I have been melting aluminum in a DIY furnace for a few months in order to make lost wax casts. I was thinking that since bismuth has a much lower melting point than aluminum, that I could add a small amount of bismuth to lower the melting point (9 parts Al, 1 part Bi). Qualitatively this seems to be working. But I am confused.
Looking up a phase diagram for Al-Bi, I find:
Which if I understand it correctly seems to mean that the melting point actually went up. Am I reading it correctly? If both metals separately have a lower melting point than the alloy at that ratio (and I am not reaching the new melting point), then what am I making?
Besides lowering the melting point, my hope was also to lower the viscosity so that the mix fills in my mold better. Will adding bismuth help accomplish this goal? Should I be adding tin instead? Is there a tin-bis-al ratio that would yield minimum viscosity at temperatures below 1500 °F (ideally mostly made out of Al)?