What is the difference between anodized aluminum and regular aluminum - Metals, equipment, instructions
Today, aluminum remains a very important and sought-after material for the manufacture of all kinds of parts, fakes, etc.
You can list a lot of its advantages, for example, light weight, sufficient strength, does not corrode, and is easy to process for further use. But despite all this, many are not attracted by its appearance.
If you have ever tried to paint aluminum, then your attempts may have ended unsuccessfully, because paint sticks to aluminum very poorly. If you use it without paint, then very soon it will become covered with dark spots.
To prevent all this, aluminum anodizing technology was developed. We invite you to consider the question of what anodized aluminum is, what types of it exist, in what areas anodized aluminum is used and whether it is possible to anodize this material with your own hands.
Anodizing - what is it?
Anodizing means anodic oxidation. That is, this is a process as a result of which an oxide coating is formed or appears on the surface of aluminum. As a result of this process, oxidation of the metal occurs. As a result, aluminum becomes invulnerable to negative external influences. That is, the oxidized place becomes much stronger.
Why anodize?
As mentioned above, when aluminum interacts with oxygen, a film forms on its surface. It prevents oxidation. But there is an important nuance here: this natural oxide film is very thin. As a result, it can break through. And to eliminate this, it was decided to anodize the aluminum. As a result, the metal acquires much better technical characteristics.
Thus, anodized aluminum does not corrode. The resulting film is wear-resistant. Over time, this coating will not even peel off. Here it is important to understand one more nuance, why this became possible. Some metals are coated with chromium or zinc. In the case of aluminum, it is not coated with anything. This film forms directly on the metal itself.
So, this procedure is resorted to with the goal of giving the metal a more decorative appearance, for example, a particular shade. It is noteworthy that the anodizing color can be changed. To do this, you should use aniline dyes, which are used when dyeing clothes.
If we talk about industrial technologies, then aluminum is anodized in a 20 percent sulfuric acid solution. As for home conditions, this technology is unsafe, so it is necessary to use another technique.
Application of anodized aluminum
There are many areas of use to achieve completely different goals. Now let's look at them:
Anodizing techniques
Aluminum can be anodized in different ways, at least we will mention two:
Let's look at the important features of each technology.
Warm anodizing
This work is performed at room temperature from 15 to 20 degrees Celsius. The procedure is known to be easily repeatable. With simple manipulations you can get a beautiful result.
However, this method does not allow achieving excellent anti-corrosion protection. When the material comes into contact with an aggressive environment, corrosion may occur. Also, the workpiece will not have good mechanical protection.
For example, the coated material can be easily scratched even with a needle, and sometimes it can be wiped off by hand.
But on the other hand, this coating serves as an excellent basis for further processing of the material. The anodizing process takes place in the following sequence:
Cold anodizing
This means that the anodizing process occurs at temperatures from -10 to +10 degrees Celsius. Thanks to this, much better quality, hardness and strength of the anodic coating can be achieved. The cold process perfectly demonstrates the low rate of dissolution of the outer film. As a result, a thick layer is formed. The situation is completely opposite with a warm process.
So, to achieve such results, it is necessary to create forced cooling conditions. Without this, it will be impossible to create a beautiful and wear-resistant coating. If we talk about the disadvantage of this technology, it is as follows: the surface cannot be painted with organic dyes.
The technological process of cold anodizing of aluminum looks like this:
- The surface is thoroughly degreased.
- The workpiece is mounted in a hanger.
- The anodizing process takes place in the bath until a dense shade is formed.
- Washing is carried out in cold and hot water.
- Next, the process of cooking the workpiece in distilled water occurs. The product is also steamed. These actions allow you to consolidate all the resulting layers.
Think about safety
So, you can perform this process at home, but to do this you should be extremely prudent and follow safety precautions. It's best to do this outdoors. After all, acid is a very dangerous substance. And this is even despite the fact that you will be using a large concentrate of acid.
Important! If it gets on your skin, you will experience unpleasant itching. But if it accidentally gets into your eyes, it can lead to serious consequences.
So, you should use protective clothing, gloves and goggles for work. Plus, always have a solution of soda or a bucket of clean water nearby.
Conclusion
So, here we have learned what anodized aluminum is. We looked at the areas of its use and options on how to do similar work yourself.
In addition to everything, we suggest watching a video that will consolidate all the knowledge gained from this article on how to anodize aluminum with your own hands.
We are confident that you will cope with all the work yourself without outside help.
Previous post
Floor insulation with expanded clay
Next post
DIY porch
Source: https://spb-metalloobrabotka.com/chem-otlichaetsya-anodirovannyy-alyuminiy-ot-obychnogo/
What is the difference between anodized aluminum and regular aluminum?
The properties of the anodic oxide coating on aluminum are unique among other coatings. Therefore, they have found wide application in various aspects of human life.
Anodized aluminum as a base for painting
This was the first industrial application of anodic coatings since the invention of aluminum anodization (in chromic acid) in the twenties of the last century.
This was a standard surface treatment for aluminum (duralumin) aircraft parts and is still specified in standards, such as the modern British military standard DEF STAN 03-24/3.
This combination of an organic coating with a chrome anodic coating gives maximum life to the paint layer on the protective coating and provides protection to the metal even after paint damage.
Sulfuric acid anodic coatings with bichromate filling are also used as a protective layer and a base for applying organic paints. This protective coating has a long service life, including in sea water.
Anodized aluminum - corrosion protection
The unpainted chrome anodic coating has high corrosion resistance, including in salt environments. It is used to protect aluminum aircraft parts from corrosion when they cannot be painted.
Sulfuric acid anodic coatings with hydrothermal filling are widely used for corrosion protection of aluminum structures in marine and industrial atmospheres.
In recent decades, anodic coatings, colorless and colored, have been widely used for external and internal building materials and parts, including windows, doors, building facades, internal partitions and railings.
Military aluminum structures and machine parts, especially those that must withstand long periods of storage and operate in tropical and marine environments, are also most often protected with anodic coatings.
