Aluminum Bronze questions

Hi Folks, I'm just an amature at casting of metals, and would like some info about alloying copper and aluminium. When I add a piece of aluminum to the molten copper I find that there is alot of waste material that develops and makes a mess of what I am trying to do. I figure this is due to the aluminum that I am using having other elements alloyed with it and not melting at the same temperature and or the oxidation of the aluminium.

I am doing a project on ancient coins and am trying to create a bronze / brass that has a nice yellow colour or subtle variations from red copper to orange to yellow. I have had some nice pieces already but there is a lot of waste from the process so far.

I use a ceramic crucible and acetylene torch to melt with, and I melt between 200 g to 250g of copper at a time. When I add the aluminium it absorbs into the molten copper immediately but then a unmeltable slush forms. I can pour some of the mixture out and it's nice looking metal but there is almost 1/4 of the material left in the crucible that has to be scraped out. I use Borax as a flux.

Just so you know I hand engrave my own designs on steel then take the coin blanks and strike them between the dies with a 10 lbs hammer.

Any advice? any decent how too books out there?

thanks for you help :) Kyle Mutcher.

Reply to
Kyle Mutcher
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Most likely the copper has oxygen gas and oxides dissolved in it (try a pure copper pour, I bet you'll get a massively blistered, bubbly product) and the aluminum reacts with it, forming aluminum oxide (high melting point, hard, slaggy, etc.). You need better process control. Much better.

Use zinc and tin. Aluminum bronze does not cast well.

Use a flux, for one.

The problem with that is then the aluminum content will react with the silica or borate based slag, leaving silicon and boron in the metal, so you have to use an alkali based flux, which will rape your crucible. Supposedly, chloride salts are used, but last time I tried it evaporated in no time (real high vapor pressure).

Borax is probably being broken down, as well as dissolved oxygen content.

Tim

-- "California is the breakfast state: fruits, nuts and flakes." Website:

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Reply to
Tim Williams

No comment on the other reply as to probable sources of difficulty but thought you'd want to know that aluminum foil should be pure aluminum. In general pure metals are the most maleable so that foils are generally high purity.

Of course foil also has a high surface area to volume ratio so there will be more aluminum oxide, on a unit mass basis, in the foil than in an ingot of pure aluminum. Dunno if that will be enough to be a problem.

Reply to
fredfighter

IF you are trying to do ancient coins you probably want to use the same sort of alloys. TIn bronzes to tin-zinc bronzes. You can go from red to gold to white with those.

Keeping your flame reducing while adding the aluminum (if you must) MAY help.

So do I, and a number of people I know. Depending upon what period of coin you are trying to re-create, using punches to make your dies, may be more accurate than engraving. Stating that one or the other was POSITIVELY and EXCLUSIVELY used for a perticular coin, is a good way to start an agrement on the moneyers list.

If you are using a 10 lb hammer, I can deduce that A: you are a gorilla :), and B: You are probably striking the planchets cold.

Emerichs WKMG handbook, and my Pensic Class notes. sca snipped-for-privacy@yahoogroups.com

jk

Reply to
jk

I strongly recommend that you use prepared alloys, you can buy a wide range of bronzes in many colors. Alan Black

Reply to
Alan Black

I suggest you try something besides aluminum bronze. Here is a quote from a professional tool and die maker I know.

"Aluminum Bronze has some amazing properties. Minimum as cast tensile of 70,000, some are heat treatable to 120,000 tensile. It is hard, corrosion resistant and makes a good bearing for extreme service. "

In other words, the stuff is very hard and would not be suited to your method of coining.

Although you are not machining the alloy, you'll frequently encounter remarks such as these, another quote:

"Some of the bronze alloys can be extremely difficult to machine, manganese bronze being one of them, aluminum bronze another."

In other words, aluminum bronze is very hard, it's hard to machine, and, people also tell me it is almost impossible to silver-solder.

Try something else.

My 2¢

Orrin

Reply to
Orrin Iseminger

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