JP2963808B2 - Manufacturing method of electric Al-Zn alloy plated aluminum alloy sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0101]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric Al which can be plated with an Al--Zn alloy having excellent phosphatability and post-coating corrosion resistance as a base for coating, especially as a base for electrodeposition coating.
The present invention relates to a method for producing a Zn alloy-plated aluminum alloy plate.

[0092]

2. Description of the Related Art In recent years, from the viewpoint of preventing air pollution, improvement in fuel efficiency of automobiles has been called for, and as a part thereof, weight reduction of vehicle bodies has been promoted. In order to reduce the weight of a vehicle body, steel materials have been conventionally made thinner by increasing the tensile strength of steel materials, but recently, the use of aluminum alloy plates has attracted attention. JIS 5000 series (Al-
Mg-Cu) or JIS6000 (Al-Mg-Si)
Wrought materials such as hoods, trunk lids, front and rear fenders are mainly used.

Manufacturing of automobiles using steel materials is usually performed in the order of degreasing, phosphate treatment, cation electrodeposition undercoating, intermediate coating, and topcoating after assembling parts into a vehicle body. However, even when a part of an aluminum alloy plate is partially used, it is manufactured in this step. Therefore,
Phosphating properties are also required for aluminum alloy sheets.

[0093]

However, since the surface of an aluminum alloy plate is covered with an oxide film,
There was a problem that the phosphate treatment was poor and it was difficult to obtain a dense and uniform film. As a result, along with the composition of the aluminum alloy plate, remarkable blister corrosion and thread-like corrosion may occur under the coating film after coating.

Therefore, the present inventors have devised to apply Al—Zn alloy plating as a method for preventing the occurrence of such corrosion. That is, in the phosphate treatment, the object to be treated is eluted with the free acid in the treatment solution, and the phosphate is precipitated by an increase in the pH during the elution, but the Al-Zn alloy has a passivation on the surface. Since the etching property is superior to that of the aluminum on which the film is formed, the phosphating property is improved. In addition, since the Al—Zn alloy has better corrosion resistance than Zn plating, corrosion under the coating film is less likely to occur after electrodeposition coating.

However, there is no suitable method for industrially plating an Al—Zn alloy on an aluminum alloy plate. For example, the hot metal plating method uses an aluminum alloy plate and an Al-
The melting point of the Zn alloy is close and difficult. In addition, the electroplating method cannot be performed from an aqueous plating bath because the potential of Al is lower than that of hydrogen. Furthermore, in the vacuum plating method, the aluminum alloy plate becomes considerably hot due to the heating of the substrate and the heat of condensation of the Al ions, so that the shape is damaged.

007

SUMMARY OF THE INVENTION Accordingly, the present invention provides a method for producing an Al-Zn alloy-plated aluminum alloy sheet by a method capable of industrially plating an Al-Zn alloy on an aluminum alloy sheet. The present inventors have conducted various studies in order to develop a method capable of plating an Al-Zn alloy on an aluminum alloy plate at a relatively low temperature. As a result, the present inventors have developed an electroplating method using a molten salt bath and completed the present invention.

That is, the present invention provides a molten salt bath consisting of (A) an alkali metal chloride-aluminum chloride-zinc chloride or (B) a molten salt bath consisting of (a) aluminum chloride-organic nitrogen-containing onium chloride-zinc chloride. , Zn /
The aluminum alloy plate was immersed in a bath in which the ratio of Al was 0.0015 to 0.035 by mass, and the current density was 0.3 k.
It is characterized in that electrolysis is performed at A / m ² or more, and an aluminum alloy plate is subjected to Al—Zn alloy plating with a Zn content of 3.0 to 50 mass% on at least one surface in a range of 0.2 to 10 g / m ² .

[0099]

When the Al-Zn alloy is applied by electroplating, Zn
Are not segregated, and Zn is uniformly and microscopically dispersed in Al. In the case of a molten salt bath composed of alkali metal chloride-aluminum chloride-zinc chloride, the melting point is 90 to 200.
In the case of a molten salt bath composed of aluminum chloride-organic nitrogen-containing onium chloride-zinc chloride at a melting point of 60 ° C. or less, the shape of the aluminum alloy plate is not impaired by plating.

As the alkali metal chloride in the molten salt bath, L
One or more of iCl, KCl, NaCl and the like may be used, and as the organic nitrogen-containing onium chloride, one or more of alkyl imidazolium chloride and alkyl pyridinium chloride may be used. I just need.

In order to precipitate zinc in the molten salt bath, the ratio of Zn / Al in the bath is set to 0.0 by mass in any of the baths.
015-0.035, and the current density is 0.3 k.
It is necessary to conduct electrolysis at A / m ² or more. These ranges are ranges in which zinc deposition is diffusion-controlled. If the Zn / Al ratio and the current density deviate from the above ranges, the Zn-content in the plating layer is 3.0 to 50 mass% in an Al-Zn alloy. Cannot be plated industrially stably.

FIG. 1 shows an aluminum alloy plate (JIS 606) plated with Al—Zn alloys having different Zn contents.
1, O material, plate thickness of 1.2 mm) is a graph showing the phosphatability and the corrosion resistance after electrodeposition coating (the size of the coating blister width from the cross-cut portion). It can be seen that when the Zn content is 3 mass% or more, the phosphatability is improved. If the Zn content is less than 3 mass%, uniform phosphate crystals do not precipitate due to a small amount of Zn having good reactivity with the phosphating solution.

