JPH07232501A - Aluminum alloy member and aluminum wheel - Google Patents

Abstract

PURPOSE:To prevent any decrease in corrosion resistance even when a bed is exposed by a casting defect, the defect of a Cr plated layer or the insufficiency of a plated layer thickness, by applying Cr plating treatment on the material cast with an aluminum alloy, and forming a chromate treated layer on its surface. CONSTITUTION:An aluminum wheel includes a Ni-P plating layer 3, a semi-gloss Ni plated layer 4a, a glass Ni plated layer 4b, a Cr plated layer 5, a chromate treated layer 6 and a clear coating layer 7 formed successively by applying alkali degreasing and formation treatment on the surface of the casting material 2 made of an aluminum alloy (for example, AC4CH material). Furthermore, the Ni-P plating layer is composed of an electroless plating layer, the semi-gloss Ni plated layer and gloss Ni plated layer are composed of an electrolytic plated layer (except the Cr plated layer) and the clear coating layer is composed of a coating layer. These plated layers are excellent in their corrosion resistance and the surface having desired metallic luster can be easily obtained even when there are a casting defect and the defect of a Cr plated layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy member obtained by subjecting an aluminum alloy to a surface treatment, and particularly to an aluminum wheel.

[0002]

2. Description of the Related Art A vehicle wheel has been conventionally made of steel, but recently, for the purpose of reducing the weight of the vehicle and improving its appearance and design, it is made of an aluminum alloy wheel (hereinafter referred to as an aluminum wheel). ) Is increasing the rate of wearing. An aluminum wheel is generally formed with a coating film on its surface in order to improve weather resistance and corrosion resistance.

Further, in recent years, there is an increasing demand for highly decorative aluminum wheels having a Cr plating layer having metallic luster on the design surface. The Cr plating layer is stable in the air, does not discolor, and has a very high Vickers hardness of 800 to 1100, and thus has excellent wear resistance and has an advantage that it is not easily scratched.

[0004]

The material of aluminum wheels is often manufactured by a low pressure casting method or a die casting method using an Al-Si alloy containing 6 to 13% by weight of Si. However, casting defects (pinholes, etc.) for materials cast with aluminum alloys, although they differ in quantity,
It is difficult to eliminate all. When Cr plating is applied to an aluminum wheel having pinholes on the surface of the material, blisters occur at the pinholes, resulting in poor corrosion resistance and the desired aesthetic appearance cannot be obtained.

Further, even if there are almost no pinholes on the surface of the material, defects (pits, cracks, etc.) may occur in the Cr plating layer or the thickness of the plating layer may not be uniform. Even in this case, the corrosion resistance is poor, and a desired aesthetic appearance cannot be obtained. Especially in the case of aluminum wheels, since the shape is complicated, the plating film thickness on the back side of the design surface, the back of the air hole, the back side of the tire surface, etc. tends to be insufficient, so the Al base material itself which is the base of Cr plating May be exposed, and it is difficult to avoid the deterioration of corrosion resistance caused by this.

Therefore, an object of the present invention is to provide an aluminum alloy member, particularly an aluminum wheel, which is excellent in corrosion resistance even when there is a casting defect, a defect of the Cr plating layer, or a portion where the undercoat is exposed due to an insufficient plating film thickness. To provide.

[0007]

[Means for Solving the Problems] The present inventors have studied a Cr plating layer in order to achieve the above object. As a result, when the thickness of the Cr plating layer exceeds 1 μm, cracks are likely to occur. To prevent this, it is desirable to set the thickness to 1 μm or less. It was found that the corrosion resistance and metallic luster of the member are insufficient. As a result of further intensive studies based on such knowledge, it was found that by forming a chromate treatment layer on the surface of the Cr plating layer, the corrosion resistance can be improved without depending on the thickness of the Cr plating layer. did.

Therefore, the present invention is an aluminum alloy member having a Cr plating layer and a chromate treatment layer sequentially laminated on the surface. Further, when the Cr plating layer having a film thickness of 1 μm or less is formed and the metallic luster is insufficient, the metallic luster can be supplemented by forming an electrolytic plating layer such as a Ni plating layer as the base plating.

