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Flashcards in Metals Deck (43)
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1

Define specific gravity

Specific gravity is the ratio of the density of a substance to the density of a reference substance

2

Define light metals

Metals who have specific gravities less than 5

3

Which 4 light metals are used in production

Magnesium
Titanium
Aluminium
Beryllium (limited use as toxic to 1/5 of population)

4

What structures do the 4 light metals have

Aluminium - FCC
Mg, Ti, Be - HCP
Ti at 822deg - BCC

5

What are the 6 main additives to make Al alloys

Cu
Mn
Si
Mg
Zn
Li

6

Al alloy groups

1XXX - 99% Al
2XXX - Cu
3XXX - Mn
4XXX - Si
5XXX - Mg
6XXX - Mg & Si
7XXX - Zn

7

List disadvantages of alloying Al

1. Deformability is impaired
2. Corrosion resistance is best for pure Al
3. Surface finish is best for pure Al
4. Density increased
5. Conductivity is best for pure Al

8

List advantages of alloying Al

1. Increase strength (work/age hardening)
2. Improved castability (add Si)

9

What are the two families of alloys

- heat treatable (2xxx,6xxx,7xxx)
- non-heat treatable (1xxx,3xxx,5xxx)

10

Describe general production route for alloys

1. Casting
2. Pre-working treatments
3. Hot working
3. Cold working
5. Post processing
6. Finishing

11

Why is homogenisation important in alloying

pre hot working step, can last 24hrs at elevated temperature to reduce micro/macro segregation in the material

12

Describe effects of the quenching process

- can lead to residual stresses causing distortion (reduce risk by quenching in hot water)
- slower quenching leads to a reduction in achievable strength. (due to allowing time for microstructural change)

13

Alloy conditions.

F = as fabricated
H = cold worked
O = annealed
T = fully heat treated
W = solution heat treated

14

Definition of annealed

Material that is cooled slowly, allowing for micro structural change and increasing toughness. This reduces high strength potential however.

15

At what temperature is homogenisation and solution treatment held at

Heated to below the eutectic point

16

Why is quenching process important

- Used to prevent precipitates forming and to keep the microstructure that was achieved at treatment temperature.
- if it is allowed to slow cool (i.e. quenching does not take place) then small precipitates will form in between the grain boundaries - this decreases mechanical properties and the material would be more brittle

17

Why is natural ageing important

- Very small precipitates are formed in the grains

18

Describe dislocation motion

- happens on particular slip systems
- a half plane of atoms is forced to one side and dislocations will be stopped by grain boundaries, or other

19

Definition: slip plane

plane of greatest packing density

20

Definition: slip direction

closest-packed direction within a plane

21

Definition: creep

The movement of vacancies when material is in an elevated temperature - progressive deformation

22

List obstacles and assists to dislocation

Obstacles:
- other dislocations
- grain boundaries
- precipitates
- cracks

Assists:
- elevated temperature
- availability if slip system

23

What does the Charpy test measure

Measures the energy absorbed on impact vs. Temperature

24

What does Von mises criterion state about plastic deformation

For plastic deformation to occur, at least 5 independent slip systems must be operational

25

How many slip systems do these have:
FCC
BCC
HCP

FCC - 12 slip systems, 5 independent i.e. always ductile

BCC - 48 slip systems, highly temperature dependent
(depends on DBTT)

HCP - 12 slip systems, temperature dependent

26

What does DBTT stand for

Ductile Brittle Transitional Temperature

27

Describe process of cold working/work hardening and how it strengthens a material

- Deforming a crystal, we get dislocation movement in certain directions
- Dislocations are also generated and they all obstruct each other
- This increases the materials strength

28

Disadvantages to cold working/work hardening

1. The increase in strength means ductility decreases
2. The material becomes much more brittle

29

What process is used to overcome cold working/work hardening

Annealing

30

What is the advantage of having small grain sizes

- harder for dislocations to move
- also improves ductility and toughness