Anodized aluminum in design
Thanks to the ability of anodic coatings to absorb dyes, a wide range of “colored aluminum” is obtained. This method is called absorption and it is widely used for various aluminum products - cast, pressed, stamped.
A more durable color coating - electrolytic - is obtained in various electrolytes, most of them in solutions of nickel, cobalt and tin salts. Its “range” of colors is much narrower than that of the adsorption one, but quite diverse.
Anodized aluminum - clean hands
When using aluminum without an anodic coating, for example, for the manufacture of stairs, chairs, railings or handrails, you can often hear complaints that aluminum leaves gray marks - “gets dirty”.
Anodizing completely solves this problem and is used, for example, for all aluminum parts in trains, buses, trolleybuses and trams. Aluminum knitting needles have gained popularity precisely because of anodization: they no longer stain fingers.
An important role in achieving this property of anodized aluminum is played by filling the pores of the anodic coating.
Anodized aluminum in floodlight reflectors
Sulfate anodizing is used to protect the surface of floodlight reflectors. An initial small loss in reflectivity is considered acceptable as this condition will persist for years, whereas unprotected aluminum will continually corrode and reduce its ability to reflect light. Additionally, anodized aluminum is much easier to clean than regular, bare aluminum.
Anodized aluminum in thermal reflectors
Anodizing has long been used for aluminum heating reflectors - they can be found in every home. Their surface is easy to clean and can withstand even the humidity of bathrooms.
The effectiveness of anodized aluminum as a reflector of thermal radiation is ensured by the fact that the thickness of the anodic coating is only about one micron.
The heat-reflective properties of thicker anodic coatings are used in the manufacture of cooling radiators - “combs” in electronic devices, including every computer. To increase the thermal emissivity of the anodic coating, it is often painted black.
Anodized aluminum to combat friction and wear
The anodic coating is much harder than the base aluminum, so the wear resistance and “anti-marking” of the product are significantly increased. Before hydrothermal hydration of the anodic coating began to be used, its physical filling with oils, waxes and similar substances was widely used.
Filling the anodic coating with lubricating oils has found application in those engineering solutions where constant lubrication is required on given surfaces. This is widely used in aluminum pistons of gasoline and diesel engines. Filling of the anodic coating with graphite suspensions is also used.
Hard anodic coating with a typical thickness of 40 to 60 microns has been successfully used on various machine parts, for example, hydraulic and pneumatic cylinders.
Anodized aluminum as an electrical insulator
Although the anodic coating is a good electrical insulator, the danger of local electrical breakdown due to minor defects limits the use of anodized aluminum wires.
However, anodized aluminum tape has been used for many years for some types of transformers where it is important to reduce their weight.
Anodic oxide coating resists heat much better than organic electrical insulating materials, so it is often chosen for high temperature applications.
Source: https://varimtutru.com/chem-otlichaetsya-anodirovannyy-alyuminiy-ot-obychnogo/
What is anodized aluminum?
The properties of the anodic oxide coating on aluminum are unique among other coatings. Therefore, they have found wide application in various aspects of human life.
Anodized aluminum in floodlight reflectors
Sulfate anodizing is used to protect the surface of floodlight reflectors. An initial small loss in reflectivity is considered acceptable as this condition will persist for years, whereas unprotected aluminum will continually corrode and reduce its ability to reflect light. Additionally, anodized aluminum is much easier to clean than regular, bare aluminum.
What is the difference between anodized aluminum and regular aluminum?
The use of aluminum profiles for decorative finishing of facades and interiors has been used for more than half a century.
A beautiful, ductile and very light metal in a humid atmosphere quickly became covered with a gray coating of oxides.
Preserving the silvery shine and expressiveness of the metal decor turned out to be possible only by applying a special coating.
The appearance of anodized aluminum remained virtually unchanged, the colors became brighter, and corrosion could be forgotten once and for all.
How Anodizing Works
To understand that this is anodized aluminum, you need to look a little more closely at how the protective film is formed.
Most metals are protected either by protectors or insulators made of alloys and compounds that are more resistant to oxygen and moisture.
The anodized protective layer is ordinary oxidized aluminum Al2O3, but not in the form of a soft amorphous microfilm, which is always present on its surface, but as a crystalline structure, with properties reminiscent of corundum or spinel.
Anodized film has the following characteristics:
- Microcrystalline structure;
- The presence of a huge number of pores in the surface layer of the anodized film and a super-dense and durable structure at the base;
- Incredibly strong adhesion of the oxidized layer to the metal.
For your information! If the technological process is strictly followed, there is no clear boundary between the metal and the anodized film. A complex network of microcrystals smoothly transitions into metal without a clearly defined boundary.
What does this mean? This means that an anodized aluminum film will not peel off from the base under any load even after 40 years, while a nickel or paint coating slowly peels off from the aluminum matrix over time.
Depending on the selected conditions for obtaining an anodized surface, the technology allows you to obtain several options for the protective layer.
An ultra-thin oxidized film of an ordered structure with a thickness of 10-25 microns on the surface of an aluminum mirror is not even visible to the naked eye.
However, the thinnest anodized layer on the aluminum mirror makes it possible to protect the metal from oxidation and simultaneously transmit up to 95% of the light flux.
Aluminum anodizing technology
The process of obtaining protective anodized coatings on the surface of aluminum is based on the anodic oxidation of aluminum in an electrolyte solution. Depending on the desired result, three types of electrolytes are used for anodized oxidation:
- Treatment with low currents at constant voltage in a weakly acidic electrolyte;
- Application of anodized coating on dichromate-acid electrolyte;
- Oxidation of aluminum in an alkaline electrolyte.
In all three cases, a protective film is formed due to oxidation, compaction and transformation of oxidized aluminum into a dense crystalline structure. The result is a coating reminiscent of glass microflakes.
For your information! In this case, the dimensions or external dimensions of the part do not change; the anodized metal coating seems to grow deeper into the aluminum until the resulting film breaks the electrical contact.
