JPH0544087A - Coating surface preparation method of aluminium die cast product - Google Patents

Abstract

PURPOSE:To remarkably improve corrosion resistance and adhesive strength of the coating film of the Al die cast product by sealing pore in a water solution of ammonium chromate after sulfuric acid anodic oxide coating. CONSTITUTION:As a coating surface preparation, anodizing treatment is executed by electrolyzing to the Al die cast product at 20 deg.C bath temp. with 16V bath voltage and 2A/dm<2> anode current density for 15mins in 15% sulfuric acid. Next, pore sealing treatment is executed at 90 deg.C for 5mins in a water solution containing 60g/l ammonium chromate. After that, the well-known cation electrodeposition coating is executed. As the result, more excellent corrosion resistance and adhesive strength of the coating film than that of any conventional treatment is attained.

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 for coating aluminum die cast products, and more particularly to a method for imparting excellent coating adhesion and corrosion resistance.

[0002]

2. Description of the Prior Art Aluminum die-cast materials have extremely high silicon content of 10% or more, and also contain heavy metals such as copper and zinc, so that they are extremely susceptible to corrosion, and the adhesion of the coating film is poor, particularly When exposed to a corrosive environment, corrosion progresses under the coating and the coating tends to peel off.
There has never been a method to completely prevent corrosion of this material.

The aluminum die cast products are painted to give them aesthetics and corrosion resistance. Known chromate treatments and alumite treatments are known as the surface treatment methods for coating. However, none of the methods can achieve complete corrosion protection and sufficient adhesion of the coating film, and the products treated by these methods can peel the coating film and remove the base metal in a relatively short time in a corrosive environment. Causes corrosion.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a coating base treatment method for imparting complete corrosion resistance and coating adhesion to an aluminum die cast product which itself has poor corrosion resistance and coating adhesion. That is.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in order to solve the above-mentioned problems, and after performing a relatively short time alumite treatment on an aluminum die cast product by a known method, chromium It was discovered that the high degree of corrosion resistance and coating adhesion can be specifically imparted by performing the sealing treatment in an ammonium acid aqueous solution.

First, the sulfuric acid alumite treatment in the present invention will be described. A known method, for example, the working standard of JIS H 9500 can be applied to the sulfuric acid alumite treatment bath and working conditions. In the conventional sulfuric acid alumite treatment, electrolysis in a sulfuric acid bath usually requires 30 to 50 minutes. However, it has been found that even with a relatively short electrolysis time of 3 to 15 minutes, sufficient corrosion resistance and coating adhesion can be obtained after treatment according to the present invention. Of course, electrolysis may be performed for a longer time, but there is no plus in the treatment effect.

Next, the sealing treatment in the present invention will be described. Conventionally, when the alumite treatment is performed as the coating base treatment, the pore sealing treatment is not performed, or the pore sealing treatment is performed in pure water or an aqueous solution of nickel acetate. However, in either case, it was not possible to impart complete corrosion resistance and coating adhesion to the aluminum die cast product. On the other hand, when the sealing treatment is performed according to the present invention, sufficient corrosion resistance and coating film adhesion can be obtained. It is particularly advantageous to carry out the sealing treatment by immersing the solution in an aqueous solution containing 10 to 100 g / liter of ammonium chromate at a temperature of 80 ° C. or higher for 3 to 10 minutes.

The method of the present invention allows for a coating pretreatment that imparts specific corrosion resistance and coating adhesion to aluminum die cast products that is superior to any conventional treatment method. In fact, as can be seen from the examples below, the aluminum die cast products treated by the method of the present invention are
2 after being coated by powder coating or electrostatic coating
It was found that no corrosion occurred even in the combined cycle corrosion test and salt spray test for 000 hours, and that excellent corrosion resistance was exhibited.

[0009]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Example 1 The following experiment was conducted in order to demonstrate the effect of the method of the present invention as a base treatment for cationic electrodeposition coating.

