Yes before painting any metal you must prime the metal prior to painting it using a metal paint primer.
If you don't prime the metal surface prior to painting it then the paint will flake off sooner than it should and the paint won't stick to the metal surface properly.
The paint job may also show through on the metal which will cause the paint job to turn out bad.
So before painting the metal make sure any debris is off the metal and then prime the metal with a metal paint primer of your choice.
Then let the primer cure on the metal surface overnight and then you can paint the metal normally like you would with the regular paint that you want to paint the metal with.