Chapter 6 Copper and Copper Alloys
Overview of copper alloys Main characteristics High electrical, ease of Relative electrical and thermal conductivities (at 20 o C)
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 firestone)
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
Classification of copper alloys
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
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
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
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
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
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
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
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.]
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,
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
Copper-Aluminum alloys So-called Aluminum Bronze Quite hard, high strength Good corrosion resistance due to aluminum
Structure of Cu-Al alloys Increasing strength, ductility ~9.5% Al, decomposition Rapidly quenched to RT transformation Cu-Al phase diagram
Mechanical properties of Cu-Al alloys ~10% Al, β phase increase - drops off rapidly - but it has good tensile strength for bearings
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
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
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
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
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