When two metals with different potentials are in contact with each other and immersed in the electrolyte, it can be found that the corrosion rate of the metal with a negative potential is increased, while the corrosion rate of the metal with a positive potential is slowed down and protected, which is called galvanic corrosion.
1) In engineering technology, the combination of different metals is inevitable, almost all machines, equipment and metal structural parts are composed of different metal material components, galvanic corrosion is very common.
2) The principle of galvanic corrosion allows for sacrificial anode cathodic protection of useful components by the sacrifice of base metals.
1) Combination of metal parts (including conductive non-metallic materials, such as graphite).
2) Metal coating.
3) Conductive non-metallic film on metal surface.
4) Metal deposits caused by air or liquid flow.
1) Corrosion potential difference between the metals.In the galvanic sequence, the larger the potential difference between metals or alloys that are far apart, the more likely galvanic corrosion will occur.
2) Solution resistance.The higher conductivity of the solution enlarges the invaded surface of the active metal, thus reducing the severity of erosion.If the conductivity of the solution is low and the erosion is concentrated near the contact surface, the local erosion is large.
1) Select a metal with electrode potential as close as possible (preferably not more than 50 millivolts) in the working environment as a contact pair. Try to select metal combinations that are close together in the couple sequence.
2) Reduce the area of metal with positive electrode potential and increase the surface area of metal with negative electrode potential as much as possible;
3) Try to insulate the metal in contact, and increase the resistance of the medium:
4) Make full use of the protective layer, or try to add protective potential. When using metal coating and non-metal coating on metal, do not only cover the anode material, but also cover the negative polar material together. When selecting the protection method, the influence of the area and the influence of corrosion products should be considered.
