Application Potential of Copper and Copper Alloys in Metallurgical Engineering Industries

By Dr Thoguluva Raghavan Vijayaram PhD

Senior Lecturer, Department of Manufacturing Process and System, Faculty of Manufacturing Engineering, UTeM Universiti Teknikal Malaysia Melaka

Copper is an important engineering metal that has been in use for over 6000 years. Copper is the backbone of the electrical industry. It is also the major metal in a high number of highly important engineering alloys, namely the brasses and bronzes. Pure copper in its annealed state has a tensile strength of about 200 MPa, with an elongation of nearly 60%. The copper alloys also lend themselves nicely to the whole spectrum of fabrication processes, including casting, machining, and welding. Unfortunately, copper is heavier than iron. Although the strengths can be quite high, the strength/weight ratio for the copper alloys is usually less than that for the weaker aluminium and magnesium alloys.

Ornaments and coins were fashioned from it throughout the history of mankind. Although virtually all copper goes towards electrical and plumbing use, copper still has many ornamental uses. Copper is unique in color; no metal has the same color. Brass and bronze, both copper alloys, are not as bright orange as copper. Copper easily bends, and is usually alloyed with other metals to toughen it. Normally, it is alloyed with tin and/or zinc, but it may also be mixed with silver and nickel. When mixed with considerable amounts of tin, the alloy is known as bronze, and when mixed with considerable amounts of zinc the alloy is known as brass. Copper may also be alloyed with both tin and zinc. However, no demarcation is drawn between brass and bronze. Other names given to alloyed copper are: Monel Metal: an alloy of copper and nickel, German Silver: an alloy of copper and silver, Halfbreed: an alloy of copper and silver. Halfbreed usually refers to a natural mixture of copper and silver. Copper is ductile and malleable and a very good conductor of electricity, second after Silver. Copper is also used in pigments, insecticides, and fungicides, although it has of lately been largely replaced by synthetic chemicals.

Copper is a vital modern metal. Copper and copper alloys meet the challenges of modern life in many ways. Often seen in plumbing systems and good quality roofing, they are also frequently unseen providing essential services inside equipment in houses, offices, commercial and industrial buildings. They are amongst the most necessary materials needed to provide the means to keep home, commerce and industry running. Copper is probably the most versatile metal in common use. The surface lustre and warm colour of copper and copper alloys makes them beautiful to look at and this means they find widespread use in architecture. The unique combination of properties offered by copper and its alloys results in benefits when they are used in the many industries referred to. In many instances the ideal property combination required can be met only by a copper base material. There may be no better alternative material choice - other material types such as iron base alloys (carbon, alloy and stainless steel), nickel base alloys, aluminium alloys and alloys based upon titanium do not, in very many cases, combine all the required properties or their cost may be too high.

Copper is widely used in its unalloyed condition as well as in alloys with other metals. In the unalloyed form, it has an extraordinary combination of properties which make it the basic material in the electrical industry, some of those properties being its high electrical conductivity and corrosion resistance, ease of fabrication, reasonable tensile strength, controllable annealing properties, and general soldering and joining characteristics. The wide variety of brasses and bronzes it forms with other metals, however, also have associated useful properties that make alloyed copper indispensable for many additional engineering applications. Copper comes from two principal sources: ores and copper scrap. Most copper is derived from copper sulfide ore deposits from which the copper sulfide is concentrated by various ore-dressing procedures to yield a product that can be smelted at a profit.

Unalloyed copper is a metal with high electrical conductivity, hence used to a larger extent in the electrical industry. Electrolytic tough pitch: ETP copper is the least expensive of the industrial coppers and is used for the production of wire, rod, plate, and strip. ETP copper has a nominal oxygen content of 0.04%. Oxygen free high conductivity: OFHC copper is produced by casting the ETP copper under a controlled reducing atmosphere, thereby eliminating oxygen and hydrogen embrittlement.

