Copper and its alloys

Copper alloy selection criteria

Mechanical properties

Corrosion resistance

• In atmosphere, seawater, steam and in many chemical environments due to formation of protective passive film.

• Can still be attacked by common reagents and environments

• ADD

Electrical and thermal conductivity

Surface finish and colour

• Used for aesthetic purposes due to the attractive colour

Ease of fabrication

Strengthening mechanisms

• Solution hardening:

Pure coppers

• Contain at least 99.3% Cu

• Soft, ductile, very modest strength

• Responds very well to work hardening

• High thermal and electrical conductivity

• Good fabricality (forming and joining) but casting is difficult

Wrought coppers: According to oxygen and impurity contents

Oxygen free coppers

• Applications requiring high electrical and/or thermal conductivity (around 100% IACS)

• 0.001wt%O or less

• Most expensive

• Produced by electrolytic refining of Cu

• Used for high currents and super corrosion resistant, best of all coppers

• Exceptional ductility

• Low softening temp. 150

• Adding:

  • S, Cd, Fe, Co, Zr imparts resistance to softening at times and temps in soldering.

  • Te, S for good machinability

• Dispersion strengthening with Al oxides inhibits softening at elevated temps.

• Applications: electric conductors/connectors, heat exchangers, microwave tubes, chemical plant equipment, gaskets

Tough pitch copper

• Contain up to 0.05% O

• Have Cu2O inclusions which affects strength, hardness and ductility slightly

• Prone to H2 embrittlement. Heating to above 400 in an H2 containing atmosphere leaves a porous structure so cannot be used in reducing environments.

• Not easily brazed

• Less suitable for fabrication by CW but produces small solidification shrinkage - less scrap loss.

• May contain small amount of elements to impart softening resistance.

• Electrolytic tough pitch copper (Cu-ETP) has a high conductivity of pure copper (100% IACS). Contains enough oxygen to ensure that residual impurities are present as oxides rather than in solution.

• Applications: electrical wires and cables, roofing and architectural trim

Phosphorus deoxidised coppers

• P added to reduce oxygen in copper when in the molten state.

• P reacts with dissolved O to form POs that will pass as immiscible slag

• Unreacted P is dissolved in Cu

• Different grades depending on amount of residual P.

  • Example: Phosphorus deoxidised high residual phosphorus contains 0.01% to 0.04% P. Reduction in electrical conductivity. 15% conductive than tough pitch coppers.

• Can be welded without danger of hydrogen embrittlement.

• Applications: piping and tubing

Types of coppers

Silver bearing copper and silver bearing tough pitch copper

• Example C11300 - 100% IACS

• Non heat treatable alloy

• Addition of 0.05% Ag reduces conductivity by 1% but increases recrystallisation from 150 to 340 degrees.

• Solder of electrical conductors to hard drawn contacts eg segments of electric motors. Solder at temps of less than 340.

Tellerium copper

• Example C14500 - 93% IACS

• 0.5% Te improves machinability as it forms a chip breaker

• Does not vastly affect conductivity

• Corrosion resistant

• Applications: high duty electrical contacts in machines and switch gears for ships and chemical parts, forgings and screw machines (lathe) products

High copper content alloys:

• Contain up to 5% alloying elements exs: Be, Cd, Cr, Fe, Zr, Ni, Co, Sn. Used to impart higher strength, thermal stability (softening resistance) while retaining sufficient electrical conductivity.

• Wrought: C16200-C19900; Cast: 81400-C82800

• Retain FCC structure of Cu

  • Cadmium copper:

    • Cd is toxic and has little effect on conductivity of Cu.

    • Raises softening resistance, wear resistance, strength, toughness, fatigue resistance of Cu.

    • Resistant to arc erosion.

    • Non heat treatable alloy.

    • Strength by work hardening and solid solution strengthening.

    • Example: C16200 (99% Cu, 1% Cd), TS - 276-655MPa; YS 100-490MPa; 90% IACS

    • Applications: overhead transmission cable, overhead conductors for trams, aircraft wiring

  • Chromium copper:

    • Precipitation hardenable (cast and wrought)

    • Containing up to 1.2 wt% Cr for higher strength and improved thermal softening resistance 350

    • Electric conductivity >80%IACS.

    • Exs: C18200 (99Cr-1%Cr), 80%IACS (TH04 temper) and 40%IACS at TB00temper (YS 400MPa and TS 460MPa at TH04 temper)

    • Quenched from 1000 oC to produce a soft and ductile alloy with low electrical conductivity.

    • Dissolved Cr will hinder flow of electrons, same for all alloys.

    • Heating for 2 h at 500 oC restores electrical and mechanical properties.

    • Excellent workability coupled with medium to high conductivity.