By changing the acidity and temperature of the electrolytic bath, the current and operating voltage at the anode and cathode, it is possible to obtain anodized aluminum films with very different properties.
With a small amount of current, an elusive patina is formed. It is difficult to feel even when touching the surface of anodized aluminum with your fingers.
The only sign of the presence of a protective film is the uniform color of the metal and the absence of the effect of getting your hands dirty.
Ordinary aluminum, under the influence of sweat and fat secretions from the skin of the fingers, can dissolve to form aluminates of organic acids. As a result, dark gray spots remain on the hands. Therefore, most aluminum products are protected by anodizing.
The essence of the anodizing process
The mechanism of formation of a protective coating on the surface of aluminum is based on the direct transformation of the metal into an oxide with a crystalline structure.
If you simply fix the anode on an aluminum plate, fix the cathode on a carbon electrode, apply voltage and immerse it all in an acidic or alkaline electrolyte, then you will not get an anode film. The metal will simply dissolve in the electrolyte.
In order for a crystalline film to form on the surface of aluminum, high voltages and currents are required.
The process of formation of the anodized layer itself is accompanied by a large release of heat, so the bath with electrolyte must be cooled to several degrees.
The process is so intense that microscopic plasma lights flash on the aluminum plate.
The metal instantly melts, oxidizes, and the pressure firmly seals the electrolyte to the base.
That's why in the photo the anodized film looks like crocodile skin.
The operating modes of the installation for the production of anodized aluminum are not a secret and have long been published in the technical literature.
Practical Applications of Anodized Aluminum
Traditionally, the anodizing process is used to produce several types of oxidized films:
- Ultra-thin microcrystalline coatings with a thickness of 20-25 microns;
- Decorative films made of anodized aluminum;
- Electrical insulation based on crystalline Al2O3;
- Special protective films 1.5-2.0 mm thick.
Aluminum polished to a mirror reflects up to 98% of the light flux, but within a day, due to oxidation, a plaque forms, which turns into a gray film.
Most optical instruments equipped with polished aluminum reflectors are protected by an ultra-thin microcrystalline film of colorless corundum.
The dense, non-porous structure reliably blocks the access of oxygen and water vapor to easily oxidized aluminum, while maintaining 95-97% light transmission. Anodized aluminum film protects 99% of all headlights, high-power flashlights, reflectors and optical devices.
Decorative materials
The anodized aluminum coating has a rather interesting structure. The outer 35-50 micron films are a microporous, sponge-like surface with very narrow and deep pores.
Even a small amount of dye penetrates deeply into anodized aluminum, turning it into a very durable and at the same time bright coating. Colorless microcrystals refract the light falling on the anodized coating, as a result of which the colors become bright and saturated.
The applied paint coating does not fade or lose its intensity.
Most modern paints and varnishes with an iridescent effect are made by adding microscopic flakes coated with oxidized aluminum.
The thinnest film of anodized metal ensures high resistance of the filler to ultraviolet radiation and organic solvents, so the paint does not lose saturation for decades.
The popularity of coatings has increased so much that metal is sprayed onto steel and even cast iron structural parts for subsequent oxidation and anodized protection.
Instead of unsafe zinc coating or very expensive alloy steels, anodized aluminum is widely used today.
For example, a metal facade made of double-glazed windows of a multi-story shopping center would have to be repaired within five years, but with anodized aluminum frames the structure could last for several decades.
Crystalline metal oxide coatings have seriously displaced the most resistant powder and ceramic paints, which were previously widely used to protect facades and structural elements made of aluminum alloys.
Cutting aluminum at home
Special anodized aluminum films
In addition to high decorative qualities, anodized aluminum films have a number of very useful properties. For example, high hardness and wear resistance.
The microcrystalline structure of corundum is practically not afraid of any abrasive.
Sand and cement dust, and even metal carbides and silicides are not able to significantly damage the corundum protection.
Therefore, anodized parts cannot be cleaned with sandpaper or polishing or grinding paste.
A thick layer of crystalline Al2O3 on the surface of rubbing parts increases the service life of any mechanism by two to three times.
Protection made of oxidized aluminum is used for high-temperature painting of wheel rims, suspension elements of quarry machines and long-haul equipment.
Application of anodized aluminum coating:
- Does not degrade under the influence of frost, heat, ultraviolet radiation or chemically active substances, withstands direct contact with acids, alkalis, and organic solvents;
- Does not generate dust and does not wear out during repeated washing, cleaning, or under abrasive loads;
- There is no filamentary or gaseous form of corrosion; if the anodized aluminum layer is manufactured in compliance with the technology, then the service life of the coating can easily reach 60-80 years.
Source: https://steelfactoryrus.com/chem-otlichaetsya-anodirovannyy-alyuminiy-ot-obychnogo/
What is anodized aluminum - yourdomstroyservis.rf
New Year's Promotion: When ordering a log house, you receive a 3*3 meter log bathhouse as a gift. The promotion period is limited, Hurry!
Today, aluminum remains a very important and sought-after material for the manufacture of all kinds of parts, fakes, etc. You can list a lot of its advantages, for example, light weight, sufficient strength, does not corrode, and is easy to process for further use. But despite all this, many are not attracted by its appearance.
If you have ever tried to paint aluminum, then your attempts may have ended unsuccessfully, because paint sticks to aluminum very poorly. If you use it without paint, then very soon it will become covered with dark spots. To prevent all this, aluminum anodizing technology was developed.
We invite you to consider the question of what anodized aluminum is, what types of it exist, in what areas anodized aluminum is used and whether it is possible to anodize this material with your own hands.
Anodized coating: what is it, where is it used, how is it made
Anodizing is an electrolytic process that is used to increase the thickness of the layer of natural oxides on the surface of products. This technology got its name because the material being processed is used as an anode in an electrolyte. As a result of this operation, the material's resistance to corrosion and wear increases, and the surface is prepared for the use of primer and paint.
