Etchants for aluminum. Etching aluminum at home How to etch an aluminum part to make it snow-white

I have been looking for a long time for an acceptable method of blackening metal that could be used at home and obtain acceptable blackening quality.

The most affordable option seemed to be to buy a can of matte black paint and paint over the necessary parts. But even this method is not so simple. We need to prepare the environment, and definitely not in the apartment, but at least in the garage. And besides, the paint can be easily scratched.

I will generally keep silent about the anodizing method; it requires increased safety precautions and all sorts of experiments with sulfuric acid do not suit me.

Just recently I learned about the method of blackening with ferric chloride. Purely by chance - one person at the market said that he dips shiny parts in waste from etching printed circuit boards and thus gets a good blackening. I thought, good idea, but in general it is not necessary to look for work, it is enough just to find ferric chloride (FeCl3) and make the same solution.

I found ferric chloride and ordered it online from a private seller on a bulletin board; a 200 g bag cost me about 50 UAH with postage.

I was pleasantly surprised, since ferric chloride is mainly sold for radio amateurs. I myself used to be interested in radio engineering, about 15 years ago, and I thought that now this industry had long been supplanted by Chinese ready-made radio solutions. It turned out that they were not forced out, since there is a supply for ferric chloride, there is also a demand. But I won’t go off topic, further on…

I ink aluminum, duralumin, steel and brass using this method. And I can say that it worked best with aluminum. The duralumin was slightly worse, but acceptable. The steel did not turn black, but became covered with a coating reminiscent of rust, it stopped shining, at least this way, it was still a little better than it was. The brass changed color a little - it became a little redder, stopped shining, became matte, but did not turn black.

Method of blackening aluminum with ferric chloride

I needed to blacken a couple of duralumin rings for macrofur and a couple of aluminum adapters. For such a small number of parts, 15-20 grams of ferric chloride is sufficient.

Ferric chloride in a container for preparing a solution

First you need to dilute it with a small amount of water. For such a small amount of iron, very little water is needed. It is important that the result is a thick mixture. so that it does not spread but is spread on the surface. I did it by eye - the thicker the solution, the better.

While the solution is “infused,” we prepare our parts for blackening. We clean them from possible dirt and dust and degrease them. I just washed them with soap under the tap, that was enough.

Now that the solution is ready, take some kind of stick. for example, for cleaning ears with cotton wool on the tip. and carefully coat the inner surfaces of the adapter. I only ink them, preferring to leave them shiny on the outside. Make sure that the solution remains on the surfaces and does not run off.

Part with ferric chloride solution applied

In my case, the aluminum parts turned black after 7-10 minutes. The duralumin took a little longer to darken, maybe 20 minutes, but I didn’t track the exact time.

The duralumin ring has darkened

As a result, the surface became dark gray and matte. Doesn't glare, which is what we wanted.

If you are not satisfied with the result, you can rinse the parts and go through again with the remaining solution. I did this with duralumin, steel and brass, in the hope that it would turn out better.

Dural began to look noticeably better, steel and brass remained the same. You can also leave them spread for a longer time.

Once blackened, the parts can be washed running water and dry. Then you can use them.

The surface of the same ring after washing and drying. I'm happy with the blackening.

After I blackened the macro bellows ring, which was initially shiny, the contrast in the photos improved a lot, especially when shooting black details with long exposures.

Another aluminum part, blackened using the same method

But what happened to the brass? It didn’t darken at all, but became dull and changed color a little

Here is a relatively simple and high-quality blackening method. I hope that it will be useful not only to me, but also to other enthusiasts.

Etching is a process in which part of the metal is removed from the surface by chemical means. This method is used for final processing of a part, when preparing a workpiece before applying a coating (electroplating), as well as for creating all kinds of drawings, ornaments and inscriptions.

The essence of the method

Metal etching involves careful surface treatment. A protective coating is applied to the product, which is erased in the place of the design. Then either acids or an electrolyte bath are used. Unprotected places are destroyed. How more time exposure, the deeper the etching of metals occurs. The drawing becomes more expressive and clear. Exist various ways obtaining an engraving (inscription): the image itself or the background can be etched directly. Often such processes are combined. Multilayer etching is also used.

Etching Types

Depending on the substance used to destroy the surface of the material, there are following methods etching.

