6.4- Corrosion Flashcards
What happens to an active metal that loses an electron easily?
Extremely susceptible to corrosion.
What is electrochemical reaction?
Commonly known as galvanic action.
What is microbiological action?
Microbial attack from things like mould and bacteria.
What is stress corrosion?
Intergranular cracking of the metal which is caused by a combination of stress and corrosion.
Give some of the effects of corrosion on steel.
Red rust known as hydrated ferric oxide.
What do aluminium and its alloys exhibit as corrosion?
Crevice, stress and fretting
White grey surface rust
What is the most corrosive metal to aluminium?
Mercury.
What happens to magnesium when it corrodes?
Grey powder and severe pitting of the surface.
What is filiform corrosion?
Cell or crevice corrosion from oxygen concentration.
Occurs in 78-90% humidity and slightly acidic surface.
What happens if filiform corrosion is not removed?
It can lead to intergranular corrosion.
How can filiform corrosion be removed?
Glass bead blasting or sanding.
What is electrochemical corrosion?
Often mistaken as galvanic due to similar events, however its caused by an external current.
What is pitting corrosion?
Most common corrosion between aluminium and magnesium. Appears as white powder on surface and extends vertically.
What is exfoliating corrosion?
Advanced form of intergranular where the surface grains are lifted up by the expansion of corrosion.
What is most prone to exfoliating corrosion?
Wrought products such as extrusions, thick sheets and thin plates with elongated grain structures.
