Note 3: Matrix Material

Question 1

What are the properties on Aluminium Alloys?

Answer 1

Aluminium has quite low density approximately one-third as much as steel.
- Quite reactive (casting alloys - with Si).
- Easy to process (wrought alloys - with Mg).
- Moderate properties (structural alloys -with Cu or Zn/Mg).

Aluminium resists the kind of progressive oxidation that causes steel to rust away. The exposed surface of aluminium combines with oxygen to form an inert aluminium oxide film only a few ten millionth of an inch thick, which blocks further oxidation.

Question 2

What are the properties of Magnesium Alloys?

Answer 2

• Lowest density.
• Very reactive.
  Harder to process (Cast alloy, with Al, Mn).
• Less strong, stiff, tough (aircraft forging alloys, with Zn, Zr).

Question 3

What are the properties of Titanium Alloys?

Answer 3

• Higher density.
• Stiffer, stronger.(Pure titanium).
• Higher temperature resistance (Alpha Titanium with Al, Sn).
• Quite reactive at high temperature (Beta Titanium with V, Fe, Al)>

Question 4

Give a summary of the metal matrix materials.

Answer 4

1. Al Alloys - cheapest, tough, easy to process.
2. Mg Alloys - Lightest, most brittle.
3. Ti Alloys - Strongest, tough, highest melting point, most expensive.

Question 5

What are the properties of Aluminium Oxide (Alumina) - Ceramic?

Answer 5

Density: 3,900 (kg/m^3)
Melting Point: 2045 C
Young’s Modulus: 340 GPa
Strength: ~ 400 MPa
Toughness: 4 (MPam^1/2)

Question 6

What are the properties of Zirconium Oxide (Zirconia)- Ceramic?

Answer 6

Alloyed with magnesium (or ytrrium) oxide for extra toughness.
Density: 5,700 (kg/m^3).
Melting point: ~ 2660 C
Young’s Modulus: 205 GPa
Strength: ~ 400MPa
Toughness: 4 (MPAm^1/2)

Question 7

What are the properties of Glass Ceramic - Ceramic?

Answer 7

Most commonly lithium aluminosilicates (LAS)
Density: 3,500 kg/m^3
Melting point: ~ 1,300 C
Young’s Modulus: 80GPa.
Strength: ~150MPa.
Toughness:1.5 (MPam^1/2)

Question 8

What are the properties of Carbon - Ceramic?

Answer 8

Large variations in structure and properties.
Main benefit - very high temperature strength (with no oxygen).
With oxygen, oxidises from 400 C

Question 9

Give a summary for ceramic matrix material.

Answer 9

1. Alumina - High temperatures in air, high stiffness.
2. Zirconia - higher temperature.
3. Glass Ceramic - Easier processing due to lower melting temperature, less stiff and tough.
4. Carbon - For high temperature (no air).