I was playing around with some aluminum the other day while working on a turbo kit for a friend's Camaro. I noticed some pitting and "pepper" anomolies on the surface of the bead. I was playing with argon flow rate and AC balance for quite some time trying to clean the bead's appearance, here's the best i could come up with at the time:
Well, i was having issues with a local welding supply store not honoring a discount they were supposed to, so i switched gas suppliers thinking maybe i had some contaminated gas (this has happened multiple times before). When i got back to the shop, this is the first bead i ran, after testing on some scrap pieces:
MUCH better....
...so i thought. This must have been a fluke because since welding that piece, i've had some more light pitting/peppering issues. I've played with all kinds of settings on the machine and techniques as well. The only thing that i can think of, is maybe my gas lens isn't doing its job. i BELIEVE it is a radnor but i'm not certain. i was wondering if anybody had any experience with different types of lenses causing issues like this? Is there any other possible explanation for my pitting problem?
How about Mix-and Match countries of origin for the parts?
Your problem welds appeared to involve straight sections, while the "stack-o-dimes" was on Ells at a fitting. If the pipe comes from China, and the ells from India, and the fittings from Europe or USA, you have a hodgepodge.
There are NO enforceable standards for what an importing country can call "4043" or "6061".
I cut out defective fittings (welds failed that shoudn't have) that were clearly labeled "304L", yet I could pick them up with my retrieval magnet.
I suspect the material, and the best you can do in that case is wire wheel the crap out of it, and call it good.
I've definately encountered problems with cheaper grade materials. I try never to use "ebay" tubing, but sometimes its what the customer brings me The "308" welds like crap every time.
This instance, however, i can rule that out. the problem welds were done on pieces cut from the bends you see pictured below them. While i can not verify their origins, i CAN say they are of identical chemistry.
...and to add to that, i cleaned the piss out of it, like always. i have a dedicated stainless brush for aluminum that i use AFTER a light sanding of the weld area, then a good wipe down with acetone and i weld it immediately.
Gas line leak, depending on how the lead is laying?
I'm stretching, but there's no reason for a bottle of gas, or a gas lens, or tungsten, or any other consumable, to perform fine on one weld, and not on another of the same material. Something else is in play.
that's what i was thinking at the time too. it's a water cooled torch. I ALWAYS have the lead laying away from obstacles and never kinked up or pinched and it doesn't get stepped on either.
I check for leaks all over, sprayed soapy water on the regulator and on the bottle valve, then on the torch head with the handle off while gas was flowing....that was after a thorough visual check. I couldn't come up with anything.
yeah i guess i'll just buy a couple different lenses and see what happens. Mine isn't clogged or anything, it's just the only thing i can think of that might cause my problem....and i agree, it seems like a stretch, but i can't find any leaks and i know the metal is clean, or reasonably clean.
I reviewed the pictures again, and I have another thought.
In the image of the weld you're dissatisfied with, one part has dimples from the vise of the mandrel bender. Perhaps embedded contaminants in those dimples were gassing off into your weld zone?
These dimples do not appear in the photo of the "pretty" one.
Anything is possible, but those dimples weren't all the way around the tube and the weld had a uniform appearance all the way around...it wasn't concentrated around the die marks...but yes there's no telling what was embedded in the material in those areas.
I have had issues with gas lens going bad causing similar issues but in my case it would weld fine in the flat postion but weld like crap doing vertical or tubing. I think it weird how it welded nice once and then weld like crap. Did you change your tungsten stickout when you the one you like?
I was working contaminated metal, that "spit back" a lot. Ruined several inches of tungsten. The "spit back" clogged and disrupted the screens in the gas lens. It was so turbulent, the gas might as well not have been on.
The "308" welds like crap every time. 
