armour havelock, helmet neck guard
錏 centers on protective armor for the neck: a havelock or helmet neck guard, typically made of metal plates.
錏 combines 金 (metal) with 亞, which likely contributes the sound and may relate to the idea of a secondary or subordinate covering, fitting a neck guard worn under a helmet.
The metal 金 on the left and the shape 亞 on the right suggest layered metal plates: imagine a helmet with a neck guard made of overlapping metal pieces.
For ア, picture the armor neck guard as an 'ah'-shaped curve protecting the neck: the sound 'ah' cues ア while the metal plates form the guard.