A risk of galvanic corrosion respectively contact corrosion is given when constructions are built with mixed materials. For example in lightweight constructions, Aluminium and CFRP (Carbon fibre reinforced plastic) are often used together. In case of mixed material construction a galvanic cell can establish when the conductive materials are in contact, and when a water film is present on the surface. E.g. automobiles and aeroplanes are exposed to the atmosphere and therefore, water can cover the outer material surface by rainwater, precipitation of moisture or fog. Inside of an aeroplane or of an automobile, the condensation of humidity causes a thin film of water on the surface. A formation of a water film cannot be avoided, particular in aeroplanes since the huge temperature changes during the take off and landing could lead to condensed water on the surface. The water can form a conductive pathway between the different materials. In the water, the electrochemical reactions occur at the water/metal and water/CFRP interface with metal dissolution and O2 reduction.
In case of a galvanic cell, the less noble material will corrode. Aluminium is less noble than CFRP. Aluminium is then the anode and CFPR the cathode.
In order to avoid dangerous galvanic corrosion, usually the CFRP components are covered with an insulating coating.
Coatings can have pinholes, pores, invisible failure, single C-fibres which stick out and scratches. For the non-destructive detection of theses failures, the CAMIP device is recommended.
Once a failure in surface insulation is detected, it can be marked and then sealed. The CAMIP device is also useful for improving the manufacturing process of the surface coating, this can be done by checking the insulating properties of the coating after adjusting or fine-tuning of the production steps and used technique. The TREMA is useful in the same manner.
CAMIP offers an easy method to determine failures in insulating coatings on CFRP parts in aviation industry and automobile industry.
In order to avoid galvanic corrosion it is important that the total resistance of the coating has a known high enough value. A high resistance of the intact coating, which has no failures, is important.