    • Applications: resistance welding electrodes; current carrying shafts; moulds; circuit breaker parts; trolley wire for high speed trains.

  • Beryllium copper:

    • Cast and wrought alloys

    • Precipitation hardenable containing up to 2%Be (wrought); 2.85% (cast), and sometimes small amounts of Co, Ni and Fe.

    • Can be formed in soft condition.

    • High strength copper alloys.

    • Two classes:

    • High strength alloy:

    • Ex: C17000 (98Cu-1.7Be-0.3Co) YS THO4 1200MPa 25%IACS

    • Used when mechanical properties are needed rather than electrical properties. Softened by heating at 800 oC and quenched to allow cold work and machining. Heat treated at 300-320 oC for 2 h.

    • Applications: pressure gage, bourdon tubes, hand tools in explosive environments (no sparks!), flexible bellows, fasteners,), welding equipment, plastic injection moulds (cast); pitot tube housing in high speed aircraft, golf club heads.

    • High conductivity alloy:

    • Ex: C17600 (Cu 0.25-0.5Be 1.4-1.7Co 0.9-1.1Ag) YS TH04 690-825MPa; 50-60%IACS.

    • Applications: A high-conductivity alloy designed especially for resistance welding electrodes for spot, seam, flash, and projection welding methods; electrical connectors, clips.

Brasses (general)

• Alloy of copper and zinc (up to 50%) in various amounts to get a range of brasses with varying properties

• >15% Zn, alloy prone to SCC dealloying

• Both wrought and cast alloys

• Pb provides high machinability and Sn is added to high Zn brasses to improve corrosion resistance.

• Subgroup of high strength brasses alloyed with Mn, Fe, Sn, Al, Si and/or Co

• Brasses most common cast copper alloys due to their excellent castability and good combination of strength and corrosion resistance

• Pb provides pressure tightness by sealing shrinkage pores

• Applications: decoration, low friction (locks, gears, bearings), good acoustic properties (bells, instruments)

Wrought brasses

Common brasses:

• Zinc is the primary alloy

• Low zinc retains FCC (alpha)

• High Zn (>39wt% Zn) like muntz comprises of the hard BCC beta’ phase

• Between 32%-39% Zn may have a duplex alpha + beta’ structure, easy to hot work and machine

• Increasing Zn produces stronger alloys but with a decrease in corrosion resistance

• Produced as sheets for stampings (springs, switch components), tubes (drains, plumbing), and rod (fasteners and forgings)

• Adequate corrosion resistance in most atmospheric environments.

• Subject to dezincification in stagnant and acidic aqueous environments.

• May fail by SCC in presence of moist ammonia, amines, mercury components.

• High electric conductivity example: Cartridge brass (30% zinc, used in common electrical hardware has conductivity of 28% IACS, bullet cases strong and ductile)

• Selection based on formability (cartridge optimum), corrosion resistance (low Zn%), colour (reddish pink to pale yellow with increasing Zn content)

• Increase zinc, become cheaper

• Examples:

  • Gilding Metal (<5% Zn – C21000) – ( Excellent CW; Good HW) coins, medals, fuse caps, plaques, jewelry base

  • Commercial Bronze (~10% Zn – C22000) – ( Excellent CW, Good HW) screen cloth, screws, rivets, marine hardware

  • Jewelry Bronze (~12.5% Zn – C22600) - ( Excellent CW, Good HW) fasteners, costume jewelry, base for gold plate

  • Red Brass (~15% Zn – C23000) - ( Excellent CW, Good HW) fasteners, conduit, heat exchanger tubing, plumbing pipe, radiator cores

  • Low Brass (~20% Zn – C24000) ( Excellent CW) – battery caps, musical instruments, bellows, clock dials

  • Cartridge Brass (~30% Zn – C26000) – ( Excellent CW) radiator tanks/cores, lamp fixtures, fasteners, locks, hinges, ammunition components, pluming accessories, rivets

  • Yellow / standard Brass (~ 35% Zn – C27000) – ( Excellent CW) uses same as cartridge brass but not for ammunition.

  • Basis Brass (~37% Zn) Cheapest of the cold working brasses but hot works well. It lacks ductility and only capable to withstand simple forming operations

  • Muntz Metal (40% Zn – C28000) – ( Excellent HW) Not suitable for cold working. Relatively cheap. Architectural panels sheet, large nuts and bolts, heat exchanger tubing, brazing rod, hot forgings

Wrought leaded (Cu-Zn-Pb):

• Lead (0.5 - 3%) added to provide high machinability by acting as a chip breaker and tool lubricant.

• Available as rod, bar, shapes and tubing.

• Ar added to inhibit dezincification (C35330)