By forming a coating layer on the surface of the chromate-treated layer, the corrosion resistance can be improved. Further, the corrosion resistance can be further improved by forming the electroless plating layer or the electrolytic plating layer (excluding the Cr plating layer). Further, corrosion resistance is improved by forming two or more electrolytic plating layers (excluding the Cr plating layer) having potential differences with each other as the electrolytic plating layer.

In the present invention, what is desirable from the viewpoint of corrosion resistance and metallic luster is that an electroless plating layer, an electrolytic plating layer, a Cr plating layer, a chromate layer, and a coating layer are sequentially laminated on the surface. Is an aluminum alloy member.

Further, according to the studies by the present inventors, excellent corrosion resistance can be obtained by sequentially forming an electroless plating layer, a Cr plating layer, and a coating layer on the surface of an aluminum alloy.

Therefore, according to the present invention, the electroless plating layer is formed on the surface, and the Cr formed on the surface of the electroless plating layer is formed.
It is an aluminum alloy member having a plating layer and a coating layer formed on the surface of the Cr plating layer. In order to further improve the corrosion resistance, an electrolytic plating layer can be appropriately provided. The electroplated layers have a potential difference with each other, and it is desirable to form two or more layers.

The aluminum alloy member of the present invention is suitable for aluminum wheels because it has excellent corrosion resistance and metallic luster.

Therefore, the present invention is an aluminum wheel having a Cr plating layer on the surface and a chromate treatment layer formed on the surface of the Cr plating layer. Further, it is an aluminum wheel in which an electroless plating layer, a Cr plating layer, and a coating layer are sequentially laminated on the surface. Furthermore, on the surface,
Electroless plating layer, electroplating layer, Cr plating layer,
The aluminum wheel is formed by sequentially laminating a chromate layer and a coating layer.

[0015]

In the aluminum alloy member and aluminum wheel of the present invention, the Cr plating layer and the chromate treatment layer are sequentially laminated on the surface, whereby a casting defect, a Cr plating layer defect, or the plating film thickness is insufficient and the base is exposed. Excellent corrosion resistance can be obtained even if there is a portion that has been damaged.

By forming the chromate-treated layer,
It is considered that the corrosion resistance is improved because it is possible to cover the entire surface including the defective portion. The thicker the chromate layer is, the better the corrosion resistance is, but the golden color of the chromate layer becomes darker in proportion to the thickness of the chromate layer.
Since the metallic luster of the Cr plating layer is impaired, it is desirable to form the chromate treatment layer to the extent that the metallic luster of the Cr plating layer is not impaired. The thickness of the chromate treatment layer is p
It is possible to control the plating conditions such as the composition of the plating solution and the temperature that affect H and the potential. Since the chromate treatment layer is a thin film, it is difficult to measure the film thickness. Therefore, it is desirable to control the amount of chromium deposited corresponding to the film thickness. Cr
In order not to hinder the metallic luster of the plating layer, it is desirable that the amount of chromium deposited on the chromate-treated layer be 20 mg / m ² or less, and more desirable amount of chromium deposited is 1 to 4 mg.
/ M ² or so.

Although the reason is not clear, the chromate-treated layer tends to form a smooth surface without irregularities even when the surface has irregularities, which is desirable from the viewpoint of aesthetics. That is, even if there are some casting defects and defects due to plating before the formation of the chromate treatment layer, the chromate treatment is performed to fill the surface irregularities and obtain a surface without irregularities.

Since the electroless plating layer is applied to fill in defects such as pinholes and pits so that the surface treatment in the subsequent step such as electrolytic plating is uniformly formed, the electroless plating layer is formed before the electrolytic plating layer is formed. It is desirable to form an electrolytic plating layer. The electroplating layer is formed by immersing the casting material in a plating solution, but it is difficult to form in defective parts such as pinholes and pits, and the plating layer is not formed inside the defects and the surface of the defect is apparently formed. To cover. Therefore, the plating solution remains inside the defect and becomes a starting point of corrosion.

