Materials And Corrosion

Question 1

What two categories are metals and alloys divided into?

Answer 1

Ferrous & Non Ferrous

Question 2

What 3 metal standards do we use?

Answer 2

British Standards (BSI)
French Standards (AFNOR)
American Standards (SAE)

Question 3

What materials do not need a certificate of conformity?

Answer 3

Materials supplied by the federal military stock, underwritten by the department of defence national quality assurance authority.

Question 4

What is used as a rapid means of material identification?

Answer 4

Colour coding

Question 5

What does annealing do?

Answer 5

Changes the metal into a very soft and malleable state

Question 6

What does heat treatment do?

Answer 6

Changes the metal into a soft condition, but not as soft as when annealed.

Question 7

What does refrigeration storage do to a metal?

Answer 7

slows down the natural age process, remain in heat treated or quenched condition for longer

Question 8

What is artificial age treatment?

Answer 8

Precipitation treatment, artificially heated to get the maximum strength of an alloy

Question 9

What is the natural age process?

Answer 9

Room temperature natural process, starts immediately when cooled

Question 10

What does aluminium and magnesium alloy corrosion look like?

Answer 10

White to grey powdery deposits

Question 11

What does iron and steel corrosion look like?

Answer 11

Red rust

Question 12

Define Corrosion

Answer 12

Corrosion is the tendency of a metal to revert to its thermodynamically more stable oxidised state

Question 13

Whats surface corrosion?

Answer 13

Direct reaction of a metal surface with oxygen, or unpainted metal contact with the following:

Sea-air
Aircraft exhaust gases
Funnel smoke

Question 14

What is stress corrosion?

Answer 14

Cracks occurring on stressed parts of the aircraft in a corrosive environment

Question 15

What is fatigue corrosion?

Answer 15

Cyclic stresses from an external load

Question 16

Whats fretting corrosion?

Answer 16

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

Question 17

Whats crevice corrosion?

Answer 17

High ratio of cathode to anode area involved due to oxygen concentration between inside and outside the crevice

Question 18

Whats filiform corrosion?

Answer 18

Corrosion starting at fasteners and extends beneath protective paints which may not be visible until it has become severe. Shallow and not structurally dangerous.

Question 19

Whats exfoliation or layer corrosion?

Answer 19

When corrosion occurs at layers parallel and beneath the surface which wedges and lifts the surface.

Question 20

Whats dissimilar metal corrosion (electrochemical/galvanic)?

Answer 20

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.

Question 21

Define erosion

Answer 21

The loss of material from components by the action of small particles such as grit, sand, stones, ice and water.

Question 22

What are the 3 high temperature environments aircraft are subjected to?

Answer 22

Desert Regions

Arid Salt Laden

Hot & Humid

Question 23

What are the 3 main consequences of corrosion?

Answer 23

Reduction in static strength

Stress corrosion cracking

Shortening of fatigue life

Question 24

Blank

Question 25

What are the two different methods of corrosion removal?

Answer 25

Mechanical and chemical

Question 26

Depending on wether a metal is supplied to a British, American or French standard, how will its thickness be measured?

Answer 26

British - Standard Wire Gauge
American - thousandth of an inch
French - mm

Question 27

What can you do to slow down the natural age hardening process?

Answer 27

Refrigeration

Question 28

What is the most significant form of environmental damage?

Answer 28

Corrosion

Question 29

What type of corrosion is caused by cyclic stress from an external load?

Answer 29

Fatigue

Question 30

Which method of corrosion removal is used on magnesium alloy?

Answer 30

Phosphoric

Question 31

What would you use and in what ratio to neutralise an acid spillage?

Answer 31

An aqueous solution of 10% by weight

Question 32

What would you use and in what ratio to neutralise an alkali spillage?

Answer 32

Chromic acid 5% by weight

Question 33

What PH should cleaning water be?

Answer 33

Between 5 and 9

Question 34

When should acid and alkali spillages be re-examined?

Answer 34

At weekly intervals

Question 35

What primer is more resistant to water and ester based lubricants?

Answer 35

Epoxy

Question 36

What type of corrosion occurs where there is a leakage of highly corrosive fluid such as battery acid?

Answer 36

Pitting corrosion

Question 37

How do you remove acid spillage?

Answer 37

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

Question 38

How do you remove alkali spillage?

Answer 38

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

Question 39

How to remove micro organisms?

Answer 39

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