1. Chemical method(it is also called liquid). In this case, special acid-based solutions are used. In this way, ornaments and inscriptions are applied to alloys.

2. Electrochemical etching of metal - involves the use of an electrolyte bath. It is filled with a special solution. Lead salts are also often used to prevent over-etching. This method has a number of advantages. Firstly, the drawing is clearer, and the time required to complete the process is significantly reduced. In addition, this metal processing is economical: the volume of acid used is much less than with the first method. Another undoubted advantage is the absence of harmful gases (the mordant does not contain caustic acids).

3. There is also an ion plasma method (the so-called dry method). IN in this case the surface is minimally damaged. This method is used in microelectronics.

Steel pickling

This treatment is mainly used to remove scale and various oxides. This procedure requires careful adherence to technology, since over-etching of the base metal is undesirable. In the process it is used as chemical method, and electrolyte baths. Hydrochloric and sulfuric acids are used to prepare solutions. All parts require thorough degreasing of the surface. Even a small fingerprint can ruin the workpiece. As protective coating use varnish based on rosin, turpentine, tar. However, it is worth remembering that the components are flammable substances, so preparing the varnish requires great concentration and caution. After the metal processing is completed, the etching process itself occurs. Upon completion, the part must be cleaned of varnish.

Mordants used for steel

Very often, a solution of nitric acid is used for pickling steel. Salt and tartar are also used (with small additions of nitrogen). Hard steel grades are pickled with a mixture of nitrogen and acetic acid. Glyphogen is a special liquid based on water, nitric acid and alcohol. The surface is treated with this composition for several minutes. Then they are washed (a solution of wine alcohol in purified water) and quickly dried. This is pre-etching. Only after such manipulations are the workpieces placed in the etching solution. Cast iron pickles well in a sulfuric acid solution.

Pickling of non-ferrous metals

Copper and alloys based on it are etched using sulfuric, hydrochloric, phosphoric or nitric acids. The process is accelerated by solutions of chromates or nitrates. The first stage is the removal of scale, then the brass is directly etched. Aluminum (and its alloys) are etched in a caustic alkali solution. For casting alloys, nitric and hydrofluoric acids are used. Spot welded workpieces are treated with phosphoric acid. Titanium alloys are also etched in two stages. First - in caustic alkali, then in a solution of sulfuric, hydrofluoric, nitric acids. Titanium etching is used to remove the oxide film before electroplating. Molybdenum is treated with a solution based on sodium hydroxide and hydrogen peroxide. In addition, metals (such as nickel, tungsten) are etched using water, hydrogen peroxide and formic acid.

There are several ways to etch boards. In the first case, water and ferric chloride are used. You can make it yourself. To do this, iron filings are dissolved in hydrochloric acid. The mixture is kept for some time. Printed circuit boards are also etched using nitric acid. The whole process lasts about 10 minutes. At the end of the process, the board must be thoroughly wiped with baking soda, as it perfectly neutralizes the remaining caustic substance. Another etching composition includes sulfuric acid, water, hydrogen peroxide (in tablets). It takes much longer to etch boards with the following composition: hot water, table salt, copper sulfate. It is worth noting that the solution temperature must be at least 40 degrees. Otherwise, etching will take longer. You can also etch boards using direct current. Glassware can be used for this process, plastic container(it does not conduct current). Fill the container with a solution of table salt. It is this that is the electrolyte. You can use copper (brass) foil as a cathode.

Etching process for other materials

A type of glass processing such as etching is currently widespread. Vapors of hydrofluoric acid and hydrogen fluoride are used. First, the surface is acid polished, then a pattern is applied. After these manipulations, the product is placed in a bath with an etching solution. Then the glass is thoroughly washed and cleared of the protective coating. As the latter, you can use a mixture based on beeswax, rosin, paraffin. Etching glass with hydrofluoric acid is used to give it a haze. There is also the possibility of color etching. Silver salts give the surface yellow, red, blue shades, copper salts - green, black, red. To obtain a transparent, shiny pattern, sulfuric acid is added to hydrofluoric acid. If deep etching is necessary, the process is repeated several times.

