If you want to make a liquid out of two different metals, one of them has to be the fusible element
The reason is because if you tried to do this with only one metal, it would end up so hot that it would melt itself into a liquid, and then you'd have no way of separating the pieces
The other challenge is finding the right metals
You don't want a type of metal that's too hard or brittle, because then it won't flow easily through a pipe. And you also don't want one that's too soft or plastic-y, because again, it'll just melt into a liquid before you can use it for anything useful.
forging happens when metal is melted into a liquid