Copper and copper alloys can be used in an extraordinary range of applications. Some of these applications include: · Power transmission lines · Architectural applications · Cooking utensils · Spark plugs · Electrical wiring, cables and busbars · High conductivity wires · Electrodes · Heat exchangers · Refrigeration tubing · Plumbing · Water-cooled copper crucibles Structure Copper has a face centred cubic crystal structure. It is yellowish red in physical appearance and when polished develops a bright metallic lustre. Key Properties of Copper Alloys Copper is a tough, ductile and malleable material. These properties make copper extremely suitable for tube forming, wire drawing, spinning and deep drawing. The other key properties exhibited by copper and its alloys include: · Excellent heat conductivity · Excellent electrical conductivity · Good corrosion resistance · Good biofouling resistance · Good machinability · Retention of mechanical and electrical properties at cryogenic temperatures · Non-magnetic Other Properties · Copper and Copper alloys have a peculiar smell and disagreeable taste. These may be transferred by contact and therefore Copper should be kept clear of foodstuffs. · Most commercially used metals have a metallic white colour. Copper is a yellowish red. Melting Point The melting point for pure copper is 1083ºC. Electrical Conductivity The electrical conductivity of copper is second only to silver. The conductivity of copper is 97% that of silver. Due to its much lower cost and greater abundance, copper has traditionally been the standard material used for electricity transmission applications. However, weight considerations mean that a large proportion of overhead high voltage power lines now use aluminium rather than copper by weight, the conductivity of aluminium is around twice that of copper. The aluminium alloys used do have a low strength and need to be reinforced with a galvanised or aluminium coated high tensile steel wire in each strand. Although additions of other elements will improve properties like strength, there will be some loss in electrical conductivity. As an example a 1% addition of cadmium can increase strength by 50%. However, this will result in a corresponding decrease in electrical conductivity of 15%. Corrosion Resistance All Copper alloys resist corrosion by fresh water and steam. In most rural, marine and industrial atmospheres Copper alloys also resistant to corrosion. Copper is resistant to saline solutions, soils, non-oxidising minerals, organic acids and caustic solutions. Moist ammonia, halogens, sulphides, solutions containing ammonia ions and oxidising acids, like nitric acid, will attack Copper. Copper alloys also have poor resistance to inorganic acids. The corrosion resistance of Copper alloys comes from the formation of adherent films on the material surface. These films are relatively impervious to corrosion therefore protecting the base metal from further attack. Copper Nickel alloys, Aluminium Brass, and Aluminium Bronzes demonstrate superior resistance to saltwater corrosion. Surface Oxidation of Copper Most Copper alloys will develop a blue-green patina when exposed to the elements outdoors. Typical of this is the colour of the Copper Statue of Liberty in New York. Some Copper alloys will darken after prolonged exposure to the elements and take on a brown to black colour. Lacquer coatings can be used to protect the surface and retain the original alloy colour. An acrylic coating with benzotriazole as an additive will last several years under most outdoor, abrasion-free conditions. Yield Strength The yield point for Copper alloys is not sharply defined. As a result it tends to be reported as either a 0.5% extension under load or as 0.2% offset. Most commonly the 0.5% extension yield strength of annealed material registers as approximately one-third the tensile strength. Hardening by cold working means the material becomes less ductile, and yield strength approaches the tensile strength. Joining Commonly employed processes such as brazing, welding and soldering can be used to join most copper alloys. Soldering is often used for electrical connections. High Lead content alloys are unsuitable for welding. Copper and Copper alloys can also be joined using mechanical means such as rivets and screws. Hot and Cold Working Although able to be work hardened, Copper and Copper alloys can be both hot and cold worked. Ductility can be restored by annealing. This can be done either by a specific annealing process or by incidental annealing through welding or brazing procedures. Temper Copper alloys can be specified according to temper levels. The temper is imparted by cold working and subsequent degrees of annealing. Typical tempers for Copper alloys are · Soft · Half-hard · Hard, spring · Extra-spring Yield strength of a hard-temper Copper alloy is approximately two-thirds of the materials’ tensile strength. Copper Designations Designation systems for Copper are not specifications, but methods for identifying chemical compositions. Property requirements are covered in ASTM, government and military standards for each composition. The method for designating Copper alloys is an expansion upon the system developed by the U.S. copper and brass industry. Their old system used 3 digits, the new Unified Numbering System for Metals and Alloys (UNS) system uses five digits preceded by the letter C. As an example the forging brass known as Copper alloy 377 is known as C37700 under the UNS system. Wrought compositions are included in the designations from C10000 through to C79900. Casting alloys are assigned numbers from C80000 through to C99900 The UNS designations are summarised in the following table: UNS Numbers | Types | Alloy Names | C10000-C19999 | Wrought | Coppers, High-Copper Alloys | C20000-C49999 | Wrought | Brasses | C50000-C59999 | Wrought | Phosphor Bronzes | C60600-C64200 | Wrought | Aluminium Bronzes | C64700-C66100 | Wrought | Silicon Bronzes | C66400-C69800 | Wrought | Brasses | C70000-C79999 | Wrought | Copper nickels, nickel silvers | C80000-C82800 | Cast | Coppers, High-Copper Alloys | C83300-C85800 | Cast | Brasses | C86100-C86800 | Cast | Manganese Bronzes | C87200-C87900 | Cast | Silicon Bronzes and Brasses | C90200-C94800 | Cast | Tin Bronzes | C95200-C95800 | Cast | Aluminium Bronzes | C96200-C97800 | Cast | Copper Nickels, Nickel Silvers | C98200-C98800 | Cast | Leaded Copper | C99300-C99750 | Cast | Special Alloys | |
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