Weld porosity causes

Aluminum and porosity go together like milk and cookies!

If you are experiencing porosity when welding aluminum, look for a source of hydrogen. There are many sources of hydrogen. Did the welder wear clean gloves if GTAW was used? Did the welders use air powered tools to prepare the joint or for interpass cleaning? Were the tools used to prepare the joint, wire brushes, files, etc. cleaned with a suitable solvent before and during use? Did the workers blow off standing water with compressed air (after all, compressors are lubricated with oil)? Was the base metal flushed with a suitable solvent to remove oil based cutting or machining fluids? Did the workers wipe the surfaces to be welded with paper towel, cotton wiping rags, or other materials composed of cellulose or other hydrocarbon based materials? Did the workers clean the material with "Scot-brite" abrasives. The "nylon" mesh can leave a reside on the surfaces.

I prefer to flush all surfaces with isopropyl alcohol as the final cleaning in preparation for welding. Some people use acetone, but I find it leaves a residue. Isopropyl alcohol doesn't.

Good luck.

Best regards - Al

I'm not familiar with P-22 aluminium. Is it a 6xxx alloy?
As said above, welcome to the world of porosities.
First you need to eliminate ALL sources of hydrogen and/or oxygen.
If, after you're sure you are working with clean materials, you still have porosities, you should try increasing the frequency with which you're welding. But first make sure there is no source of impurities from "outside" the weld (like on the filler rods, files, scotch-brite, wire brushes, the oxide layer, ...)

What was the weather report that day? Were the shop doors open ?

No matter how much experience you have welding steel, you cannot just walk up to aluminum and be immediately successful.

Lots of the above suggestions are useful, but aluminum requires a holistic approach (not to mention a bay that is isolated from the rest of the fab shop).

I recommend you contact one of the major domestic wire suppliers, they offer comprehensive guides to fabricating aluminum.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

Suradach... Caution. We are professionals who WILL expect complete information from YOU... to provide YOU reasonably informed opinions and observations in-return.
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What exactly is P-22 [alloy and specification]???

Exactly WHAT alloy/specification is the weld-filler???

EXACTLY what is Your welding process specification???

I could NOT find any 2-digit alloy designators in the Aluminum Association - Aluminum Standards and Data.

Also... there is NO 'temper' or H [strain-hardness] associated in Your term 'P-22'.

FYI. The Aluminum Association WATP23 Welding Aluminum - Theory and Practice MIGHT be useful for general information on aluminum alloy welding... but not necessarily for this mysterious aluminum alloy[?] 'P-22'.

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
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To Wil's point, no P-22 aluminum alloy comes up on a Google search...

Quote (WKTaylor)

What exactly is P-22 [alloy and specification]???

It is aluminum pipe containing 2.25% chromium and 1% molybdenum obviously.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

LOL! Careful, ironic, someone might take you seriously!