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'Tiger Stripe' phenomenon in Black Anodize Electrolytic Coloring

Hi all,

I believe you all had heard about the 'Tiger Stripe' phenomenon in Black Anodize Electrolytic Coloring in AL 6061 T6 and also in AL 5053 H32. Currently is there any fact or root cause that cause the 'Tiger Stripe' phenomenon? I had done fews Design of Experiment, and roughly have a gut feel that this phenomenon is related to the surface roughness (Ra value). The very fine surface (Ra32~64, bead blasting surface) also will not have this phenomenon.

This are some of my finding, can somebody have more experience on this experience and make my finding more concrete.

I also would like invite those who know the chemical behind this process to share with us, and maybe we can have some ideas or brainstorm on what is going wrong.

Thanks

Collin, Chris
Undergrad Student - Singapore
2006