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White Powder/Salts on Anodized Aluminum

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Q. Hi,

I am experiencing a similar issue with white "powder" or "salts" on cast aluminum aerospace parts. The parts are chromate Type II, Class 3, then Anodize Type II, class 2.

These are coming from a vendor, and I have not yet reached out to them about their process. I attach a photo:

white salts on anodized aluminum

Let me know if this is similar to what others have seen regarding this issue.

Patrick Hawn
Manufacturing Engineer - Portland
June 28, 2022

⇩ Related postings, oldest first ⇩

Q. We manufacture aluminum (62SN-T8 and T9 which is comparable to 6020) transmission valves. The valves are anodized (AMS2469D)and then finish ground. The problem we have is white powder that collects on the parts. Infrequently the powder is seen on the parts post-anodize, pre-finish grind. Most of the time the powder becomes evident once the parts dry after finish grind. There is great variation in the problem, some lots will be 100% bad, while others might only be 5%. We make approximately 40 different parts that all have this problem. We are not able to clean the parts to remove the powder, we can only do it manually (think toothbrushes!)
In the past when we ran only 6262-T8 we did not have this problem. It was only after we switched to the lead-free material that we started experiencing this. The rest of the process and our suppliers (anodizing and grinding are outsourced) is exactly the same.
If anyone has any insight on this problem I would be extremely grateful as we are at our wits end trying to figure it out.

Tracy Skupien
Operations - Detroit, Michigan

A. Aluminum How-To lists about 30 different causes for "white spots" and smut. By far the most frequent is calcium salts left behind from the seal, which you see only after the water evaporates. The second most frequent cause is galvanic corrosion usually between titanium rack sand stainless tanks/heaters. Come back to us with more information on the racking, tank materials and whether or not the dye and seal are made up with deionized water and whether tap water is dragged into the dye and seal. This problem CAN be beat.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

Is white dust from anodized aluminum harmful

Q. Hi we manufacture signs and name plates. One of our customers machine-engraves anodised aluminium plates which we provide.

We out-source the anodising, though print and seal ourselves.

The customer complains that there is a white dust and is concerned if it is a health issue.

We have asked anodisers for a data sheet, which is not forth coming. So my question: is the white dust harmful?

I have searched web and cannot see.

September 6, 2018

A. Hello Lee. If you are saying that the parts are free of dust until your customer starts engraving them, then the engraving process generates dust, it sounds like what one would expect. The anodized surface is not metallic aluminum, but is a ceramic comprised of aluminum oxide and hydroxides. Depending on the engraving or machining methods, it may come off as a powder or grit rather than adhering to the aluminum 'chips'.

You may want to insure that your anodizers are not using chrome sealers which could contain hexavalent chrome (they probably aren't for signs and nameplates). It is not safe to inhale significant quantities of any dusts regardless of their chemical makeup -- lungs are very delicate micro-machines -- but aluminum oxides comprise more than 10% of the earth's crust, so the dust is probably not a hazardous material in my opinion (additional opinions and citations are certainly encouraged).


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

simultaneous replies


LEV = local exhaust ventilation

A. Hi Ted,
Aluminium oxide can be quite hazardous if it gets into the lungs.
Its presence can lead to fibrosis, lung cancer and long term inflammation.
So Lee's employer should invest in appropriate LEV in order to mitigate against this hazard.
They should be aware of their duty towards Lee under the 1974 Health and safety at Work Act.
Best regards

Mark Lees
- a sunlit though wind rock in the Irish Sea

A. In UK, legal limits are defined in "workplace exposure limits EH40", which is available on line.
For both aluminium and its oxides the limits for respirable dust (less than 10 microns) is confusingly given as 10 and 4 mg/metre cube.
No specific health warnings are given
This is for long term exposure (8 hour time weighted average)
No short term limits are given, i.e., it is considered a nuisance dust rather than a significant hazard.
It seems extremely unlikely that any dust present on an anodised plate could get anywhere near this level.

BUT Why are you sending out anodised plates with surface dust?

geoff smith
Geoff Smith
Hampshire, England

A. I guess Lee's wording was confusing because 3 readers have read it 3 different ways :-)

My understanding was that Lee shipped the plates to a customer, and when the customer engraved them it generated a dust which the customer was concerned about.

Speaking personally, I have had emphysema for decades, which I attribute 90-95% to the fact that I smoked. But I also know that I never had the common sense to be careful to avoid inhaling dusts from woodworking, rust removal sanding, dusty attic visits, power lawn mowing, blowing the dust off this & that, smoke from candles blown out, etc. Now that my lungs are very bad, I can immediately feel and know how toxic it is to keep re-lighting & re-extinguishing the candles on birthday cakes for the perfect photo ... but I don't recall even once in my life our regulatory agencies warning us to be mindful about this *general* crap we should not coat our lungs with :-)
I feel that our regulatory agencies do a bit of a disservice concentrating on 'hazardous material dusts' because it lets them and us point the finger at "the bad guys" while removing people's focus from what seems to me is the far more important issue of warning people to try to avoid inhaling any smokes or dusts :-)

In my local TV area, I hear ads from NYC attorneys every night talking about widespread cancer in residents living in the 9-11 area. I don't think it's nearly as important to ascertain exactly what size and material of dust resulting from the collapse of the skyscrapers is causing cancer as it is to simply recognize that excessive inhalation of most such dust is a problem.

Perhaps it's possible to do this machine engraving with at least a continuous water wash to capture the dusts.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

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