Aluminum is used in many areas of our life and now it is very difficult to imagine mechanical engineering, electrical engineering, house construction, and other things without the use of aluminum alloy.
Aluminum is a very light metal, wear-resistant, ductile, conducts electricity and heat well, and has no magnetic properties. Aluminum has a light silvery color and is covered with a thin oxide film on top. It is this film that is the main source of aluminum corrosion protection. The oxide film has self-healing properties and is very durable.
Aluminum is resistant to environmental influences but can undergo contact corrosion if in contact with dissimilar metals. Under certain conditions, aluminum can form a strong galvanic pair with some metals. Dissimilar metals have different electrode potentials. So, for example, aluminum will act as the cathode, and the copper rivet with which you connected the aluminum sheet will become the anode. A chemical reaction will begin between them, the result of which will be the appearance of corrosion.
In what areas we can use aluminum
We use aluminum in many areas of production. Its alloys silumin and duralumin are used in metallurgy. We also use aluminum alloys in architecture, shipbuilding, construction of houses, shops, supermarkets, and other buildings, used in the manufacture of electrical engineering, in the space industry, and aircraft construction.
What kind of objects made of aluminum come across to us most often in everyday life? Let’s look at some examples.
A thin aluminum strip in rolls is supplied for the food industry and then cooling elements for radiators are made from it.
Aluminum pipes are very durable. We use them in finishing works, production of pipelines, water pipes, gutters, and gas pipelines.
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Aluminum wire is used to make eclectic cables. Aluminum has a high electrical conduction property.
They make bushings of aluminum. They are easy to handle, install and use in production to connect the ends of a metal cable.
For manufacturing bolts, shafts, nuts, spindles, we use an aluminum bar.
Aluminum also enters the human body with food. We find small amounts of aluminum in peas, rice, and wheat.
Also, aluminum is used for manufacturing dishes. True, we do not recommend cooking acidic foods in such dishes, because a reaction will occur and aluminum will enter the food. As you can see, this is a widespread metal that, unfortunately, corrodes if it is used improperly, when exposed to the environment. What is aluminum corrosion and how to deal with it further in our article.
Types of aluminum corrosion
Corrosion renders the material unusable and severely spoils it. Sometimes parts that have corroded can be partially replaced, and sometimes this is not possible. To understand how to protect aluminum from the effects of corrosion, you need to know what types of corrosion exist. Depending on weather conditions, the aggressiveness of the environment, contact with saline solutions and alkalis, the effect of electric current on the material, the following types of corrosion are distinguished:
- surface corrosion;
- crevice corrosion;
- continuous metal corrosion;
- galvanic corrosion;
- electrical corrosion;
- thermal corrosion;
- intercrystalline corrosion;
- pitting corrosion of aluminum.
Any of the above destruction of metals under the influence of the above factors can jeopardize the integrity of your structure, parts. Improper connection of aluminum parts with other types of metal can also aggravate the process of destruction of the crystal lattice of the metal at the molecular level.
How to understand the galvanic corrosion process
When two dissimilar metals hit, we can observe the process of galvanic corrosion. Such corrosion occurs only when two metals with different electrochemical properties are close to each other under the influence of an electrolytic liquid, corrosive environment, or electrolyte film.
When such a process occurs, the metals enter a chemical reaction with electrolytes to create a cell. This cell corrodes one metal at the expense of another.
The process of galvanic corrosion
All materials have different electrode potentials. It is this difference in potentials between metals that touch and create an electric current. Material with positively charged particles – the cathode moves to the material with negatively charged particles – the anode. If the anode forms a more active metal, accordingly, the cathode will be less active. Because of this effect, the anode metal corrodes faster. Sometimes the metal that acts as a cathode may not undergo any changes at all and remain strong and intact.
What galvanic corrosion looks like
The destruction of the crystal lattice at the molecular level has certain characteristics. Visually, you can distinguish one type of metal corrosion from another. Galvanic corrosion has such essential features as:
- located directly in the place where aluminum contact with other metals;
- the process of metal destruction occurs deeply, visually resembles holes, craters, and depressions in the plate;
- this process does not spread over the entire surface of the plate ant other aluminum things;
- has a uniform character.
Conditions for galvanic corrosion of aluminum
For the process of destruction of the crystalline structure of the material to occur, we must meet three conditions:
- presence of electrolyte;
- the contact with various types of materials and metals;
- exposure to an electric current;
- exposure to aggressive environments (salt, alkali, acids).
It is under these conditions that aluminum will react with another dissimilar metal, and galvanic corrosion will occur.
How aluminum paired with steel corrodes
The process of destruction of the crystalline structure of the material can be negligible and virtually nil and invisible. It all depends on what kind of metal we paired.
Aluminum – galvanized steel
If you look at the table of the galvanic range of aluminum with other metals, you see that zinc is more electronegative than aluminum. If you connect an aluminum sheet and use all kinds of galvanized steel fasteners, then over time there will be a slight destruction of the crystal lattice of the metal. Such an impact can only spoil the visual perception of galvanized fasteners, which will damage the aluminum sheet.
Aluminum – unalloyed steel
We often use screws, nuts, bolts from ordinary steel in aluminum constructions, and fasten aluminum sheets with them. We expose such structures to climate and weather. But experience shows that such compounds are subject to a minor process of destruction of the crystalline structure of the material. Slight rust may occur, and small stains may form on the aluminum surface. Such corrosion does not affect the structure but only spoils the surface, and how we perceive it visually.
Aluminum – stainless steel
This pair is least of all exposed to the impact and destruction of the crystal lattice under the influence of water, alkalis, salt, and other aggressive conditions. Here, the potential difference is approximately 650 MV. We increasingly use stainless steel as a connecting material, bolts, brackets, plugs, nuts, etc are made from it.
How to protect aluminum from the destruction of the crystal lattice
Use rigid anodes when pairing aluminum with steel. Most often they are made from galvanized, unalloyed steel or stainless steel.
We should also note that destruction of the crystal lattice occurs not only in water. We can find the formation of galvanic groups in any electrolyte. More often it could be moist soil, air, chemical sediment, and others.
The electrical current must not pass through the material, or we must ground it. Whenever possible, try to protect aluminum materials from corrosive conditions. Knowing with which metals it is better to combine aluminum, you will prevent its corrosion, and the structure or part will serve for over one year.