What is corrosion?
When a metal returns to a metal compound such as an oxide.
What corrodes more easily, noble or active metals?
Active
How can corrosion damage be reduced?
By using corrosion resistant metals finishes
How are some aluminium alloys protected from corrosion?
Anodising and primed
How can steel and metals such as brass be protected from corrosion?
Sacrificial plating such as cadmium.
How can magnesium alloys be protected from corrosion?
Special chemical
Electrochemical
Paint finishes
What is electrochemical action, and it’s alternate name?
Corrosion cased by dissimilar metals in an electrolyte.
Also called galvanic corrosion.
What can cause microbial corrosion?
Microbes such as fungi, bacteria, and moulds
What is stress corrosion?
Intergranular cracking caused by a combination of stress and corrosion
What does steel corrosion look like?
Dark deposits then rusting if moisture is present.
How does corrosion affect aluminium?
A white gray powder is left behind
How does aluminium react with mercury?
Rapid and severe corrosion of the aluminium
How does corrosion affect magnesium?
Grey powder with severe pitting
How is copper affected by corrosion?
Green powdery product
What can affect corrosion on metals?
Temperature Type of metal How dissimilar metal are Presence of electrolytes Oxygen available Microbes Exposure time Heat treatment
How is Filiform corrosion identified?
Worm like traces been the paint film
When can filiform corrosion happen?
On metals with an organic coating system, starting at the breaches
70-80% humidity with acidic surface
What can happen if filiform corrosion is not dealt with?
Intergranular corrosion
How can filiform corrosion be removed?
Glass bead blasting
Sanding
Portable abrasive equipment
What are some environments that stress corrosion cracking?
Salt solutions and sea water for steels and aluminium
Magnesium alloys in moist air
How does shot peening affect metals?
Increases resistance to stress corrosion
What is pitting corrosion?
Starts with white powdery deposits on the surface, then extends vertically into the materially
What is intergranular corrosion?
Attack on the grain structure with no warning.
Can lead to delamination of the material
What is exfoliation corrosion?
Similar to intergranular corrosion, but lifts the metal through the expansion of the corrosive products
