Discoloration on welded and polished Aluminum after polishing

[brianthechemist]

Hi All,

I've got a strange issue here: I'm a metal sculptor and have started working with Aluminum (Mig Welding with 4043 wire and a spool gun). When I go to polish my finished piece, (after sanding from 80-400, then polishing with black then white rouge) I'm getting discoloration on the areas where the weld was (but has the same nice smooth surface finish as the surrounding material).

Oddly enough, this discoloration is not present until AFTER the polishing process. (The very smooth post 400 grit surface does not show the discoloration).

Any thoughts? I'm not sure what specific alloy the bulk aluminum was (scrapyard special) if it has an effect.

Thanks
Brian

[Rasper]

If you are going to polish welded metal you have to use the same alloy for filler rod as the piece is made from. Every alloy is a different color. I do my aluminum sculpture in 1100 alloy and of course 1100 wire is available. I also use 304 stainless. 308 rod is pink compared to the 304 so I got a local sheet metal friend to slice up a bunch of thin strips of 304 on the shear at the shop where he works. I use that as filler rod.

Richard

[brianthechemist]

I thought I'd give an update here,

I figured out that the Aluminum alloy I was using was 6061, and by switching to 5053 MIG wire I was able to make pieces that matched perfectly.

I'm not sure why the discoloration was not showing up until after the polishing, but I suspect there was just an optical illusion hiding it until polished smooth.

[Rasper]

Your information about 5053 wire is good to know. I occasionally use 6061.

Polished metal shows all.

R