JPH0598498A - Method for protecting aluminum surface - Google Patents

Abstract

PURPOSE: To apply a surface of a dark yellowish green color to an Al alloy and to prevent the corrosion of this surface by immersing the Al alloy into an aq. sulfuric acid soln. of a specific concn., then passing the Al alloy through an aq. sodium bicarbonate soln. and immersing the Al alloy in a sodium bichromate bath.

CONSTITUTION: The surface of the Al alloy contg. Mn, V, V, Cr, W, Nb, Ta, SiC, Fe, Si, etc., is washed and is then immersed into a sulfuric acid bath of 20 to 25°C having a concn. of 150 to 250 g/l, a voltage of 18 to 25 volts is impressed for the time up to 30 minutes to the alloy to generate columnar base bodies forming an initial protective level on the alloy surface. The alloy is then moved into a cold water bath and, in succession, the alloy is passed through the inside of the sodium bicarbonate-contg. bath to neutralize the residual sulfuric acid. The alloy is thereafter passed through the cold water bath and is then immersed into the bath contg. the sodium dichromate and surfactant. The sodium dichromate flows into the gaps of the columnar base bodies described above, thereby sealing the pores of the alloy surface against the ambient environment. The sodium dichromate develops the dark yellowish green color on the surface of the alloy by reacting with the alloy.

COPYRIGHT: (C)1993,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for sealing the surface of an aluminum-based alloy to protect it from the ambient environment, and at the same time, developing a false color on the surface of the alloy. Aluminum-based alloys include Mn; V; Cr; W; Nb; Ta and S
It is derived from the combination of Al, Fe and Si with at least one element or compound selected from the group consisting of iC.

[0002]

BACKGROUND OF THE INVENTION Aluminum alloys, which are strong, ductile, and rapidly solidified, are components used in aerospace projects and have replaced many specialty metals. One such aluminum-based alloy is described in U.S. Pat. No. 4,729,790, which alloy retains both strength and ductility at ambient temperatures and temperatures up to 400 ° C. To prevent surface corrosion of such alloys, it is common to coat the surface with some type of protective material. Protected by U.S. Pat. No. 3,625,8
No. 41, No. 3,761,362 and No. 4,571,362
Obtained by anodic coating as described in No. 87. This anodic oxide film, that is, the anodic coating, is colored and formed on the aluminum article by electrolysis. During electrolysis, the article becomes an anode in an aqueous solution containing at least one acid and a metal salt as the electrolyte. The color of the resulting coated article depends on the time of electrolysis and the metal salt used as the electrolyte, as described in US Pat. No. 4,571,287. For example, many outdoor signs, such as those used as highway traffic guide conduits, are green. According to one method of coloring outdoor signs to green, epoxy paint is applied to such signs. This method was acceptable, but after a certain period of time without repainting, the paint will fade due to the effects of the surrounding environment, making it difficult to read the information written on the sign. Or the paint has come off,
The surface will be directly exposed to the surrounding environment. Later, by adding copper ions during anodization, as described in US Pat. No. 4,043,880,
The green color is now available as part of the aluminum protection process. This method of developing a dark green color is acceptable as a method of coloring many aluminum articles used in industry. Unfortunately, the use of copper ions for coloring aluminum articles causes problems when the aluminum articles are used in aircraft fuel control. Therefore, this method of coloring and the use of the anticorrosion effect provided by it are limited to components that are not in contact with the fuel used in the aircraft.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide corrosion protection for aluminum alloys so that components made from rapidly solidified aluminum alloys can be operated in hazardous environments without oxidation. That is. Another object of the present invention is to provide an aluminum alloy by an anodizing process such that the dark yellow-green color imparted to the aluminum alloy is not affected by the corrosive environment under the operating conditions where the temperature reaches 400 ° C. It is to be. These advantages and objectives should become apparent upon reading this specification.

