Here in Ohio the road crews use a lot of salt in the winter for snow and ice melt.
Salt can really do a number on Aluminum.
And of course, steel is completely unaffected, right?
Aluminum is under most conditions is a great metal for a variety of purposes because it has a hard oxidation layer that is durable preventing further oxidation of the metal.
But aluminum’s oxidation layer is leached away by sodium chloride. And those chloride ions will just sit there eating away that oxidation layer until you have a nice pit in the aluminum.
Steel also has the advantage that it can have rusted portions cut out and patches welded in fairly easily. Aluminum requires a very skilled welder to do the same type of work.