The application of additional protective layers after anodizing the metal is carried out at a much higher quality compared to the original material. The anodized coating itself, depending on the method of its application, can be porous, easily absorbing dyes, or thin and transparent, emphasizing the structure of the original material and reflecting light well. The formed protective film is a dielectric, that is, it does not conduct electric current.
Why is this done?
Anodized coating is used where it is necessary to provide protection against corrosion and avoid increased wear in the contacting parts of mechanisms and devices. Among other methods of surface protection of metals, this technology is one of the cheapest and most reliable.
The most common use of anodizing is to protect aluminum and its alloys. As is known, this metal, having such unique properties as a combination of lightness and strength, has an increased susceptibility to corrosion.
This technology has been developed for a number of other non-ferrous metals: titanium, magnesium, zinc, zirconium and tantalum.
The process under study, in addition to changing the microscopic texture on the surface, also changes the crystal structure of the metal at the interface with the protective film. However, with a large thickness of the anodized coating, the protective layer itself, as a rule, has significant porosity. Therefore, to achieve corrosion resistance of the material, additional sealing is required.
At the same time, a thick layer provides increased wear resistance, much greater compared to paints or other coatings, such as spraying. As the strength of the surface increases, it becomes more brittle, that is, more susceptible to cracking from thermal and chemical influences, as well as from impacts.
Cracks in the anodized coating during stamping are by no means a rare occurrence, and the developed recommendations do not always help here.
Invention
The first documented use of anodizing occurred in 1923 in England to protect seaplane parts from corrosion. Initially, chromic acid was used. Later, oxalic acid was used in Japan, but today in most cases, classic sulfuric acid is used in the electrolyte to create an anodized coating, which significantly reduces the cost of the process. Technology is constantly being improved and developed.
Anodized coating is done to improve corrosion resistance and prepare for painting. And also, depending on the technology used - either to increase roughness or to create a smooth surface.
At the same time, anodizing in itself is not capable of significantly increasing the strength of products made from this metal.
When aluminum comes into contact with air or any other gas containing oxygen, the metal naturally forms an oxide layer 2-3 nm thick on its surface, and on alloys its value reaches 5-15 nm.
The thickness of the anodized aluminum coating is 15-20 microns, that is, a difference of two orders of magnitude (1 micron is equal to 1000 nm). Moreover, this created layer is distributed in equal parts, relatively speaking, inside and outside the surface, that is, it increases the thickness of the part by ½ the size of the protective layer.
Although anodizing produces a dense and uniform coating, microscopic cracks in the coating can lead to corrosion. In addition, the surface protective layer itself is subject to chemical decomposition due to exposure to an environment with high acidity levels.
To combat this phenomenon, technologies are used that reduce the number of microcracks and introduce more stable chemical elements into the oxide composition.
Application
Processed materials are used very widely. For example, in aviation, many structural elements contain aluminum alloys under study, and the situation is the same in shipbuilding. The dielectric properties of anodized coating predetermined its use in electrical products.
Products made from processed material can be found in various household appliances, including players, flashlights, cameras, and smartphones. In everyday life, anodized iron coating is used, or rather, its soles, which significantly improves its consumer properties. When cooking, you can use special Teflon coatings to prevent food from burning.
Usually such kitchen utensils are quite expensive. However, an uncoated, anodized aluminum frying pan can provide a solution to the same problem. At the same time, with less money spent. In construction, anodized profiles are used for installation of windows and other needs.
In addition, multi-colored parts attract the attention of designers and artists, and they are used in various cultural and art objects around the world, as well as in the manufacture of jewelry.
Technology
To carry out work on an industrial scale, special galvanic workshops and production facilities are created, which are considered “dirty” and harmful to human health. Therefore, recommendations for carrying out the process at home, advertised in some sources, should be taken with extreme caution, despite the apparent simplicity of the technologies described.
An anodized coating can be created in several ways, but the general principle and sequence of work remain classic.
In this case, the strength and mechanical properties of the resulting material depend on the original metal itself, the characteristics of the cathode, the current strength and the composition of the electrolyte used.
It must be emphasized that as a result of the procedure, no additional substances are applied to the surface, and the protective layer is formed by transforming the original material itself. The essence of galvanics is the effect of electric current on chemical reactions. The whole process is divided into three main stages.
First stage - preparation
At this stage, the product undergoes thorough cleaning. The surface is degreased and polished. After which the so-called etching occurs. It is carried out by placing the product in an alkaline solution and then moving it into an acidic solution. These procedures are completed by washing, during which it is extremely important to remove all chemical residues, including hard-to-reach areas. The final result largely depends on the quality of the first stage.
Second stage – electrochemistry
At this stage, the anodized aluminum coating is actually created. The carefully prepared workpiece is hung on brackets and lowered into a bath of electrolyte, positioned between two cathodes. For aluminum and its alloys, cathodes made of lead are used.
Typically, the electrolyte contains sulfuric acid, but other acids can also be used, for example, oxalic, chromic, depending on the future purpose of the processed part.
Oxalic acid is used to create insulating coatings of different colors, chromic acid is used to process parts that have a complex geometric shape with small diameter holes.
The time required to create a protective coating depends on the temperature of the electrolyte and the current strength. The higher the temperature and lower the current, the faster the process. However, in this case the surface film turns out to be quite porous and soft.
To obtain a hard and dense surface, low temperatures and high current densities are required. For sulfuric acid electrolyte, the temperature range is from 0 to 50 degrees, and the specific current strength is from 1 to 3 Amperes per square decimeter.
All parameters for this procedure have been worked out for years and are contained in the relevant instructions and standards.
Third stage - consolidation
After electrolysis is completed, the product with an anodized coating is fixed, that is, the pores in the protective film are closed. This can be done by placing the treated surface in water or in a special solution. Before this stage, effective painting of the part is possible, since the presence of pores will ensure good absorption of the dye.