When the thickness of the electroless plating layer is less than 5 μm,
Since the effect of filling defects is insufficient, it is preferable to form an electroless plating layer of 5 μm or more. Further, by forming the electroless plating layer of 10 μm or more, the surface of the material can be uniformly coated and the corrosion resistance is improved.
It is desirable to set it as above. If the thickness of the electroless plating layer exceeds 30 μm, the electroless plating layer may peel off due to compressive stress, so the thickness is preferably 30 μm or less. As electroless plating, Ni-P plating, Co-
P plating, Cu plating, etc. are desirable.

The electrolytic plating layer (excluding the Cr plating layer) is
It is applied in order to improve the corrosion resistance by prolonging the time until the corrosion from the pores or cracks present in the Cr plating layer reaches the Al material. It is possible to form an electrolytic plating layer other than the Cr plating layer on the surface of the Cr plating layer, but in the case of an aluminum wheel, a metallic luster is required, so Cr
It is preferably formed as a base of the plating layer. Also, N
If an electrolytic plating layer (excluding the Cr plating layer) such as an i plating layer or a Cu plating layer is formed as a base of the Cr plating layer,
It is possible to compensate for the lack of metallic luster when the thickness of the Cr plating layer is 1 μm or less.

The thickness of the electrolytic plating layer (excluding Cr plating) is preferably 5 to 60 μm. When the thickness is less than 5 μm, it is difficult to uniformly cover the surface with the electrolytic plating layer (excluding Cr plating), a potential difference occurs between the uncoated portion and the electrolytic plating layer, and a local battery is formed, rather reducing corrosion resistance. To do. Further, in order to stably produce in industrial production, it is desirable that the thickness is 10 μm or more. Even if the electrolytic plating layer is formed to have a thickness of more than 60 μm, the effect of corrosion resistance is saturated, the plating takes time, and the cost becomes high, which is not desirable in industrial production.

Further, in order to obtain higher corrosion resistance, it is effective to apply multi-layer electrolytic plating having a potential difference to each other instead of single-layer electrolytic plating. As an example, Cr
Bright Ni plating underneath and semi-bright N underneath
There is a two-layer Ni plating for i plating. The characteristic of these two types of Ni plating lies in the presence or absence of sulfur content. Generally, bright Ni plating contains 0.05% sulfur and semi-bright Ni plating does not contain sulfur. To maximize corrosion resistance,
The ratio of the thicknesses of the bright Ni plating layer and the semi-bright Ni plating layer is preferably 6: 4, and the total thickness is at least 10
It is preferably at least μm.

The anticorrosion mechanism of this two-layer Ni plating is as follows. When corrosion holes caused by pores or cracks in the Cr plating penetrate the bright Ni layer and reach the semi-bright Ni layer, the bright Ni layer containing sulfur has a spontaneous potential with respect to the semi-bright Ni plating layer containing no sulfur. Semi-gloss Ni> Gloss N
Therefore, the bright Ni plating layer is anodized and melts preferentially to prevent corrosion of the semi-bright Ni plating layer. Therefore, it is possible to prevent the corrosion from progressing on the surface of the aluminum alloy.

The coating layer is a non-conductive substance, and since it is unlikely to generate a potential difference that causes corrosion with the substrate, it has an effect of improving corrosion resistance. When forming a coating layer on an aluminum wheel, in order to take advantage of the metallic luster of the Cr plating layer,
Clear coating is desirable. For clear coating, a water-soluble or solvent-type resin coating material such as acrylic resin, polyester resin, melamine resin can be used. The thickness of the coating layer is
8 to 30 μm is desirable. If it is less than 8 μm, the effect of improving the corrosion resistance is not obtained so much, and if it exceeds 30 μm, the effect of improving the corrosion resistance is saturated.

The surface treatment layer of the aluminum alloy member and aluminum wheel of the present invention can be formed as follows. The Cr plating layer is formed under the conditions of a bath temperature of 40 to 60 ° C. and a current density of 10 to 60 A / dm ² using a bath in which chromic anhydride is used as a chromium ion source and a catalyst root such as sulfuric acid is added to the chromium ion source.

