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Corrosion resistance beyond hard coat anodizing?

(-----) November 23, 2016

Q. While researching good coating options for a new set of low pressure cast aluminum wheels. I came across a company that claims to have a 15,000 hr salt spray anodize coating.

I'm pretty sure they are using accelerated testing, so the accuracy is questionable, but they are claiming a couple of hours in caustic as well.

While reading through the patent it looks like they using heat to convert the Aluminum Hydroxide to Aluminum Oxide. The temperatures specified in the patent don't seem to be high enough to change Aluminum Oxides crystal structure at all.

It is confusing to me, as I had read that sulfuric hard coat anodize always creates hexagonal crystal structures, so either they are converting the hydroxide (assuming here that he hydroxide is amorphous?) to oxide with heat, or they have a different process that usually lays down amorphous aluminum oxide / hydroxide?

The patent also mentions using ultrasonic cleaning, so I am supposing that they may be anodizing, sealing, heating, cleaning, and anodizing again?

I reached out them for information, but I figured as this a very interesting claim (to me) I'd ask here as well.

So my questions are:
1. Does this sound feasible at all, especially if anodize is normally crystalline (they claim their coating works because it converts an amorphous to 'micro-crystalline', which I take to mean 'partially crystalline')
2. Does anyone have any ideas on replicating this process, or at least extending 'normal' hard coat anodizes salt spray endurance?
3. What is the longest proven anodize salt spray resistance that would be believed by someone in the industry, normally?
4. Is it worthwhile to add a paint / powder coat layer on top of hard coat anodize to extend its salt spray endurance, and how much could legitimately be expected of it?

Their president talking about the coating:

The patent (skip to summary):

They are claiming that they use one of / some of the following to fill the pores:
1. A metal acetate, and metal nitrate salt blend, heating in air at 150-300 °C for 1/2 hr
(assuming the nitrate consumes the acetate, to leave behind oxide / hydroxide)
2. An alkaline solution
3. A metal fluoride & a surfactant
4. Ultrasound without the fluoride & surfactant

Why does the fluoride need a surfactant to work?

Michael Simon
Arm Chair Engineer! - Burning River, Ohio, USA

"Surface Treatment & Finishing of Aluminium and Its Alloys"
Wernick, Pinner & Sheasby
from Abe Books

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November 2016

Hi Michael. I used to live in the Cleveland area -- you didn't extinguish the Cuyahoga river yet?   :-)

Let me start by saying that we have a general problem in even discussing your question. Once there are three or four companies offering a process, we can openly talk in generic & technical terms about a technology. But when you are talking about one specific company and their claimed exclusive processes, we can't say much -- because companies welcome positive web reviews, but may threaten to sue us if we even exhibit skepticism. Over the years finishing.com has been threatened with legal action at least 3 times for that, not counting more veiled "suggestions" :-(

Another problem is companies generally conflate their patents and their sales literature such that it can become almost impossible to understand what is actually patentable and patented.

But in general I certainly don't believe that conventional sulfuric acid anodizing and hard coat anodizing is the final ultimate aluminum finish and can't be improved upon. Spark anodizing (a concept which we probably can now discuss because there are multiple vendors) can be an improvement, and I have no reason to believe that this Micralox may not be an improvement as well. I would certainly expect that people will be "working around the edges" of any patents and that we'll soon be able to discuss the general technology.

Sorry that we can't say more, but what would be the point of allowing the posting of a positive review from anyone if we know we couldn't post a negative one if it came in?


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

Best anodizing for "Dishwasher Safe"?

November 23, 2016 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hello,

There seems to be a lot of mixed information online regarding anodizing and being "dishwasher safe".

I'm working on a kitchen product that will need to be washed in a dishwasher. Several sources have specifically mentioned not to put hard-coatings in the dishwasher, yet there are numerous kitchen products on the market labeled as Hard Anodized & Dishwasher safe.

The material I'm working with is 6061.

Can someone provide any insight into this?

Matt B
- Hilliard, Ohio, USA

November 2016

A. Hi Matt. We appended your inquiry to a thread about a caustic-resistant finish. There may also be sealing technology which renders hard anodizing "dishwasher safe" but I'm not personally familiar with it. Good luck.


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

November 25, 2016

Q. I came across something that seems promising in regards to a dishwasher-safe finish for 6061. Perhaps someone here has some experience with this? Basically, a Teflon Hardcoat.

Matt B [returning]
- Hilliard, Ohio, USA

November 2016

Hi again, Matt. We have several threads on line here about Teflon "infused" anodizing. I put the word "infused" in quotes because most experts feel that anodizing pores are too small to absorb Teflon, and that it's actually a Teflon coating. Letter 11225 also asked the question of whether Teflon coated anodizing is dishwasher-safe. I suspect that it is, but don't have any actual knowledge of it.


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

May 20, 2017

Q. After discussing it with the Anodizing shop they indicated they could well exceed the ~300 hour salt spray of Type III MIL spec, but that the coating was so fragile it would typically fall right off.

Assuming that is accurate. I'm thinking the best solution (pun intended) would be to infuse the open pores with silicone oil.

I have a spare wheel that was anodized along with the other 4. I'd like to build a salt spray chamber, and coat half of it in silicone oil, while leaving the other half type III. To see what the salt spray resistance is.

They are low pressure cast aluminum truck wheels. They came out a beautiful light grey. I have no idea what the alloy is, as the producer didn't know.

Do you guys have any recommendations for building a salt spray chamber, or know of a company that can perform the service? I never asked the anodizing shop I went to.

Michael Simon
Arm Chair Engineer! - Burning River, Ohio, USA

  ^- Privately respond to this RFQ -^

May 2017

Hi Michael. I'm not sure that I even understand the original question anymore, let alone this issue of fragile coatings falling off, but be cautious with silicone oil as it will prove impossible to remove, and impossible to plate or powder coat over (see letter 39979, "Cleaning Silicone Contaminated Parts")

We have a few threads about building your own salt spray chamber including letter 9721, "Need to buy or design/build salt spray chamber"; please continue that discussion there.


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

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