Development of anodizing technologies
To obtain a super-strong oxide film on the surface of aluminum, a method was developed using a complex composition of various electrolytes in a certain proportion in combination with a gradual increase in electric current density. A kind of “cocktail” of sulfuric, tartaric, oxalic, citric and boric acids is used, and the current strength gradually increases fivefold in the process. Due to this effect, the structure of the porous cell of the protective oxide layer changes.
Separately, mention should be made of technologies for changing the color of an anodized object, which can be done in different ways. The simplest is to place the part in a solution with hot dye immediately after the anodizing procedure, that is, before the third stage of the process.
The dyeing process using additives directly into the electrolyte is somewhat more complicated.
Additives are usually salts of various metals or organic acids, which make it possible to obtain a wide variety of colors - from absolutely black to almost any color from the palette.
Source: https://FB.ru/article/474539/anodirovannoe-pokryitie-chto-eto-gde-primenyaetsya-kak-izgotavlivaetsya
Types of finishing
During protective anodizing, a layer of oxide film up to 10 microns is grown on the surface of aluminum. As a rule, this type of anodizing is used as a “temporary” coating to protect the surface from mechanical damage and corrosion for further powder painting of the surface of the product.
Decorative anodizing
This type of anodizing is most often used for products that are used indoors. This can be: frame elements of cabinet furniture, handles and guides of sliding wardrobes, showcases, commercial equipment, navigation signs, etc.
The oxide film has a thickness of 10-15 microns and well protects the surface of the product from mechanical damage and corrosion. The main feature of decorative anodizing is the rich and respectable appearance of the surface. There are two types of surface coating: matte and glossy.
To give the surface a matte tint, the product goes through a stage of preliminary surface preparation with fine shot and then goes to the anodizing line. A glossy surface is achieved without pre-treatment. To obtain the required shade, special dyes are used.
The most common shades are “Gold”, “Silver”, “Champagne”, “Bronze”, “Cognac” and “Black”.
Architectural anodizing
Architectural anodizing produces a finish that is harder than glass, meaning it is less susceptible to damage, wear, and can be sanded down if necessary to restore its original shine.
Advantages of anodized aluminum in architecture:
Aesthetics
The clear oxide layer highlights the rich metallic appearance of the aluminum rather than hiding it like paint. The oxide layer, unlike powder painting, does not flake off or peel off.
Corrosion resistance
The oxide layer is resistant to corrosion and this is one of the most important advantages of anodized aluminum.
The aluminum oxide layer is durable, hard and self-renewing because aluminum spontaneously forms a thin but effective protective oxide layer that prevents further oxidation or corrosion when mechanically damaged.
Anodized aluminum will not patina like copper and zinc, and will not rust like steel. It is an excellent material for use in marine and coastal environments.
Anodized aluminum is highly weather resistant, even in many industrial environments where other metals often corrode. The main pollutants in urban environments are carbon monoxide and carbon dioxide, which do not affect anodized aluminum surfaces.
Durability
Featuring a highly durable and abrasion-resistant oxide layer, anodized aluminum is strong enough to withstand harsh and hostile climates.
Resistance to mechanical damage
Aluminum oxide is a very hard compound, ranked second only to diamond on the Mohs scale of mineral hardness. Therefore, the anodized aluminum surface provides excellent scratch and abrasion resistance.
No peeling
Anodizing is an electrolytic process that converts the surface of a metal into an oxide layer integrated into the metal itself. It is not a coating applied to metal surfaces. Consequently, there is no risk of destruction of the anode film associated with processes such as dusting, the formation of bubbles, cracks, chips or peeling.
No fading
Shades such as silver, champagne, bronze, gold and black do not contain organic elements. These coatings do not fade throughout their entire service life.
No dust
Dusting is the formation of a fine powder on the painted surface of a film under the influence of atmospheric phenomena (grains of sand carried by the wind). It can cause significant deterioration in surface appearance with reduced gloss, surface gloss and color.
Anodized aluminum is not subject to this problem: it is resistant to negative environmental influences and is equally stable in hot (desert), sea or humid climates.
No filamentous corrosion
Filiform corrosion is an attack on the hidden area between the aluminum and the paint layer, causing corrosion to spread beneath the paint layer.
When anodizing, the anodic (oxide) layer is integral with the aluminum, and the interlayer layer is simply absent. This means that the coating will never be subject to thread-like corrosion.
Moreover, in the event of surface damage from an impact or puncture, aluminum will simply restore itself through natural oxidation.
Uniform coverage
When anodizing, the product is completely immersed in the bath, which ensures uniform coverage of the surface with an oxide film.
Hard Anodizing
Coating thickness up to 50 microns.
Hard anodizing is anodizing to produce a coating that is primarily intended to provide high wear resistance or microhardness.
Advantages:
- High resistance to abrasion;
- high corrosion resistance;
- high hardness;
- high resistance to electrical breakdown;
- high temperature resistance;
- excellent thermal insulation properties.
Application:
- Pneumatic and hydraulic cylinders;
- pistons;
- Automotive industry;
- aviation and aerospace industry;
- defense industry.
Chemical polishing
Coating thickness from 5 to 25 microns
Chemical polishing is a pre-treatment of aluminum before anodizing to obtain a decorative effect of a mirror or polished surface. During the chemical polishing process, the top layer of metal is dissolved. When dissolved, all micro-irregularities are removed and the surface of the part becomes shiny. Aluminum profiles and chemically polished parts are actively used in many areas of industry, including furniture.
Organic dyeing
Coating thickness from 5 to 25 microns.
Organic coloring is a technological process of applying various dyes to the anodized surface of aluminum. Organic dyeing produces a wider range of colors than conventional anodizing.
Oxide films on aluminum and its alloys obtained by electrochemical anodization are characterized by high adsorption capacity. They absorb and retain mineral salts and organic compounds – dyes – well. Organic dyes color the film by adsorbing in its pores, mainly along their outer part.
The most suitable organic dyes for coloring are oxide films formed in a sulfuric acid electrolyte. The purest tones are obtained by painting oxide films on aluminum and its alloys with magnesium or manganese.
