An aluminum
guardrail wouldn't have much strength (unless very
thick) compared to steel. Maybe aluminum ones are
used for decoration. Guessing you guys live in
the east.

around pennsylvania rust is a major problem, coating guardrails only
helps till the coating is damaged by say someone scraping it.

road salt causaes much of the problem, i will try a magnet on some this
week.

i suppose they could spot weld the guardrails to the uprights to make
them more vandal resistant.

i took a bunch of scap in recently they now make a copy of your drivers
license, no doubt the poilce will be called if you take in guardrails
or light poles.