It should be of no interest to you what material this is (most likely all Aluminium). You are making a much too big story out of it. Just grind off those patches and things are fine again. There is no need of a surface treatment, aside for cosmetic reason. Just wipe the barrel off after use before longterm storage.
A different case would be if that corrosion stretches inside, under the aperture ring, maybe even hampering twisting it, then a barrel disassemly might be needed and further grinding.
This is just a lens, use it as intended and have fun with it. Any collector's value, if you are considering such, it lost long ago.