When oxidized, casting alloys such as silumin form a dark, spotted film, which cannot be painted in light colors and obtain a uniform color. Organic dyeing is used in the automotive, shipbuilding, aviation and furniture industries.
Source: http://www.aluminas.ru/projects/the-decorative-processing/the-types-of-finishing/
Anodizing aluminum at home - Metalworker's Guide
- Characteristics
- Process
- Materials
- Aluminum
- Titanium
- Steel
- Copper
- Anodizing at home
In the modern world there are a large number of methods for processing metals and metal products. They are used both on an industrial scale and at home.
Anodizing Characteristics
Anodizing is a procedure for forming an oxide film on the surface of various metals by anodic oxidation. The growth of the oxide film is carried out in a conducting medium. This film adheres quite well to the metal surface.
The growth of the oxide film can also be carried out using the method of increasing the temperature regime. However, it turns out to be low in strength and does not last for a long time. Thanks to the electrochemical method of forming the oxide film, it is of optimal thickness and adheres well to the surface of the material.
Different types of metals can be anodized. The main requirement is that they must be able to form only one oxide. It must have the maximum level of stability. If a metal has the ability to form several oxides at once, this can lead to the film simply starting to crack and no protective effect appearing. It is for this reason that cases of anodizing iron or copper occur only at rare industrial facilities.
In addition, the oxide film on the surface of metals must have a porous structure. This is necessary so that electrolytes penetrate into it better. As a result, it turns out that only a small part of all metals on earth can satisfy these parameters. These include aluminum, tantalum, titanium. In the industrial and domestic spheres, the most common treatment is anodizing aluminum material.
Anodizing process
The technology for anodizing various types of metals is simple. The main thing is to have at hand everything you need to implement it.
It is carried out in several stages:
- Preparation of metals for the formation of an oxide film.
At this stage, preparatory work for anodizing is carried out. They consist of thoroughly cleaning and washing the metal surface. First, all dirt and deposits are removed. Then the material is washed using water or special solutions. After this procedure it must be dried.
At this stage, a solution with an acidic or any other medium is prepared and connected to the positive plus of the current source.
- Coating the surface of metals or their alloys with an oxide film.
At this stage, the metal or product made from it is immersed in the prepared solution.
Anodizing materials
Today, various metal materials are used for anodizing.
Currently, the following types of anodizing are distinguished depending on the materials used, such as:
Aluminum anodizing
This process is most common today. It consists of coating an aluminum material with an oxide film. In the process, aluminum is lowered into an acidic environment, and the positive plus of the current source is passed to it. As a result, a thin oxide film appears on the material.
Titanium anodizing
Everyone knows that titanium belongs to the category of metals that are widely used in industry, but they have a low level of wear resistance. To give it strength and resistance to different environmental conditions, an anodizing procedure is used. In this case, all anodic processing of the metal is carried out in an acidic environment at a temperature of 40 to 50 degrees Celsius.
Anodizing steel
Anodizing steel is a complex process. For this, either an alkaline or acidic medium is used. As a result, an oxide film is formed, which imparts a high level of strength.
Copper anodizing
Copper is a fairly flexible type of metal. Various methods are used to give it strength. One of them is anodizing. By placing the copper material in an acidic environment, a dense oxide film is formed on the surface, which gives the material a large number of useful characteristics.
Table. Compatibility table of metals and alloys
MaterialAluminiumBronzeDuraluminBrassCopperNickelTinTin-lead alloy (POS solder)Unalloyed steel (carbon) / cast ironChromeZinc| Aluminum | Joint | Not compatible | Joint | Not compatible | Not compatible | Not compatible | Not compatible | Not compatible | Joint | Not compatible | Joint |
| Bronze | Not compatible | Joint | Not compatible | Joint | Joint | Joint | Soldering | Soldering | Not compatible | Joint | Not compatible |
| Duralumin | Joint | Not compatible | Joint | Not compatible | Not compatible | Not compatible | Not compatible | Not compatible | Joint | Not compatible | Joint |
| Brass | Not compatible | Joint | Not compatible | Joint | Joint | Joint | Soldering | Soldering | Not compatible | Joint | Not compatible |
| Copper | Not compatible | Joint | Not compatible | Joint | Joint | Joint | Soldering | Soldering | Not compatible | Joint | Not compatible |
| Nickel | Not compatible | Joint | Not compatible | Joint | Joint | Joint | Soldering | Soldering | Joint | no data | Joint |
| Tin | Not compatible | Soldering | Not compatible | Soldering | Soldering | II | Joint | Joint | Joint | no data | Joint |
| Tin-lead alloy(POS solder) | Not compatible | Soldering | Not compatible | Soldering | Soldering | Soldering | Joint | Joint | Joint | no data | Joint |
| Unalloyed steel (carbon)/cast iron | Joint | Not compatible | Joint | Not compatible | Not compatible | Joint | Joint | Joint | Joint | Joint | Joint |
| Chromium | Not compatible | Joint | Not compatible | Joint | Joint | no data | no data | no data | Joint | Joint | Joint |
| Zinc | Joint | Not compatible | Joint | Not compatible | Not compatible | Joint | Joint | Joint | Joint | Joint | Joint |
Anodizing at home
In the modern world, a large number of metal objects are used in the household sphere, which are used for various purposes. Each owner wants to protect them from corrosion so that they last a long period of time. Anodizing at home is suitable for this purpose.
Important: The procedure for home anodizing of any metal must be carried out outdoors or on the balcony.
First you need to prepare a solution. To do this, you need to mix distilled water and acid in a certain proportion. It is important to handle sulfuric acid with extreme care, because if it comes into contact with the eyes or skin, it can lead to an unpleasant situation.
After this, you can prepare metal parts for processing. All kinds of substances are used for this purpose. They are able to clean them for the procedure.