[0004]

Means for Solving the Problems US Pat. No. 4,729,
In an effort to form a corrosion protection system for aluminum-based alloys as described in US Pat. No. 790, the alloys were anodized in a sulfuric acid bath and then neutralized in a cold sodium bicarbonate bath to remove heavy metals. It has been discovered that sealing with a solution of sodium chromate imparts a deep yellow-green color to the alloy. It was unexpected that in any of the baths used to form the anticorrosion system, the article turned a dark yellow-green color in the absence of copper ions. Inspection of the article revealed that a deep yellow-green color was spread over the anodized surface layer formed on the aluminum-based alloy. One advantage of this method of preventing corrosion of aluminum-based alloys is that it gives the aluminum-based alloy a deep yellow-green color during the process of DC electrolysis and sealing without the need to add copper ions to the sulfuric acid bath. is there.

Looking at the strength and stability of the aluminum-based alloy described in US Pat. No. 4,729,790 when exposed to temperatures up to 225 ° C., the mechanical properties and resistance of this alloy are examined. Destructiveness is useful for application in many aerospace equipment components. The strength and stability of this alloy is obtained due to the slower grain coarsening rate of the silicide compared to the dispersoids found in other high temperature aluminum alloys. This alloy is free of coarse needle-like crystals or plate-like intermetallic phases that deteriorate the ductility and fracture toughness of the alloy.
Moreover, because this particular alloy contains iron at a high transition concentration, it has a high volume fraction of silicide and maintains mechanical properties during exposure to high temperatures. In aerospace applications, component corrosion protection is often required to meet operating standards.

For the reasons of simplicity and safety, it was concluded that anodic oxidation by direct current electrolysis in an electrolytic solution would be the best way to prevent corrosion of this alloy. An article made from this aluminum alloy is immersed in an aqueous solution containing a low concentration of sulfuric acid and connected as a cathode to a voltage source. As a result, the anodic oxide film formed on the surface of the aluminum alloy is initially colorless,
When it is immersed in a bath containing sodium dichromate for about 20 minutes, it turns dark yellow green.

[0007]

EXAMPLES Samples of aluminum-based alloys such as those described in US Pat. No. 4,729,790 for the purpose of evaluating the proposed method for carrying out anodizing corrosion protection of aluminum-based alloys. Got The weight percentages of the components of the sample were as follows.

Fe = 8.53; V = 1.2; Si = 1.8; and Al = 88.47 total 100.00

A sample of this aluminum-based alloy, without a coating, when a hard anodized coating is formed according to the generally accepted method of anodizing with sulfuric acid and oxalic acid, and corrosion protection is ensured. For the purpose of evaluation, the case of forming an anodized film according to the principle of the present invention utilizing a sulfuric acid treatment was evaluated. As a result of the treatment, the film formed on the surface of the alloy sample was about 0.0001 ″, that is, 0.00000254 cm. In the sample having the hard anodized film and the sulfuric acid film of the present invention, those films were formed. , Unexpectedly turned dark yellow-green without the addition of any dye or reaction with copper ions, which was previously required to make the surface green.These samples were untreated, i.e. without coating. ASTM B117 and US Mil-A-862 along with exposed surface samples
A salt spray test was performed according to the test procedure specified in the 5E standard. Untreated samples no longer meet the acceptance criteria of the test after 24 hours, but samples with a hard anodized coating and those with a sulfuric acid anodized coating are required to have 336 hours of salt water as required by the test procedure. It did not show any visible effect after being sprayed. The dark yellow-green color was uniform over the entire surface of the anodized film and did not fade during the salt spray test. Moreover, this dark yellow-green color is similar to the camouflage colors used by many military vehicles and facilities to obscure them.

