Aluminium (element)
鋁 centers on the metal aluminium. It is a specific element name with no broader conceptual cluster.
鋁 is a modern character created for the chemical element aluminium. It combines the metal radical 金 with the phonetic component 吕 (リョ), which indicates the on-reading.
The left side 金 means metal, and the right side 吕 looks like two stacked ingots. Picture aluminium ingots stacked beside a metal marker: 鋁 is the metal aluminium.
For リョ, imagine a low, soft aluminium can: low -> リョ, and the metal is light and low-density.