Aluminum die casting alloy JIS-AD
The C12 die-cast product was used as a test piece in the experiment.
The alloy composition was as follows: Si 10.8%,
Cu 2.0%, Fe 0.9%, Zn 0.5%, M
n 0.16%, Mg 0.2%, Ni 0.05%, balance Al test piece 1: (treated in accordance with the present invention) According to JIS-H-9500 alumite working standard
16V bath voltage at a bath temperature of 20 ° C in a 15% sulfuric acid bath,
After electrolysis for 15 minutes at an anode current density of 2 A / dm ² for alumite treatment, 60 g of ammonium chromate /
A sealing treatment was performed by immersing in an aqueous solution containing 1 liter at a temperature of 90 ° C. for 5 minutes. After performing this coating base treatment, cationic electrodeposition coating was performed. As the paint, a cationic electrodeposition paint Power Top U600 (epoxy resin paint) manufactured by Nippon Paint Co., Ltd. was used, and a coating film of 20 μm was applied by a known method.

Test piece 2: (for comparative test) After alumite electrolysis under the same working conditions as for test piece 1 for 40 minutes, it was immersed in pure water at 90 ° C. for 20 minutes for sealing treatment. .. After performing this coating base treatment,
The same cationic electrodeposition coating as that for the test piece 1 was performed.

Specimen 3: (for comparative test) After performing a known chromate treatment using Alodine # 1200, the same cationic electrodeposition coating as that for Specimen 1 was performed.

The coating film of each test piece was provided with a cross cut reaching the base material and subjected to a combined cycle corrosion test.

The test conditions are as follows: Soaking in salt water at 50 ° C for 2 hours 2. Dry at 50 ° C for 1 hour 3. Salt spray 1 hour at 50 ° C 4. Wet exposure One cycle of 50 hours at 1 hour to 6 hours.

The results of each corrosion test are as follows: Specimen 1: After 333 cycles (2000 hours), no swelling of the coating film or corrosion of the base metal was observed, and no abnormality was observed.

Specimen 2: After 167 cycles (1000 hours), a bulge having a width of 6 mm was generated at the cross cut portion, and white rust was observed from the base metal.

Test piece 3: 10 cycles (60 hours)
After that, a coating film having a width of 8 mm was peeled off at the cross-cut portion, and severe corrosion of the base metal was observed.

Example 2 The following experiment was conducted to demonstrate the effect of the method of the present invention as a surface treatment for powder coating.

The aluminum die-cast alloy used in the experiment is the same as in Example 1.

Test Specimen 1: (Treatment in accordance with the present invention) A coating base treatment was carried out in the same manner as in Test Specimen 1 of Example 1, and then powder coating was carried out by a known method. Paint is POWDAX P-6 from Nippon Paint Co., Ltd.
0 (polyester resin paint) was used to obtain a powder coating film having a thickness of 30 μm.

Test Specimen 2: (For Comparative Test) After subjecting to coating undercoating (alumite treatment) in the same manner as for the test specimen 2 of Example 1, the test specimen 1 of Example 2 was subjected to The same powder coating was performed.

Test Specimen 3: (For Comparative Test) A coating base treatment (chromate treatment) was performed in the same manner as for the test specimen 3 of Example 1, and then, for the test specimen 1 of Example 2. The same powder coating was performed.

A cross cut reaching the substrate was put in the coating film of each test piece. The salt spray test was performed by the method of JIS-Z-2371.

The test results are as follows.

Test piece 1: No abnormality was found after 2000 hours of salt spray.

Test piece 2: After 600 hours of salt spray, peeling of a coating film having a width of 3 mm and occurrence of white rust were observed in the cross-cut portion.

Test piece 3: After 120 hours of salt spray, peeling of a coating film having a width of 8 mm was observed at the cross-cut portion, and severe corrosion of the base metal was observed.

[0029]

INDUSTRIAL APPLICABILITY The method of the present invention has the same excellent effects not only for the electrodeposition coating and powder coating shown in the examples but also as a coating base treatment for a coating method such as electrostatic coating. It has been confirmed as a result of an experiment that it exerts The coating surface treatment method of the present invention is capable of imparting complete corrosion resistance and coating adhesion to an aluminum die-cast product which is inherently inferior in corrosion resistance and coating adhesion. It is an excellent invention that contributes to development.

Claims (1)

[Claims] 1. A method for treating a groundwork for coating an aluminum die-cast product, which comprises performing an alumite treatment on a sulfuric acid and then performing a sealing treatment in an aqueous solution of ammonium chromate.