Pickling safety precautions

Metal etching is a rather unsafe activity that requires a lot of concentration. This is due to working with aggressive materials - acids and their mixtures. First of all, for this process it is necessary to wisely choose a room with good ventilation. Ideal when used for etching pull out drobe. If one is not available, then you need to take care of a respirator to avoid inhaling harmful fumes. When working with acids, you should wear rubber gloves and an apron. Should always be at hand baking soda, which - if necessary - can neutralize the effect of the acid. All etching solutions must be stored in special containers (glass or plastic). Don’t forget about the stickers that will indicate the composition of the mixture and the date of preparation. There is one more rule: jars of acids should not be placed on high shelves. Their fall from a height is fraught with serious consequences. Artistic metal etching is not complete without the use of nitric acid, which is quite caustic. In addition, in some mixtures it can be explosive. Nitric acid is most often used for sterling silver. Etching solutions prepared by mixing acids with water. It is also worth remembering that in all cases the acid is added to the water, and not vice versa.

Etching various parts at home from copper is already quite well known to modellers. But I always didn’t like the fact that the parts obtained using this method most often need to be painted - after all, for example, copper is practically not used in aviation.
How much more interesting it would be, I thought, if the parts were made of white metal, and besides, this metal is literally “lying under your feet.”
I tried many times to etch aluminum from beer cans, but it didn't work out well. However, I finally got a result that allows me to think that not everything is so hopeless.. ;)

The material used was a cut Red Bull Cola can. I read that some modellers prefer Red Bull because the foil on the cans with it is thinner.

The etching solution was the familiar “Mole”, which is often used to remove paint from models.

The protective layer was laser printer toner applied with an iron from a backing sheet of self-adhesive film. This method is well known and I will not describe it in detail.

The aluminum can is coated with a protective layer on both sides. I removed this layer from one side sandpaper.

Why one? Yes, because before that I deleted from both sides. But it’s not for nothing that “Mole” is used to remove paint. It peeled off the protective layer from reverse side which I made with white nitro and I got unpredictable double sided etching instead of single sided

Therefore, I decided to use the transparent protective layer located inside the can on the other side for protection.

The design was transferred to the cleaned surface with an iron and the plate was sent for etching.

At first I etched aluminum with ferric chloride, but I was unable to achieve good results. In the article “Chemical milling of metals” based on materials from the book “The ABC of Ship Modeling” I read: “It is better to etch aluminum and its alloys in a 10-15% solution of caustic soda. It should be remembered that chemical milling occurs very slowly. When the solution is heated to 60- 80° in 20 minutes, a layer of metal with a thickness of only 1 mm will dissolve. After etching, the part is thoroughly washed with water and polished."
Caustic soda in pure form They are unlikely to sell it to you, but “Mole” consists of caustic soda plus some additives. I used dry "Mole" in a bag.

I made a saturated solution (I filled it with water in a bottle so that the powder did not dissolve completely, but remained at the bottom).

ATTENTION! CAUSED SODIUM IS A VERY DANGEROUS SUBSTANCE! THE PRECAUTIONS ARE WRITTEN ON THE PACKAGE AND I WANT TO WARN THAT IT MAY MELT THE BOTTOM OF THE PLASTIC BOTTLE IF DISSOLVED!
Therefore, it is better to use glassware.

After this, fill the mayonnaise jar one-tenth full and add water to make a “10-15% solution of caustic soda.” I placed the jar in an ice cream bucket, into which I poured boiled water to maintain the temperature of the etching solution at 60-80° C.

Etching occurs with the release of gas bubbles. Using them you can easily control the process. I avoided very violent gas formation, since in this case the toner may peel off, and the etching proceeds, as it seemed to me, very unevenly.
If the reaction proceeds very quickly, then you can either dilute the solution more or lower the temperature.

I didn’t monitor the temperature (I was working on a model), periodically adding hot water from the tap, and in about a couple of hours my record began to show through. The drawing was not completely etched, but I didn’t wait for it.

That's why I had the following considerations. Firstly, due to lateral etching, the boundaries of the pattern deteriorate. Secondly, the toner did not adhere well, and etching went through it, which was noticeable by the rare bubbles that formed directly on the painted areas.

Taking out the plate, I washed it in hot boiling water.

After that I washed off the toner

The most commonly used agent for etching aluminum is an aqueous solution of caustic soda with or without additives. It is used for general cleaning where oxide, grease or sub-surface debris must be removed with longer etching times to achieve a glossy or matte finish. It is used in the production of nameplates or decorative architectural elements, for deep engraving or chemical etching. This etching method is quite cheap, but at the same time it can become too complex to perform.