On the other hand, when the Zn content exceeds 50 mass%,
Corrosion resistance after electrodeposition coating has dropped sharply,
This is because the Al-Zn alloy plating layer having a high Zn content exists under the phosphate layer, and this layer is selectively corroded. Therefore, in the Al—Zn alloy plating, it is necessary to set the Zn content to 3.0 to 50 mass%, and preferably it can be said to be 5.0 to 30 mass%.

In order to improve the phosphatability of the aluminum alloy sheet by the Al-Zn alloy plating, it is necessary to make the coating weight 0.2 g / m ² or more. If it is less than 0.2 g / m ² , the surface cannot be completely covered, and the phosphate crystals become non-uniform. On the other hand, although the phosphatability does not change even if the plating adhesion amount is increased, it is economically disadvantageous to increase it too much, so that at most 10 g / m ² is sufficient.

[0151]

【Example】

Example 1 An aluminum alloy plate (JIS6061, O material, plate thickness: 1.2 mm) subjected to electrolytic degreasing and pickling by a conventional method was subjected to electrolytic activation treatment and electric Al-Zn alloy plating under the following conditions to obtain Zn. Electric Al- with different content and plating weight
A Zn alloy plated aluminum alloy plate was manufactured. Table 1 shows the Zn content in the plating layer.

(1) Electrolytic activation treatment (bath composition) Ethyl methyl imidazolium chloride 507 g / l Aluminum chloride 865 g / l (treatment conditions) Bath temperature 80 ° C. Current density 0.3 kA / m ² Treatment time 15 seconds

(2) Electric Al-Zn alloy plating (bath composition) Ethyl methyl imidazolium chloride 507 g / l aluminum chloride 865 g / l zinc chloride 0.1 to 15 g / l (plating conditions) Bath temperature 80 ° C. Plating solution flow rate 1 0.0 m / s Current density 0.1 to 6.0 kA / m ²

[0182]

[Table 1]

Example 2 The same aluminum alloy plate subjected to electrolytic degreasing and acid washing as in Example 1 was subjected to electrolytic activation treatment under the following conditions,
An n-alloy plating was performed to produce aluminum Al-Zn alloy-plated aluminum alloy sheets having different Zn contents and different amounts of plating. Table 2 shows the Zn content in the plating layer.

(1) Electrolytic activation treatment (bath composition) 294 g / l sodium chloride 153 g / l potassium chloride 1154 g / l aluminum chloride (treatment conditions) bath temperature 230 ° C. current density 0.3 kA / m ² treatment time 15 seconds

(2) Electric Al-Zn alloy plating (bath composition) Sodium chloride 294 g / l Potassium chloride 153 g / l Aluminum chloride 1154 g / l Zinc chloride 0.5 to 20 g / l (Plating conditions) Bath temperature 230 ° C Plating solution Flow velocity 1.0 m / s Current density 0.1 to 6.0 kA / m ²

[0222]

[Table 2]

Example 3 Electric Al—Zn alloy-plated aluminum alloy sheets were manufactured by the manufacturing methods of Examples 1 and 2, and their phosphatability and corrosion resistance after painting were investigated. Table 3 shows the case according to the manufacturing method of Example 1, and Table 4 shows the case according to Example 2. Also,
FIG. 1 shows the effect of the Zn content in the plating layer on phosphatability and corrosion resistance after painting.

(1) Phosphate treatment property An Al—Zn alloy-plated aluminum alloy plate was degreased by a conventional method, and then immersed in a phosphate treatment solution [SD5000, manufactured by Nippon Paint Co., Ltd.] at 40 ° C. for 2 minutes. The phosphate treatment was performed, and the precipitation form of phosphate crystals was observed by SEM observation at a magnification of 1000 times, and evaluated by the following three levels. ○ Precise and uniform phosphate crystals precipitated △ Coarse and uneven phosphate crystals precipitated × Phosphate crystals hardly precipitated

(2) Corrosion Resistance after Painting A cationic electrodeposition paint [Power Top U80, manufactured by Nippon Paint Co., Ltd.] was applied to an electric Al—Zn alloy-plated aluminum alloy plate that had been subjected to a phosphate treatment in the above-mentioned manner by 20 μm. After a cross cut, a salt spray test according to JIS Z 2371 for 1 hour → dry → wet test (50 ° C., 98% relative humidity) for 7 hours → combined corrosion test with dry as one cycle was performed for 50 cycles. The maximum coating blister width from the cross cut was measured.

[0262]

[Table 3]

[0279]

[Table 4]

[0285]

As described above, according to the method of the present invention, Al
Since the -Zn alloy can be applied, an electric Al-Zn alloy-plated aluminum alloy plate having a good shape can be manufactured.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the Zn content of an Al—Zn alloy plated on an aluminum alloy plate, phosphatability, and corrosion resistance after painting.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-57-89493 (JP, A) JP-A-4-72089 (JP, A) JP-T-62-500249 (JP, A) (58) Investigation Field (Int.Cl. ⁶ , DB name) C25D 1/00-3/66 C25D 5/30 C25D 13/00 C25D 13/20

Claims (1)

(57) [Claims] 1. A molten salt bath composed of (A) an alkali metal chloride-aluminum chloride-zinc chloride, or a molten salt bath composed of (B) an aluminum chloride-organic nitrogen-containing onium chloride-zinc chloride. The aluminum alloy plate was immersed in a bath having a Zn / Al ratio of 0.0015 to 0.035 by mass, and was electrolyzed at a current density of 0.3 kA / m ² or more. Rate is 3.0-50m
ass% Al-Zn alloy plating on at least one side 0.2
To 10 g / m ² preparation of electric Al-Zn alloy-plated aluminum alloy sheet, wherein the subjecting.