Aluminum die casting

[Bada Bing]

We are in the process of Die Casting some of our Aluminum parts but having a hard time Hard Anodizing the die cast parts and am not sure what grade alloy they are using.

I was wondering if you could give me some pointers and possibly a process and grade of alloy we can get the best result on esthetically? As well I believe the silicone in the alloy is giving us the porous and dull finish so is there any recommendations on how to improve that?

[Geof]

Have you talked to the people doing your anodizing to see if they have any suggestions.

Many years ago I tried making some parts using cast aluminum and could never get a good anodized finish. My anodizer said it was mainly due to the silicone in the casting alloy and the foundry said they had to use a high silicone alloy to have good fluidity in the melt so it would enter the mold detail.

After a couple of years I gave up and switched to machining from solid.

[Bada Bing]

Have not talked with them yet, will do so soon. Thank you for the reply.

[olfoundryman]

Bada,
Years ago I worked for a brake parts manufacturer. They semi hard anodised their master and slave brake cylinders. These were gravity die cast from either 356 or 319 alloys both of which contain a fair amount of silicon. The anodic film was sort of glass like but was an opaque grey colour. The silicon in the alloy is unaffected by the anodising process and is thus present in the anodic film just as it was in the cast metal, this colours the film grey and makes it opaque. You can still dye the films but you can not get the bright clear colours that wrought aluminium gives when anodised and dyed.
It does not really help much to use those cast alloys that do not contain silicon – e.g. the 40 E alloy. I have tried this alloy (casts well, machines very well) and it too anodises with dull film although not as dull and grey as the silicon containing alloys produce To my knowledge there is no cast Aluminium alloy that will produce a clear anodic film. If you want a colourful and clear anodic film you will have to make your parts from wrought Aluminium and machine to shape.
Martin
Old foundrymen never die they just break their crucible

[olfoundryman]

Bada,
On second thoughts you could ask about the Aluminium-Magnesium, alloys 214 and 220. These may anodise better. But they are difficult to handle in the foundry and you may not find people willing to die cast them (Are you talking pressure diecasting or gravity (permenant mold) die casting?

Martin,
Old founfrymen never die they justy lose thier sand

[Bada Bing]

Thank you for all of your input.