Originally Posted by
Aubergine
if we can assume the OP correctly identified the bike it's definitely steel. The 520s were completely steel up to 2020 or so, when they added an aluminum fork (sacrilege!!) to the steel frame.
No problem. It's why I said "seems" though aluminum or steel the answer is basically the same.
Note, I'd added a BTW referencing my n steel frame that died the same way roughly 5 years after a seemingly minor collision.