The U.S. copper industry through the Copper Development Association used 

 to designate alloys by a three-digit identification system. This recently 

 has been expanded to five digits, following a prefix letter C, and made part 

 of the Unified Numbering System for Metals and Alloys (UNS) developed and 

 managed jointly by ASTM and the Society of Automotive Engineers (SAE) . In 

 the UNS system, numbers CI 0000 through C79999 denote wrought alloys. Cast 

 alloys are numbered from C80000 through C99990. Within these two catagories, 

 the alloy compositions are grouped into families of coppers and copper alloys 

 as presented in Table 27. 



Copper like other metals that have a recrystallization temperature, or 

 softening temperature, above room temperature can be hardened by cold working. 

 If the cold-worked metal is exposed to temperatures above a certain critical 

 temperature determined by the amount of cold work received and the composition 

 of the metal or alloy, the microstructure changes from marked distortion to a 

 recrystallized structure. Yield strength, tensile strength, and hardness are 

 reduced to the same as the alloy had before cold working. The recrystalliza- 

 tion temperature or softening temperature of copper can be raised by adding 

 sufficient quantities of silver, phosphorous, cadmium, tin, arsenic, or 

 antimony. Such coppers are often alloyed to raise the softening temperature 

 to above that at which soldering is to be performed so that the benefits of 

 increased strength due to cold working can be retained in the final product. 



Copper alloys that are precipitation hardenable contain beryllium, 

 chromium, zirconium, or nickel in combination with silicon or phosphorus. 

 Alpha aluminum bronze containing cobalt or nickel is also precipitation 

 hardenable. During hardening, these alloys are heated to an elevated 

 temperature, held a sufficient time for solid solutioning to occur, then 

 rapidly cooled to room temperature, followed by aging at an intermediate 

 temperature. Beryllium copper (CI 7200) in the solution annealed and aged 

 condition has a usual tensile strength of 1 210 megapascals (175 000 pounds 

 per square inch) . 



Copper and copper alloys have useful corrosion resistance for marine 

 application. Most corrosion resistant to seawater are aluminum brass, 

 classified as a miscellaneous copper-zinc alloy; inhibited admiralty, a tin 

 brass containing elements which inhibit the loss of zinc; and the copper- 

 nickel alloys. These alloys form films of corrosion products that provide 

 protection even in flowing seawater. The limiting velocity where these 

 films are lost depends on the alloy. Copper and copper alloys are attacked 

 by ammonium hydroxide due to the formation of a soluable component. Copper 

 alloys containing more than 15 percent zinc are susceptible to stress 

 corrosion cracking due to ammonium ion, and also dezincification, i.e., the 

 loss of zinc due to selective corrosion. Stress corrosion cracking occurs 

 at areas of high stress that can become more anodic than the surrounding 

 metal . Corrosion occurs at the interfaces of the metal crystals that are 

 perpendicular to the stress, weakening the bonding between crystals until 

 cracking occurs. Dezincification occurs in waters having a high oxygen and 

 carbon dioxide content. 



d. Other Alloys . Nickel aluminum bronzes and-two phase aluminum 

 bronzes are transformation hardenable. These alloys are heat treated by 

 heating to an elevated temperature to form a single phase solid solution, 



210 



