Agreed, but these don’t turn into rusted swords so much as pieces of rebar sticking out of a stump.
Everything but the blade itself will disintegrate pretty quickly. Since cheap “swords” don’t have a deep tang, there won’t be much of a “handle” or anything for long. Same with any adornments.
The metal itself will corrode pretty quickly overall.
It will look like a straight piece of rusty scrap metal moreso than a sword.