The chromate-treated layer can be formed by immersing it in a chromate chromate conversion solution for 2 minutes or more, followed by drying at 80 to 120 ° C. for 10 minutes and then at 150 to 220 ° C. for 10 minutes. Chromate chromate conversion liquid is chromic acid,
Inorganic acids such as sulfuric acid, nitric acid, hydrofluoric acid and phosphoric acid are the main components, and tungsten salts etc. are added as accelerators,
The pH is adjusted to 1.5 to 3.8 before use.

When the Ni-P plating layer is formed as the electroless plating layer, the nickel concentration is adjusted to 4 to 6 g / l with nickel sulfate, nickel chloride or the like, and hypophosphite, a complexing agent, a pH buffering agent, Using reaction accelerator, bath temperature 80-9
It is formed by immersion under the conditions of 5 ° C. and pH 4 to 12. When a bright Ni plating layer is formed as the electrolytic plating layer, the Ni concentration is 40 to 40 with nickel sulfate and nickel chloride.
120 g / l, using boric acid 30-40 g / l, sulfonic acid 2-15 g / l in a bath, pH 3-5,
It is formed under the conditions of a bath temperature of 40 to 70 ° C. and a current density of ^{2 to} 10 A / dm ² .

If a semi-bright Ni plating layer is formed as a base plating layer of the bright Ni plating layer, a multi-layer electrolytic plating layer having a potential difference is formed. In that case, the nickel concentration is adjusted to 40 to 120 with nickel sulfate and nickel chloride.
g / l, using a bath containing 30-40 g / l of boric acid, pH 3-5, bath temperature 45-60 ° C, current density 2-10
It is formed under the condition of A / dm ² . As the coating layer, a water-soluble or solvent-type resin coating material such as acrylic resin, polyester resin or melamine resin is used. A baking process is performed by heating at 30 ° C. for 20 to 30 minutes.

(Embodiment 1) An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a vertical sectional view of an aluminum wheel according to an embodiment of the present invention. FIG. 2 is an enlarged schematic view showing the film structure of the surface treatment layer formed on the surface 2a of the casting material 2 shown in FIG. The aluminum wheel 1 shown in FIG.
As shown in FIG. 3, the casting material 2 and the Ni-P plating layer 3, the semi-bright Ni plating layer 4a, the bright Ni plating layer 4b, the Cr plating layer 5, the chromate treatment layer 6, and the clear coating layer 7 which are sequentially formed on the surface 2a of the casting material 2 are formed. Have. The Ni-P plating layer is an electroless plating layer, a semi-bright Ni plating layer and a bright N plating layer.
The i plating layer is an electrolytic plating layer (excluding the Cr plating layer), and the clear coating layer is a coating layer.

The aluminum wheel 1 can be manufactured, for example, by the following steps. Casting material 2 made of an aluminum alloy (for example, AC4CH material) is subjected to alkali degreasing and chemical conversion treatment. As the chemical conversion treatment,
For example, double zincate treatment can be performed.

Next, the Ni-P plating layer 3 and the semi-bright Ni plating 4 are sequentially formed on the surface 2a of the casting material 2 thus pretreated.
a, a bright Ni plating layer 4b and a Cr plating layer 5 were formed. The Ni-P plating layer 3 was made of nickel sulfate and nickel chloride to have a Ni concentration of 6.8 g / l, a bath temperature of 85 ° C,
A film having a thickness of 10 μm was formed under the conditions of pH 5 and mechanical stirring.

The semi-bright Ni plating layer 4a has a Ni concentration of 80 g / l with nickel sulfate and nickel chloride,
35 g / l of boric acid and 0.2 g / l of butynediol were added, and 30 μm was formed under the conditions of a bath temperature of 50 ° C., pH 4, and a current density of 2 A / dm ² . The bright Ni plating layer 4b has a Ni concentration of 80 g due to nickel sulfate and nickel chloride.
/ L, boric acid 35 g / l, saccharin sodium 8
g / l, butynediol 0.2 g / l were added, and the bath temperature was 2
20 μm was formed under the conditions of 0 ° C., pH 4, current density of 2 A / dm ² , and air stirring. The Cr plating layer 5 uses a bath of chromic anhydride 250 g / l and sulfuric acid 2.5 g / l, and is 0.3 μ under the conditions of a bath temperature of 50 ° C. and a current density of 25 A / dm ^2.
m formed.

