Copper alloying element

PERCENT- COPPER ALLOYING ELEMENT PERCENT ALLOYING ELEMENT CONDUCTIVITY (ohm-cm) 1... 

For example,copper has relatively good corrosion resistance under non-oxidizing conditions. It can be alloyed with zinc to yield a stronger material (brass), but with lowered corrosion resistance. Flowever, by alloying copper with a passivating metal such as nickel, both mechanical and corrosion properties are improved. Another important alloy is steel, which is an alloy between iron (>50%) and other alloying elements such as carbon. 

The lead—copper phase diagram (1) is shown in Figure 9. Copper is an alloying element as well as an impurity in lead. The lead—copper system has a eutectic point at 0.06% copper and 326°C. In lead refining, the copper content can thus be reduced to about 0.08% merely by cooling. Further refining requites chemical treatment. The solubiUty of copper in lead decreases to about 0.005% at 0°C. 

Residual alloying elements such as copper, nickel, or tin are usually considered undesirable. Their main source is purchased scrap. Because of the generally high consumption of hot metal in the basic-oxygen process, the residual alloy content is usually sufficiently low, depending on the quaUty of the purchased scrap. 

The physical and mechanical properties of steel depend on its microstmcture, that is, the nature, distribution, and amounts of its metaHographic constituents as distinct from its chemical composition. The amount and distribution of iron and iron carbide determine most of the properties, although most plain carbon steels also contain manganese, siUcon, phosphoms, sulfur, oxygen, and traces of nitrogen, hydrogen, and other chemical elements such as aluminum and copper. These elements may modify, to a certain extent, the main effects of iron and iron carbide, but the influence of iron carbide always predominates. This is tme even of medium alloy steels, which may contain considerable amounts of nickel, chromium, and molybdenum. 

Alloying elements either enlarge the austenite field or reduce it. The former include manganese, nickel, cobalt, copper, carbon, and nitrogen and are referred to as austenite stabilizers. 

Alloying elements such as nickel, chromium, molybdenum, and copper, which may be introduced with scrap, can increase the hardenability, although only slightly, because the concentrations are ordinarily low. However, the heat-treating characteristics may change, and for appHcations in which ductihty is important, as in low carbon steels for deep drawing, the increased hardness and lower ductiHty imparted by these elements may be harmful. 

For slightly less than 10% of products, alloying elements are introduced to produce properties not available for carbon steels where the functional elements are usually considered to be carbon, siHcon (to 0.6%), and manganese (to 1.65%). Copper, which may be present up to 0.6 wt %, is relatively rare compared to the ubiquitous siHcon and manganese. 

The important (3-stabilizing alloying elements are the bcc elements vanadium, molybdenum, tantalum, and niobium of the P-isomorphous type and manganese, iron, chromium, cobalt, nickel, copper, and siUcon of the P-eutectoid type. The P eutectoid elements, arranged in order of increasing tendency to form compounds, are shown in Table 7. The elements copper, siUcon, nickel, and cobalt are termed active eutectoid formers because of a rapid decomposition of P to a and a compound. The other elements in Table 7 are sluggish in their eutectoid reactions and thus it is possible to avoid compound formation by careful control of heat treatment and composition. The relative P-stabilizing effects of these elements can be expressed in the form of a molybdenum equivalency. Mo (29) ... 

Both sodium sulfide and the bisulfide are used in the flotation process for copper minerals and as a depilatory for animal liides (see Copper Copper ALLOYS Leather). Also, sodium polysulfide can be produced from Na2S, and elemental sulfur can be produced if H2S is generated as an intemiediate. 

Copper is primarily alloyed to increase strength, however, electrical and thermal conductivities, corrosion resistance, formabiUty, and color are also strongly affected by alloying. Elements typically added to copper are 2inc, tin, nickel, iron, aluminum, siUcon, chromium, and beryUium. 

The output from brass mills in the United States is spHt nearly equally between copper and the alloys of copper. Copper and dilute copper alloy wrought products are melted and processed from electrically refined copper so as to maintain low impurity content. Copper alloys are commonly made from either refined copper plus elemental additions or from recycled alloy scrap. Copper alloys can be readily manufactured from remelted scrap while maintaining low levels of nonalloy impurities. A greater proportion of the copper alloys used as engineering materials are recycled than are other commercial materials. 

Copper alloys can also be grouped according to how the principal elemental additions affect properties. This grouping depends primarily on whether the additions that dissolve in Hquid copper can form discrete second phases during either melting/casting or in-process thermal treatment. AHoy constitution that relates to limits of soHd solubiUty and equiUbrium phases that form in binary and ternary combinations with copper are found in the Hterature (2,3). 

Precipitation Hardening Alloys. Copper alloys that can be precipitation hardened to high strength are limited in number. In addition to the metallurgical requirement that the solubiUty of the added element(s) decrease with temperature, the precipitated phase that forms during aging must be distributed finely and have characteristics that act to resist plastic deformation. 

Copper—chromium and copper—nickel—silicon—chromium alloys are also precipitation hardenable. The precipitates are nickel sdicides, chromium silicides, and elemental chromium. If conductivity is critical, the chromium—silicon ratio should be held at 10 1 so that appreciable amounts of either element are not left in soHd solution in the copper after aging. Lithium can be used as a deoxidizer in copper alloys when conductivity is important. For a discussion of the principle of age- or precipitation-hardening copper alloys, see Copperalloys,wrought copperalloys. 

Effect of Various Alloying Elements. The mechanical properties of cast copper alloys are a function of alloying elements and their concentrations. The specific effects of a number of these alloying elements are given in the following sections. 

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). 

When electrons traverse an alloy rather than a pure metal, tire scattering of electrons is different at tire ion core of each chemical species and so the conductivity reflects a mixture of the effects due to each species. In a series of copper alloys it was found that the resistance, which is the reciprocal of the conductivity, is a parabolic function of tire concentration of the major element... 

As you can see from the tables in Chapter 1, few metals are used in their pure state -they nearly always have other elements added to them which turn them into alloys and give them better mechanical properties. The alloying elements will always dissolve in the basic metal to form solid solutions, although the solubility can vary between <0.01% and 100% depending on the combinations of elements we choose. As examples, the iron in a carbon steel can only dissolve 0.007% carbon at room temperature the copper in brass can dissolve more than 30% zinc and the copper-nickel system - the basis of the monels and the cupronickels - has complete solid solubility. 

Finally, Table 10.4 shows that copper is not the only alloying element that can age-harden aluminium. Magnesium and titanium can be age hardened too, but not as much as aluminium. 

Figure 21-6 shows the possibility of reducing the overvoltage of cathodic hydrogen evolution. One can also reduce restrictions in the O2 reduction hy using copper in lead alloys. Such alloying elements can be very effective because they... 

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]. 

Because it is difficult to remove alloying elements such as copper and zinc from an aluminum melt, separate collection and separate reutilization of different grades of aluminum scrap are necessary. Note that secondary aluminum... 

Low-carbon, low-alloy steels are in widespread use for fabrication-welded and forged-pressure vessels. The carbon content of these steels is usually below 0.2%, and the alloying elements that do not exceed 12% are nickel, chromium, molybdenum, vanadium, boron and copper. The principal applications of these steels are given in Table 3.8. 

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