JPS59583B2 - Pitting corrosion resistant aluminum alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an aluminum alloy having excellent pitting corrosion resistance.

Conventionally, metal aluminum, which generally belongs to the JIS 100O number, has been widely applied in various fields because it has relatively good corrosion resistance, thermal and electrical conductivity, weldability, moldability, etc., and in particular, the metal aluminum The reason why it exhibits extremely good corrosion resistance in neutral environments such as freshwater and seawater is due to the formation of a strong natural oxide film on its surface.

However, if this oxide film inevitably contains impurities or is mechanically scratched, these areas will not be able to exhibit sufficient corrosion resistance, and therefore these areas will be selectively damaged. This often resulted in significant localized corrosion, or pitting.

In particular, this tendency for pitting corrosion occurs when heavy metal ions such as Cu ions are contained in the environment to which metallic aluminum is exposed, and on the other hand, the purity of metallic aluminum is low, and Fe, S
This was noticeable when relatively large amounts of impurities such as i and Cu were contained.

For this reason, when the metal aluminum is used in an environment where there is a risk of pitting corrosion, it is necessary to use an electrochemically base aluminum alloy, such as JI87072 alloy (Al-0, 8-1.3
It has also been proposed to clad the aluminum alloy with 707
2 alloys are prone to uneven corrosion in water, and in this case, local corrosion that penetrates the cladding layer cannot be avoided, which causes the cladding layer to peel off from the metal aluminum. Even if metal aluminum is clad with the 7072 alloy, the anti-corrosion effect will be exhibited only in a narrow area in fresh water where the specific resistance of the solution is high, but it will not be possible to prevent pitting corrosion in environments containing heavy metal ions. It is almost impossible to completely prevent the risk of pitting corrosion occurring in the metal aluminum itself.

From the above-mentioned viewpoint, the present invention provides an aluminum alloy that has the properties of metal aluminum such as good thermal and electrical conductivity, weldability, and formability, and also has excellent pitting corrosion resistance. , purity 99-99.9
Zn: 0.1-0.
By containing 4% by weight, the strength of the natural oxide film with excellent corrosion resistance that had been formed on the surface of the metal aluminum is reduced, and the corrosion form becomes general corrosion, thereby preventing local corrosion and porosity. This aluminum alloy is characterized by its ability to suppress corrosion.

In the alloy of this invention, if the Zn content is less than 0.1%, the desired excellent pitting corrosion resistance cannot be imparted, whereas if the Zn content exceeds 0.4%, uneven corrosion or pitting may occur. Since corrosion occurs and the amount of corrosion increases, the content was limited to 0.1 to 0.4.

Note that this Zn content of 0.1 to 0.4 is all Al.
Since the amount is solid-solved in the aluminum metal, the properties of metal aluminum are not impaired and the pitting corrosion resistance is improved.

Next, the aluminum alloy of the present invention will be explained through examples and in comparison with comparative examples.

EXAMPLE An aluminum alloy of the present invention containing 0.2% Zn (hereinafter referred to as the AA gold alloy of the present invention) was prepared by a conventional melting and casting method. Al, Zn: 0.5%
A comparative aluminum alloy containing Zn (hereinafter referred to as comparative AA gold alloy) and a JIS 7072 alloy containing 1% Zn (hereinafter referred to as conventional A1 alloy) were prepared.

Next, the resulting various Al and A1 alloys were subjected to (a) a 16-hour CASS test, and (b) immersion for one week in a trivalent NaCl aqueous solution at 60°C containing 5 ppm of Cu ions. Retention (hereinafter referred to as Na
CA aqueous solution immersion test), (c) 30° containing 1 ppm Cu ion.
Each of the tests (a) to (c) above was conducted by immersing the sample in tap water of No. C for one month (hereinafter referred to as tap water immersion test).

The test results are shown in the attached table.

As shown in the attached table, the A1 alloy of the present invention showed the amount of corrosion in the CASS test, the NaCA aqueous solution immersion test, and the tap water immersion test, which correspond to severe usage environment conditions, despite taking the form of full-scale corrosion. It shows excellent pitting corrosion resistance without increasing much.

On the other hand, conventional Al shows significant pitting corrosion in all tests, conventional A1 alloy shows significant pitting corrosion except in the CASS test, and pitting occurs in the comparative A1 alloy in the tap water immersion test. It was something.

Since the alloy of this invention has electrochemically less base properties than metal aluminum, the alloy of this invention is clad with metal aluminum instead of JI87072 alloy in order to impart pitting corrosion resistance. You can also use

As mentioned above, the alloy of the present invention exhibits excellent pitting corrosion resistance even when used in any severe corrosive environment without significantly increasing the amount of corrosion.

Claims (1)

[Scope of Claims] A pitting corrosion-resistant aluminum alloy characterized by having a composition containing 0.1 to 0.4% by weight of I Zn, with the remainder consisting of Al and unavoidable impurities.