The chromate-treated layer was immersed for 2 minutes in a chromate chromate conversion solution containing chromic acid, hydrofluoric acid and a tungsten salt and having a pH of 1.8, and then 100
It was dried at 10 ° C. for 10 minutes and then at 180 ° C. for 10 minutes to form a chromium adhesion amount of 2 mg / m ² . Acrylic resin paint is used for clear painting, and this paint is about 20 μm
20 to 30 at a temperature of about 150 ° C.
A baking treatment was performed by heating for minutes to form a coating layer. Under the above chromate treatment conditions, coloring due to the chromate treatment layer was not seen, and the metallic luster due to Cr plating was maintained. JI is used to evaluate the corrosion resistance of the obtained aluminum wheels.
It was performed according to the Cass test method shown in SH 8617. As a result, it was defect-free in 80 hours in the cass test,
It showed very good corrosion resistance.

For comparison, aluminum wheels are used,
Cass test was conducted in the same manner. The aluminum wheel used was a Ni-P plating layer with a film thickness of 6 μm, a semi-bright Ni plating layer with a film thickness of 30 μm, and a film thickness of 20 on the aluminum alloy surface.
A μm bright Ni plating layer and a 0.3 μm thick Cr plating layer are sequentially laminated. As a result of the cass test, defects such as blister occurred in 50 hours.

Example 2 15 mm × 15 mm × 7 mm
The same surface treatment as in Example 1 was applied to the surface of the aluminum alloy of No. 1 to 3 were prepared, the corrosion resistance was evaluated by the pitting potential, and shown in Table 1. In addition, Ni-P shown in the table
Represents a Ni-P plating layer which is electroless plating. Semi-bright Ni and bright Ni are the two-layer electrolytic plating layer, semi-bright N
The i plating layer and the bright Ni plating layer are shown. Cr represents a Cr plating layer, chromate represents a chromate treatment layer, and clear coating represents a clear coating layer which is a coating film. The thickness of the surface treatment layer is
Ni-P plating layer 10 μm, semi-bright nickel plating layer 3
0 μm, bright nickel plating layer 20 μm, Cr plating layer 0.4 μm, clear coating layer 20 μm.

For comparison, the corrosion resistance was also evaluated for the aluminum alloy (Sample No. 4), which is the base material not subjected to the surface treatment, the chromate treatment layer, and the clear coating layer (Sample No. 5). The evaluation method of corrosion resistance is JIS G
According to the pitting potential measurement method according to 0057. Incidentally, Vc'10 in the table, Vc'100 shows each current density 10 .mu.A / cm ^2, the pitting potential when the 100μA / cm ² (mV).

[0037]

[Table 1]

From Table 1, by performing chromate treatment and / or clear coating on the surface of the Cr plating layer,
Pitting potential (at Vc'100) is only for Cr plating (N
Cr plating + chromate (No. 1) is about 2 times, Cr plating + chromate + clear coating (No. 2) is about 10 times, Cr plating + clear coating (No. 3) It is about 7 times, and it can be seen that chromate treatment and / or clear coating has a great effect on the improvement of corrosion resistance.

(Experimental Example) Since the aluminum alloy member and the aluminum wheel of the present invention may form a Cr-plated undercoat layer, the effect of the chromate-treated layer on the undercoat plating layer was evaluated. 15mm x 15mm x
Electroless Ni-P plating or semi-bright Ni plating was further applied to a 7 mm aluminum alloy base material, and chromate treatment was further applied, and the aluminum elution amount when immersed in 1 M hydrochloric acid for 12 minutes was measured by ICP emission spectrometry. Are shown in Tables 2 and 3. The film thickness in the table is electroless Ni-P
The film thickness of the plating layer or the semi-bright Ni plating layer is shown.

