Metal surface painting is a way to protect metal from oxidation and corrosion. The corrosion phenomenon around us refers to the damage, performance degradation or state degradation of all kinds of materials under the action of environment (including chemical,
electrochemical and a number of physical factors). Painting on metal surface is a very important means of metal corrosion protection. A good protective layer of spray painting can be a barrier to prevent the invasion of corrosive medium.
As corrosion is an irreversible spontaneous process, even the high-quality paint coating retention layer is difficult to protect the metal from corrosion, especially when the paint coating layer on the metal surface is not well combined,
damaged, or has pinholes, blisters, cracks, peeling and other defects, the protective effect of the paint coating will be greatly reduced, and even lead to the deterioration of metal corrosion. Therefore, it is necessary to analyze the factors of metal
corrosion in painting and take effective countermeasures.
Corrosion mechanism of painting metal
Generally speaking, metal corrosion is the result of many factors, and some of them play an important role in the process of corrosion. The metal
surface is painted to form a coating protective layer, and the area where the metal corrodes is the interface area between the coating film and the metal surface, and the corrosion expands to the depth of the metal matrix.
If the paint coating layer
on the metal surface can effectively isolate the penetration of water, oxygen, electrons, stray ions, etc., it can greatly slow down or avoid the corrosion of the painted metal. If the isolation effect is not good, the anticorrosion and anti-corrosion
protection effect of the paint retention layer on the metal is not good. The production practice shows that the permeability of the protective coating to water seriously affects the adhesion of the metal painting surface, while the permeability of oxygen
greatly affects the corrosion performance of the metal. There are many kinds of corrosion forms of painting metal, but the root cause of corrosion is closely related to the chemical and electrochemical effects.
Influence of metal material and other
The corrosion of painting metal is closely related to the corrosion resistance of metal material itself. The metals used for painting are steel, aluminum, copper or magnesium. There is no doubt that the corrosion resistance and corrosion
resistance of metal painting are different. For the difference of surface state of metal materials, the effect of anti-corrosion and anti-corrosion protection of the coating is obviously different after painting. For example, the steel plate parts treated
by sandblasting and purification and the steel plate parts of the same brand with natural corrosion are protected by the same painting. Due to the adverse effect of corrosion, the corrosion rate of the steel plate parts with natural corrosion is dozens
of times higher than that of the steel plate parts treated by sandblasting, and the corrosion protection effect is significantly lower than that of the latter. Defects on the metal surface, such as inclusions, microcracks, stresses, etc., and adsorption
of moisture and active ions (Cl -, Br -, etc.) in the atmosphere will affect or even accelerate the corrosion of painting metal to varying degrees.