Just tested printing with flux core wire and the first layer printed very well, but as soon as the second layer started the melting stopped completely - I think it lost its conductivity due to a layer of less conductive material covering the metal. With the steel wire the socond layer melted, but the melted material did not fused together...

I also tested aluminum wire. It fused together but was very brittle.

Will test thicker steel wire, maybe it helps when there is more melted material at once.