Alloys with Added Copper

Adding copper to the aluminium-zinc-magnesium system produces the aluminium alloys with the highest mechanical resistance in the T6 temper. 

Products capable of resisting corrosion in aggressive atmospheres, which are particularly resistant to stress corrosion in the short-transverse direction can be obtained by duplex ageing (tempers T73 and T76) however, this leads to a decrease in mechanical strength of about 20%. 

AUoy 7075 is most often used as rolled, extruded, die-forged and hand-forged products in the fields of aerospace, mechanics, and sport and leisure equipment. 

The need for products with a thickness above 80 mm has triggered the development of 7050 and 7010, two variants, which differ from 7075 in that 

Alloy 7049A can be considered as one of the commercial aluminium alloys with the best mechanical properties in the T6 temper. Its average mechanical properties are 

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High copper alloys For the wrought products, these are alloys with designated copper content of less than 99.3 wt.% Cu but more than 96 wt.% Cu that do not fall into any other copper alloy group. The cast high copper alloys have designated copper content in excess of 94 wt.% Cu, to which silver may be added for special properties. 

Copper, lead, zinc, tin, mercury, and cadmium are often grouped together simply because they are not used to alloy with iron. Copper metal conducts electricity well and can be shaped into wires, so it has been used mainly in electric lines and electric motors. Lead and mercury are used much less than in the past because of their toxicity. Lead is still used in batteries for vehicles, and mercury is used in some batteries, electrical switches, and for some chemical compounds. Zinc or tin are used in protective coatings for steel to keep it from rusting. Zinc oxide is added to paint to produce a white color and to a variety of lotions to prevent sunburn. Many so-called tin cans contain tin plated on other metals. 

Beryllium is added to copper to produce an alloy with greatly increased wear resistance it is used for current-carrying springs and non-sparking safety tools. It is also used as a neutron moderator and reflector in nuclear reactors. Much magnesium is used to prepare light nieial allo>s. other uses include the extraction of titanium (p. 370) and in the removal of oxygen and sulphur from steels calcium finds a similar use. 

Copper Alloys. Tellurium is alloyed with copper for various purposes. Frequently the tellurium is added to molten copper as a copper teUuride (46.3% Te) master alloy, taking advantage of the peritectic melting point of 1051°C. 

Tin Bronzes. Tin bronzes may be the most familiar of copper alloys with roots going back into ancient times. Whereas bronze is stiU used for statuary, these alloys are found in many modem appHcations, such as electrical connectors, bearings, beUows, and diaphragms. The wrought tin bronzes are also called phosphor bronzes because 0.03 to 0.35 wt % phosphoms is commonly added for deoxidation and improved melt fluidity. 

Copper-alloy corrosion behavior depends on the alloying elements added. Alloying copper with zinc increases corrosion rates in caustic solutions whereas nickel additions decrease corrosion rates. Silicon bronzes containing between 95% and 98% copper have corrosion rates as low as 2 mil/y (0.051 mm/y) at 140°F (60°C) in 30% caustic solutions. Figure 8.2 shows the corrosion rate in a 50% caustic soda evaporator as a function of nickel content. As is obvious, the corrosion rate falls to even lower values as nickel concentration increases. Caustic solutions attack zinc brasses at rates of 2 to 20 mil/y (0.051 to 0.51 mm/y). 

The resistance of a metal to erosion-corrosion is based principally on the tenacity of the coating of corrosion products it forms in the environment to which it is exposed. Zinc (brasses), aluminum (aluminum brass), and nickel (cupronickel) alloyed with copper increase the coating s tenacity. An addition of V2 to 1)4% iron to cupronickel can greatly increase its erosion-corrosion resistance for the same reason. Similarly, chromium added to iron-base alloys and molybdenum added to austenitic stainless steels will increase resistance to erosion-corrosion. 

The addition of cathodically active elements to pure lead was the main objective of investigations to improve its corrosion resistance to H2SO4 [42,44]. Best known is copper-lead with 0.04 to 0.08% Cu. By adding combinations of alloying elements, it was possible to produce lead alloys that not only had much better corrosion resistance, but also had greater high-temperature strength. Lead alloy with 0.1% Sn, 0.1% Cu and 0.1% Pd is an example [45]. 

Induced dissolution is also a well known phenomenon and frequently applied in chemical analysis. To dissolve platinum easily it was suggested by Ropp that the sample should be alloyed with silver or copper, the alloys being easily soluble even in dilute acids. Anhydrous chromic chloride, insoluble in water and dilute acids, becomes easily soluble by adding metallic magnesium or zinc to the dilute acid . In this case the chromium(III) compound is reduced to chro-mium(II), which will be oxidized by the solvent to water-soluble chromium(III)... 

Rhodium can be added as the fourth member of this group—particularly since skeletal isomerization over rhodium also involves C5 cyclic intermediates 42). Its alloying with copper results in the appearance of C5 cyclic products 43). 

The dialkylzincs up to the dibutyl derivatives readily ignite and bum in air. The higher alkyls fume but do not always ignite [1]. During preparation of dialkylzincs, reaction of the copper—zinc alloy with mixed alkyl bromides and iodides must begin (exotherm, often after a long induction period), before too much halide mixture is added, or violent explosions may occur [2]. Reactions with water may be explosive [3]. 

Both of these alloys are solid solutions, which occur when the constituents of the alloy are soluble in each other, like ethanol is soluble in water. Unlike ethanol and water, which are completely miscible, if too much tin is added to copper and too much carbon to iron, they will exceed their solubilities. The result is a polyphase alloy, with characteristics that are different from solid solutions. This book will skip polyphase alloys to focus on solid solutions and the important question they pose Why are the solid solutions called bronze and carbon steel stronger and harder than their constituents ... 

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