Principle of cyclic corrosion test

Corrosion is generally divided into two types, namely chemical corrosion and electrochemical corrosion. Chemical corrosion refers to the presence of metals in dry gases and non-electrolyte solutions.

Corrosion caused by chemical changes without the intervention of water; electrochemical corrosion occurs under the action of electrolyte and water, and a current is generated during the reaction to form a battery; in electrochemical corrosion, the metal with low electrode potential is the anode, and the metal with high electrode potential As the cathode, the anode loses electrons and enters the electrolyte to form anode corrosion, while the cathode receives electrons and transfers them to the medium ions in the electrolyte to continue the reaction.

Due to the constant changes in temperature and humidity, the cyclic salt spray test sometimes has water intervention, which belongs to electrochemical corrosion, and sometimes does not have water intervention, which belongs to chemical corrosion. In the test, after the salt spray particles settled and attached to the surface of the material, they quickly absorbed water and dissolved into the chloride water solvent. Under certain temperature and humidity conditions, this chloride water solvent or dissociated chloride ions penetrate into the material system through the pores of the paint film, coating or other materials, thereby causing corrosion of the metal substrate.

The test generally goes through multiple cycles to simulate extreme weather conditions such as humidity and dry heat in the actual environment, especially in the test stage of water evaporation and salt deposition, the high-concentration salt solution on the surface of the dry sample will accelerate the corrosion of the coating surface In addition, in the process of changing from wet to dry, the corrosion reaction is directly accelerated due to the full contact of the surface with oxygen.