Solutions for decorative etching can contain from 4-10% or more caustic soda, the operating temperature will be 40-90ºC, and it may also be necessary to use a wetting agent to disperse grease and to obtain a light foam coating, as well as to use other additives. Normal operating temperature for cleaning and decorative processing is 60ºС. The figure shows the metal removal rate at various concentrations and temperatures during a 5-minute etching of 99.5% aluminum sheet. These curves apply to a freshly prepared solution, with lower values ​​referring to the period after aluminum is immersed in the solution. Springe and Schwall published data regarding the etching rates of 99.5% pure aluminum sheet extruded 6063 in 10, 15, 20% sodium hydroxide solutions at temperatures ranging from 40 to 70ºC. Chaterjee and Thomas also conducted a detailed study of caustic soda etching of extrusion 6063 and sheets 5005, 3013.

Etching rate of 99.5% aluminum in caustic soda.

Aluminum dissolves in caustic soda, releasing hydrogen and forming a compound aluminate, which exists only in an alkaline solution. The reaction occurring in this case can be written in two ways:

The amount of free caustic soda decreases as the reaction proceeds, along with this the etching rate decreases, electrical conductivity decreases, and viscosity increases. If no caustic soda is added to the bath at all, the reaction proceeds very slowly, but eventually the clear or brownish solution becomes milky white, from which point the etching rate begins to increase again, and grows to a value slightly less than initial etching speed. The reaction observed at this stage can be written as follows:

The formed aluminum oxide hydrate or Gibsite has the form of a suspension, and during the reaction, caustic soda is also released, which is so necessary for the continuation of etching.

Ionic structure of aluminate in solutions having high level pH is a rather complex issue, fortunately the operator is not actually affected by this problem. Moolenaar, Evans and McKeever conducted studies of the infrared and Raman spectra of solutions of sodium aluminate in water and deuterium oxide (heavy water), and they also studied the nuclear resonance spectrum of Na and Al. For aluminum concentrations below 1.5 M, they derived 4 vibration zones, two of which were infrared active at 950 and 725 cm-1, as well as 3 Raman zones active at 725, 625 and 325 cm-1. For aluminum there was also a thin resonance line. All these facts are quite easy to correlate with the existence of tetrahedral Al(OH)4-, which is the main carrier of aluminum in solution.

When the aluminum concentration exceeds 1.5M, a new vibration zone appears at 900 cm-1 for the infrared zone and the Raman zone at 705 and 540 cm-1, while the nuclear resonance zone for aluminum will be significantly expanded without changing position. All these observations can be explained in terms of condensation of Al(OH)4-, with increasing concentration and the formation of Al2O(OH)62-, and in solutions of 6 M sodium aluminate these two forms coexist in parallel. It was found that caustic soda solution, when used continuously, would absorb aluminum until the volume of free caustic soda was reduced to approximately one-quarter of the original volume, after which etching would continue with free caustic soda fluctuating at approximately the same level with amplitude , which depends on temperature, intensity of use and pause period. The hydrate will then slowly settle or crystallize on the bottom and sides of the tank to form a very hard hydrate which is very difficult to remove and unfortunately tends to settle on the surface of the heating coils. Here we observe the third reaction, i.e. dehydrogenation reaction of aluminum hydroxide to form aluminum oxide:

The nature of this transformation is shown in Fig. 4-10, where different amounts of aluminum are dissolved in a 5% (wt) solution of caustic soda, and measurements are carried out on free caustic soda immediately after each addition, as well as after three weeks. Up to 15 g/l of aluminum remains completely in solution without changing the amount of free caustic soda, but as soon as the precipitation of aluminum oxide begins, which occurs shortly before the appearance of a clearly visible precipitate, the free caustic soda is reduced to 4%, i.e. up to 80% of its initial value. With prolonged use, this value for such a solution can range from 1 to 1.5%, sometimes increasing to 2.5% in case of downtime lasting several hours. A similar ratio corresponds to a higher concentration of sodium hydroxide, and these values ​​are virtually independent of temperature.

Effect of dissolved aluminum on free caustic soda.

