Thanks, that was my gut feel but good to hear confirmation.
Yes, no surprise there. 6061 was my intention, which already contains a lot of chromium, so a little bit more from a surface layer wouldn't matter much I would guess. I was more worried about things like iron, which Alodine contains if I understand the "proprietary" chemistry correctly.
And no, this wouldn't be for any structurally critical welds. I'm looking at some welded aluminum fuel tanks that I've been flying for many years. The welds are truly a work of art, so I was curious what process was used and whether I could ever get that good.
In retrospect the only leaking issues with these tanks were from threaded penetrations--inadequate sealants. Let's say I wanted to provision for an in-cabin auxiliary fuel tank for long ferries and such adventures: welding one in the right shape with penetrations on top seems like the safest option.
Yes, I'm aware of the toxic fumes, have fresh air feed to face mask.