The 60.00 series of aluminum alloys contains both silicon and magnesium 

 in approximate equal proportions which combine during melting to form 

 magnesium silicide. Alloys of this series are heat-treatable, and possess 

 good formability and corrosion resistance with medium strength. One of the 

 most versatile heat-treatable alloys is the major alloy of this series, 

 6061. 



Zinc is the major alloying element of the 7000 series, and when coupled 

 with a smaller percentage of magnesium results in heat-treatable alloys of 

 very high strength. Small amounts of other elements such as chromium and 

 copper also may be added. Alloys in this series are used in air-frame 

 structures and for high-stressed parts. Among the high strength aluminum 

 alloys, 7075 can be heat treated to 565 megapascals (82 000 pounds per 

 square inch) tensile strength, and 496 megapascals (72 000 pounds per square 

 inch) yield strength. 



The complete designation of aluminum alloys includes the temper designa- 

 tion, separated from the alloy designation by a hyphen, as for example 7061- 

 T6. The basic temper designations are as follows: 



F as fabricated - no special control is exercised over thermal con- 

 ditions or strain hardening. 



annealed - heat treated to obtain lowest strength temper and improved 

 ductility. 



H strain hardened (wrought products only) . 



W solution heat treated (applies only to alloys hardenable by thermal 

 heat treatment) - an unstable temper, describing the condition 

 between solution treatment before aging. Subfreezing is sometimes 

 used to preserve this temper against natural aging. 



T thermally treated to produce stable tempers other than F, 0, or H. 



Numbers following the basic temper designations further describe the 

 specific combination of operations affecting the temper and in turn the 

 mechanical properties. Specifications, such as those of the American 

 Society for Testing and Materials (ASTM) , fully define the alloy composition, 

 mechanical properties and other requirements for applicable aluminum mate- 

 rials. Alloys 5083, 5086, 5052, and 6061 are the most popular aluminum 

 alloys for applications exposed to marine atmospheres. The 5000 series of 

 alloys are the most corrosion resistant, but the 1000, 3000, and 6000 alloys 

 have been used in marine atmospheres. These aluminums may be also employed 

 in the splash zone, but are not recommended for continuous immersion in 

 seawater . 



c. Copper and Copper Alloys . Copper has several unique properties. 

 Properties such as high thermal and electrical conductivity, excellent corro- 

 sion resistance in normal atmospheric conditions, good workability, and 

 availability at reasonable cost make copper a first choice for conductors in 

 electrical equipment. Copper can be alloyed to produce alloys having improved 

 strength, corrosion resistance, creep resistance, and machinability. 



209 