Historically, copper alloy castings were among the earliest metallic objects made by man from molten metal. Since copper could be found as native metal, it has been worked into artifacts, far back into antiquity. Copper melting and casting by artisans are known to have occurred as early as 3000 B.C. The full value of copper alloys as casting materials, however had to await the metallurgical developments of the past several hundred years, discoveries which made the metal more abundant, with a greater variety of useful properties. It may be noted that sand casting processes account for the greater percentage of castings produced in these alloys. Certain engineering advantages are inherent in the use of copper alloys for castings. Some of these include: electrical and thermal conductivity, corrosion resistance, appearance, nontoxicity, and bearing qualities.

Copper may be alloyed with many elements, singly and in combinations, with beneficial effects on the properties of the alloy. Hence it is not surprising that the number of alloys which might be used for castings purposes is great. The variety of alloying possibilities is so numerous that their classification necessititates separation of the metals into major groups differing broadly from each other in composition. Copper Development Association System: CDAS has classified copper alloys into two groups: Wrought alloys and Cast alloys. Copper base alloys have a low enough freezing range so that they may be cast in permanent molds or dies under pressure. These alloys have been found favorable in view of the requirement of resistance to tearing, pressure tightness, and good mechanical properties. Rapid cooling of copper alloys in metal molds favors better properties than slow cooling in sand molds.

Wrought copper alloys are used to produce bus conductors, waveguides, vacuum seals, transistor components, coaxial cables and tubes, klystrons, microwave tubes, rectifiers, radio parts, printing rolls, rivets, auto parts, bus bars, radiator cores and tanks, lamp fixtures, fasteners, locks, hinges, ammunition components, pins, brazing rod, condenser plates, heat exchanger tubing, hot forgings, bellows, diaphragms, fuse clips, springs, welding equipment, nuts, bolts, stringers and threaded members, machine parts, marine protective sheathing and fastening, communication relays, ferrules, and resistors

Cast copper alloys are processed to manufacture electrical and thermal conductors, safety tools, molds for plastic parts, cams, bushings, bearings, valves, gears, flanges, pipe fittings, pump castings, plumbing goods, water pump impellers and housings, ornamental fixtures, belts, corrosion-resistant castings, marine fittings, piston rings, seal rings, steam fittings, worms, bushings, valve seats and guides, pickling hooks, and elbows used for sea water corrosion resistance.

Copper is an ancient metal and famous for its distinctive reddish brown color. Copper and copper alloys are classified according to a designation system administered by the Copper Development Association: CDA. In this system, numbers from C100 through C799 designate Wrought alloys and numbers from C800 to C999 Cast alloys. The common wrought copper alloys are listed below in Table-1. Commonly Cast Copper alloys are listed below in Table-2. Coppers have a miniumum copper content of 99.3% or higher. High coppper alloys have less than 99.3% copper, but more than 96%, and do not fit into the other copper alloy groups. The wrought coppers are classified according to their oxygen and impurity contents. They are Electrolytic Tough-Pitch, Oxygen-Free, and Phosphorus Deoxidized Wrought Coppers.

Table 1

Serial Number	Wrought Copper Alloy Type	Commercial Name
1	COPPER-ZINC	BRASSES
2	COPPER-ZINC-LEAD	LEADED BRASSES
3	COPPER-ZINC-TIN	TIN BRASSES
4	COPPER-TIN	PHOSPHOR BRONZES
5	COPPER-ALUMINIUM	ALUMINIUM BRONZES
6	COPPER-SILICON	SILICON BRONZES
7	COPPER-NICKEL	NICKEL BRASSES
8	COPPER-NICKEL-ZINC	NICKEL SILVER

Table 2

Serial Number	Cast Copper Alloy Type
1	CAST COPPERS
2	CAST HIGH-COPPER ALLOYS
3	CAST BRASSES
4	CAST-MANGANESE-BRONZE ALLOYS
5	CAST COPPER-ZINC-SILICON ALLOYS
6	CAST COPPER-TIN ALLOYS
7	CAST COPPER-TIN-LEAD ALLOYS
8	CAST COPPER-TIN-NICKEL ALLOYS
9	CAST COPPER-ALUMINIUM-IRON ALLOYS
10	CAST COPPER-NICKEL-IRON ALLOYS
11	CAST COPPER-NICKEL-ZINC ALLOYS

Electrolytic Tough-Pitch Copper: Type ETP, CDA 110 has a miniumum of 99.9% copper and a nominal 0.04% oxygen content. The normal limits of oxygen in ETP copper are between 0.02 and 0.05%. It is the least expensive of the industrial coppers and is used extensively for the production of wire, rod, plate, and strip. The oxygen converts some impurity elements to their oxides; on casting the oxygen forms an even dispersion of blow holes that prevents pipe cavities from forming. Upon hot working,these small blow holes are welded together.

