Non-ferrous Metals and Alloys

UNIT - VI

COPPER AND COPPER ALLOYS

Copper:

The properties of copper that are most important are high electrical and thermalconductivity, good corrosion resistance, machinability, strength, and ease of fabrication.In addition, copper is nonmagnetic, has a pleasing color, can be welded, brazed, andsoldered, and is easily finished by plating or lacquering. Certain of these basic propertiesmay be improved by suitable alloying. Most of the copper that is used for electricalconductors contains over 99.9 percent copper and is identified as electrolytic tough-pitchcopper (ETP) or oxygen-free high-conductivity copper (OFHC). Electrolytic tough-pitchcopper is also used for roofing, gutters, downspouts, automobile radiators and gaskets,kettles, vats, pressure vessels, and distillery and other process equipment. Electrolytictough-pitch copper contains from 0.02 to 0.05 percent oxygen, which is combined withcopper as the compound cuprous oxide (Cu2O). As cast, copper oxide and copper forman inter dendritic eutectic mixture. After working and annealing, the inter dendriticnetwork is destroyed, and the strength is improved. Oxygen-free copper is used inelectronic tubes or similar applications because it makes a perfect seal to glass.

The most important commercial copper alloys may be classified as follows:I .Brasses-alloys of copper and zinca. Alpha brasses-alloys containing up to 36 percent zinc1. Yellow alpha brasses 20 to 36 percent zinc2. Red brasses 5 to 20 percent zincb. Alpha plus beta brasses 54 to 62 percent copperII .Bronzes-up to 12 percent of alloying elementa. Tin bronzes .b. Silicon bronzesc. Aluminium bronzesd. Beryllium bronzesIII. Cupronickels-alloys of copper and nickelIV. Nickel silvers-alloys of copper, [nickel, and zinc]

Brasses:

General Brasses are essentially alloys of copper and zinc. Some of these alloys havesmall amounts of other elements such as lead, tin or aluminum. Variations in compositionwill result in desired color, strength, ductility, machinability, corrosion resistance, or acombination of such properties. The solubility of zinc in the alpha () solid solutionincreases 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. (bodycenteredcubic) 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 tothe ordered structure which is still b.c.c. but with the copper atoms at the corners andzinc atoms at the centers of the unit cubes. The ordering reaction is so rapid that it cannotbe retarded or prevented by quenching.

Alpha Brasses Alpha brasses containing up to 36 percent zinc possess relatively goodcorrosion resistance and good working properties. The color of brasses varies accordingto percentage of copper content from red for high-copper alloys to yellow at about 62percent copper.

Yellow Alpha Brasses These contain 20 to 36 percent zinc, combine good strength with highductility and are therefore suited for drastic cold-working operations. It is commonpractice to stress-relief anneal these brasses after severe cold working to prevent seasoncracking. Season cracking or Stress corrosion cracking is due to the high residualstresses left in the brass as a result of cold working.

Red Brasses:These contain between 5 and 20 percent zinc. They generally have better corrosionresistance than yellow brasses and are not susceptib1e to season cracking ordezincification. 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 begold-plated or highly polished

Alpha Plus Beta BrassesThese contain from 54 to 62 percent copper. phase is more brittle than the phase. Therefore, these alloys are more difficult to cold-work. At elevatedtemperatures the phase becomes very plastic, and since most of these alloys may beheated 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, theterm is now used for any copper alloy, with the exception of copper-zinc alloy, thatcontains up to approximately 12 percent of the principal alloying element.Tin Bronzes: These are generally referred to as phosphor bronzes. Since phosphorus isalways present as a deoxidizer in casting. .The usual range of phosphorus content is inbetween 0.01 and 0.5 percent, and of tin between 1 and 11 percent. The phosphor bronzesare characterized by high strength, toughness, high corrosion resistance, low coefficientof 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 inthe casting properties and toughness with little effect on Wear resistance. Lead is oftenadded to tin bronze to improve machinability and. wear resistance. High-lead tin bronzemay contain as much as 25 percent lead. The leaded alloys are used for bushing andbearings under moderate or light loads.

