Chapter 6. Copper and Copper Alloys. /MS371/ Structure and Properties of Engineering Alloys

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1 Chapter 6 Copper and Copper Alloys

2 Overview of copper alloys Main characteristics High electrical, ease of Relative electrical and thermal conductivities (at 20 o C)

3 Overview of copper alloys Cu + Zn ( 黃銅 ) : good! high Zn, high strength: edge of stairs, coin small damping capacity: instrument ( 징 ) Cu + Sn ( 靑銅 ) : good resistance statue Cu + Ni : 100 圓, 500 원 Cu + Pb : good mechanical work Cu + Be : material of (no spark, not such as flint or firestone)

4 Production of copper Copper sulfide Impurity in Cu bad effect on expected Cu properties high purity Cu is preferable * Simplified process: Cu 2 S + O 2 2Cu (blister copper) + SO 2 - just by, copper sulfide reacts with oxygen in the atmosphere then, copper is deposited at the bottom - at the end of this converter blow, some of Cu is oxidized to Cu 2 O

5 Classification of copper alloys

6 Electrolytic tough-pitch (ETP) copper minimum 99.9% Cu, 0.04% O (oxygen limit: 0.02~0.05%) least of the industrial coppers (wire, rod, plate..) Oxygen is almost in Cu

7 Microstructure of tough-pitch copper Cu 2 O interdendritic eutectic above 400 o C, Cu 2 O + H 2 ( Hot-rolled stringers of Cu 2 O and complete recrystallization in Cu) 2Cu + H 2 O (steam) - deoxidation to occur in using H 2 containing reducing gas Internal hole by steam along grain boundary - small hydrogen atoms are able to diffuse into the solid copper - however, the formed by the reaction is insoluble in copper - thus, electrolytic tough-pitch copper cannot be used above 400 o C

8 Oxygen-free high conductivity (OFHC) copper Removal of oxygen by flowing gas of CO, N Hot-worked oxygen-free copper Oxygen-free copper exposed to H2 at 850C for 0.5h By removing oxygen, - free of, clear structure, absence of hydrogen - however, it is not used for due to high cost, but for electronics

9 Cu-Zn alloys ( 황동, Brass) (coin) Cartridge brass - best combination of and occurs at 70Cu-30Zn - very important in industry Muntz metal for heat exchanger

10 Structure of Cu-Zn alloys Commercial brass can be divided into 2 groups α brass with the α structure and containing up to about 30% Zn brass with the α + β twophase structure, which is mainly based on a 60Cu:40Zn ~30% Zn ductility and toughness is increasing up to ~30% Zn Phase diagram of the copper-zinc

11 Structure of Cu-Zn alloys 90% Cu - 10% Zn 70% Cu - 30% Zn with a higher Zn content, more annealing are observed in α grains

12 Effect of small amount of plastic deformation Pure copper deformed 5% cellular distribution of dislocation tangles Red brass (85% Cu - 15% Zn) deformed 10% planar arrays of dislocations developing High brass (63% Cu 37% Zn) deformed 10% well-defined planar arrays of dislocations

13 Change in dislocation arrangements Increasing Zn content lowering the stacking-fault energy ( ) of Cu In pure Cu, high SFE dislocation can cross slip easily easy slip With Zn, lower SFE difficult short stacking-fault ribbons Effect of Zn content on the stacking-fault energies of Cu-Zn brasses [After J. Hedworth and G. Pollard, Metal. Sci. J. 5(1971):42.]

14 Corrosion of Cu-Zn alloys (Brass) stress corrosion cracking Intergranular stress-corrosion crack in cartridge brass (70%Cu-30%Zn) Dezincification of cartridge brass tube α brass containing more than 15% Zn stress-corrosion cracking (SCC) SCC occurs usually along the corrodes preferentially and leaves a porous residue of Cu and corrosion products in, for example,

15 Cu-Sn alloys ( 청동, Bronze) Sn addition to prevent ; tin bronze P addition as a agent during casting; phosphor bronzes High strength, wear resistance, good sea-water corrosion resistance Comparison of purpose Brass Good formability Bronze Excellent corrosion resistance

16 Copper-Aluminum alloys So-called Aluminum Bronze Quite hard, high strength Good corrosion resistance due to aluminum

17 Structure of Cu-Al alloys Increasing strength, ductility ~9.5% Al, decomposition Rapidly quenched to RT transformation Cu-Al phase diagram

18 Mechanical properties of Cu-Al alloys ~10% Al, β phase increase - drops off rapidly - but it has good tensile strength for bearings

19 Cu-Si alloys Silicon Bronze contains 1~3% Si Low-cost substitute for Tin Bronze Good corrosion resistance Above the Si solubility(4% Si), the good properties drop off Cu-Si phase diagram

20 Cu-Be alloys Containing 0.6~2% Be with 0.2~2.5% Co -hardened and heat-treated as high as 212 ksi strength developed in commercial copper alloys

21 Cu-Be alloys - Precipitation hardened with 2% Be : Supersaturated solid solution GP zones γ γ (flat plates) GP zones parallel to (010) and (100) matrix planes Intermediate ordered γ CuBe phase Eutectoid-type precipitation of ordered CuBe γ phase in a disordered α-matrix

22 Cu-Ni alloys Cu + 10, 20, 30% Ni : cupronickels Used for condenser tubes and plates, heat exchangers, chemical process equipment Copper and nickel are completely soluble in all proportions in the solid state

23 Effect of nickel on mechanical & electrical properties solid solution hardening high electrical resistivity Strength of nickel Strength of copper low dependency of temp mechanical properties electrical properties