At the last stage of home anodizing, metal parts are immersed in a solution and an electric current is connected.
anodizing at home
Source: https://ssk2121.com/anodirovanie-alyuminiya-v-domashnih-usloviyah/
Sulfate anodizing of aluminum
The main parameters of sulfate anodizing of aluminum and aluminum alloys include:
- concentration of sulfuric acid in the anode electrolyte;
- temperature of the anode solution - sulfuric acid solution;
- current density flowing through the electrolyte onto the surface of the aluminum profile.
How do these parameters affect:
- increase in the thickness of the anodic coating,
- pore sizes,
- appearance of anodized surface?
How does the chemical composition of aluminum and aluminum alloys affect the quality of anodizing?
Barrier layer
Any anodic oxide coating (hereinafter referred to as the anodic coating) consists of two layers - a relatively thick porous layer and a thin dense layer, which is called a barrier layer (Figure 1). The thickness of this barrier layer depends on the composition of the electrolyte and technological parameters. When anodizing, the barrier layer is formed first, and its thickness directly depends on the anodizing voltage.
Picture 1
Porous layer
After the barrier layer is formed, on its outer side, if the electrolyte has sufficient dissolving ability, a porous crystalline structure begins to form.
The growth mechanism is still the subject of debate, however, according to most scientists, its formation occurs due to the following cause-and-effect chain: local dissolution of the barrier layer - increased current - increased temperature - increased dissolution rate. This interaction of influences leads to the formation of pores.
Painting anodized aluminum
To obtain a colored anodic coating, mainly two methods are used (Figure 2):
- adsorption - impregnation of the porous layer with dyes;
- electrolytic coloring – electrochemical deposition of various metals (tin, copper, manganese, etc.) into the pores.
Much less commonly used is the so-called integral coloring, which is provided by special alloying of aluminum alloys. Coloring occurs due to the precipitation of particles in the volume of the porous layer, and not in the pores.
In addition, so-called interference staining is used to a limited extent: a variant of electrolytic staining that requires an additional bath to expand the pores near their bottom.
Figure 2 – Methods for color anodizing of aluminum
Why hexagon?
As they grow, the anodic cells, including the pores themselves and the surrounding aluminum oxide, form a hexagonal structure, which apparently ensures the implementation of some principle of minimal energy. The hexagonal shape of the anode cells does not depend on the type of electrolyte. This clearly indicates that this form is of purely energetic origin.
Standard anodizing
Sulfate anodization of aluminum and aluminum alloys is the most common. Sometimes it is called standard.
- The concentration of sulfuric acid in the electrolyte ranges from 10 to 20% by volume, depending on the coating requirements.
- The current density is usually from 1 to 2 A/dm2 at a voltage of 12 to 20 volts, a temperature of 18 to 25 ° C and an anodizing time of up to 60 minutes.
Pore growth rate
On most aluminum alloys, this electrolyte produces a colorless, transparent anodic coating. During sulfuric acid anodization, the pore growth rate is constant at a constant current density. At a current density of 1.3 A/dm2, this speed is 0.4 µm/min. Since the thickness of the barrier layer remains constant, this means that the bottom of the pore dissolves at the same rate.
Anode cell dimensions
The dimensions of the anode cells directly depend on the anodizing parameters (Table 1). With increasing voltage, the size of the anode cell increases, and the number of pores correspondingly decreases. The relationship between cell size and voltage is approximately linear, that is, the higher the voltage, the larger the cell size.
Table 1
Anodic coating growth
The thickness of the anodic coating increases with increasing anodizing time. However, the degree of thickness growth depends on several factors, such as the type of electrolyte, current density, processing time, etc.
Initially there is a rapid and constant increase in the actual thickness, and then the rate of increase in thickness begins to decrease until a stage is reached in which the thickness remains approximately constant despite the continued application of electrical current.
This is due to the fact that during anodization there is both a continuous increase in the thickness of the coating and its dissolution under the influence of an electrolyte (sulfuric acid solution).
Faraday's law
The actual thickness is calculated as the theoretical coating thickness minus the dissolved alumina thickness (Figure 3). The theoretical thickness is proportional to the anodizing time at constant current density and is determined by Faraday's law, which states that the amount of oxide formed is proportional to the electrical charge that has passed through the anode.
Figure 3
Impurities
In principle, pure aluminum anodizes better than its alloys. The appearance of the anodic coating and its properties (wear resistance, corrosion resistance, etc.) depend both on the type of aluminum alloy and its metallurgical biography, so to speak.
The size, shape and distribution of intermetallic particles also affect the quality of anodizing an aluminum alloy.
The chemical composition of the aluminum alloy is very important in some products that require high-gloss anodizing, which require the level of insoluble particles to be as low as possible.
The anodic coating on Al 99.99 aluminum will be clean and transparent, but at an iron content level of 0.08% it is no longer so pure and becomes increasingly cloudy as the coating thickness increases.
At a level of insoluble particles similar to that of aluminum 1050 (AD0 grade aluminum), the coating becomes completely “cloudy” compared to a purer metal. Of all aluminum alloys, the alloys of the 5xxx and 6xxx series produce the best decorative and protective coatings.
Some 7xxx series alloys also provide clean coatings with good functional properties. Color coatings of aluminum alloys of the 2xxx series are usually of poor quality.
Intermetallic particles
The behavior of intermetallic particles during anodization depends on the type of particles and the anode solution. Some intermetallic compounds oxidize or dissolve faster than aluminum (eg β-Al-Mg particles), resulting in a porous structure.
Other intermetallic particles, such as silicon particles, are practically insoluble during anodization and therefore precipitate as inclusions throughout the thickness of the anodic coating. Intermediate between these two extreme cases are compounds (FeAl3, α-Al-Fe-Si, etc.
), which partially dissolve and partially remain in the coating, which negatively affects the quality of the coating, especially colored ones.
Effect of anodizing temperature
The effect of increasing the electrolyte temperature is proportional to the increase in the rate of dissolution of the anodic coating, resulting in a thinner, more porous and softer coating (Figure 4).
