Finish on cast aluminum parts ie cylinder head

[tmvolumex]

I am trying to determine what the (Fiat / Lancia) factory finish is on cast aluminum heads. As new, and if taken care of, a bright shiny finish is evident on the top of the head and on all the "as cast" surfaces. This surface hold up to gasoline, Gunk hydrocarbon engine cleaner etc. What ever the surface treatment is, it does not hold up to Castrol's engine cleaner, it is stripped right off. Does anyone know what the factory finish is? It does not appear to be paint as it does not chip off. Maybe it is a conversion coating apppied right after casting? Anyone know how to restore it?
Tom McGaffigan

[Guy Croft]

Interesting question, I rang my foundry!

I do know that cast aluminium like that comes out of the mold naturally shiny. Aluminium oxidises almost instantaneously in the presence of oxygen (ie: in air) so on the surface - when you see a new casting you're actually looking at aluminium oxide. Those shiny manifolds stay shiny for years too. When you machine them they are shiny too!

The shiny appearance is certainly nothing to do with mold (casting) release agents - but as for any coating process applied to production heads to keep them that way I don't know. Could be a lacquer I guess, maybe applied by the dealer at point of sale. Interesting that your engine cleaner strips it off, I have never seen that happen.

As you know there are all sorts of proprietary agents for making/keeping aluminum shiny, internet search will show. In my exp half of them don't work.

For those who have no idea what we're talking about here are two GC inlet manifolds, both sand cast same as Tom's cylinder head, one shiny, the other matt due to stress relieving heat treatment.

GC

[Entech]

Hello Tom,

The shiny finish you see on the cast can be an chemicaly hardened oxide layer ,
you could name it a sort off anodising . (AIt turns black when caustic cleaner is aplied)
We have it on the castings we use.
There are maybe more coating types?
Regards, Klaas Troost

[tmvolumex]

Thanks all for the responses. Guy your photos do show the effect that I am talking about. The Castrol engine cleaner made my head look just like your heat treated manifold! I will do some more research but I think it is just a as cast surface with maybe a dip in a chemical riach after casting. The heads stay bight and shiny if you stay away from any etching type product.
Thanks,
Tom McGaffigan