Oxygen-Free Copper can be produced from electrorefined cathode copper by melting and casting under a reducing atmosphere of carbon monoxide and nitrogen so that oxygen is prevented from entering the copper. The electrical conductivity of oxygen free, 99.95% copper is about the same as ETP copper. If selected cathodes of high purity copper are remelted, 99.99% oxygen free copper can be produced, and is preferred for many electronics applications. Due to the special processing of the oxygen free coppers, they are more expensive than the ETP coppers.

Deoxidized Coppers: With the addition of sufficient phosphorus, all the available oxygen in the copper will be converted to Phosphorus Pentoxide. Since phosphorized high conductivity coppers contain very little retained phosphorus normally less than 0.009%, the high conductivity of copper is maintained. Higher levels of phosphorus are used in the deoxidised high phosphorus copper; CDA 122, so that these alloys may contain as high as 0.040 residual phosphorus, resulting in a lower electrical conductivity of about 85% IACS. The excess phosphorus in the copper prevents the adsorption of oxygen during hot working and annealing and allows this material to be welded.

Copper-Zinc alloys are categorized as brasses. The copper-zinc brasses consist of a series of alloys of copper with up to about 40% zinc. It has additional elements such as tin, aluminium, silicon, manganese, nickel, and lead are referred to as Alloy Brasses. Brasses are also able to be nickel and chromium plated and have sufficient thermal conductivity to be used for heat transfer media. The best combination of ductility and strength occurs at 70% copper and 30% zinc, and hence this alloy can be used for its excellent deep drawing ability. The 70% copper and 30% zinc alloy is descriptively called as Catridge Brass and used for other applications such as radiator cores and tanks, and lamp fixtures. Copper-60% and Zinc-40% is otherwise called as Muntz metal. Small amounts of lead from 0.50 to 3% are added to many types of brasses to improve their machinability and are called as leaded brasses. The addition of 1% tin to catridge brass: 70% Copper and 30% Zinc, improves its corrosion resistance in sea water. Since this alloy was adopted by the British Admiralty in the 1920s, it became known as Admiralty Brass. It was later found that small additions of arsenic, around 0.04% could almost eliminate a common corrosion condition called Dezincification and hence arsenical admiralty brass was used for a long time for marine condensers. Still later it was discovered that replacing the tin with aluminium gave the brass a self healing protective oxide on its surface. The hard aluminium type oxide film makes the alloy more resistant than admiralty brass to the impingement of high velocity water. Today, a 77.5% Copper-20.5% Zinc-2% Aluminium alloy: Aluminium brass; with an arsenic addition to inhibit dezincification has replaced admiralty brass for marine condensers. The addition of 1% Tin to Muntz metal improves its corrosion resistance and forms an alloy called Naval Brass.

High brasses contain 60% to 80% Copper, and 40% to 60% Zinc. These brasses, because of their high zinc contents have increased strengths. Small additions of alloying elements, such as 1% tin, to the brasses do not greatly affect their mechanical properties. However, multiple additions of manganese, iron, and tin, for example, to convert Muntz metal to manganese bronze significantly increase the strength of the muntz metal. Because of its increased strength, manganese bronze is best worked in the hot condition. The addition of up to about 3% lead to improve the machinability of brasses has practically no effect on the tensile strength and hardness of the leaded brasses. However ductility,\'and hence cold working ability of the brasses is reduced by the lead additions.

Unalloyed brasses are used to make coins, medals, bullet jackets, primers, plaques, jewellery base for gold plate, screen cloth, weather stripping, lipstick cases, marine hardware, angles, chains, fasteners, heat exchanger tubing and radiator cores. Besides, such brasses are processed to manufacture battery caps, musical instruments, clock dials, pumplines, flexible hose, and flashlight shells. Alloy brasses are processed to produce distilling tubes, aircraft turn-buckle barrels, propeller shafts, connecting rods, shafts, wear plates, clutch disks, and ferrules.

