An electrochemical model was developed to predict the transient distribution of species generated during corrosion of carbon steel (CS) /aluminum alloy (AA) galvanic couples under thin NaCl electrolyte films at room temperature (24 °C). Using specific geometrical configurations, strong acidification of the electrolyte, localized above the AA surface and close to the carbon steel electrode, was predicted. However, a small zone evolved (also above the AA surface) between the strong acidified area and the AA/CS joint, where the pH was neutral due to the OH- production on the CS surface. Moderate acidification of the electrolyte was predicted above the rest of the AA surface. Both diluted and concentrated electrolytes were taken into account. Surprisingly, the less concentrated the electrolyte, the more significant the drop of pH on top of the AA electrode.
Transient experimental measurements were achieved with the help of an innovative setup, and findings corroborated the theoretical predictions. These results provide enough evidence to properly discuss whether such an acidification process is due to the production of intermediate aluminum compounds or by the fast consumption of hydroxyl ions (OH-) produced by the cathodic reaction on the steel surface.
With a vast demand for solutions for decreasing the emission of pollutants, the transport industry is developing new ideas in many fields: catalyst converters, new energies, better quality of fuels, lighter materials, etc. With regards to lighter vehicles, the automotive industry has been looking for the best steel components such as frames and chassis to be replaced by light alloys. This task is not straightforward as light alloys have inferior mechanical properties to steel, and the substitution of any part of a vehicle should be carried out avoiding designs that violate any mechanical standard.
On the other hand, it is well known that producing structures by combining different metallic components leads to a galvanic corrosion phenomenon, which takes place when two metallic samples (with different corrosion potential) are put together in contact with a common electrolyte. The more active material undergoes more aggressive corrosion than if it was just in contact with the electrolyte (but without the second metallic material). On the other hand, coatings (the artificial barrier to avoid contact between the metallic couple and the electrolyte) are just a non-permanent solution since they always end up failing.
