide. By performing the above, a sound joint can be obtained, thereby preventing a weld crack at the time of forming the rim. Therefore, in the present embodiment, the oxide layer 15 having a reduced thickness is provided.

The thickness of the oxide layer 15 was reduced by two-step pickling of the base material 11 using a sulfuric acid solution and a nitric acid solution, and adjusted by adjusting the length of the pickling time. Thus, the reduced thickness oxide layer is formed on the surface of the base material 11.
15 is formed.

The thickness of the oxide layer 15 is desirably 100 ° or less. This is because if the thickness of the oxide layer 15 is larger than 100 mm, the effect of preventing cracks in the welded portion is reduced. From such a viewpoint, it is not necessary to set the lower limit of the preferable range of the thickness of the oxide layer 15, but since the oxide layer 15 is immediately oxidized in the air, the thickness of the oxide layer 15 is less than 10 mm. Since it is difficult to reduce the diameter to about 10 mm, and about 10 mm has a sufficient effect of suppressing cracks at the welded portion, it is more desirable and practical to set it to 10 mm or more and 100 mm or less.

The necessary ranges 16a, 16a for forming the oxide layer 15
b may be at least (plate thickness t × 2) times the length from the sides 13a and 13b. That is, according to the present embodiment, the upset allowance is reduced to about twice the plate thickness t.
The range in which the amount of oxides needs to be reduced is also a range of (sheet thickness t × 2) times the length. In FIG. 1, the oxide layer 15
The hatched areas 16a and 16b are indicated by oblique lines.

In this embodiment, the oxide layer 15 is used as a base material.
11 was formed on the entire surface. This is because if the oxide layer 15 is formed only in the necessary ranges 16a and 16b, the necessary ranges 16a and 16b
This is because it is necessary to take measures such as masking the remaining area other than 16b, and considering the man-hours, it is cheaper to form the oxide layer 15 over the entire surface in terms of cost.

It is also desirable to reduce the thickness of the oxide layer on the side surface of the base material 11 as in the case of the surface 14. This further reduces the amount of oxide flowing into the junction.

Therefore, in the aluminum alloy plate 10 for a wheel rim of the present embodiment, the thickness of the oxide layer on the surface of the aluminum alloy strip as the base material 11 is, for example, 10 to 100 mm.
It is most suitable to cut the aluminum alloy strip to a predetermined length and manufacture it after forming the oxide layer 15 of the present embodiment, and to implement it on an industrial scale.

The aluminum alloy plate 10 for a wheel rim according to the present embodiment is used as a material for a wheel rim, and is manufactured by a known wheel rim manufacturing process under exactly the same conditions as in the past. Aluminum alloy plate for wheel rim 10
Can be applied to all known wheel rim manufacturing processes, and is not limited to specific processes, manufacturing conditions, welding types, and welding conditions.

The aluminum alloy plate 10 for a wheel rim according to the present embodiment can obtain high DC butt welding strength because the thickness of the oxide layer 15 on the surface thereof is reduced. Cracks in the welded portion can be prevented, the amount of upset can be reduced, the yield can be improved, and the frequency of replacement and polishing of the welding electrode can be reduced.

The aluminum alloy plate 10 for a wheel rim according to the present embodiment does not need to change the composition of the material to be used from the conventional one. It can be easily applied to all rim production lines.

In particular, when a 5000 series aluminum alloy plate is used, the upset allowance is three times or less the plate thickness, specifically, 2 times.
In addition, the amount of electrode wear and the frequency of electrode replacement during continuous production can be significantly reduced.

Further, the aluminum alloy plate 10 for a wheel rim of the present embodiment is intended not to directly remove the oxide on the end face to be DC-butt-welded, but to reduce the oxide layer on a flat surface. In addition, the removal operation can be performed quickly, easily, and at low cost, and the mass productivity of the aluminum alloy plate 10 for wheel rim is sufficiently maintained.

[0039]

EXAMPLES The present invention will be described in detail with reference to experimental data.

[Method of Forming Test Material and Oxide Layer] An aluminum alloy strip (aluminum alloy plate A5454 stipulated in JISH 4000) having a shape shown in FIG. 1 and having a thickness t: 5 mm and a width of 160 mm was used. An aluminum alloy strip for a wheel rim of a two-piece automobile wheel was manufactured by controlling the thickness of an oxide layer in the base material 11 by performing the following treatments on the entire surface of the base material 11.

Triclean steam degreasing: 3 minutes → degreasing alkali treatment: 70 ° C. × 10 seconds → water washing → pickling treatment: concentration 40
3% immersion in a nitric acid solution at ~ 50%, 70 ° C → water washing (thickness control by pickling time length) Pickling (nitric acid / water = 1): 20-60 seconds → water washing (thickness by pickling time length) Control) The thickness of the oxide film of the aluminum alloy strip for a wheel rim thus obtained was measured by an Auger electron spectrometer. The measurement results are shown in graphs in FIGS. FIG. 2 shows the case where the entire surface is pickled.
(Oxide layer thickness: 39 mm), FIG. 3 shows the case where only the end faces 12a and 12b are simply masked and pickled (Oxide layer thickness: 283 mm), and FIG. If not
(Thickness of oxide layer: 504 mm).

