Cu alloys

Question 1

Extraction of Cu from ores

Answer 1

We can find Cu in two main forms in nature: sulfides or oxides.
- The first step is melting
- Then blowing O2 to oxide sulfides to obtain blister copper.
- Blowing air to oxide blister Cu.
- Then de-oxides copper.

Question 2

General properties of Cu

Answer 2

• FCC structure
• Density high
• Medium melting temp
• High thermal cond.
• Middle thermal expansion
• medium E

Question 3

Factors affecting conductivity

Answer 3

Electrical resistivity is affected by three factors:
1) dissolved elements
2) temp
3) lattice defects

Question 4

Pure copper grades

Answer 4

Are distinguished by the achievable conductivity
- Oxygen free: highest grade
- Electrolytic tough pitch copper: small residual oxygen
- Phosphorous-deoxidized copper: P is strong de-oxidizer but deplets conductivity.

Question 5

Cu-Zn alloys (Brass)

Answer 5

• Extended solid solution for ALPHA phase (FCC) with higher strength and workhardening ability.
• For Zn>36% the BETA phase field is involved featuring a disordered BCC structure at high temp, but becomes ordered and stronger at temp below 460°C.
• P is insoluble in Cu and forms a dispersion of globules that helps the chip breakage and lubrication.
• A typical BETA brass alloy is C36000 that present an improved machinability.

Question 6

Other alloys

Answer 6

• Cu-Sn phosphor bronze
• Cu-Al for hot and cold forming
• Cu-Ni for coinage

Question 7

Precipitation strengthening

Answer 7

Some alloys as Cu-Be, Cu-Cr-Zr combi e good electrical thermal cond. with significantly high strength for some applications requiring wear resistance, non-sparking, non-magnetic.

Question 8

Thermal treatments

Answer 8

• Apart from precipitation strengthening other Cu alloys are simply subjected to annealing to recover stresses of workhardening.

Question 9

Mechanical properties improvements

Answer 9

• Alloying and workhardening.
• Precipitation strengthening.

Question 10

Colours of Cu alloys

Answer 10

• Red –> copper
• Bronze-gold –> bronze
• Tan-gold –> red brass
• Yellow-gold –> brass
• Pink –>Copper-nickel
• Gray-white –> Nickel-silver

Question 11

Corrosion resistance

Answer 11

• Copper behaves as a noble metal and is almost immune from galvanic corrosion
• A passivating film protect the metal in the most of enviroments
• The oxide layer is red bu with time can appear a green CuCO copper carbonate.
• In brass alloy a de-zincification can be a matter of concer because it leave a porous Cu structure.
• Stress corrosion cracking occours when an alloy is subjected to load and a chemical exposure to critical reagents like ammonia or ammonium compounds
• Copper present also a excellent antibacterical property.

Question 12

Key features of Copper

Answer 12

• High thermal cond.
• High electrical cond.
• Good machinability
• Excellent corrosion resistance
• Good formability
• Good castability
• Fully recyclable
• Good weldability

Question 13

Applications of copper

Answer 13

Roof, circuits, wires, heat exchanger, bottles, silos, pothydraulic components

Question 14

Applications of brass

Answer 14

• Screw, bullets, achitecture parts or fornture parts, electrical components, bearing components, musical stuff.

Question 15

Nickerl silver applications

Answer 15

• Clarinet component, jewels, glasses, cameras.