Beryllium Bronzes:The solubility of beryllium in the a solid solution decreases from 2.1 percent at 1590°Fto less than 0.25 percent at room temperature. This change in solubility is alwaysindicative of age hardening possibilities. The optimum mechanical properties areobtained in an alloy containing approximately 2percent beryllium. A typical heattreatingcycle 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 percentat 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 percentaluminum.

Nickel Silvers:These are essentially terinary alloys of copper, nickel and zinc. The addition of nickel tothe copper- zinc alloy gives it a pleasing silver- blue white colour and good corrosionresistance to food chemicals, water, and atmosphere. These alloys make excellent basemetals for plating with chromium, nickel, or silver. They are used for rivets, screws,tableflatware, Zippers, Costume jewelry, name plates and radio dails.

Aluminum and its alloysThe best-known characteristic of aluminum is its light weight, the density being aboutone-third that of steel or copper alloys. Certain aluminum alloys have a better strength-toweightratio than that of high strength steels.1. Aluminum has good malleability and formability, high corrosion resistance, and highelectrical and thermal conductivity. An ultra pure form of aluminum is used forphotographic reflectors to take advantage of its high light reflectivity and nontarnishingcharacteristics.2. Aluminum is nontoxic, nonmagnetic, and non-sparking. The nonmagneticcharacteristic makes aluminum useful for electrical shielding purposes such as bus-barhousings or enclosures for other electrical equipment.3. Although the electrical conductivity of electric-conductor (EC) grade aluminum isabout 62 percent that of copper, its light weight makes it more suitable as an electricalconductor for many industrial applications.4. Pure aluminum has a tensile strength of about 13,000 psi. However, substantialincreases in strength are obtained by cold working or alloying. Some alloys, properlyheat-treated, approach tensile strengths of 100,000 psi.5. One of the most important characteristics of aluminum is its machinability andworkability. 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 forapplications where good formability or very good resistance to corrosion (or both) arerequired and where high strength is. not necessary. It has been used extensively forcooking utensils, various architectural components, food and chemical handling andstorage equipment; and welded assemblies.

Aluminum-Copper Alloys (2xxx Series):The maximum solubility of Copper in aluminum is 5.65 percent at 1018°F, and thesolubility decreases to 0.45 percent at 5720 F. Therefore, alloys containing between 2:5and 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 roomtemperature. This structure transforms to body centered cubic beta at 16250F.Commercially pure titanium is lower in strength, more corrosion-resistant, and lessexpensive than titanium alloys. It is used for applications requiring high ductility forfabrication but little strength, such as chemical process piping, valves and tanks, aircraftfirewalls, tailpipes, and compressor cases.

Titanium Alloys:The addition of alloying elements to titanium will influence the alpha to betatransformation temperature. It is common practice to refer to alloying elements as alphaor beta stabilizers. An alpha stabilizer means that as solute is added, the alpha to betatransformation temperature is raised.

Alpha AlloysMost of the alpha alloys contain some beta-stabilizing alloying elements. Thecompositions of these alloys are balanced by high aluminum content so that the alloysare essentially one-phase alpha. Coarse, plate like alpha in a Ti-5At-2.5Sn alloy afterhot working and annealing. The alpha alloys have two main attributes, weld ability andretention of strength at high temperatures. The first results from the one phasemicrostructure, the second from the presence of aluminum. Alloying elements insolution strengthen the alpha-phase alloys, and aluminum is the most effectivestrengthener of alpha alloys..Alpha-Beta Alloys These contain enough beta-stabilizing elements to cause the betaphase 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 alphaphase. Aging at elevated temperature causes precipitation offline particles of alpha inthe volumes that were beta grains prior to quenching. This fine structure is stronger thanthe coarse, annealed alpha-beta structure. In some cases, quenched titanium alloystructures may be of an unstable form of alpha designated alpha prime and calledtitanium martensite.