The specific sulfuric acid anodizing method performed on the sample is as follows. The sample is passed through a vapor degreasing chamber of 1,1,1 trichloroethane to remove any oil that has adhered to the surface of the sample after manufacture. After passing through the degreasing chamber, dip the sample in a suppressive alkaline bath,
Further clean the alloy. The alkaline bath contains a detergent product sold under the trade name Aldet. 4-6 oz
/ Gal, that is, 50 to 80 gm / liter of Aldet,
This produces a concentration at which 12 pH should be maintained in the alkaline bath. The temperature of the alkaline bath was kept at 48-60 ° C and the sample was washed for about 5 minutes. After removing the sample from the inhibitory alkaline bath, the sample is rinsed in a water bath to stop the cleaning action and return the alloy to a substantially neutral state. Then Aluton
Soak the sample for 3 minutes in a pickling bath containing a deoxidizer sold under the tradename e) at a temperature of at least 20 ° C. Alutone at a concentration of 10% ± 1% is sufficient to remove any oxides or contaminants that may have adhered to the surface of the alloy during manufacturing or as a result of exposure to the ambient environment. After pickling, the washed sample was immersed in a bath containing sulfuric acid at a concentration of 150-250 g / l at a temperature of 20-25 ° C. At room temperature and at this concentration, working with a sulfuric acid bath is relatively safe. The material was connected to the anode of the voltage source. Zero voltage between anode and cathode
Gradually ramp from 20 volts to 20 volts at a low rate of about 3 volts per minute and maintain this voltage for about 30 minutes. The voltage between the anode and cathode may vary between 18 and 25 volts depending on the time available to generate the columnar substrate on the surface of the alloy. A columnar substrate having a nominal height of 0.00016 inches, or 0.0004 cm, forms an initial level of protection on the surface of this alloy.

Once the substrate is formed, the alloy is removed from the sulfuric acid bath and rinsed in a cold water bath to interrupt the reaction of sulfuric acid with the alloy and terminate columnar substrate formation. Throughout this specification, when the term cold water bath is used, the temperature of the water is below 20 ° C. and when referring to room temperature or hot water baths, it is above 20 ° C. Although the cold water bath effectively removes sulfuric acid from the surface of the alloy, it is possible that some sulfuric acid has entered between the individual columns of the columnar substrate. 40-60 to ensure complete reaction
The sample was passed through a room temperature bath containing sodium bicarbonate at a concentration of gram / liter. After about 1 minute, the sodium bicarbonate would have reacted with and neutralized the sulfuric acid that had accumulated in the interstices of the columnar substrate on the surface of the sample.

Since sodium sulfide is generated as a residue by the reaction of sodium bicarbonate with sulfuric acid, it is washed with the remaining sodium bicarbonate in a warm water bath.
When the sample is removed from this bath, the anodized surface layer is essentially gray.

A gray sample with sodium dichromate,
It was immersed in a bath containing a surfactant. Sodium dichromate at a concentration of 5% adjusted with sodium hydroxide to obtain a pH of 5-6 when maintaining a temperature of at least 90 ° C is sufficient for sealing the columnar substrate. Should be. As the surfactant, a product sold under the trade name of Intravon was used at a concentration of 0.01%. After about 20 minutes, this surfactant reduced the surface tension of the columnar substrate to the extent that sodium dichromate flowed into the gap and filled the surface of the sample and sealed it against the surrounding environment. This bath, consisting of sodium dichromate, surfactant, and water, was orange in color, but when the sample was pulled out of the bath, the color was surprisingly dark yellow-green.

The sample, which had been dark yellow-green when taken out from the sodium dichromate bath, was first placed in a warm water bath below 20 ° C. to remove excess dichromic acid from the columnar substrate that had been subjected to the sealing treatment. The sodium was removed. Then, the sample was immersed in a warm water bath whose water temperature was kept higher than 50 ° C. to raise the temperature of the sample uniformly. Once the desired temperature was reached, the sample was removed from the hot water bath, transferred to a chamber with circulating hot air above 25 ° C. and allowed to air dry.

Using this anodizing method, ASTM B1
The samples were sealed and protected according to the requirements of 17 and Mil A-8625E. Examination of the samples after the salt spray test showed no appreciable weight loss on the samples and no visible corrosion was observed.

