JPS6045272B2 - Chemical conversion coating treatment method for aluminum materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a chemical conversion coating treatment method for an aluminum material, and particularly to a chemical conversion treatment method for forming a coating with excellent corrosion resistance on the surface of an aluminum material.

Recently, heat exchangers such as automobile radiators and car cooler evaporators are made of aluminum or aluminum alloy (hereinafter referred to as aluminum material) in order to reduce their weight.

), but aluminum materials are susceptible to corrosion, especially pitting corrosion, due to water, especially water containing corrosive substances such as heavy metal ions and halogen ions. When such pitting corrosion progresses, it penetrates the liquid passage pipes, and as a result, the heat exchanger becomes unusable. Therefore, many chemical conversion treatment methods using chromium compounds such as chromate and dichromate have been developed as corrosion prevention methods for aluminum materials, such as the BV method, MBV method, and EW method. However, chromium compounds, especially hexavalent chromium compounds such as dichromate, are harmful to the human body, so the chemical conversion treatment method that uses large amounts of these compounds poses problems in terms of pollution and waste liquid treatment. It is now extremely difficult to use it industrially. In addition, there are aluminum clad materials that are coated with aluminum alloy containing zinc etc. as a surface layer as a sacrificial anode, but depending on the type of water, pitting corrosion occurs instead of full-scale corrosion, and pitting corrosion cannot be suppressed. may not be reached.

The present invention was made in order to eliminate the various drawbacks of the conventional methods as described above.Ammonium nitrate, nickel nitrate,
This is a chemical conversion coating treatment method for aluminum material, which is characterized by immersing the aluminum material in an aqueous solution containing lithium nitrate and an alkali metal hydroxide.

In addition to industrial pure aluminum, the aluminum materials used in the method of the present invention include wrought aluminum alloys containing alloying elements such as copper, manganese, silicon, magnesium, zinc, chromium, and nickel. For example 1
5,,25,,35) 1050, 1100, 3003,
5005, 6061, 6063, 7072, 7075,
There are aluminum materials such as 7N01 material.

The treatment liquid used in the method of the present invention contains 0.2-5% by weight of ammonium nitrate, 0.1-2% by weight of nickel nitrate, 4-1% by weight of lithium nitrate, and 2-6% by weight of alkali metal hydroxide. %, particularly ammonium nitrate 0.5 to 2% by weight, nickel nitrate 0.2%
It is preferable to contain up to 1% by weight of lithium nitrate, 5 to 1% by weight of lithium nitrate, and 3 to 5% by weight of alkali metal hydroxide.

Examples of the alkali metal hydroxide include sodium hydroxide, potassium hydroxide, lithium hydroxide, etc., and sodium hydroxide is most preferred. Nitrate ions in the treatment liquid components are
This is to provide an effect of suppressing corrosion caused by alkali metal hydroxide to aluminum material and to help form an oxide film on the aluminum surface. On the other hand, ammonium nitrate and nickel nitrate are used because lithium nitrate and alkali metal hydroxide alone have low treatment capacity. To immerse aluminum materials in the treatment solution, degreasing, cleaning, neutralization, and
An aluminum material that has been pretreated by water washing and drying is immersed in a pretreatment solution at a liquid temperature of 60 to 95°C, preferably 70 to 90°C, for 1 to 1 minute, preferably 2 to 5 minutes, and then washed with water. and then drying.

By applying chemical conversion coating treatment in this way, an oxide film is formed on the surface of the aluminum material and an excellent anti-corrosion effect can be obtained, but if necessary, further sealing treatment with hot water or steam or electrodeposition coating may be performed. Of course it is possible.

Next, the method of the present invention will be explained in more detail with reference to Examples.

Example 1 Thickness 1Wr! n1 size 40w1m x 10'' 3003
After degreasing the aluminum 3 aluminum material with trichlorethylene, it is immersed in a 0.5% by weight aqueous sodium hydroxide solution at a temperature of 70 to 75°C for 1 to 2 minutes, then washed with water, and then soaked in a 1% by weight nitric acid aqueous solution. The aluminum material was pretreated by neutralization and further washing with water.

Next, the aluminum material that had been subjected to the previous four treatments was treated with 1% by weight of ammonium nitrate and 0% by weight of nickel nitrate. % lithium nitrate, 7% by weight of lithium nitrate, 4% by weight of sodium hydroxide, and 87% ion-exchanged water. The aluminum material was subjected to a chemical conversion coating treatment by immersing it in a chemical conversion treatment solution having a liquid temperature of 80'C and having a liquid temperature of 80'C, followed by washing with water and air drying. In this way, chemical conversion coating treatment was carried out.30
03 aluminum material and untreated 3003 aluminum material were each treated with GM corrosive solution (Cu++1ppm1C1
100ppm. ．． HC03-200ppm and SO4
A corrosion test was conducted by immersing the specimen in -300 ppm) for 30 days, and after removing the corrosion products from the test piece, the depth of pitting corrosion was measured using a microscope focusing method.
The results in the table were obtained.

Example 2 A 7072 aluminum material was subjected to chemical conversion coating treatment in the same manner as in Example 1.

The 7072 aluminum material treated with the chemical conversion coating and the untreated 7072 aluminum material were treated with a corrosive solution (200 ppm of Cu..1 ppm of Cu++).
) for 30 days at 8 (generations) to conduct a corrosion test.
After removing the corrosion products from the test piece, the depth of pitting corrosion was measured using a microscope focusing method, and the results shown in Table 2 were obtained.

As is clear from the results in Tables 1 and 2, pitting corrosion was completely suppressed in this test for 300 crucibles.

Regarding 707 crucible, although some pitting corrosion was observed even when chemical conversion treatment was applied, there was a large difference when compared with untreated material, and similarly, a sufficient effect of suppressing pitting corrosion was observed. It was done. As described above, in the method of the present invention, since harmful ROM compounds are not used as the chemical conversion treatment liquid, the treatment of the waste liquid is extremely simple.

Claims (1)

[Scope of Claims] 1. A method for treating an aluminum material with a chemical conversion coating, which comprises immersing the aluminum material in an aqueous solution containing ammonium nitrate, nickel nitrate, lithium nitrate, and an alkali metal hydroxide. 2 Ammonium nitrate 0.2 to 5% by weight in the aqueous solution,
Nickel nitrate 0.1-2% by weight, lithium nitrate 4-12%
% and 2 to 6% by weight of alkali metal hydroxide. 3. The method according to claim 1 or 2, wherein the alkali metal hydroxide is sodium hydroxide. 4. The method according to any one of claims 1 to 3, wherein the immersion treatment is performed at a liquid temperature of 60 to 95°C for 1 to 10 minutes.