Unit 6


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Unit 6

  1. 1. Non-ferrous Metals and Alloys UNIT - VI
  2. 2. COPPER AND COPPER ALLOYS Copper: The properties of copper that are most important are high electrical and thermal conductivity, good corrosion resistance, machinability, strength, and ease of fabrication. In addition, copper is nonmagnetic, has a pleasing color, can be welded, brazed, and soldered, and is easily finished by plating or lacquering. Certain of these basic properties may be improved by suitable alloying. Most of the copper that is used for electrical conductors contains over 99.9 percent copper and is identified as electrolytic tough-pitch copper (ETP) or oxygen-free high-conductivity copper (OFHC). Electrolytic tough-pitch copper is also used for roofing, gutters, downspouts, automobile radiators and gaskets, kettles, vats, pressure vessels, and distillery and other process equipment. Electrolytic tough-pitch copper contains from 0.02 to 0.05 percent oxygen, which is combined with copper as the compound cuprous oxide (Cu2O). As cast, copper oxide and copper form an inter dendritic eutectic mixture. After working and annealing, the inter dendritic network is destroyed, and the strength is improved. Oxygen-free copper is used in electronic tubes or similar applications because it makes a perfect seal to glass.
  3. 3. The most important commercial copper alloys may be classified as follows: I .Brasses-alloys of copper and zinc a. Alpha brasses-alloys containing up to 36 percent zinc 1. Yellow alpha brasses 20 to 36 percent zinc 2. Red brasses 5 to 20 percent zinc b. Alpha plus beta brasses 54 to 62 percent copper II .Bronzes-up to 12 percent of alloying element a. Tin bronzes . b. Silicon bronzes c. Aluminium bronzes d. Beryllium bronzes III. Cupronickels-alloys of copper and nickel IV. Nickel silvers-alloys of copper, [nickel, and zinc]
  4. 4. Brasses: General Brasses are essentially alloys of copper and zinc. Some of these alloys have small amounts of other elements such as lead, tin or aluminum. Variations in composition will result in desired color, strength, ductility, machinability, corrosion resistance, or a combination of such properties. The solubility of zinc in the alpha () solid solution increases from 32.5 percent at 1657°F to about 39 percent at 850°F. Since copper is. f.c.c. (face-centered cubic), the solid solution is f.c.c. The beta () phase is a b.c.c. (bodycentered cubic) electron compound and undergoes ordering, indicated by a dot-dash line, in the region of 850 to 875°F. On cooling in this temperature range the b.c.c. ( phase, with copper and zinc atoms randomly dispersed at lattice points, changes continuously to the ordered structure which is still b.c.c. but with the copper atoms at the corners and zinc atoms at the centers of the unit cubes. The ordering reaction is so rapid that it cannot be retarded or prevented by quenching.
  5. 5. Alpha Brasses Alpha brasses containing up to 36 percent zinc possess relatively good corrosion resistance and good working properties. The color of brasses varies according to percentage of copper content from red for high-copper alloys to yellow at about 62 percent copper. Yellow Alpha Brasses These contain 20 to 36 percent zinc, combine good strength with high ductility and are therefore suited for drastic cold-working operations. It is common practice to stress-relief anneal these brasses after severe cold working to prevent season cracking. Season cracking or Stress corrosion cracking is due to the high residual stresses left in the brass as a result of cold working. Red Brasses: These contain between 5 and 20 percent zinc. They generally have better corrosion resistance than yellow brasses and are not susceptib1e to season cracking or dezincification. The most common low zinc brasses are gilding metal (95Cu-5Zn). Gilding metal (95Cu-5Zn) has higher strength than copper and is used for coins, medals, tokens, fuse caps, primers, emblems, plaques, and as a base for articles to be gold-plated or highly polished
  6. 6. Alpha Plus Beta Brasses These contain from 54 to 62 percent copper. phase is more brittle than the phase. Therefore, these alloys are more difficult to cold-work. At elevated temperatures the phase becomes very plastic, and since most of these alloys may be heated into the single-phase region, they have excellent hot-working properties. Bronzes:- In general, the term bronze was originally applied to the copper tin alloys. However, the term is now used for any copper alloy, with the exception of copper-zinc alloy, that contains up to approximately 12 percent of the principal alloying element. Tin Bronzes: These are generally referred to as phosphor bronzes. Since phosphorus is always present as a deoxidizer in casting. .The usual range of phosphorus content is in between 0.01 and 0.5 percent, and of tin between 1 and 11 percent. The phosphor bronzes are characterized by high strength, toughness, high corrosion resistance, low coefficient of friction and freedom from season cracking. They are used extensively for diaphragms, bellows, lock washers, cotter pins, bushings, clutch disks, and springs. Zinc is sometimes used to replace part of the tin; the result is an improvement in the casting properties and toughness with little effect on Wear resistance. Lead is often added to tin bronze to improve machinability and. wear resistance. High-lead tin bronze may contain as much as 25 percent lead. The leaded alloys are used for bushing and bearings under moderate or light loads.
