JPH1119587A - Surface treating method for aluminum alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure a high corrosion resistance and external appearances in a stable manner, when a corrosion resistant spray coating is performed without using an electrolysis on an alumite, by completely suppressing the formation of cracks in a ground alumite due to the heat of burning. SOLUTION: By the time a hot-water cleaning is conducted before a paint is applied onto an alumite, impurities in pits of the alumite that may cause corrosion are washed and removed. Therefore, water cleaning, water quality for acid cleaning and temperatures after forming an alumite are controlled within a certain range of conditions. And controlling temperatures of hot-water cleaning is important as a counter measure against cracks of ground alumite. Further, in order to completely eliminate occurrence of cracks of the alumite that may cause the deterioration of external appearance and corrosion, burning temperatures for paint are lowered to 80-100 deg.C and semi-hardening paint is used and burning is conducted at low temperatures for a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method in which aluminum and an aluminum alloy are subjected to alumite treatment and then spray-painted.

[0002]

2. Description of the Related Art Hitherto, when aluminum is used in a part where high corrosion resistance and weather resistance are required, alumite treatment alone is not sufficient, and in some cases, coating is performed on alumite. In particular, in an alkaline atmosphere, coating on alumite was indispensable.

[0003] At that time, most commonly, anionic electrodeposition coating on alumite is performed.
Since the temperature becomes as high as about 180 ° C., cracks are formed in the base alumite due to thermal stress, which is a factor inhibiting corrosion resistance.
In particular, in the case of clear coating, cracks were a cause of appearance defects.

As countermeasures against such cracks, the temperature of hot water after alumite is reduced to 80 ° C. or less, or the film thickness is reduced.
For example, there is a method of controlling the thickness to 2 to 7 μm. However, when the hot water washing temperature is lowered, the acid content in the alumite film cannot be completely washed out, resulting in inferior corrosion resistance. Decreasing the film thickness also causes a reduction in corrosion resistance.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a surface treatment method capable of improving appearance quality and corrosion resistance by preventing cracks in an alumite film at the time of coating and firing.

[0006]

When spray coating is performed on an alumite film, an electric conductivity of 30 to 1 is used in order to remove impurities in the alumite pores which are a factor inhibiting corrosion resistance.
Rinse with water of 00 μS / cm, and then perform immersion treatment at 70 to 85 ° C. for 5 to 10 minutes using water having an electric conductivity of 30 μS / cm or less.

Next, in order to completely suppress cracks in the base alumite, which is a factor that hinders corrosion resistance and appearance, coating is performed using a reaction-curable paint. Here, the firing conditions are as follows: a firing temperature of 80 to 100 ° C .;
Firing takes 50 minutes and time.

[0008]

[Example] The material is A6063, size 30 × 200mm
Pretreatments such as degreasing, etching, and pickling were performed by a conventional method using the flat test piece. Later, 15-20w
Using a t% sulfuric acid aqueous solution, the alumite film is 3 μm,
6 μm was formed.

Thereafter, at room temperature, the electric conductivity is 30 to 10
After washing with water at 0 μS / cm, as shown in FIG.
Electrical conductivity After immersion in warm water at 75 ° C. using various types of water, clear coating of a spray-cured acrylic-silicon reactive curing type was performed.

The firing conditions are 150 ° C. × 20 minutes, 80 ° C. ×
The test was performed under the condition of 2/40. And a warm water immersion test (40
° C) and a salt spray test, and the coating quality was compared and evaluated.
The sealing conditions are shown in Table 1, the coating conditions are shown in Table 2, and the evaluation results are shown in Tables 3, 4, 5, and 6.

[0011]

[Table 1] (Condition: 70 ° C. × 5 minutes) (A to D: water, E: nickel acetate 0.5% aqueous solution)

[0012]

[Table 2]

[0013]

[Table 3] The salt spray test is based on JISZ2371. In the water resistance test, after immersion at 40 ° C. × 240 H, a gobang test was performed.

[0014]

[Table 4] The salt spray test is based on JISZ2371. In the water resistance test, after immersion at 40 ° C. × 240 H, a gobang test was performed.

[0015]

[Table 5] The salt spray test is based on JISZ2371. In the water resistance test, after immersion at 40 ° C. × 240 H, a gobang test was performed.

[0016]

[Table 6] The salt spray test is based on JISZ2371. In the water resistance test, after immersion at 40 ° C. × 240 H, a gobang test was performed.

[0017]

According to the present invention, it is possible to apply a coating excellent in corrosion resistance by spraying without using electrolysis on alumite. In addition, since alumite cracks due to heat during firing can be completely suppressed, high corrosion resistance and appearance can be more stably secured. As an additional effect, the paint can be applied by spray painting, so the degree of freedom in color has increased.

Claims (1)

[Claims] 1. A surface treatment method in which aluminum and an aluminum alloy are subjected to alumite treatment and then spray-painted.
Alumite treatment is performed at 50 to 250 A / m ² , and washing is performed with water having an electric conductivity of 30 to 100 μS / cm. Thereafter, immersion treatment is performed in a hot water bath having an electric conductivity of 30 μS / cm or less and a temperature of 70 to 85 ° C. for 5 to 10 minutes, and drying is performed later. A coating method for aluminum and an aluminum alloy, wherein a reactive curing type spray coating of acrylic, urethane, or the like is performed as the subsequent coating, and firing is performed at 80 to 100 ° C. for 30 to 50 minutes.