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


-----

Black finish needed as alternative to Anodizing for Al 380 alloy

June 16, 2009

Hi,

We're planning to die cast a finned heatsink about 2 inches in diameter and 3 inches tall. We'd like a black finish to improve radiant heat loss, but we're aware that the high silicone content of the 380 alloy we plan to use makes anodizing difficult. Two questions:
1. Can anyone recommend a way to successfully black anodize 380 alloy? and/or
2. Can you recommend an alternate finish?

We've heard that paint finish may work, and the term black 'oil pant' has been used, but we're not sure what is meant by 'oil paint'. Is this an industrial option (or just for hobbyists)? We are familiar with epoxy based paints, but are concerned these may work as insulators.

Thanks.

Anthony Honeyfield
product designer - Sydney, NSW, Australia

---

There is 380 and 380 and 380, every batch seems to be different, lots of range in the recipe lots of difference where the thin areas cool faster and bring more silicon to the surface. The best you can do with a particular casting is to deox in 50% Nitric Acid with one pound per gallon ammonium bifluoride. Some go in the lab and try adding some sulfuric acid, Be reminded that organic black dye will not withstand very much heat without fading.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

June 18, 2009