fuse, melt
鎔 centers on melting and fusing metal. The core idea is applying heat to turn solid metal into a liquid that can be shaped or joined.
鎔 combines 金 (metal) with 容, which likely contributes the sound and the idea of containing or shaping. Together they suggest melting metal to fit a mold.
The metal radical 金 beside 容 (a shape that suggests a container or mold) shows metal being melted and poured into a form to fuse or shape it.
For ヨウ, imagine a metalworker yelling 'Yo!' as he pours molten metal into a mold: Yo -> ヨウ, and the metal fuses into shape.