Does rust rust: myths and the reality of corrosion

The tin rusts when the protective zinc layer is damaged, after which the irreversible electrochemical process of oxidation of the ferrous metal begins. If you notice small chips, scratches or bloating paint on the car body, it means that the aggressive environment has reached the base of the material. Despite the widespread belief that the "eternity" of galvanizing, corrosion unavoidable in case of violation of the integrity of the coating, especially in operating conditions on roads treated with reagents. Water, salt and oxygen trigger a reaction that turns the durable metal into loose iron oxide, which over time can lead to through holes in the body.

It is important to understand that the speed of this process depends on the type of metal processing and the storage conditions of the vehicle. Galvanic galvanization It provides more protection than hot, as zinc acts as an active protector. Even if the paint layer is damaged, zinc will oxidize first, sacrificing itself to preserve the steel structure. However, this resource is not infinite, and ignoring the primary signs of corrosion leads to serious financial costs for recovery. bodywork.

Physico-chemical processes of oxidation

To understand why tin is susceptible to destruction, it is necessary to consider the mechanism of interaction of metals with the environment. The base of tin is low carbon steel, which is chemically unstable and tends to return to its natural oxide state. Zinc coating creates a barrier, but in the presence of electrolyte (moisture with salts) and oxygen access, a galvanic vapor occurs. In this pair, zinc acts as an anode and iron as a cathode, which causes zinc to dissolve, protecting the base.

⚠️ Attention: The corrosion rate increases many times with an increase in air temperature and salt concentration, so the winter period is critical for the condition of the body.

The oxidation process is not always visible visually in the early stages. Under the layer of paint can form microscopic foci that grow wide, peeling off the paint coating. If this process is not stopped by mechanical cleaning and chemical neutralization, the rust will penetrate deep into the structure of the metal. Electrolytic reaction It is especially active in welded joints and joints of panels, where moisture access is difficult, but constant.

Technical details of corrosion

Within the metal, electrons flow from zinc to iron. Zinc loses electrons and becomes a solution in the form of ions, forming a white coating (zinc oxide). As long as there is zinc nearby, the iron does not give up its electrons and remains intact.

There is a misconception that if a metal is coated with zinc, it becomes inert. This is not so: zinc is also oxidized, just the products of its corrosion are less voluminous and often form a dense film that prevents further penetration of moisture. However, if mechanical damage or prolonged exposure to aggressive acids (e.g. from bird droppings or industrial emissions) protection breaks through. Black metal Under the layer of zinc begins to rust instantly as soon as the protector bond disappears.

Types of galvanizing and their persistence

Not all tin is equally rust-proof, and this is a key point when choosing a car or repair materials. Manufacturers use different technologies for applying zinc, and it depends on how many years the body will resist the onslaught of corrosion. Hot galvanizing It is considered one of the most reliable methods where steel is immersed in a zinc melt at a temperature of about 460°C. As a result, an alloy of iron and zinc is formed, which is very firmly held on the surface.

• 🚗 Galvanic galvanization: It is electrolytically applied, the layer is thin (9-15 μm), but very uniform and holds the paint well, providing excellent cathode protection.
• 🏗️ Hot galvanizing: It produces a thick layer (40-60 μm or more) that is mechanically stronger but may have irregularities ("tears") that require additional processing before painting.
• 🎨 Zinc-containing soils: They are not formally galvanized, since zinc is in the form of a powder in the paint, and the protection works only until the first serious chip.

Cars with full galvanizing of the body are more expensive, but also serve much longer without the appearance of "redheads". Partial galvanizing is often used only at the most vulnerable places: thresholds, bottom, doorways. The remaining panels can be simply covered with a phosphate layer and soil. Phosphation improves paint adhesion, but does not provide the electrochemical protection that zinc provides. Therefore, such areas rust faster when the LCP is damaged.

When buying a used car, it is important to know what type of protection the manufacturer used. For example, some European brands are famous for using high-quality products. electroplatingWhile others rely on thick layers of soil and high-quality assembly, minimizing gaps for moisture. If the tin has not been galvanized at all (as on old models or the budget segment of the last century), it will begin to bloom after 2-3 years of operation without additional anti-corrosion treatment.

Factors accelerating body corrosion

Even high-quality galvanizing can not withstand the aggressive effects of the external environment, if the operating conditions are extreme. The main enemy of metal are road reagents, which are processed by highways in winter. A mixture of calcium and magnesium chlorides creates a highly concentrated electrolyte on the surface of the body, which penetrates into microcracks. Electrochemical corrosion In such conditions it goes many times faster than in a dry climate.

In addition to chemical reagents, mechanical damage has a destructive effect. The sandblasting effect of the wheels in front of the cars is stripping away the protective layer of varnish and paint, baring zinc or steel itself. Micro-strikes Gravel creates entry points for moisture. If such chips are not painted immediately, the rust will get under the neighboring areas of the coating, causing its detachment. Moisture lingering in hidden cavities (spargerons, racks), also contributes to the rotting of the metal from the inside.

⚠️ Attention: Long idle car on the street without movement accelerates corrosion, as there are no vibrations that could shake off moisture, and the ventilation of the cabin does not work.

The influence of the environment is enhanced by temperature changes. During the day, the metal heats up, expands and absorbs moisture, freezes at night. Ice, expanding in pores and microcracks, breaks protective films. Atmospheric corrosion In industrial areas, where the air is saturated with sulfur and acidic compounds, also quickly disables even a well-protected body. Therefore, the frequency of washing and the quality of drying a car directly affect the lifespan of the car.

Diagnosis of the condition of the paint coating

Timely identification of problems is the key to preserving the body. Regular inspection of the car allows you to notice the beginning of corrosion at the stage when you can still do with minimal investment. Particular attention should be paid to the edges of the doors, hood, trunk, as well as the lower part of the sills and arches. This is where dirt and moisture most often accumulate. Visual examination in good lighting helps to identify changes in the color of enamel or the appearance of matte spots.

For a deeper diagnosis, a magnetic thickness meter can be used. This device shows the thickness of the paint and putty layers. If the readings are very different from the factory or differ in neighboring areas, this may indicate hidden foci of corrosion or previous poor-quality repairs. Bubble of paint - a sure sign that under the layer of the LCP is already an active process of rusting, and the metal began to expand.

Surveillance area	Typical signs of rust	Recommended frequency of inspection
Wheel arches	Bloating paint, chipping stones	After every winter.
Thresholds (lower)	Mud detachment, red streams	Once in 3-4 months
Dough	The rust on the bolts, the cracking of the mastic	On the lift, once a year.
Door edges	Small dots ("redheads"), chipped	Every washing.

Do not ignore the appearance of small points of rust. Many owners paint them with a proofreader, thinking that they have solved the problem. However, without stripping to metal and processing the rust converter, the process will continue under a layer of new paint. Diagnostics should be comprehensive: inspection from the outside, checking hidden cavities through technological holes and monitoring the state of drainages.

Protection methods and anticorrosion treatment

If the tin has started to rust or you want to prevent this process, you need to use proven protection methods. The modern industry offers a variety of products, from simple waxes to complex polymer compositions. Anti-corrosion treatment It is divided into the outer (for visible parts) and the hidden (for cavities). For hidden cavities, oil-based compounds are used, which do not dry completely and have penetrating ability, displacing moisture.

• 🛡️ Mastics: thick layer coatings on a bitumen or polymer basis to protect the bottom from stone impacts and moisture.
• 💧 Oil formulations: They penetrate into microcracks, displace water, ideal for hidden cavities, but require regular updating.
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