Color fade Issue with anodized aluminum

[pro_robo]

I have anodized aluminium products in a very specific shade of color. It is hard anodized. Our usual customer base is in the Dry region, for the first time we shipped it to the West coast of USA. Within the first few weeks, we started noticing patches of faded colour on the product.

I would like to know what might be the reasons for the defect to appear, our anodizing vendor doesn't seem to have a clue on why its happening.

Thank you, appreciate your time.



I hope those white patches are visible, sorry couldnt get a better quality image.

 

[SWComposites]

Where exactly on West Coast? desert dry area? wet, humid area? right on the ocean (salt fog zone)?

 

[ctopher]

Maybe an issue with the material type, or not cleaned properly before anodize?

 

[3DDave]

Dyes are less stable molecules. Black dye tends to fade or turn other shades as the components decompose at different rates.

Hard anodize has less porosity so it retains less dye than typical anodize.

Was it sealed properly? This is key, post-dye, to cause the pores to be closed.

 

[Compositepro]

"Fading" is a conclusion that has not yet been established. The observed splotches could also be due to corrosion leaving white deposits. This should be observable under a microscope. Does it appear silvery or white?

 

[EdStainless]

Is there a sealer or topcoat on the dye?
For tougher environments you may need one.

 

[pro_robo]

Where exactly on West Coast? desert dry area? wet, humid area? right on the ocean (salt fog zone)?

Is in the Bay area by the sea.

The supplied raw aluminum is white anodized (not sure of the grade), then we send it for reanodizing (hard anodizing to prevent scratches).
The patches are not completely white; they are off-blue and tend towards ash white color.

Post blue coat it was sealed in hot water.

 

[pro_robo]

Dyes are less stable molecules. Black dye tends to fade or turn other shades as the components decompose at different rates.

Hard anodize has less porosity so it retains less dye than typical anodize.

Was it sealed properly? This is key, post-dye, to cause the pores to be closed.

Do you recommend anodizing type II for this application?

We choose hard anodizing to prevent scratches during usage.
Usual practice at our vendor is to seal the color at 95 °C water.

What sort of coating did the previous version of iPhone (aluminum back) used to have? We are looking to get something similar to that.

 

[SWComposites]

if its Bay Area by the sea then I highly suspect salt fog corrosion. I'm 5 miles from the ocean in San Diego and we get lots of corrosion and rust here; its way worse close to the ocean.

 

[EdStainless]

Water isn't a sealer, you need a polymer sealer to prevent this.
The dyes are not super stable, and the anodize is porous.
It has to be in order to absorb the dye.
But it will absorb salt water also and lead to all kinds of issues.

 

[3DDave]

The boiling water causes hydrated crystal growth to close the pores, sealing the dye in place.

See https://finishingandcoating.com/index.php/anodizingcat/1220-the-sealing-step-in-aluminum-anodizing for much more info.

I've only been on the specification end and generally color and hardcoat were mutually exclusive. There were attempts at some teflon filled anodize, but I don't recall that working all that well either.

I would suggest going to finishing.com as that is where a large number of platers and anodizers who run plating and anodizing shops hang out.

 

[IRstuff]

I'm 5 miles from the ocean in San Diego and we get lots of corrosion and rust here; its way worse close to the ocean.

Having lived 30 ft from the Southern California ocean, I can confirm that brand new nickel satin door hinges can start to show rust within months of installation.

 

[pro_robo]

I found some new images for reference
This is a close up photo,