[0040]

[Table 2]

[0041]

[Table 3]

The surface treatment conditions are as follows. The electroless Ni-P plating was performed with nickel sulfate and nickel chloride to a nickel concentration of 6.8 g / l, a bath temperature of 85 ° C,
Formed by mechanical stirring at pH 5. The semi-bright Ni plating has nickel concentration of 80 g / l with nickel sulfate and nickel chloride, boric acid 35 g / l, butynediol 0.2 g / l added, bath temperature 50 ° C., pH 4, current density 2 A / dm ² . Formed below. The chromate-treated layer was dipped in a chromate chromate conversion solution of chromic acid, hydrofluoric acid and tungsten salt adjusted to pH 1.8 for 3 minutes, then at 100 ° C for 10 minutes, then at 180 ° C for 1 minute.
It was dried for 0 minutes and formed so that the amount of deposited chromium was 3 mg / m ² .

Comparing the electroless Ni-P plated layer and the Ni plated layer with a film thickness of 6 μm with and without chromate treatment, the elution amount of Al after chromate treatment was 1/20 with Ni-P plating compared to before chromate treatment. , It was reduced to 1/3 with semi-bright Ni plating, and it can be seen that the corrosion resistance is improved in both cases. Especially, the corrosion resistance of Ni-P plating is remarkably improved. From this result, it is possible to cover the entire surface of the aluminum wheel with a chromate film by performing chromate treatment, and because the electroplating is poor, the film thickness becomes insufficient and corrosion resistance is insufficient. Since the semi-bright Ni plating layer, the bright Ni plating layer, the electroless Ni plating layer and the surface of the aluminum alloy that are exposed to the etc. are covered with the chromate treatment layer, if there is an insufficient plating film thickness, The unblocked pinholes are blocked by the chromate layer to prevent blistering, and the corrosion of the plating layer can be suppressed.

[0044]

According to the present invention, there is provided an aluminum alloy member and an aluminum wheel having excellent corrosion resistance even when there is a casting defect, a defect of the Cr plating layer, or a portion where the underlayer is exposed due to an insufficient plating film thickness. To do.
Moreover, a surface having a desired metallic luster can be easily obtained.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an aluminum wheel showing an embodiment of the present invention.

FIG. 2 is an enlarged schematic view of a surface 2a of the casting material 2 in FIG.

[Explanation of symbols]

1 Aluminum Wheel, 2 Casting Material, 3 Ni-P Plating Layer, 4a Semi-bright Ni Plating Layer, 4b Bright Ni Plating Layer, 5 Cr Plating Layer, 6 Chromate Treatment Layer, 7
Clear paint layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C25D 3/12 101

Claims (11)

[Claims] 1. An aluminum alloy member characterized in that a Cr plating layer and a chromate treatment layer are sequentially laminated on the surface. 2. The aluminum alloy member according to claim 1, which has a coating layer on the surface of the chromate-treated layer. 3. The aluminum alloy member according to claim 1, which has an electroless plating layer. 4. The aluminum alloy member according to claim 1, which has an electrolytic plating layer (excluding a Cr plating layer). 5. The aluminum alloy member according to claim 1, which has two or more electrolytic plating layers (excluding a Cr plating layer) having potential differences from each other. 6. An aluminum alloy member having an electroless plating layer, a Cr plating layer, and a coating layer sequentially laminated on the surface. 7. The aluminum alloy member according to claim 6, which has an electrolytic plating layer (excluding a Cr plating layer). 8. The aluminum alloy member according to claim 6 or 7, which has two or more electrolytic plating layers (excluding a Cr plating layer) having potential differences from each other. 9. An aluminum wheel characterized in that a Cr plating layer and a chromate treatment layer are sequentially laminated on the surface. 10. An aluminum wheel having an electroless plating layer, a Cr plating layer, and a coating layer sequentially laminated on the surface. 11. An aluminum wheel characterized in that an electroless plating layer, an electroplating layer, a Cr plating layer, a chromate treatment layer, and a coating layer are sequentially laminated on the surface.