I ultrasonically cleaned some 2024 aluminum parts with a alkaline soap and a 3 minute cycle time. When the last batch finished, I forgot to remove them and left them in the tank for 30 minutes with the machine off. The parts all turned a bronze color, similar to tarnished silver. I can partially rub off the color with my fingers. Is there any simple chemical that I can use to remove the tarnish?
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Bad chemical reaction with ultrasonic cleaning soap
- Thread starter Goff
- Start date
- Replies 16
- Views 6,145
eKretz
Diamond; Mod Squad
- Joined
- Mar 27, 2005
- Location
- Northwest Indiana, USA
Nope. Don't leave aluminum in the US tank. This is pretty much ultrasonic 101.
Larry Dickman
Titanium
- Joined
- Jan 30, 2014
- Location
- Temecula, Ca
you need a de-smutter. A mildly acidic solution should work. Vinegar maybe? The desmut we used to buy was sulfuric acid based.
eKretz
Diamond; Mod Squad
- Joined
- Mar 27, 2005
- Location
- Northwest Indiana, USA
That will remove the color but the finish is still going to be permanently altered. O.P. are you only worried about the color? If that's the case you should be able to use Larry's suggestion.
AARONT
Stainless
- Joined
- Feb 19, 2013
- Location
- Madison, WI
Try Drano. That stuff gets everything off.
Poor it into a bucket and let the parts soak in it for about a minute and a half, then wash them off. Repeat until it comes off.
Poor it into a bucket and let the parts soak in it for about a minute and a half, then wash them off. Repeat until it comes off.
sfriedberg
Diamond
- Joined
- Oct 14, 2010
- Location
- Oregon, USA
Drano is lye. Lye eats aluminum. If you thought you had issues leaving the aluminum parts in the ultrasonic bath, you will be asking where your parts went if you leave them in a Drano bath. RINSE.
Thanks for the comments. The parts are tumbled and the ultrasonic is just to get the tumbling dust off.
I will try some acids. I have vinegar & sulfuric. It is strictly a cosmetic issue.
I can re-tumble the parts if there is a slight etch. The outside is not a problem. The inner cavities and tapped holes look bad. These are not high tolerance parts and a mild etch will not cause problems.
I will try some acids. I have vinegar & sulfuric. It is strictly a cosmetic issue.
I can re-tumble the parts if there is a slight etch. The outside is not a problem. The inner cavities and tapped holes look bad. These are not high tolerance parts and a mild etch will not cause problems.
The "brown" stuff left by the soap (which is most likely mildly alkaline, which caused some etching of the 2024) is "smut", basically - alloying elements left on the surface of the 2024 after the alkaline etch removed some aluminum.
I would simply retumble them to get the outside texture match the other parts again, as for the smut, there is a very "laymans" sort of way, take a bathroom cleaning gel, the ones that remove rust, calcium deposits etc, some of them have chlorine in them, avoid that stuff (chlorine has a distinctive smell to it), using these cleaners as opposed to pure acids has the benefit of the gel to "lift" the smut, it will come off much much easier than just by dipping them in weak acids, some mechanical help may still be required, like a sponge or a brush.
The side effect of all this is that the parts surface is left very active, slight moisture on it and it will corrode quickly, may lead to ugly pitting, normally one would immediately follow with some sort of protective treatment, conversion coating, anodizing or at least spray with wd40.
I would simply retumble them to get the outside texture match the other parts again, as for the smut, there is a very "laymans" sort of way, take a bathroom cleaning gel, the ones that remove rust, calcium deposits etc, some of them have chlorine in them, avoid that stuff (chlorine has a distinctive smell to it), using these cleaners as opposed to pure acids has the benefit of the gel to "lift" the smut, it will come off much much easier than just by dipping them in weak acids, some mechanical help may still be required, like a sponge or a brush.
The side effect of all this is that the parts surface is left very active, slight moisture on it and it will corrode quickly, may lead to ugly pitting, normally one would immediately follow with some sort of protective treatment, conversion coating, anodizing or at least spray with wd40.
Bill D
Diamond
- Joined
- Apr 1, 2004
- Location
- Modesto, CA USA
When I worked as a dishwasher the soap is a caustic in a belt feed machine. One day a throw away Al pieplate got trapped in the machine within 8 hours it was more then half gone with big holes eaten completely through over about 35% of the surface.
Lesson is caustic will eat Alumninum but acids are fine. Reverse for iron.
Bill D.
Lesson is caustic will eat Alumninum but acids are fine. Reverse for iron.
Bill D.
thermite
Diamond
- Joined
- Sep 21, 2011
"Sort of".
Pure Aluminium is a fence-sitter. It can react willingly with EITHER Oxidizers (Acids included) or Reducers (Caustics included).
What makes it appear Acid-tolerant is that the immediate first stage of Oxidation can form Aluminium Oxide, AKA synthetic Sapphire - the very "anodized" and tightly adhered surface protective finish usually sought as a desired product. And paid-for.
Aluminium Oxide is a far, far, tougher cookie than its parent metal, so it generally stops there - at least short-term.
Not really an all-circumstances "absolute" to be trusted though.
Aluminium is actually in the record for its reaction with common acids:
Aluminium>>reactions of elements [WebElements Periodic Table]
that oxide on aluminum in acids is not just forming and staying there, is is dissolving (at much slower rate than dissolving al in causting of course, because no oxide barrier ever forms), hence why you can get only sub 40 micron thickness for typeII and <70 for typeIII anodizing -> the newly formed oxide is growing at the same rate that it is dissolving in the acid, I know of people achieving >100um for specific applications, like making gold nano needles via depositing gold in those 100+um long anodizing pores and later dissolving everything-non-gold away, but that is another subject 
thermite
Diamond
- Joined
- Sep 21, 2011
Not sure the "needles" he is talking about could even be seen in any colour with the unaided Mark One human eyeball.
Pore may be 100 um long, but he said "needle" not "disc", so OY! the diameter!
steve45
Stainless
- Joined
- Jan 16, 2012
- Location
- Midland, Texas
Aluminum is unaffected by Nitric acid. Don't know if it will help in this case.
I've found some strong soaps will attack aluminum in my ultrasonics and some will not. What for "fuzzy" bubbles appearing very soon after the objects are put into one of the attacking soaps. The bubbles are visibly different from what you get cleaning other metals. Look on the labels, usually it says what is attacked and what is not.
ranchak
Cast Iron
- Joined
- Dec 4, 2007
- Location
- Southern California
I just had a similar instance with aluminum threaded rods. This is first time I have cleaned aluminum in the ultrasonic cleaner. I originally used hot water and Palmolive dish soap (I was out of Dawn). I noticed that the bottom of the threads had a brown "smut" on them. I originally thought that the dish soap was the culprit. I then tried hot water without soap. Same problem. Next came cold water, same problem. I'm starting to think that it might be residue from the coolant (Trim 585XT) that is causing this.
greif1
Aluminum
- Joined
- Oct 1, 2013
- Location
- Rochester, NY, USA
Try the Alconox line of laboratory detergents. You can get alkaline, neutral, or acidic which will work in ultrasonic. In addition to the detergent reaction, you may have seen galvanic if the parts were in contact with stainless for a long time.
https://alconox.com/product-catalog/
https://alconox.com/product-catalog/
