Vibratory Tumbler - Staining on Aluminum?

jcorsico · Apr 10, 2021

I ran a batch of 7075 parts in my vibratory tumbler and some of them appear to be 'stained'. Has anyone seen this before? Is this corrosion?

I cannot feel any surface finish change in the stained area. Even looking at it with a loupe, it appears to be just as smooth as the adjacent aluminum.

Thank you!
Jon

Finegrain · Apr 10, 2021

Freshly exposed Al is highly reactive, especially 7075. The tumbler is constantly eroding the oxide surface layer exposing fresh metal, so any chemical that is in the tumbler (including trace chemicals from previous tumblings) that could react with Al, will react with the 7075.

When I run 7075 parts, they get rinsed in plain water and dried as soon as they come out of the machine. No tumbling. All deburring is done in the VMC or by hand.

Regards.

Mike

Guest · Apr 10, 2021

Everything Finegrain said. Even humidity will get to a 7075 part that was immediately cleaned and dried after machining. That isn't a stain it is corrosion.

jcorsico · Apr 10, 2021

Interesting. Thanks guys. The tumbler is new to me, so I haven't done a lot of this. I'm guessing I screwed up when I left the parts in the tumbler overnight. Normally, I've been tumbling and then immediately removing them - haven't seen this corrosion when I've done that.

Will experiment some more, but 7075 may be out.

Thank you!
Jon

jz79 · Apr 10, 2021

it is completely unacceptable to leave tumbled aluminum (any alloy) parts wet, sitting in the tumbler for any length of time because of the reasons explained my Mike in post #2

even when you take them out of the tumbler they shouldn't be left by themselves to air dry (if you're not using a corrosion inhibitor), the residue from tumbling left on them makes air drying take longer, long enough for corrosion to start, which looks like small dark specks on the parts after they are anodized (and stripping and reanodizing doesn't fix that), you should rinse them, blow off with air (paying special attention to blind holes), preferably wipe down if there are any droplets left and then leave them to air dry, it takes just couple minutes to do this and saves you a lot of grief and a fight with the anodizer who presumably has ruined your parts

p.s. read the other recent topic regarding 7075 and corrosion - 7075 handling after machining

triumph406 · Apr 10, 2021

jcorsico said:
Interesting. Thanks guys. The tumbler is new to me, so I haven't done a lot of this. I'm guessing I screwed up when I left the parts in the tumbler overnight. Normally, I've been tumbling and then immediately removing them - haven't seen this corrosion when I've done that.

Will experiment some more, but 7075 may be out.

Thank you!
Jon

Nothing wrong with tumbling 7075, just don't leave it in the tumbler overnight, that was your mistake.

Tumble some 7075, at the end of the tumbling, take half out, wash and dry, leave the other half in overnight. I'd venture to guess you'll have half the parts nicely tumbled, and the other half left in the tumbler would show signs of corrosion.

jcorsico · Apr 10, 2021

Very helpful. Thanks again guys. Luckily, this corrosion seems cosmetic. Even when I run the surface tester over it, it still measures the same (around 8uin Ra) as the non-corroded surfaces.

Guest · Apr 10, 2021

jcorsico said:
Very helpful. Thanks again guys. Luckily, this corrosion seems cosmetic. Even when I run the surface tester over it, it still measures the same (around 8uin Ra) as the non-corroded surfaces.

I would Scotch-Brite those spots off.

eaglemike · Apr 10, 2021

jcorsico said:
Interesting. Thanks guys. The tumbler is new to me, so I haven't done a lot of this. I'm guessing I screwed up when I left the parts in the tumbler overnight. Normally, I've been tumbling and then immediately removing them - haven't seen this corrosion when I've done that.

Will experiment some more, but 7075 may be out.

Thank you!
Jon

I tumble 7075 and anodize later often. Use the appropriate solution with the plastic media, and blow them completely dry after. If you don't use the right solution, the chance for corrosion goes way up. 7075 is more sensitive to this than 6061, but not bad at all once you get the process under control. As noted in another thread, don't even think about Simple Green! It's caustic to aluminum in my experience.
I also machine 17-4 H900 parts. If they are left sitting in a tumbler not running for a while, even that can stain. Just get the process under control, and you'll be fine.
Maybe even talk to a media or tumbler supplier and ask for help. They are often quite useful.
Good luck!

neilho · Apr 10, 2021

I'll pile on.

6061-T6 stains when left in the tumbler, too.

If you want that tumbled look, just tumble them again.

Ross Shafer · Nov 30, 2023

Happy I found this thread, thanks for the info all!

??? · Nov 30, 2023

Galvanic reaction. I recently machined some 7075 and it had the same look where it contacted the mill table if it stayed on too long. 7075 has a lot of zinc in it.

Search

Largest Manufacturing Technology Community on the Web

Search

Vibratory Tumbler - Staining on Aluminum?

jcorsico

Aluminum

Finegrain

Diamond

Guest

Guest

jcorsico

Aluminum

jz79

Stainless

triumph406

Diamond

jcorsico

Aluminum

Guest

Guest

eaglemike

Stainless

neilho

Titanium

Ross Shafer

Plastic

???

Titanium

Similar threads