V-12 Engine castings. Which alloy is better?


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Posted by Tom Kay on September 03, 19100 at 09:31:23:

This is a repeat of a question that I posted in the metalworking news group. I'm trying to get a bunch of respsonses so I can have a fair idea of which metal to use. So far, there's no clear consensus. Thanks to all who might answer!

I am close to doing some pourings for my quarter-scale

V-12 Merlin. I think I'll start with the cylinder blocks (minus the heads)as the shape is simpler than either the head or crankcase. I'm sure it'll have its own problems, but overall I hope it'll be a decent "beginner" part.

So, I need advice on which alloy of aluminum to choose, for various parts, such as cylinder heads or blocks or crankcase. And let me give some details about what I hope to achieve, so anyone answering can see what I'm up against. It's investment casting for all parts.

1. The aluminum must flow into the ceramic shell easily, and this

includes fairly thin sections. It will be a basic, well gated

investment casting, with proper investment (not plaster shelled) and the mold will be burned out and preheated as you'd expect. But if the 6 cylinders line up like barrels without tops or bottoms, I'd say the common wall between each pair of cylinders is the thinnest part. And it's about 2.5 inches high, so I'm concerned about the metal freezing and not flowing to the bottom of this area to fill it up. Clear as mud, right?

2. I want to be able to heat treat it to achieve decent strength and hardness for machining. Machining "gummy" aluminum is a mess. All of the castings will need some machining. Of course, if there is an alloy which machines well and needs NO heat treat, AND flows well into thin sectioned-molds, well that's perfect. Especially if it has decent strength, etc.

3. I have no objection to using good scrap if it will do the job.

Someone once told me that LawnBoy pistons are the best scrap he's ever used, and that would be fine if true. (never tried it). But I need an alloy that is common enough to find, and a place to buy it from. I live in Ottawa, so local would be good, but I can buy it anywhere from the USA as well and have it shipped in small loads. I'd be happy to hear from you English blokes, especially since you invented the Merlin, but I probably wouldn't go as far as to import metal from across the pond.

4. I was leaning toward A-356, thinking that it's a very common alloy and has most of the properties I need. Opinions?

Last, thanks so much for any help from anyone, and if anyone would like to see the occasional picture of the wood patterns or metal bits that I make, I'd be happy to show them. We'll all be grandfathers or dust before this project is done, but I don't mind showing the progress. I have a hockey website already, so I might just stick them up on some unused back page. Let me know.

Cheers, Tom.

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