Another important influence of aluminum is that as the aluminum content increases, the etching rate drops, quite clearly, this is reflected in the figure. In practice, this means that if it is necessary to maintain a constant etching rate, it is necessary to increase the free caustic soda content as the amount of aluminum in the bath increases.

The final reaction in this case will occur between aluminum and water with the release of hydrogen and aluminum. In theory, etching can thus continue indefinitely, with loss of caustic soda occurring only through entrainment. This method of working with an etching tank is indeed applicable in practice, but one must remember that it is necessary to periodically remove the solid hydrate sediment. According to current experience, when operating in this mode, the service life of the tank can be up to 2 years. Filtration of caustic soda solutions has not been as successful due to the fact that very fine sediment tends to clog the filter very quickly, but otherwise no problems have been identified with this technique.

Etching rate in sodium hydroxide 50 g/l, sodium nitrate 40 g/l at 60ºС depending on aluminum concentration.

Chemical control of the solution, used before precipitation or in a stable state after sedimentation, includes determination of total soda and free caustic soda. The content of the latter can be calculated with sufficient accuracy for practical application by titration with hydrochloric acid, which is carried out until the phenolphtoleic indicator loses its color. As an alternative, potentiometric titration can also be proposed. To make up for losses due to entrainment, it is enough to maintain general content caustic soda at a fixed level, since it is not possible to control the fluctuations of free caustic soda in the solution. For an accurate determination, in which carbonate and dissolved aluminum are also taken into account, a more complex calculation method is used, which is given in the table.

One of the most common problems with caustic soda etching is the tendency to cause pitting or "burning" of part or all of the part, which is accompanied by an increase in etching speed of up to 300%. This usually occurs in heavily loaded solutions that are used so intensively that they have no possibility of recovery. In this case, the hydrate crystallizes on the part, which leads to an increase in the intensity of local etching, an increase in temperature and an effect on grain boundaries, which has the properties of acid etching. It is sometimes quite difficult to avoid pitting in this type of solution when attempting to remove the anodic film. If this happens, then it is necessary to lower the temperature.

Thus, it can be seen that, despite the apparent simplicity of the etching process, in practice there can be many competing reactions that must be recognized to obtain a good result. The main factors responsible for etching are the content of free caustic soda in the solution, the presence and amount of additives in the bath, the temperature of the solution, as well as the aluminum content in the solution. The influence of solution composition has already been discussed earlier, but the temperature of the solution has an effect strong influence on the etching speed. This factor can usually be easily controlled, but in practice, due to the exothermic nature of this reaction, it is often necessary to cool the pickling baths, especially when they are in continuous use. Most pickling baths are used at temperatures between 55 and 65ºC, since at more high temperatures Contamination due to etching during transfer may occur, especially for sheet materials.

The boss once set me a task. It is necessary to make a duplicate keyboard to control the machine controller, since the factory one quickly became unusable because it was made of transparent self-adhesive film, onto which a design is applied at the factory.

I work at a small enterprise that produces spices. I am engaged in servicing packaging machines, electrical equipment, local network etc., in short, all the technology, smart and not so smart.
So there you go! After much thought and debate with the boss, I finally convinced him that for our lammer-operators, the keyboard case would be best suited from “alloy gun steel”, :cool:, but in the absence of it we decided to use high-strength aluminium case type 203-125B, dimensions 121x66x35 mm from Pros Kit.

Idea

The milling machine ordered aluminum buttons. The case was purchased from a store. And then the question arose of how to make indelible inscriptions on the buttons and body. I tried to scratch it and fill it with paint. It came out completely "meh"! Can be engraved! So I don’t have a Dremel, but I can’t help but search through friends.

Laziness, my friends, is the most powerful engine of progress. After some thought, I remembered that I had once accidentally dripped ferric chloride onto an aluminum radiator. While I wiped away the drop, there was a stain on the radiator and a small indentation. Yeah...

What if you make a stencil from photoresist and then etch it? The guinea pig was a piece of duralumin plate. Everything turned out great!

Preparing the surfaces

Let's start with preparing the surfaces. First we sand dry with sandpaper No. 80-100, spreading it on a flat substrate, then we remove large scratches with an emery sponge No. 180-200, moistening the surface and sponge with water. From time to time we rinse everything with water.

Rice. 1. Surface preparation.

