Types of corrosion

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Imagen trenes corrosión Inelca

Corrosion is defined as the deterioration of a material when interacting with its environment, the metal loses or decreases its physical and / or chemical properties. The corrosion process is accelerated by factors such as oxygen, humidity, temperature, chemicals and the change in the physical-chemical composition of the material.

Through the galvanizing process, a layer of zinc that acts as a sacrificial metal is deposited on the surface of the steel.

The different types of corrosion that occur in a steel treated with a coating of Zn and its alloys are presented below:

  • White corrosion or Zinc oxide: Zn + O2 à ZnO

Zinc is a very durable coating that acts as a sacrificial protection of steel, as it corrodes more slowly. White corrosion is a substance of that colour that can form on zinc when exposed to oxidizing environment. Optimum storage conditions are vital so that their properties are not affected.

  • Red corrosion or Iron corrosion: Fe + O2 à FeO

When the base metal is in contact with oxygen it oxidizes easily. This phenomenon causes iron to lose its properties and become fragile and brittle. That is why it is necessary to protect it by coatings.

Main objectives of the coatings

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The benefits of metal surface coatings are so broad that they become indispensable for many areas.

There are coatings of different types which contribute some characteristics or others to the material on which they are deposited:

  • By means of electrochemical metal depositions, such as galvanized, Zinc alloys (Zinc Nickel, Zinc Iron, Zinc Cobalt, Zinc Cobalt Iron), tin plating, electrolytic nickel plating, decorative chrome plating, hard chrome.
  • Through chemical depositions, such as acid zinc and aluminum chromatizing.
  • Obtained by conversion, such as anodizing of aluminum and titanium, blued and phosphating.
  • Hot dip, such as galvanized, aluminized, tinned and leaded.
  • Metallization by projection or vacuum deposition.
  • Through plasma obtaining surface hard layers with PVD and CVD.
  • Paints, polyurethanes, electrophoresis, electrostatic powder, etc.
  • Coatings with PVC, rubber or Teflon plastics.

Depending on the type of coating used, the following improvements can be obtained:

  • Improvement of corrosion protection
  • Improvement of mechanical characteristics
    • Hardness
    • Wear resistance
    • Ductility

 

  • Improvement of specific properties
    • Weldability
    • Conformability
    • Electrical contact
    • A combination of several (color, abrasion resistance, friction coefficient, etc.)