Copper-Tin alloys: Alloys consisting of principally copper and tin are properly called tin bronzes. Since phosphorus is usually added to these alloys as a deoxidizing agent during casting, the tin bronzes are commerically known as phosphir bronzes. These alloys possess desirable properties such as high strength, wear resistance, and good sea-water corrosion resistance. Wrought copper tin bronzes containing from 1.25% to 10% tin are termed phosphor bronzes since they usually contain up to about 0.1% phosphorus, which is added to improve castability and act as a deoxidizer. Cast Copper-Tin Bronzes have higher tin contents over about 10% and hence make copper-tin alloys unworkable, but castings containing up to 16% tin are used for high strength bearings and gear blanks. Gear-blank castings are often made by centrifugal casting process to ensure for soundness. Tin levels of about 10% are common for bearings, with variable quantities of lead being added to improve plasticity and adabtability for bearing surfaces.

Phosphor Bronzes are used to manufacture electrical contacts, flexible hose, pole-line hardware, bellows, bourdon tubing, cotter pins, lock washers, wire brushes, chemical hardware, textile machinery, bridge bearing plates, locator bars, sleeve bushings, truss wire, perforated sheets, welding rod, heavy bars and plates for severe compression, bridge and expansion plates and fittings, and articles requring good spring qualities, resiliency, fatigue resistance, good wear and corrosion resistance.

Copper-Aluminium alloys are called aluminium bronzes, although a better name would be aluminium brasses. These alloys are quite hard, have high tensile strengths, and are tough. They resist wear and fatigue and have excellent corrosion resistance due to the self healing surface film of aluminium oxide. Aluminium bronzes containing up to about 10% aluminium and with additions of about 5% Ironand 5% Nickel are exceptionally strong and tough, and have excellent corrosion and oxidation resistance at elevated temperatures. These alloys are used for high-strength bearings and gear wheels and can be used for dies for deep drawing some types of stainless steels.

Aluminium Bronzes are processed to make condenser, evaporator and heat exchanger tubes, distiller tubes, ferrules, bolts, pump parts, shafts, tie rods, overlay on steel for wearing surface, nuts, structural components, condenser tube and piping systems, mixing troughs and blending chambers, bushings and bearings,worm gears, cams, forming rolls, dies, plunger tips, glass sealing and porcelain enameling.

Copper-Silicon alloys are usually referred to as silicon bronzes or by their trade names such as Everdur or Herculoy. Most silicon bronzes contain between 1% to 3% silicon. Small additions of manganese and iron are sometimes added to improve their properties. Siliocn bronzes find engineering applications because of their resistance to corrosion and relatively high strength and toughness compared to low carbon steels. For many uses they are low-cost substitutes for the tin bronzes since, except in regard to impingement attack, they have good sea-water corrosion resistance. These alloys can be cast or hot- or cold-worked.

Silicon Bronzes are used to fabricate hydraulic pressure lines, anchor screws, bolts, cable clamps, cap screws, machine screws, marine hardware, nuts, pole-line hardware, rivets, U bolts, electrical conduits, heat exchanger tubing, welding rod, and propeller shafts.

Copper-Beryllium alloys contain between 0.6% to 2% Beryllium with additions of cobalt from 0.20 to 2.5%. These alloys are precipitation-hardenable and can be heat-treated to produce tensile strengths as high as 212 ksi, which is the highest strength developed in commercial copper alloys. Copper Beryllium alloys are used for tools which require high hardness and non sparking characteristics such as may be needed in the chemical industry. The corrosion resistance and fatigue resistance and strength of these alloys have made them useful for springs, gears, diaphragms, and valves. They are also used for electrical contacts and molds for forming plastics. Even though these alloys contain only a small amount of beryllium, their cost is relatively high and thus their use is only justified when other lower-cost alloys will not meet the engineering requirement of an application.

Copper-Beryllium alloys are used to make bellows, diaphragms, fasteners, lockwashers, springs, switch parts, roll pins, valves, welding equipment, fuse clips, relay parts, electrical conductors, resistance welding electrodes, seam welding steels, electrode holder jaws, cable connectors, current-carrying arms and shafts, circuit breaker parts, molds, spot welding tips, flash welding electrodes, electrical and thermal conductors requiring strength, and switch contacts.

