Where the
world gathers for metal finishing
Q&As since 1989


-----

Anodizing came out very dark grey

July 1, 2009

Can somebody help us with the problem?
We have anodized new part of aluminium profile and after anodizing we got very dark grey oxide film, more darker then usual. Film thickness
15-20 mkm.
The chemistry of alloy:
Si -0,4; Fe -0.35-0.47; Ñè -0.052-0.062; Ìï -0.051-0.077; Mg -0.53-0.58; Zn -
0.048-0.054; Cr -0.006-0.008; Ti -0.054-0.056; Pb -0.008-0.009.
How do you think what is the reason of such effect?

Natalie Kodzaeva
anodizer - Moscow, Russia

Hi, Natalie. But what does "usual" mean? Was usual a different alloy and this is the first part you've ever run that was made of this alloy. There is no copper and no silicon in this alloy?

Sorry, I do not understand your thickness number.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 1, 2009

---

July 6, 2009

The problem is: we are anodizing alloys from different supplies and all the time we have light grey color without any problems. But the alloys from one plant became dark grey after anodizing. The chemistry of their alloy:
Si -0,4; Fe -0.35-0.47; Cu -0.052-0.062; Mn -0.051-0.077; Mg -0.53-0.58; Zn -
0.048-0.054; Cr -0.006-0.008; Ti -0.054-0.056; Pb -0.008-0.009.
Film thickness 15-20 microns.
How do you think which element can be the reason of such effect?
And can you tell me what chemistry of alloy you can recommend for using?

Natalie Kodzaeva
anodizer - Moscow, Russia

---

Hi Natalie!
This composition means a 6063 Alloy, with a higher amount of iron, in 6063 Alloy iron must be under 0,35%; iron amount in bath and in alloy give a light darker coating.
The 6063 alloy can give a dark coating when hard anodised (brown-green).
The 6063 alloy can give in decorative anodizing a very transparent coating; use high sulfuric acid concentration (above 200 g/liter), low tension (14 a 16 V), temperature (18 - 22 °C) and aluminium dissolved not over 18 g/liter.
Atemp to desmut, the aluminium parts must be very clear before anodising.
I hope this Helps.

Franz R Wagner
- Blumenau SC Brazil
July 9, 2009