This is the third post about corrosion on aluminum and it is about Crevice Corrosion. This type of corrosion is a localized corrosion in recesses, such as overlapping zones, bolting or welding, zones under joints, and under various deposits (sand, slag, precipitates, etc.) taken from Christian Vargel´s great book "Corrosion of Aluminium".
The localized corrosion may occur in the form of pits or etch patches. An important variable in crevice corrosion is the width of the crevice opening. The aluminum-silicon alloys corrode many times faster than the aluminium-magnesium alloy when crevice corrosion has started.
Prevention by
- Applying corrosion inhibitor
- Sealing crevices with an adhesive to prevent water penetration
Several reactions happen in the crevice. Aluminum is oxidized and on the edge of the crevice oxygen is reduced. The aluminum will corrode and the oxygen is dissolved in the liquid will be consumed. Due to the limited diffusion in the crevice the environment will be drained from oxygen and then leave the crevice with an excess of aluminum ions. This will lead to an inflow of chloride ions which will make the crevice acidic leading to a severe corrosion attack.
Corrosion costs are estimated at 4.2% of the Gross Domestic Product (GDP) or over $30 billion in the United States each year. Of this amount, 35% or over $100 billion can be classified as avoidable because best practices are not used.
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