Hey!
I am taking a degree in History, and during my study, I came up with a question that, due to being on vacation, I thought to ask Reddit instead of my teacher:
How in the age of metals did humans fuse metals?
Thanks!
There are 4 main ancient options:
Melt the different pieces together, and cast the finished object in one piece (or cast an ingot that the final object can be forged from). Once copper smelting was established, this could be done for copper and gold, since efficient copper smelting (i.e., converting copper ore to metallic copper) needs about 1100C and both copper and gold melt at lower temperatures than this (at about 1085C and 1064C, respectively). This could have been done for lead much earlier, since the melting point of lead is much lower.
Pressure-welding. This is a cold process, where the surfaces of two pieces of metal are forced together and fuse. This needs very clean surfaces, and with old technology is restricted to gold (because other metals oxidise, and the surfaces can't be made clean enough). Pressure-welding gold dates back to the Bronze Age. While casting (as per option 1) was possible, some objects are easier to make in parts and then join.
Hot-welding. This is the usual process for fusing iron and steel. The melting point was prohibitively high (much higher than the temperature needed for smelting iron), so casting was impractical until quite recent times. (From the Han Dynasty onwards, cast iron (i.e., iron with 3-4% carbon) was cast in China, but iron and steel were still impractical for them.) The usual procedure for welding iron/steel was to heat the pieces to be joined in a charcoal fire (with air blown by bellows to obtain a higher temperature), and then weld them by hammering on an anvil before they cool.
Brazing and soldering. A metal with a lower melting point than the two pieces of metal to be joined is melted and used as "glue" to join them. Both the joining metal and the two pieces to be joined are heated, at least at the joint. Brazing and soldering chiefly differ in that the joining metal in brazing has a high melting point, and in soldering a low melting point - brazing is a hotter process. These are very old processes and go back to at least the 4th millennium BC.
Of course, metals can be joined without being fused, e.g., by riveting, folded joints, and gluing.
What do you mean fuse? Like the smelting of iron into steel or the mixing of tin and copper to make bronze?