Materials And Corrosion Flashcards
What two categories are metals and alloys divided into?
Ferrous & Non Ferrous
What 3 metal standards do we use?
British Standards (BSI)
French Standards (AFNOR)
American Standards (SAE)
What materials do not need a certificate of conformity?
Materials supplied by the federal military stock, underwritten by the department of defence national quality assurance authority.
What is used as a rapid means of material identification?
Colour coding
What does annealing do?
Changes the metal into a very soft and malleable state
What does heat treatment do?
Changes the metal into a soft condition, but not as soft as when annealed.
What does refrigeration storage do to a metal?
slows down the natural age process, remain in heat treated or quenched condition for longer
What is artificial age treatment?
Precipitation treatment, artificially heated to get the maximum strength of an alloy
What is the natural age process?
Room temperature natural process, starts immediately when cooled
What does aluminium and magnesium alloy corrosion look like?
White to grey powdery deposits
What does iron and steel corrosion look like?
Red rust
Define Corrosion
Corrosion is the tendency of a metal to revert to its thermodynamically more stable oxidised state
Whats surface corrosion?
Direct reaction of a metal surface with oxygen, or unpainted metal contact with the following:
Sea-air
Aircraft exhaust gases
Funnel smoke
What is stress corrosion?
Cracks occurring on stressed parts of the aircraft in a corrosive environment
What is fatigue corrosion?
Cyclic stresses from an external load
Whats fretting corrosion?
Two surfaces, one of which metal rubbing together causes the natural protection to wear away. These particles oxidise and become abrasive which form areas of corrosion
Whats crevice corrosion?
High ratio of cathode to anode area involved due to oxygen concentration between inside and outside the crevice
Whats filiform corrosion?
Corrosion starting at fasteners and extends beneath protective paints which may not be visible until it has become severe. Shallow and not structurally dangerous.
Whats exfoliation or layer corrosion?
When corrosion occurs at layers parallel and beneath the surface which wedges and lifts the surface.
Whats dissimilar metal corrosion (electrochemical/galvanic)?
When there is a difference in galvanic potential between two metals in contact, the metal of lower potential forms the anode and is oxidised or corroded.
Define erosion
The loss of material from components by the action of small particles such as grit, sand, stones, ice and water.
What are the 3 high temperature environments aircraft are subjected to?
Desert Regions
Arid Salt Laden
Hot & Humid
What are the 3 main consequences of corrosion?
Reduction in static strength
Stress corrosion cracking
Shortening of fatigue life
Blank
What are the two different methods of corrosion removal?
Mechanical and chemical
Depending on wether a metal is supplied to a British, American or French standard, how will its thickness be measured?
British - Standard Wire Gauge
American - thousandth of an inch
French - mm
What can you do to slow down the natural age hardening process?
Refrigeration
What is the most significant form of environmental damage?
Corrosion
What type of corrosion is caused by cyclic stress from an external load?
Fatigue
Which method of corrosion removal is used on magnesium alloy?
Phosphoric
What would you use and in what ratio to neutralise an acid spillage?
An aqueous solution of 10% by weight
What would you use and in what ratio to neutralise an alkali spillage?
Chromic acid 5% by weight
What PH should cleaning water be?
Between 5 and 9
When should acid and alkali spillages be re-examined?
At weekly intervals
What primer is more resistant to water and ester based lubricants?
Epoxy
What type of corrosion occurs where there is a leakage of highly corrosive fluid such as battery acid?
Pitting corrosion
How do you remove acid spillage?
1) Remove as much as possible with clean rag
2) neutralise with aqueous solution 10% by weight of sodium bicarbonate
3) use blue roll to avoid washing into inaccessible areas
4) remove blue roll and swab the areas underneath
5) flush with copious amounts of water where electrical, soundproofing and trim are not involved
6) test with universal indicator, PH between 5 and 9 👍
7) dried out, examine and reexamine on weekly intervals
How do you remove alkali spillage?
1) remove with clean rag
2) swab with 5% chromic acid solution
3) flush with clean water unless electrical, soundproofing or trim are involved
4) re examine at weekly intervals
How to remove micro organisms?
1) Slime or fungal deposits removed with bristle brush
2) apply solution of one parts defstan 78-17, five parts hot water (50 degrees centigrade)
3) rinse with copious amounts of water
4) close inspection of surface carried out
