28 



Copper and Copper-base Alloys 



spongy areas of copper in the form of layers or so-called 

 "plugs" on the affected surface. This spongy copper is 

 a consequence of the solution of fractions of the alloy in 

 the media and a redeposition of the copper by chemical 

 displacement. Arsenic, antimony, and phosphorus in 

 small fractional percentages are demonstrably effective 

 in repressing or inhibiting dezincification in the alpha 

 brasses. 



Brass that contains less than 85 per cent of copper 

 may imder certain conditions fail by stress-corrosion 

 cracking or, as it is more commonly called, "season 

 cracking." Conditions that favor this form of failure 

 are the presence of internal stress or stress gradients 

 produced by cold-working operations followed by 

 exposure to mild atmospheric corrosion. The presence 

 of traces of ammonia in the atmosphere is said to favor 

 this form of corrosion. Season cracking can be effec- 

 tively prevented by relief annealing below the recrystal- 

 lization temperature. 



A type of failure closely associated with season crack- 

 ing and known as "fire cracking" occurs when sus- 

 ceptible brasses in a stressed condition are suddenly 

 exposed to elevated temperatures. The presence of lead 

 in the brass decreases the resistance to this type of failure 

 by promoting greater inter crystalline weakness. In 

 order to avoid this form of failure it is common practice 

 to bring stressed materials up to the annealing temper- 

 ature gradually rather than precipitantly. 



In the fabrication of susceptible rod alloys it is com- 

 mon practice to flex or spring the rods prior to annealing, 

 to counteract tensile stresses produced during fabrication, 

 and thus reduce liability to fire cracking. 



Following is a table of the more important commercial 

 alpha brasses: 



Most common name 



Gilding metal 



Commercial "bronze" 



Rich low brass or red brass . . , 



Low brass 



Spring brass 



70-30 or cartridge brass 



Deep drawing 



Common high brass (2 and 1) 



Tubular rivet brass 



Brass rod 



Zinc, % 



6 

 10 

 15 

 20 

 25 

 30 

 32 

 34 

 35 

 36 



The alloy of copper and zinc containing 95 per cent of 

 copper is known as gilding metal. It is an extremely 

 easy alloy to cold-work and flows readily in the intricate 

 dies used for jewelry, emblems, plaques, and coining 

 operations. It can be readily spun, drawn, forged, and 

 upset. Its hot-working properties are comparable to 

 those of copper. This alloy has slightly higher tensile 

 properties and about the same ductility as copper but 

 its thermal and electrical properties are lower. 



Gilding metal is used extensively in the jewelry and 

 emblem industry because of its excellent cold-working 

 properties and its golden color. It is also an excellent 



base for articles that are to be gold-plated or finished to 

 a high polish in their natural color. This alloy is com- 

 mercially available in all common wrought forms. 

 Physical and general mechanical properties of the most . 

 common form — strip — are given in Table 1 on page 30. 

 Charts 1 to 13 on pages 30 to 33 give in greater detail the 

 effect of cold working and anneahng on its mechanical 

 properties. 



Brass with 90 per cent of copper through long usage 

 has become known as commercial bronze. It has excel- 

 lent cold-working properties and can be readily spun, 

 drawn, forged, and upset. Its hot-working prop- 

 erties are very similar to those of copper. 



Commercial bronze is used in the manufacture of cos- 

 tume jewelry, compacts, weatherstripping, stamped 

 hardware, forgings, screws, rivets, and various ammuni- 

 tion components. Because of its attractive color it is 

 used to a limited extent in architectural metalwork. 

 The alloy is fabricated as sheet, strip, plate, rod, wire, 

 bar, and tube. Physical and general mechanical proper- 

 ties of the more common forms (strip and rod) are given 

 in Table 2 on page 34. Detailed mechanical prop- 

 erty data are given in Charts 14 to 35 on pages 35 to 

 40. 



Rich low brass, or red brass, has excellent cold-working 

 properties and can be cold-worked to a greater extent 

 than copper, owing to a better combination of strength 

 and ductility. It is widely used for severe cold-drawing, 

 stamping, or spinning operations. Red brass can be 

 hot-worked commercially at temperatures in excess of 

 1350°F. when the lead content is less than 0.02 per cent. 

 However, red brass is not so plastic at elevated tempera- 

 tures as the other commercial brasses and for that reason 

 is seldom used for forgings or for parts requiring fabrica- 

 tion through hot working. 



Red brass has excellent corrosion-resisting properties, 

 in many cases superior to those of copper. When in 

 contact with salt or brackish waters it offers better resist- 

 ance than copper itself and it is used successfully under 

 conditions of operation that cause the higher zinc alloys 

 to fail through dezincification. 



Rich low brass is used extensively in the construction 

 of automotive radiators, in the manufacture of tube and 

 pipe for oil refineries and utilities, and in the field of 

 domestic and industrial plumbing. This aUoy is com- 

 monly fabricated in sheet, strip, plate, rod, bar, wire, 

 and tube. Physical and general mechanical properties 

 are shown in Table 3 on page 41 for the more common 

 products (sheet and strip, rod and tube). Charts 36 to 

 58 on pages 42 to 47 give more detailed information. 



Low brass has hot- and cold-working properties similar 

 to rich low brass. Its corrosion-resisting properties are 

 generally the same as those of the latter. Under certain 

 severe conditions it may dezincify or fail by season 

 cracking. 



This alloy is used for flexible hose, bellows, clock dials, 

 and numerous drawn and stamped parts. It is usually 

 fabricated in sheet, strip, rod, wire, bar, and tube. Its 



