1
Q
Explain filiform corrosion ?
A
- Occurs on surfaces with organic coating system
- Has worm like traces
- Occurs when humidity is 78%- 90%
- Starts at breaches of coating
- If not removed it can lead to intergranular corrosion
2
Q
Explain pitting corrosion ?
A
- Corrosion which produces holes in material
- Most common corrosion on magnesium and aluminium
- Can form stress corrosion
3
Q
Explain intergranular corrosion ?
A
- Cracking which accelerates over time
- Happens along grain boundary’s when protective coating is damaged allowing moisture to enter
4
Q
Explain Exfoliation corrosion ?
A
- Advanced form of intergranular corrosion
- Prone in extrusion products
5
Q
Explain fretting corrosion ?
A
- Occurs due to vibration which rubs and removes protective films exposing bare material
- Appears as pits or grooves and black/brown paste
- Use of lubrication can minimise this
6
Q
Explain crevice corrosion
A
- Attacks metal through solution in crevices ( rivet heads. Bolts etc )
- Found between assemblies where a corrosive agent has penetrated
7
Q
Explain Mercury corrosion ?
A
- Caused by small amounts of mercury
- Mercury attacks aluminium through chemical reaction ( amalgamation )
- Dangerous to aircraft and people
8
Q
What is corrosion ?
A
- Oxidisation of a metal which forms salts
9
Q
When does corrosion form on a metal ?
A
- When there is a difference in electrode potentials between two metals which are also in contact with an electrolyte.
10
Q
Why does corrosion occur ?
A
- Because of the metals tendency to return to its original state
11
Q
What two chemical changes does the corrosion process involve ?
A
Cathodic and anodic
12
Q
What’s 3 requirements for corrosion to form ?
A
- Electrical potential difference between two metals
- A conductive path between two areas with different potential difference
- A electrolyte or fluid covering two areas ( cathodic, anodic )
13
Q
How can you control corrosion ?
A
- Clean surfaces
- Dry surfaces
