Usually the fluid lines on the copper ones are copper but the fins are aluminum. On the all aluminum radiators, the lines and the fins are aluminum.
The road salts can eat away the fins the same on both. The key is to keep the radiator clean with Simple Green EXTREME, which is not corrosive and will not bother aluminum if all of it is not rinsed away. Do not use regular Simple Green. The best way is to squirt the cleaning fluid in from the front side and then apply water pressure from the backside to wash the debris out instead of forcing it deeper in to the fins.
