6063 Aluminum extrusions cracking and surface pitting surfac

Date 11-21-2013 20:20 Edited 11-21-2013 20:25

Any ideas? Could andizing process be the cause? We have been running similar part for decades with no trouble, the all of a sudden Bang.
6063 Aluminum extrusions cracking and surface pitting surface after anodizing. The AC GTA welds with 5356 filler were visually acceptable prior to grinding operations, after grinding flush the samples were 100% PT test by or level II with no indications when the parts returned from anodizing they are covered with multitudes of pits and odd little spider crack in the visible HAZ. This has been a frustrating problem recently. We’ve tried most everything listed in Welding Aluminum-Questions and Answers 2nd edition by Tony Anderson American Welding Society.
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By NMcowboy75 Date 12-03-2013 02:19

we do alot of aluminum tig welding on 5052 and 6061 t6 and as well the 6063 extrusion and have found tha it is very dificult to atache 6063 angle on a 6061 box weld flare bevel weld and grind smoth sometimes ive gotten alot of pits sometimes none and i have cleaned and used acetone etc i really think its the extrusion itself.

By NMcowboy75 Date 12-03-2013 02:22

if the welded area gets sandblasted then alonined ive seen them pits come out, but if no grinding is done on the weld you might be getting contamination from the basemetal, are you using UHP argon 99% pure?

By 803056

Date 12-03-2013 04:25

There are no surprises here. The grinding/sanding operations smears the soft aluminum. The softer metal smears and seals any porosity that may be present. I usually take a small "toothbrush" with stainless steel bristles and lightly tap the surfaces that have been ground smooth. The tapping action leaves slight depressions where the metal has been smeared over open porosity. A sharpened tungsten can be used to "pop" the depressions to reveal the porosity.

Anodizing etches the smeared metal revealing the porosity. Anodizing also removes any smeared metal that may conceal small cracks. The discontinuity is easier to see after anodizing because the chemicals initially drawn into the cavity bleeds out and stains the surrounding base metal.

The shallow "cracks" revealed by PT adjacent to the weld bead may be the result of very shallow surface melting and rapid resolidification of the aluminum. Vigorous wire brushing with a stiff bristled stainless brush is usually sufficient to remove the shallow cracks. I have heard it call arc erosion. This is usually seen when using GTAW to weld aluminum alloyed with silicon. 6061 and 6063 alloys are susceptible to this problem.

Best regards - Al