Figure 4
To obtain so-called hard anodic coatings, low temperatures (from 0 to 10 °C) are used in combination with high current density (from 2 to 3.6 A/dm2) and very active stirring of the electrolyte.
In decorative and protective anodizing of aluminum and aluminum alloys, an electrolyte temperature of 15 to 25 ºС is usually used.
If the temperature rises higher, then the maximum possible thickness of the anode layer is reduced to lower values due to the higher solubility of the electrolyte.
Effect of Anodizing Current Density
The current density range of standard aluminum sulfate anodizing is from 1 to 2 A/dm2, in special cases - 3 A/dm2. At current densities below this range, a soft, porous and thin coating is obtained.
With increasing current density, the coating is formed faster with relatively less dissolution by the electrolyte and, accordingly, with a harder and less porous coating.
At a very high current density, there is a tendency for so-called “burn-ins” - the occurrence of excessively high current in local areas with overheating (Figure 5).
Figure 5
When good and clear reflection of light is required from the anodic coating, special anodizing conditions are used with a low current density of about 1 A/dm2.
Effect of sulfuric acid concentration
The effect of increasing sulfuric acid concentration on the performance of anodic coatings on aluminum alloys is similar to the effect of increasing temperature, although the effect of temperature is stronger than the effect of concentration. Increasing the concentration limits the maximum coating thickness due to the higher dissolving power of the more concentrated solution (Figure 6).
Figure 6
Source: https://aluminium-guide.ru/anodirovanie-alyuminiya-texnologicheskie-parametry/
Hard anodizing of aluminum
A feature of aluminum alloys is the presence of an oxide film of Al2 O3 on the surface. which is formed in air due to the fact that aluminum has a significant electronegative potential.
This film imparts some passivity to the metal, but does not protect against corrosion due to its small thickness (5-20 microns) and high porosity.
The best way to protect aluminum from corrosion is to create artificial oxide films of considerable thickness on the surface - this is the oxidation of aluminum, which can be carried out chemically or electrochemically (anodizing) .
When anodizing, an oxide film is formed as a result of anodic oxidation and protects the metal well from atmospheric corrosion, serves as a primer for paint and varnish coatings, and is easy to paint.
When anodizing, it is possible to obtain oxide coatings with specified properties: electrical insulating, conductive, porous, plastic, hard, etc. The properties of the coating are determined by the type of alloy, the composition of the electrolyte and the process mode.
Aluminum anodization is carried out in sulfate, chromate, oxalic and sulfosalicylic acid electrolytes.
When anodized in a sulfuric acid electrolyte, the films have high adsorption and corrosion resistance. This is the most economical and accessible anodizing electrolyte, but the process requires cooling and acid-resistant lining of the baths. It is not recommended to anodize parts with narrow gaps or riveted joints in sulfuric acid, from which it is difficult to wash off the acid.
Chromate electrolyte is recommended for anodizing parts of complex shapes. Its advantage is the preservation of the cleanliness of surface treatment and the dimensions of parts during anodizing, high elasticity of films, and corrosion resistance without additional processing. Disadvantages of anodizing this electrolyte: the high cost of reagents, the need for heating, and the difficulty of control.
Anodization in an oxalic acid electrolyte is carried out to obtain electrical insulating coatings of varying degrees of color depending on the film thickness: silver color with a thickness of 5 µm (t = 25 0 C), yellow – with a thickness of 15 µm (t = 40 0 C), brown – 100 µm (t = 50 0 C). oxalic acid during anodizing: 40 – 60 g/l, temperature 15 – 25 0 C, anodic current density 2.5 – 5 A/dm 2. holding time 90 – 120 minutes, while the voltage on the bath reaches 120V.
Anodizing with painting in various colors
For coating An.Ox. For aluminum wrought alloys, anodization is carried out in an electrolyte containing 170 – 200 g/l sulfuric acid at a temperature of 15 – 23 0 C, DA = 0.5 – 2 A/dm 2. bath voltage 10 – 20 V. The duration of the anodizing process depends from further processing: with compaction with chromates - 30 - 50 minutes, with subsequent coloring after anodizing with organic dyes - 60 - 80 minutes.
When covering An.Ox.tv. Anodization is carried out at low temperatures from 0 to – 7 0 C at the same concentrations. Anodic current density 2.5 – 5 A/dm 2. cathodes – steel 12Х18Н9Т. As the concentration of sulfuric acid increases during anodization, the film grows more slowly, as etching and porosity occur.
An interesting type of anodization - enameling is carried out in solutions based on oxalic acid with the addition of organic acids and salts. Anodizing produces an opaque film resembling light gray to dark gray enamel with high hardness and high resistivity.
The quality of the anodizing process, of course, depends on the preparation of the surface before anodizing, as mentioned earlier (see "First steps in electroplating. Part 2").
When performing the anodizing process, you must remember safety measures (see “Safe electroplating”). In the area where electrolytes are prepared for anodizing, when working with acids, it is necessary to use safety glasses and personal protective equipment. Take care of your health!
The aluminum anodizing process is very promising . since it allows you to obtain even completely transparent films without an aluminum base with specified parameters: resistance, thickness, hardness, etc.
58 comments: Anodizing aluminum
Good afternoon, please tell me the possible reason for the failure of the sulfate anodizing bath: the electrolyte temperature was increased during operation (+27 degrees.
), a few minutes after unloading the parts from the bath, the surface of the electrolyte was covered with a “cap” of spongy black sediment, and the electrolyte itself acquired a pink tint due to a tiny pink suspension. Filters without problems.
We assume that the polarity of the rods was changed by mistake, as a result of which the lead anodes and, possibly, copper pendants dissolved (the electrolyte level was slightly higher than normal). Thank you in advance for your consultation.
Hello Irina! Of course, a black spongy deposit can only be formed by the oxidation of lead, and this is possible if oxygen is released on it, i.e. the anodic process is underway.
Source: https://respect-kovka.com/tverdoe-anodirovanie-alyuminiya/
