Each of us has come across such a definition as anodizing, which applies, in particular, to aluminum products. This metal in its pure form or its alloys are well suited for the manufacture of various crafts, which is used by many home craftsmen. The metal is lightweight, has high strength and is easy to process. But most valuable, it is resistant to corrosion. Many craftsmen conduct anodizing of aluminum at home.
But why is this done, because the material itself is strong enough and looks good? However, despite all the advantages, he also has weaknesses. And its main drawback is the interaction with air, resulting in an oxidation reaction. This leads to the formation of plaque, which significantly complicates the painting of products. In addition, the very appearance of aluminum is far from perfect. It is for this reason that aluminum undergoes anodization.
What is anodizing?
According to GOSTs, anodizing is called anodic oxidation. The main result of the electrochemical process of anodizing aluminum is the formation of a more durable oxide coating.
The fact is that during the oxidation of the metal, a protective film forms on its surface, which is easily damaged. The whole essence of anodizing is to strengthen this film, and not to apply any coating, which usually happens when chrome plating or galvanizing products. The film is formed from aluminum itself.
The process is very similar to another technology - metal burnishing by oxidation. Not only aluminum products are anodized, magnesium and titanium are also subjected to such protective treatment if necessary.
The need for anodizing and its methods
What can anodizing aluminum at home give metal? First of all, the ability to resist corrosion will increase significantly. Stronger oxide protective film will hold for a very long time and will not peel off.
In addition to this, there are a number of advantages that anodic oxidation technology provides:
- It smoothes the surface of aluminum products, that is, it hides some defects (scratches and damage of a point character, chips, strips) and gives uniformity to the metal.
- Colorful coatings hold on to such metal better due to the acquisition of a matte surface.
- Anodized aluminum profiles feature enhanced protective properties.
- Color anodizing of aluminum gives metal more attractive features.
- Large thickness of the protective film.
- Possibility for various imitations - silver, gold, pearls and more.
As for aniline dyes, there are many options. In addition, anodizing can be performed in various ways:
Consider them briefly below.
Cold anodizing
At home, a cold aluminum anodizing technique is often used. Many companies that offer services in this area also mainly specialize in this method. The operating temperature range is from -10 to +10 degrees, which is why the technique is called cold.
Among the advantages of anodizing aluminum at home in this way, one can distinguish the receipt of a thicker protective coating, which increases the resistance to corrosion.
Only processed products are difficult to process with organic colorful materials. Although the color of the metal will acquire in any case, the shade may be olive, grayish or black.
Hard anodizing
The result of solid anodic oxidation is a particularly strong protective film. Largely due to this, this technology is successfully used on a huge scale:
- industry;
- aircraft industry;
- automotive industry;
- construction.
A feature of solid anodizing of aluminum is the use of several electrolytes at once. In addition to the use of sulfuric acid, a number of other analogues are also involved: oxalic, sulfuric, citric, tartaric and boric. And this is during the process alone, in which the current density gradually rises.
The strength of the protective coating increases due to structural changes.
Color anodizing
The essence of this method is to change the color of the metal. In this case, 4 main methods can be distinguished:
- Adsorption - products are immersed in a special bath or in a coloring solution, heated to the required temperature.
- Electrolytic (black anodizing of aluminum) - initially a colorless film is obtained, after which aluminum products are dipped into acidic saline. Black is widespread in construction, but a slightly bronze shade can also be obtained.
- Interference - the technique is similar to the electrolytic, but it creates a special reflective layer, due to which the color palette is much larger.
- Integral - the essence of this method is the mixing of electrolyte and organic salts.
As you can understand, color anodic oxidation allows you to get a new shade of color, depending on preferences.
Home technology
In industry, metal anodizing is carried out with the participation of sulfuric acid, but it is extremely undesirable to conduct aluminum anodizing at home using it due to the release of a large amount of gas. One has only to form the slightest spark, and then the sad consequences cannot be avoided. The technique itself remains unchanged, but soda is used instead of acid.
But first it’s worth preparing the “equipment”:
- several baths;
- wiring;
- Battery or rectifier (current source);
- rheostat;
- ammeter.
Directly for the process itself, aluminum containers are needed. The other two are needed for the preparation of solutions, for which glass or plastic products are useful.
Alternative Electrolyte Preparation
To prepare solutions for do-it-yourself anodizing of aluminum (soda and salt), you need only warm distilled water. The components for mixing are kept in a ratio of 1 to 9 (soda or salt - water).
The solutions mix well, after which they need to be infused. And after a while they need to be poured into other containers, and try to exclude the ingress of soda sediment. The final result of the procedure will depend on the purity of the solution.
Before the item is processed, it must be cleaned, if necessary, grind the surface and degrease. The film thickness is not more than 0.05 mm, so it can not hide visible defects.
Just before the process, you need to mix the prepared solutions in one container.
Electrochemical process
The dishes in which anodizing will be performed must fully accommodate the workpiece. At the same time, it should not touch the bottom of the container. Any of the convenient options is appropriate here; it’s enough to be smart. The fixing of the part also needs to be well thought out, so traces may remain, which ideally should not be.
According to the technology of anodizing aluminum, the power source is connected as follows: “plus” is supplied to the part, and “minus” - to the bath. The duration of the procedure is at least 30 minutes. A change in color of the product will indicate the end of the process. You can disconnect the battery (usually it is used more often) and take out the part.
The processed product is well washed, and to get rid of the remains of the solution, you can hold it for some time in potassium permanganate. After it, you need to rinse it again in cold and warm water (alternately) and dry it. With the right approach, the part will have a light gray tint, evenly coated over the entire surface. Stains, stains or smudges should be absent.
Final stage
It is necessary to complete the procedure, since the resulting film is characterized by the presence of micropores, which are not good. They need to be closed, for which the part needs to be boiled in distilled water also for half an hour.
Upon completion and if desired, the part can be painted or coated with colorless varnish. Although the metal in the process acquires a natural color, which depends on the composition of the workpiece. Usually shades can vary from green to dark, but aluminum is often anodized in black. To give the part a different desired color, the part is immersed in a solution with aniline dyes (10%).
As you can see, anodizing of aluminum can be performed at home, but of all the methods, only the cold method is available, since it is safer. In addition, there is practically no particular difference between the type of solution (soda or acid), the result will be the same in any case. The main thing is to adhere to the instructions.