Copper-Nickel alloys: Nickel is added to copper to form a series of solid-solution alloys of approximately 10, 20, and 30% Nickel called Cupronickels. The nickel additions increase the strength, oxidation, and corrosion resistance of copper. The cupronickels are used for marine condensers and tubing for conducting sea water because of their moderately high to high strength and resistance to the corrosive and erosive effects of high-velocity sea water. Since the cupronickels do not work-harden rapidly, they are used for condenser tubes and plates, heat exchangers, and a wide variety of chemical process equipment.

Copper-Nickel alloys are processed to manufacture condensers, condenser plates, evaporator and heat exchanger tubing, ferrules, salt water piping systems, communication relays, electrical springs, resistors, high strength constructional parts for sea water corrosion resistance, hydrophone cases, mooring cable wire, retainer rings, screws, pins for ocean telephone cable applications, brazing alloy, lead frames, control and sensing bellows.

Copper-Nickel-Zinc alloys are commerically called as Nickel Silvers. These alloys are essentially ternary copper-nickel-zinc alloys and do not contain silver. The zinc content of the nickel silvers ranges from about 17% to 27% Zinc, while their nickel content varies from about 8% to 18%. As the nickel content is increased, the color of the nickel silvers varies from soft ivory to silvery white.

Copper-Nickel-Zinc alloys are applied to fabricate rivets, screws, slide fasteners, optical parts, etching stock, hollow ware, name plates, plater’s bars, table flat ware, truss wire, zippers, bows, camera parts, core bars, base for silver plate, costume jewellery, radio dials, springs, resistance wire, key blanks, watch plates, and watch parts.

The number of possible new copper alloys is endless, and research is constantly in progress to find materials with superior properties. Some alloying combinations have as yet proved impossible to make because of the earth\'s gravity. For this reason experimental work on new alloys has been undertaken during Skylab missions to take advantage of the weightless conditions in space. Copper or copper oxide, when contained in polyurethane plastic foams, significantly reduces the evolution of deadly hydrogen cyanide gas when such plastics are burnt. Some copper alloys have been developed which display a phenomenon known as Shape Memory Effect. These alloys find application in, for example, radiator mechanisms due to their capacity to change from one shape to another upon an alteration of temperature. New production methods have enabled the development by the International Copper Association of an enhanced efficiency car radiator. This has been achieved with the use of copper finstock rolled to much thinner gauge in modern mills, tubing made from precision strip by either high-frequency or laser welding and the use of new soldering/brazing techniques. The uses of copper and its alloys and compounds will continue to change, as they have over thousands of years, to meet modern challenges. As an essential service material that is environmentally friendly, fully recyclable and fully sustainable, there is no viable alternative to copper - the 21st century metal.

About the author:
Dr.Thoguluva Raghavan Vijayaram, currently working as Senior Lecturer in the Faculty of Manufacturing Engineering at UTeM, Universiti Teknikal Malaysia Melaka, Malaysia. He hails from India and he has completed his PhD Research Degree in Mechanical Engineering (Metal Matrix Composites: Materials Engineering) from the Faculty of engineering, Universiti Putra Malaysia. He has published quality research papers in reputed International journals, National journals, International conference proceedings and in the Malaysian broadsheet. He has a wide range of work experience, both in academics and as well as in industry, consultancy, and teaching and especially in research and development work. His areas of expertise include: Metallurgical Engineering, Mechanical Engineering and Manufacturing Engineering and his special areas of research interests are in the field of advanced casting technology and techniques, composite materials and processing, powder metallurgy, Ferrous and Non-Ferrous foundry metallurgy, solidification science and technology, solidification processing of metals, alloys and composites, microgravity solidification, squeeze casting, die casting die design, heat treatment, Metallography, microstructure-property correlation ship, new materials and process development, aerospace engineering materials, computer simulation of casting solidification, FEM analysis and advanced engineering mathematics. Besides, he is a prominent writer and possesses wider experience in editing technical papers, theses and dissertations.

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