I was quite happy with this roughness. If desired, you can polish it.

Rice. 2. Case and buttons after polishing.

Rolling photoresist

Next, we measure out the photoresist for the body and buttons.

Rice. 3. Film photoresist.

I can't say anything about the photoresist. I bought it from an online store. All that was indicated: “Film negative indicator photoresist.”

We measure a little with a margin around the edges so that it is convenient to roll. Film photoresist consists of 4 layers: the bottom (it is matte) - polyethylene, then a thin layer of glue, then, in fact, the photoresist itself, and on top there is a glossy protective layer (lavsan). Carefully pry up the matte layer with a needle or scalpel, tear off a strip 5-8 millimeters wide and glue it to the body. It is easier to roll the photoresist along the length of the body.

Yes! One more nuance. It is better to heat the housing over gas to a temperature of approximately 40 degrees. Then the photoresist sticks better. Gradually tearing off the base, we roll the photoresist onto the surface with a hard photo roller, or, at worst, with your finger. We cut off the protruding edges of the photoresist with a file to the body or a sharp knife.

Make sure that no dust particles or air bubbles get under the photoresist. In this place, ferric chloride may get in and there will be a problem. If air bubbles do occur, you can carefully pierce them with a sharp needle and roll them firmly with a photo roller.
We do not remove the top protective layer yet, because the photomask may stick to the photoresist (there have been cases).

Rice. 4. Rolled photoresist.

Making a photo template

Next, use any convenient program to prepare a photo template and print it on transparent film for printers. When printing, we indicate the maximum contrast and minimum brightness, but here you have to try. I have an Epson RX610. The settings are as follows: print quality " Best photo", "Shades of gray", paper type "Epson Matte", brightness: -25, contrast +25.

Photoresist is negative! That is, where there is no paint on the template, the photoresist will glow and will not wash off during development! Be careful.

Rice. 5. Photo template. I use film sparingly. Therefore, I print different projects on one sheet while there is space left.

Illuminate with a UV lamp

We apply a photomask and press it with glass onto the photoresist.

Rice. 6. Preparing for exposure.

Hide the buttons before exposing them. If they light up, you will need to re-roll the photoresist.
We illuminate the photoresist with a UV lamp. Exposure time is about 1 min.

Rice. 7. Photoresist exposure

Rice. 8. After illumination, the contours of the drawing appear.

We illuminate the buttons in the same way. Now you can remove the top protective film photoresist.

We show

Next is development. We prepare a solution for development from: a household glass jar 0.5 l - 1 piece, soda ash (not baking soda) - 0.5 teaspoon, hot tap water - 0.5 l (full jar).
Stir the solution until the soda is completely dissolved. Then we take a not very hard clothes brush, dip it into the solution more often and brush it almost without pressing over the photoresist. The unexposed photoresist is gradually washed off and this is the picture you get:

Rice. 9. Developed photoresist.

We poison in ferric chloride

We cover exposed areas of metal that do not need to be etched (for example, the ends) with colorless nail polish (you can steal it from your wife, like I did). Now we take a photo bath, pour in ferric chloride and throw the body and buttons there with the image DOWN.

Rice. 10. Etching.

The solution immediately begins to bubble. Aluminum displaces iron from the solution and it settles right there, at the site of etching. It should be removed with a soft, unnecessary toothbrush approximately once every 30 seconds. In this case, you need to be careful: chips of the photoresist may appear at the edges of the image. If this happens, immediately rinse, dry and correct the chip with a waterproof marker or the same nail polish. However, the varnish can corrode the photoresist, so be careful.

I etched for about 5 minutes. After etching, I get indentations about 0.5 mm deep.
We remove the photoresist. When making printed circuit boards, photoresist can be removed with a solution of caustic soda (caustic soda) or slightly diluted “Mole” for cleaning sewer pipes. But this is not suitable for aluminum. It darkens on contact with caustic. If the etched recesses are deep, then you can remove the photoresist with an emery sponge and water, if not very deep, then you can throw it in a bowl with acetone or solvent No. 646 or 647 for 15-20 minutes.

Rice. 11. After etching and removal of photoresist.

Final operations

Next we cut out the holes for the buttons.

Rice. 12. The holes are ready.

We seal the outline around the inscription with construction tape. I didn’t have construction tape, so I sealed it with aluminum.