Pyre-Vulpimorph [2014-06-11 21:04:42 +0000 UTC]
You know, a sword made of gold isn't completely unbelievable. A 18 karat gold/copper alloy, of about 75% gold and 25% copper by weight, is actually very strong. After cold working and heat treating, the alloy would rival some forms of stainless steel.
Even though pure gold is so soft it can be squished with your fingernails, it's rapidly hardened by copper up to the 75/25 ratio. Adding more copper than that would actually make it softer again. The reason for the rapid hardening is because of the stress that copper puts on gold's crystal lattice. Copper atoms are much smaller than gold atoms, so they distort the crystal lattice by quite a bit. At the 75/25 weight ratio, there is exact 1 copper atom for every 1 gold atom, yielding maximum stress, and thus, maximum strength and hardness. Even better, at that ratio, gold and copper can form a ceramic-like intermetallic compound, AuCu, that precipitates out of the metal when heat treated, increasing hardness further.
An 18 karat gold/copper alloy is called "red gold" or "rose gold" and has an reddish-orange hue. Adding other metals like silver, nickel, or zinc makes the alloy more pink, which is what "rose gold" jewelry usually contains.
So yes, you can absolutely kill people with a gold (alloy!) sword, but it would still be damn heavy (and expensive!) compared to steel or bronze.
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