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Building Design and Construction Handbook - Merritt - Ventech!

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4.78 SECTION FOUR<br />

TABLE 4.22 Finishes for Aluminum <strong>and</strong> Aluminum Alloys<br />

Types of finish <strong>Design</strong>ation*<br />

Mechanical finishes:<br />

As fabricated M1Y<br />

Buffed M2Y<br />

Directional textured M3Y<br />

Nondirectional textured<br />

Chemical finishes:<br />

M4Y<br />

Nonetched cleaned C1Y<br />

Etched C2Y<br />

Brightened C3Y<br />

Chemical conversion coatings<br />

Coatings:<br />

Anodic<br />

C4Y<br />

General A1Y<br />

Protective <strong>and</strong> decorative (less than 0.4 mil thick) A2Y<br />

Architectural Class II (0.4–0.7 mil thick) A3Y<br />

Architectural Class I (0.7 mil or more thick) A4Y<br />

Resinous <strong>and</strong> other organic coatings R1Y<br />

Vitreous coatings V1Y<br />

Electroplated <strong>and</strong> other metallic coatings E1Y<br />

Laminated coatings L1Y<br />

* Y represents digits (0, 1, 2, ...9)orX (to be specified) that describe the<br />

surface, such as specular, satin, matte, degreased, clear anodizing or type of coating.<br />

depends on heat treatment after welding. Alloys heat treated <strong>and</strong> artificially aged<br />

are susceptible to loss of strength at the weld, because weld is essentially cast. For<br />

this reason, high-strength structural alloys are commonly fabricated by riveting or<br />

bolting, rather than by welding.<br />

Brazing is done by furnace, torch, or dip methods. Successful brazing is done<br />

with special fluxes.<br />

Inert-gas shielded-arc welding is usually used for welding aluminum alloys. The<br />

inert gas, argon or helium, inhibits oxide formation during welding. The electrode<br />

used may be consumable metal or tungsten. The gas metal arc is generally preferred<br />

for structural welding, because of the higher speeds that can be used. The gas<br />

tungsten arc is preferred for thicknesses less than 1 ⁄2 in.<br />

Butt-welded joints of annealed aluminum alloys <strong>and</strong> non-heat-treatable alloys<br />

have nearly the same strength as the parent metal. This is not true for strainhardened<br />

or heat-tempered alloys. In these conditions, the heat of welding weakens<br />

the metal in the vicinity of the weld. The tensile strength of a butt weld of alloy<br />

6061-T6 may be reduced to 24 ksi, about two-thirds that of the parent metal. Tensile<br />

yield strength of such butt welds may be only 15 to 20 ksi, depending on metal<br />

thickness <strong>and</strong> type of filler wire used in welding.<br />

Fillet welds similarly weaken heat-treated alloys. The shear strength of alloy<br />

6061-T6 decreases from about 27 ksi to 17 ksi or less for a fillet weld.<br />

Welds should be made to meet the requirements of the American Welding Society,<br />

‘‘Structural Welding Code—Aluminum,’’ AWS D1.2.

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