- Singleton SCCH 26 corrosion chamber (inside dimensions: 300x120x120 cm)
Accelerated corrosion tests can be executed according to the following standards:
- ASTM B117 Salt Spray test
- ASTM G85-A3 SWAAT test (Seawater Acidified Test)
In agreement, it is also possible to execute corrosion tests which deviate from the given standards with respect to time or spray medium. The time to failure (leakage) for hollow samples can be determined exactly by means of pressurizing the samples up to a pressure of 7 bars, and registering the time of a pressure drop. Depending on the size of the samples, up to 16 samples can be connected to a pressure gauge at the same time.
Corrosion is the deterioration of proporties in a metal due to reactions with its surroundings. The corrosion rate of aluminium is in general low when exposed to most environmental conditions. Aluminium is protected by a very stable oxide. In case corrosion does occur, it is important to understand when and how this may occur.
We define three types of corrosion;
- Pitting Corrosion: is a form of extremely localized corrsion that leads to the creation of small holes in the metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic while an unknown but potentially vast area becomes cathodic, leading to very localized galvanic corrosion. The corrosion penetrates the mass of the metal, with limited diffusion of ions.
- Galvanic Corrosion: may occur where there is both metallic contact and an electrolytic bridge between different metals. The least noble metal in the combination becomes the anode and corrodes. The most noble of the metals becomes the cathode and is protected against corrosion. In most combinations with other metals, aluminium is the least noble metal. Thus, aluminium presents a greater risk of galvanic corrosion than most other structural
materials. However, the risk is less than is generally supposed.
- Uniform Corrosion: general corrosion, or uniform corrosion, occurs in the solutions where pH is either very high or very low, or at high potentials in electrolytes with high chloride concentrations. In acidic (low pH) or alkaline (high pH) solutions, the aluminum oxide is unstable and thus non-protective.