[Welding Method and Weldability Evaluation Method] The aluminum alloy strip for wheel rim thus obtained was cut into a length of 585 mm to obtain a base material 11, which was wound in a cylindrical shape in the longitudinal direction, After welding using a DC butt welding machine, a rectangular sample having a width of 160 mm, a length of 200 mm, and a thickness of 5 mm was cast from the same type of base material around the welded portion.
0 pieces were cut out and subjected to a bending test.

In the bending test, a 180 ° bending was performed at a bending radius of 5 mm, and the crack occurrence rate was determined. The bending test is an evaluation method under the strictest conditions in consideration of rim forming after welding, and it can be determined that a welded portion that does not generate cracks by the bending test does not generate cracks even during wheel forming.

The DC butt welding conditions employ a two-stage pressurizing method, the first stage pressure is 2 kg / mm ² , and the current is 230 A / mm.
² , and the upset margin was adjusted at the final electrode interval. Note that the initial electrode interval is 25 mm. The DC butt welding was performed by moving amount control, and the switching timing from the first-stage pressing force to the second-stage pressing force was 1 mm. Table 1 shows the results together with the experimental conditions.

[0045]

[Table 1]

As shown in the examples of the present invention of Sample Nos. 1 to 5 in Table 1, the defects caused by the bending test are completely eliminated. From this, according to the example of the present invention, even if the upset allowance is reduced to 3.0 times or less of the plate thickness, high DC butt welding strength can be obtained, and cracks in the weld portion in rim forming after welding can be eliminated. Is understood. Therefore, the improvement of the yield and the reduction of the welding electrode replacement / polishing frequency can both be achieved, and an aluminum alloy plate suitable for use as a wheel rim can be provided.

In the case of sample No. 5, the thickness of the oxide layer was out of the preferred range of the present invention. On the other hand, as shown in Sample No. 6 to Sample No. 8, it is understood that cracking of the welded portion occurs remarkably unless the upset margin is at least four times the plate thickness.

[0048]

[Modification] In the description of the embodiments and examples, the present invention is applied to the wheel rim of a two-piece wheel, but the present invention is not limited to such a form. For example, the present invention can be applied to the annular forming of each of the outer rim and the inner rim of a three-piece wheel including an outer rim, an inner rim, and a disk.

In the description of the embodiments and examples,
Although a 5000 series aluminum alloy was used, the present invention is not limited to a 5000 series aluminum alloy. For example, 6000 series
(Al-Mg-Si based) aluminum alloys and JP-A-6-13
The present invention is equally applicable to other aluminum alloys for wheel rims, such as the aging Al-Mg-Si-based aluminum alloy proposed in Japanese Patent No. 6493.

In the description of the embodiments and examples,
Although the case where DC butt welding is performed is taken as an example, the present invention is not limited to such an embodiment. It is equally applicable to welding used for end face butt welding of aluminum alloy plates for wheel rims, such as flash butt welding.

Further, in the description of the embodiment and the examples, the thickness of the oxide layer 15 is reduced by two-stage pickling using a sulfuric acid solution and a nitric acid solution, but the present invention is not limited to such a form. Instead, any other known means can be used. That is, since aluminum and magnesium are amphoteric metals, the oxide layer can be easily dissolved and reduced in thickness under basic conditions by appropriate means.

[0052]

As described in detail above, according to the present invention, there is no need to change the welding conditions of the conventional welding.
It is possible to secure a high welding strength and obtain a sound joint that does not cause a weld crack in the rim forming after welding, thereby reducing the upset allowance to, for example, three times or less the plate thickness, and improving the yield. It has become possible to provide an aluminum alloy plate for a wheel rim that can improve the frequency of welding electrode replacement and polishing.

That is, the present invention is to provide a novel aluminum alloy plate capable of imparting excellent weld formability that cannot be achieved by an existing aluminum alloy plate. Since it can be mass-produced, the industrial significance of the present invention is extremely remarkable.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating an example of an aluminum alloy plate for a wheel rim according to an embodiment.

FIG. 2 is a graph showing measurement results of Auger analysis of the thickness of an oxide film in Examples.

FIG. 3 is a graph showing a measurement result by Auger analysis of a thickness of an oxide film in an example.

FIG. 4 is a graph showing measurement results of Auger analysis of the thickness of an oxide film in Examples.

FIG. 5 is a longitudinal sectional view showing an example of an automobile wheel.

[Description of sign]

 10 Aluminum alloy plate for wheel rim 11 Base material 12a, 12b End surface 13a, 13b side 14 Surface 15 Oxide layer 16a, 16b Necessary forming area 17 Side surface

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Keiji Sano 3-1-1-12 Minato-ku, Nagoya City Sumitomo Light Metal Industry Co., Ltd. No. 2 Chuo Seiki Co., Ltd.

Claims (1)

[Claims] An aluminum alloy for a wheel rim excellent in weldability, characterized in that at least a part of a surface including a side forming an end face to be welded is provided with an oxide layer having a reduced thickness. Board.