Anodizing Aluminum Castings?

[engineerscott]

Has anyone had any success anodizing and dying Aluminum castings? I don't know what alloy we're using at this moment but I can find that out tomorrow. We are considering anodizing some parts (cast aluminimum heatsinks) to improve emissivity for thermal reasons, so aesthetics are not a concern. For best emissivity we would want a micro rough finish and the color would be dark blue or dark green. Counter intuitively, black is not the best color in terms of emissivity as it is not as "black" at the IR wavelenghts that matter at our temperatures. We'd like to do as little post processing after extracting the parts from the mold as possible, but a quick acid bath is probably doable. All of my anodizing experience has been with either extruded aluminum or parts CNC machined from billet. Any insight would be greatly appreciated.

Thanks,

Scott

[sswee]

I've done cast motorcycle parts and rclint does cast gun parts all the time. The material grade of all the cast parts I've done has been unknown. They tend to have a darker appearance than most due to the smut from the impurities so the darker colors do better.
SS

[kwallace]

Hard anodizing of Aluminium alloy with a high silicone content will end in tears, it cannot be coloured properly.

You need an extrusion alloy like 6061 or 6063. But casting either of these alloys is very difficult due to hot tears, you can make a rough shape then do alot of machining and it might work out.

If you have an as cast piece it will probably he high silicon which will mean a no good anodizing

[acidrain]

I've done one cast part... dyed it gold (of all colors), and it came out surprisingly great!
Seems that anodizing cast is somewhat hit and miss.

[engineerscott]

Looks like we will be casting these parts from either A360 or A380. These alloys are in the 8 to 10% Si range. I guess we'll just have to try a few samples with we get first articles back.

Thanks,

[hurricaneracing]

I had some request for cast recently. Went to Home Depot and found a cheap part. No Idea what grade of material it is but here are some pics.

[kwallace]

Originally Posted by engineerscott

Looks like we will be casting these parts from either A360 or A380. These alloys are in the 8 to 10% Si range. I guess we'll just have to try a few samples with we get first articles back.

Thanks,

Good Luck on this, if it works out please tell me I have had an enquiry recently for anodizing castings also but said we couldnt do it. I even rang a few guys up in Australia also about it, they also said no. Maybe the shiney anodize cannot be done

[rsalvarez1]

Originally Posted by acidrain

I've done one cast part... dyed it gold (of all colors), and it came out surprisingly great!
Seems that anodizing cast is somewhat hit and miss.

Hi i have other questions, how the gold color is prepared?
i try again a motorcycle part with 25 miliamp per square inch ( as the manual say) the meter show inmediate an amp drop each second and stops at 13 or 16 seconds and stay constant, i take this as an indication of the film grow, is that right or need other information? sorry if my question is not in the most apropiated way, i have too many questions

[acidrain]

My part was prepared by stripping off the paint with lacquer thinner, etching with sodium hydroxide, de-smut with caswell de-smut, and ano to .5mil.
You say your amps drop... do you mean the volts drop? The amps need to stay constant, and the volts will do whatever they need to maintan those amps as the coating grows.