  7. 7. Beryllium Bronzes: The solubility of beryllium in the a solid solution decreases from 2.1 percent at 1590°F to less than 0.25 percent at room temperature. This change in solubility is always indicative of age hardening possibilities. The optimum mechanical properties are obtained in an alloy containing approximately 2percent beryllium. A typical heattreating cycle for this alloy would be; solution-anneal at 1450°F, water-quench, coldwork, and finally age at 600°F. Aluminum Bronzes: The maximum solubility of aluminum in the a solid solution is approximately 9.5 percent at 1050°F. The phase undergoes a eutectoid reaction at 1050°F to form the ( + F2) mixture. Most commercial aluminum bronzes contain between 4 and 11 percent aluminum. Nickel Silvers: These are essentially terinary alloys of copper, nickel and zinc. The addition of nickel to the copper- zinc alloy gives it a pleasing silver- blue white colour and good corrosion resistance to food chemicals, water, and atmosphere. These alloys make excellent base metals for plating with chromium, nickel, or silver. They are used for rivets, screws,table flatware, Zippers, Costume jewelry, name plates and radio dails.
  8. 8. Aluminum and its alloys The best-known characteristic of aluminum is its light weight, the density being about one-third that of steel or copper alloys. Certain aluminum alloys have a better strength-toweight ratio than that of high strength steels. 1. Aluminum has good malleability and formability, high corrosion resistance, and high electrical and thermal conductivity. An ultra pure form of aluminum is used for photographic reflectors to take advantage of its high light reflectivity and nontarnishing characteristics. 2. Aluminum is nontoxic, nonmagnetic, and non-sparking. The nonmagnetic characteristic makes aluminum useful for electrical shielding purposes such as bus-bar housings or enclosures for other electrical equipment. 3. Although the electrical conductivity of electric-conductor (EC) grade aluminum is about 62 percent that of copper, its light weight makes it more suitable as an electrical conductor for many industrial applications. 4. Pure aluminum has a tensile strength of about 13,000 psi. However, substantial increases in strength are obtained by cold working or alloying. Some alloys, properly heat-treated, approach tensile strengths of 100,000 psi. 5. One of the most important characteristics of aluminum is its machinability and workability. It can be cast by any known method, rolled to any desired thickness, stamped, drawn, spun, hammered, forged, and extruded to almost any conceivable shape. 6.Commercially pure aluminum, 1100 alloy (99.0+ percent AI), is suitable for applications where good formability or very good resistance to corrosion (or both) are required and where high strength is. not necessary. It has been used extensively for cooking utensils, various architectural components, food and chemical handling and storage equipment; and welded assemblies.
  9. 9. Aluminum-Copper Alloys (2xxx Series): The maximum solubility of Copper in aluminum is 5.65 percent at 1018°F, and the solubility decreases to 0.45 percent at 5720 F. Therefore, alloys containing between 2:5 and 5 percent copper will respond to heat treatment by age hardening. Types of Aluminium Alloys • Aluminum-Manganese Alloy • Aluminum-Silicon Alloys • Aluminum-Magnesium Alloys TITANIUM AND TITANIUM ALLOYS Titanium metal has a close-packed hexagonal crystal structure, called alpha, at room temperature. This structure transforms to body centered cubic beta at 16250F. Commercially pure titanium is lower in strength, more corrosion-resistant, and less expensive than titanium alloys. It is used for applications requiring high ductility for fabrication but little strength, such as chemical process piping, valves and tanks, aircraft firewalls, tailpipes, and compressor cases.
  10. 10. Titanium Alloys: The addition of alloying elements to titanium will influence the alpha to beta transformation temperature. It is common practice to refer to alloying elements as alpha or beta stabilizers. An alpha stabilizer means that as solute is added, the alpha to beta transformation temperature is raised. Alpha Alloys Most of the alpha alloys contain some beta-stabilizing alloying elements. The compositions of these alloys are balanced by high aluminum content so that the alloys are essentially one-phase alpha. Coarse, plate like alpha in a Ti-5At-2.5Sn alloy after hot working and annealing. The alpha alloys have two main attributes, weld ability and retention of strength at high temperatures. The first results from the one phase microstructure, the second from the presence of aluminum. Alloying elements in solution strengthen the alpha-phase alloys, and aluminum is the most effective strengthener of alpha alloys.. Alpha-Beta Alloys These contain enough beta-stabilizing elements to cause the beta phase to persist down to room temperature and they are stronger than alpha alloys. beta- :phase as strengthened by beta alloying additions in solution. is stronger than the alpha phase. Aging at elevated temperature causes precipitation offline particles of alpha in the volumes that were beta grains prior to quenching. This fine structure is stronger than the coarse, annealed alpha-beta structure. In some cases, quenched titanium alloy structures may be of an unstable form of alpha designated alpha prime and called titanium martensite.