Building Design and Construction Handbook - Merritt - Ventech!

4.76 SECTION FOUR
alloys to indicate the compositions and the tempers of the various metals. Wrought
alloys are designated by a four-digit index system. 1xxx is for 99.00% aluminum
minimum. The last two digits indicate the minimum aluminum percentage. The
second digit represents impurity limits. (EC is a special designation for electrical
conductors.) 2xxx to 8xxx represent alloy groups in which the first number indicates
the principal alloying constituent, and the last two digits are identifying numbers
in the group. The second digit indicates modification of the basic alloy. The alloy
groups are listed in Table 4.20.
For cast alloys, a similar designation system is used. The first two digits identify
the alloy or its purity. The last digit, preceded by a decimal point, indicates the
form of the material; for example, casting or ingot. Casting alloys may be sand or
permanent-mold alloys.
Among the wrought alloys, the letter F, O, H, W, and T indicate various basic
temper designations. These letters in turn may be followed by numerals to indicate
various degrees of treatment. Temper designations are summarized in Table 4.21.
The structural alloys general employed in building fall in the 2xxx, 5xxx, and
6xxx categories. Architectural alloys often used include 3xxx, 5xxx, and 6xxx
groups.
4.52 FINISHES FOR ALUMINUM
Almost all finishes used on aluminum may be divided into three major categories
in the system recommended by the The Aluminum Association: mechanical finishes,
chemical finishes, and coatings. The last may be subdivided into anodic
coatings, resinous and other organic coatings, vitreous coatings, electroplated and
other metallic coatings, and laminated coatings.
In The Aluminum Association system, mechanical and chemical finishes are
designated by M and C, respectively, and each of the five classes of coating is also
designated by a letter. The various finishes in each category are designated by twodigit
numbers after a letter. The principal finishes are summarized in Table 4.22.
4.53 STRUCTURAL ALUMINUM
Structural aluminum shapes are produced by extrusion. Angles, I beams, and channels
are available in standard sizes and in lengths up to 85 ft. Plates up to 6 in
thick and 200 in wide also may be obtained.
TABLE 4.20 Aluminum Association
Designations for Wrought
Aluminum Alloys
Copper 2xxx
Manganese 3xxx
Silicon 4xxx
Magnesium 5xxx
Magnesium and silicon 6xxx
Zinc 7xxx
Other elements 8xxx
Unused series 9xxx