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Anodized Aluminum Particles

2007

My company manufactures hemispherical parts for the medical field that are black anodized hardcoat aluminum, MIL-A-8625 / MIL-PRF-8625 [on DLA] Type III, Class II. Recently, the parts have been leaving fine black particles on any surface it touches. The parts have been in the field for over two years, which makes me want to rule out manufacturing issues. The cleaning agents used in the field are neutral pH. Has anyone seen this before? Any ideas about what causes it?

Thanks for your help.

Gina Shepler
Medical Device Manufacturer - Fair Lawn, NJ

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First of three simultaneous responses --

We really need more information. Meanwhile, high heat will crack it off. High pressure will crack it off. If the parts were mechanically finished before anodizing, then maybe, iron media dust is embedded then bridged over by the oxide, then cracking off under either heat and/or pressure. Inadequate cleaning and/or deoxidation before anodizing would be bridged over and crack off later under service.

What is the alloy, thickness of anodizing, service requirements, cleaning cycle, mechanical pre-treatment?

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2007

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Second of three simultaneous responses --

Sounds to me like the anodize coating is being slightly crushed from use and is breaking up into fine particles.

James Watts
- Navarre, Florida
2007

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Third of three simultaneous responses --

Alloy? Organic or two-step dye? Cleaner? Thermal cycling, perhaps with steam? Is the surface easily abraded? Is the remaining surface (beneath the lost particles) still black? Any Type II salt spray and Type III Taber test results for anodize of the same vintage, on the same alloy? Also, any salt spray test results for sealed Type III per MIL-A-8625F, Amendment 1?

W/o examination or additional info, basically a guess. If no evidence of mechanical damage, chemical attack or overheating (such as loss of color), it is reasonable to presume an anodize problem.
The outer hard anodize was perhaps crumbly (as from inadequate agitation/cooling) and further softened by dyeing & sealing. Black color remaining under lost material is consistent with crumbly anodize, readily penetrated by dye. Crumbly anodize may have slowly swelled from the cleaner (or steam sterilization?) and is now shedding under touch.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2007