bronze/brass casting

[Don Halter]

Anyone familiar with mixing and casting your own bronze alloys? I've been messing around with casting now. I've been mixing my own bronze alloys in order to get specific colors/patinas. The first ones were nice...a rosy version of brass that gets a real nice warm brown patina. The last ingot I made came out really brittle, though. It was about 3:1, ornamental brass: copper. No matter what I do to the ingot, it cracks to pieces when I hammer it out. I can do it hot or cold with the same results. I tried doing multiple heat cycles (grain refinement?), which did nothing. It polishes very well, has no voids, and is fairly scratch resistant compared to regular brass, I just can't do any hammering to shape it after casting a piece. Is this typical for scrap melt brass/bronzes? Is there any way to anneal it?

[J.Arthur Loose]

Don, your brass might be a brittle alloy... try using tin, silver or another bronze to get a similar alloy color.

Also ( and maybe you know this already but here goes anyway... ) when casting non-ferrous metals sometimes the crystalline structure becomes quite large and brittle. Try hammering on it when it is around 700 F and cooling from the melt to break it up a bit before the crystalline structure becomes too large. To anneal most non-ferrous metals ( and do this after the initial beating ) heat to a dull red and quench when the redness disappears. Any alloy with lots of copper will want to be thoroughly fluxed to prevent cupric oxides, which will look like pink stains in most cases. Handy flux or Griffin flux available from Rio work well.

[Don Halter]

It looks like the crystals are the size of large grains of sand! Will multiple heat/quench break them up any? How about heat to yellow and hammer multiple times? What about a re-melt and addition of tin?

I never found a commercial bronze with exactly the color I wanted, so I decided to mess around with some scrap. The pieces with the properties I wanted are too small to do much with, so I tried to repeat it on a much larger scale!

I guess I could always use it for grapeshot out of the gonnes I'm making!

[J.Arthur Loose]

Multiple anneals can help but you can also do something called heat-hardening by keeping things at an annealing temp too long. As soon as it starts to glow stop heating and quench as soon as it stops glowing.

Cooling from the molten stage is usually what produces a brittle state of affairs. Don't hit it when it is yellow; this is usually too hot. Hit it when the redness disappears after pouring. Then anneal and if it is still brittle it is probably something in the alloy. As you cold-forge it you will need to anneal from time to time when it starts to feel hard.

Grapeshot, huh? Sounds like mayhem and entertainment all rolled into one...

[MPMetal]

I don't know all that much about this but I did some reading on it a few years ago. I remember reading that if you burn out to much of the zinc in the mix you can get a result like what you are asking about.
something about they way zinc alloys with copper makes it do odd things to the finshed product if you have to much or to little in the mix.
I get the fealing that this batch was a lot larger than the last one, that could be why more zinc was burned from the mix, the longer it is hot and the longer it takes to get it hot the more zinc is burned out.

hope that helps
MP