Clean, clean, clean.

Degrease all pieces with acetone followed by an isopropyl alcohol (90% min.) rinse.

Wire brush all pieces using a solvent cleaned austenitic stainless steel brush. Push the brush in one direction and lift on the return stroke. Push toward the weld joint.

Draw file the groove face and root face with a Vixen file that has be solvent cleaned.

Keep your stinking, dirty, oily fingers off the areas you just cleaned! Why, I can't tell you, but there is an overwhelming urge by nearly all welders (myself included) to run their finger over the groove face after cleaning it. Maybe it is to check for burrs or whatever. Resist the urge to do so. Finger prints are the kiss of death!

Try a little experiment. Look at your thumb nail in the light. It is somewhat shiny, but still it is dull looking. Now rub your thumb nail beside your nose and tell me how it looks. That gloss is from the oils that are in your skin to keep it soft and flexible. That oil doesn't help when it comes to welding.

Clean, clean, clean. After all the wire brushing and draw filing, rinse off all the joint surfaces with the 90% isopropyl alcohol and let it air dry. Don't use compressed air, it contains lubricating oil and moisture, both sources of hydrogen.

Porosity is usually linked with a source of hydrogen if the pore is silver. If the pore is discolored, I would look for a shielding problem or other sources of surface contamination.

Use a Zirconiated tungsten with aluminum when using AC, use 2% Thoriated with a tapered end if welding with DCEN.

Clean, clean, clean, this includes your filler metal. I prefer to clean the filler metal with cleaned stainless steel wool pads.

DO NOT CLEAN with aluminum oxide based abrasive materials, i.e., grinding disks, Scotch-brite, etc.

Good luck.

Best regards - Al

Joe,

Welcome.  It sounds like you're running two passes on an aluminumn tube.  The root pass is fine while the next pass has porosity.  I don't know what process.

I'd use straight argon if I were using GTAW.  I'd make sure the part was very clean (wire brush and acetone) between passes.  Also, let the part cool down between passes (275", I think for aluminum) by checking the part with a temp stick.

Good Luck,

Keith

All the above is spot on especially the Cleaning part. Another thing you can do to cool down the pass is tweak the balance function (I assume you are using AC) I usually set mine between 70%-80% but remember lower balance %= more cleaning action from the ark and less penetration, a vise versa for higher balance settings. Another tip that might help is the angle of your torch you should have a straight or slightly forward angle. Keep in mind that 17.1 will except either 0.060" - 0.090" pore size depending on thickness spending some time in Table 6.1 will be a big help for you as some porosity is very inherent to welding aluminum and subsurface porosity will be present in most welds. I have found that extinguishing the ark slowly will help with porosity in the final weld pool.

Based on what you stated I would go back to straight argon and preheat the test coupon it may sound odd but warming up the part (as much as 250 degrees) especially if it is in excess of 1/4" material thickness will give the hydrogen a little more time to escape and will yield much less porosity you can do this with either 100% argon or the mix you mentioned just don't go outside your procedure. We have to do this in parts that get "O" ring grooves machined in as we have a zero defect requirement.

Hope this helps.