Chemical Stripping of Anodizing Color

Milo,

Just some experience with brake fluid. I don't know how well the brake junction blocks were anodized however.

Thanks! We'll add brake fluid to our list of suspects.

milo

Customer's customer is mum about what might have happened.

So... someone is turning the mystery into a puzzle? Suggest applying a bit of arm twisting (or water boarding) to obtain the information. Seems like that would be the most direct route to ascertain the cause of the color removal.

Maybe the word "shadow" is a hint. While I've not seen anodize fade in the way that you described, maybe it's inside a UV exposure machine or similar where the radiation caused the pigment to loose its colour.

Either way, it's a chemical that's changed the pigment or radiation that's faded/bleached it. If the coating layer is intact, then my vote goes for concentrated radiation of some sort (heat or light).

By the way, what colour was it before and is it now "transparent" or is it truly removed?

By the way, what colour was it before and is it now "transparent" or is it truly removed?

...part came back with much of the black finish removed...

If we knew what the part was designed to do, or knew what the customer's business was, we might be better able to assist you.

Have you checked for material mix up? While the colour can be quite fast on most pure aluminum material it tend to fade on parts made out of Al Cu (2024 0r 2014) or Al Zinc (7075) alloy aluminum. Simple hardness check will reveal material mix up.

try some oven cleaner, this stuff usually removes the finish but maybe you can match the fade by removing it quickly after it's been applied.

Jersey Walt

Even the simplest "failure investigations" are not...

Assuming that the sole reason for the return was the loss of colour, and that you really want to keep this uncooperative second-tier customer: my inclination would be to start enquiries with the anodising company - i.e. ask what method was used for the black finish. If neither the process nor the environmental requirements were specified, it is likely that the black finish was an overcoat rather than being built into the anodising process; as stated by Just-an, the colour of such overcoats is readily removed (as indeed are the overcoats themselves).

Assuming that you establish that it was an overcoat, your path will depend on the relative costs of investigations to those of changing the colouring method (which will include the costs of replacement parts if the end customer has retained a number of the parts and has only returned the one as a check that all is in order).

If investigation looks to be the cheaper option, the next stage is down to marketing - establish whether maintaining the finish is actually of importance or whether the customer is simply worried that the colour change is the precursor to future failure. If the latter, it's back to to the lab to check whether the overcoat is still present (fluorescence?) and has just been bleached (in which case there is no problem).
If the overcoat has been dissolved (brake fluid is not the only organic solvent that will do this), you will want to check how much (if any) of the anodisation has also been removed. That will mean dissolving the coating over the nut (your anodiser should be able to recommend a solvent that will not attack the anodisation) and comparing the residual thicknesses of anodisation (I don't know your equipment level, so you may need to send away for this).

I have experienced anodizing removal when it comes in contact with Isopropyl alcohol and also some brands of automotive aerosol brake clean solvents, especially if the anodizing is relatively fresh.

Thanks to all for your input.

We did confirm material was correct grade.

We did confirm anodize process was that specified by customer.

We did confirm efficacy of poka yoke and validated all items in stock as to presence of compliant anodize and color.

We have demonstrated to customer that Anodized Aluminum is not chemically inert, something that they did not take into account in their design phase, especially in regards to fluids likely to be used in and around their application.

Despite our deliberately not specifying the application and end use at the time of posting, the list of substances nominated by you did include the most likely substances based on the application.

This independent corraboration by you all was an important validation/ reality check of our problemsolving analysis.

Thanks to all for the assist.

milo

A solution may be in-organic anodizing we make parts that have to withstand intense heat and use that process for our Black Parts. Its also reffered to as two-step anodizing. Instead of dye, metals are deposited in the pores. Can produce a very deep black.

I have experience with the isopropyl alcohol and brake fluid as well. However, any chemical removal of color would typically not have left a sharp smooth "shadow". Consequently, and in the tradition of all famous who-done-its, my guess is that our mum end user is a custodian at a hospital or a parts manufacturer with access to the chemicals, but also with access to the x-ray machine that they shouldn't be using but got curious enough to play with it. He took some x-rays with his anodized part exposed or imaged. He doesn't want to say anything about what really happened because he'd get fired.

Why did he return the part? If the anodized coating is intact, one would expect the object still functions. He simply has an uglier object due to his own stupidity. If that's the case, what's his beef - it's not a warranty issue. If other components of his anodized object were damaged, that might also help in solving the mystery.

Hi physics prof.

In todays world its always a warranty issue. The shadow we determined to be caused by a nut that covered an area thus protecting the anodizing there from whatever solvent was used.

Interestingly a couple of nuts with another type of /color of anodize were not affected.

Thanks so much for sharing.

milo

BTDTBTTS:


Here is one that is most common. Cationic surfactants can and do strip anodizing from Al. Have done that here. IE find out what cleaning compound is being used. Anodized parts require the use of a neutral agent. Have had the same issue here, found it was micro90 and some low zeta potential cleaning agents.

What size was the t-shirt?

milo

The Eastwood company has a spray they sell, designed to remove anodizing. I don't know what is in it though.