thin plates of metal
鍱 centers on thin, flat pieces of metal, like metal plates or sheets used in construction or armor.
鍱 combines 金 (metal) with 枼, which likely contributes the sound and may relate to thin, flat objects. The exact historical development is uncertain.
The left side is metal 金, and the right side 枼 looks like a stack of thin leaves or sheets. Picture thin metal plates stacked together like leaves.
For ヨウ, imagine a thin metal plate being bent into a YO-yo shape: YO -> ヨウ, and the metal is thin enough to shape.