WELDING AND BRAZING OF ALUMINUM BASICS AND TUTORIALS

WELDING AND BRAZING OF ALUMINUM BASIC INFORMATION
How Welding and Brazing Of Aluminum Works?


Weldability and brazing properties of aluminum alloys depend heavily on their composition and heat treatment. Most of the wrought alloys can be brazed and welded, but sometimes only by special processes.


Finishes for Aluminum and Aluminum Alloys
Types of finish Designation*
Mechanical finishes:
As fabricated M1Y
Buffed M2Y
Directional textured M3Y
Nondirectional textured M4Y
Chemical finishes:
Nonetched cleaned C1Y
Etched C2Y
Brightened C3Y
Chemical conversion coatings C4Y
Coatings:
Anodic
General A1Y
Protective and decorative (less than 0.4 mil thick) A2Y
Architectural Class II (0.4–0.7 mil thick) A3Y
Architectural Class I (0.7 mil or more thick) A4Y
Resinous and other organic coatings R1Y
Vitreous coatings V1Y
Electroplated and other metallic coatings E1Y
Laminated coatings L1Y
*Y represents digits (0, 1, 2, . . . 9) or X (to be specified) that describe the
surface, such as specular, satin, matte, degreased, clear anodizing or type of coating.


The strength of some alloys depends on heat treatment after welding. Alloys heat treated and artificially aged are susceptible to loss of strength at the weld, because weld is essentially cast.

For this reason, high-strength structural alloys are commonly fabricated by riveting or bolting, rather than by welding. Brazing is done by furnace, torch, or dip methods. Successful brazing is done with special fluxes.

Inert-gas shielded-arc welding is usually used for welding aluminum alloys. The inert gas, argon or helium, inhibits oxide formation during welding.

The electrode used may be consumable metal or tungsten. The gas metal arc is generally preferred
for structural welding, because of the higher speeds that can be used.

The gas tungsten arc is preferred for thicknesses less than 1⁄2 in. Butt-welded joints of annealed aluminum alloys and non-heat-treatable alloys have nearly the same strength as the parent metal.

This is not true for strainhardened or heat-tempered alloys. In these conditions, the heat of welding weakens the metal in the vicinity of the weld. The tensile strength of a butt weld of alloy 6061-T6 may be reduced to 24 ksi, about two-thirds that of the parent metal.

Tensile yield strength of such butt welds may be only 15 to 20 ksi, depending on metal thickness and type of filler wire used in welding.

Fillet welds similarly weaken heat-treated alloys. The shear strength of alloy 6061-T6 decreases from about 27 ksi to 17 ksi or less for a fillet weld.

Welds should be made to meet the requirements of the American Welding Society, ‘‘Structural Welding Code—Aluminum,’’ AWS D1.2.

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