Originally Posted by
berksglh
Did some searching and more reading here. There are quite a few threads here about copper additions. Some as far back as 2010.
Sounds like Edd has done quite a bit of testing and discussed balanced alloy, where Cu + Sb = Sn content. I'm convinced there is a relation ship there, but wonder if its more a balance between Cu and Sb. If Cu doesn't mix with lead, and has such a high solubility in Sb, maybe they have to have a balance of sorts.
If 3.5% Sb was where Edd was working to come to 0.3% Cu max, and we wanted a cast rnd to be able to handle more velocity, what about starting with that balance, and increasing both proportionately. Adding more Sb to make it harder, but also more Cu to keep it from becoming brittle.
It seems to me higher Cu makes it more malleable, and if more Sb makes it harder, to the point of being brittle, then use the copper to keep it from being brittle when using more antimony...
Say go to 7-10% Sb and 0.6-1.0% Cu? Or maybe more of both? As long as casting temps are reasonable.
My 1% Cu seems to squash easier then the 0.2% making me think it needs more antimony. Why use copper at all? Well at some point Sb makes it too brittle, so maybe upping the copper will compensate and keep it in balance while being able to handle more pressure.
Unless anyone has thoughts, I may have to source some antimony and further play with the idea.