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Black spots on electro-gold colored anodized aluminum

Q. Dear adviser,
I am working on Al 6063 alloy. I have a titanium salt based electro-gold color tank, where I maintain the following parameters:
Gold-salt= 4-5g/l, H2SO4=15-17 g/l, Temperature= 57-60 °C, required time= 3.0-5.30 min. Recently I'm facing a problem that showing a black spot on gold color surface after Ni-based cold sealing. It appeared between the flat profile when it is wrapped and 3-4 days later. Also appears a white powdery layer when two flat surface profile attached/bundled by wrapping paper. Please advise me how can I solve it.

Kamruddin Kamru
Nikki thai Aluminium Ind.Ltd.bd - Dhaka, Bangladesh
November 16, 2018

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