In order to confirm the results and the anticorrosion effect of the aluminum-based alloy utilizing this anodizing method, some samples based on the composition described in US Pat. No. 4,729,790 were obtained. However, 11% by volume of silicon carbide was further included in this basic composition. A sample of this alloy was anodized according to the method previously described and subjected to the salt spray test specified in ASTM B117 for the required 336 hours. Upon visual inspection, no corrosion was observed on the sample and no salt weight change as a result of the salt spray test. The thickness of the anodized layer was measured and found to be 0.00016 inches, or 0.0004 cm. The deep yellow-green color was quite uniform throughout the layers of the anodized film, i.e. the coating, of those samples. Also, only the mechanical scraper was used when stripping the coating from the sample.

As described above, the method of anodizing an aluminum-based alloy as described above not only enables corrosion protection, but also does not require the use of dyeing, so that the alloy can be used as a false color for many military vehicles and facilities. Is changed to dark yellow-green that is generally accepted as.

[0018]

By applying the method of the present invention to an aluminum alloy, the alloy can be operated in a harmful environment.

 ─────────────────────────────────────────────────── ───Continued from the front page (72) Inventor Richard J. Yogy Lattesk, Georgia USA 46628 South Bend Hetz Maple Court 3307 Indiana

Claims (2)

[Claims] 1. At least one element selected from the group of elements consisting of Mn; V; Cr; W; Nb and Ta,
A method for preventing corrosion of an aluminum-based alloy composed of Al, Fe and Si and coating a film so as to develop a deep yellow-green color on the entire surface of the alloy, oxides and contaminants adhering to the surface of the alloy. Cleaning the alloy to remove ash; immersing the cleaned alloy in a sulfuric acid bath at 20 ° C. to 25 ° C. having a concentration of 150 to 250 g / liter; Voltage for up to 30 minutes to generate a columnar substrate on the surface of the alloy that forms an initial level of protection against corrosion of the alloy; interrupting the reaction of the sulfuric acid with the alloy, Transferring the alloy from the sulfuric acid bath to a cold water bath in order to effectively terminate the generation of the columnar substrate; sulfur that may remain in the gaps in the columnar substrate and on the surface of the alloy. Passing the alloy through a bath containing sodium bicarbonate to neutralize water; passing the alloy through a cold water bath to remove residual sodium bicarbonate from the interstices of the columnar substrate and the surface of the alloy. The surface of the alloy by immersing the alloy in a bath containing sodium dichromate and a surfactant so that the sodium dichromate flows into the gap and fills the gap. Sealing the environment to the ambient environment and allowing the sodium dichromate to react with the alloy to develop a dark yellow-green color. 2. Mn; V; Cr; W; Nb; Ta and S
A coating is provided to prevent corrosion of an aluminum-based alloy consisting of at least one element selected from the group of elements consisting of iC and Al, Fe, Si, and to develop a deep yellow-green color on the entire surface of the alloy. A step of washing the alloy to remove oxides and contaminants adhering to the surface of the alloy; washing in a sulfuric acid bath at a temperature of 20 to 25 ° C. having a concentration of 150 to 250 g / liter. The step of soaking the alloy which has been made;
Applying a voltage of a volt over a period of up to 30 minutes to generate a columnar substrate on the surface of the alloy that forms an initial level of protection against corrosion of the alloy; interrupting the reaction of the sulfuric acid with the alloy. A step of transferring the alloy from the sulfuric acid bath to a cold water bath in order to effectively terminate the generation of the columnar substrate; removing sulfuric acid which may remain in the gaps of the columnar substrate and on the surface of the alloy. Passing the alloy through a bath containing sodium bicarbonate to soften; passing the alloy through a cold water bath to remove residual sodium bicarbonate from the interstices of the columnar substrates and the surface of the alloy. And; by dipping the alloy in a bath containing sodium dichromate and a surfactant so that the sodium dichromate flows into the gap and fills the gap,
Sealing the surface of the alloy to the ambient environment and allowing the sodium dichromate to react with the alloy to develop a dark yellow-green color.