Characterization of aluminium and its alloys by means of analysis of passive, pitting and galvanic behaviour in contact with CFRP by electrochemical noise and polarization methods

The recent trend for aerospace and automotive applications is aimed to improve both, weight saving and safety performance of their structural components. Therefore, lightweight material with high strength per weight ratio is required. Aluminium and CFRP are competing materials for lightweight structural components. These two materials can be combined forming hybrid material in order to promote their advantages. In practical situations, this hybrid material is exposed to different corroding environments, for example fuel or salt solutions. The major concern regarding the use of this hybrid material is the galvanic corrosion of aluminium in contact with CFRP. This galvanic contact may lead to dangerous pitting corrosion. In the present work, the galvanic corrosion of aluminium in contact with CFRP in chloride solutions is investigated. One simple way is the investigation by optical microscopy of the surface morphology after long time immersion. Another way is studying the electrochemical behaviour (active, passive, and pitting behaviour) of aluminium and CFRP separately by means of polarization and electrochemical Noise (EN) methods. Then the use of these electrochemical techniques can be combined in order to predict the galvanic behaviour of this hybrid material. The results from literature can often not be compared because of different measurement parameters. Therefore, systematic and scientific measurements with constant measurement parameters have been carried out for better understanding. Firstly, the experiments deal with aluminium, because its electrochemical behaviour is much more complex compared to the more simple CFRP. It was observed that systematic study was possible because of controlled sample preparation and measurement set-up. Active Surface of pure aluminium could be prepared the first time. For scan rate 0 (potentiostatic), there seemed to be no difference between metastable and stable pitting corrosion of pure aluminium. Moreover, long time noise measurements with high sampling rate were necessary for real analysis. Pitting transients could be identified and analysed by frequency. The polarization results have been compared with analysis of Evans diagrams. It was found that pitting corrosion of aluminium could be induced through galvanic contact with CFRP and the pitting corrosion started at the boundary of carbon and aluminium. In addition, the galvanic corrosion depends on surface area ratio of CFRP to aluminium and immersion time