I have some experience in automotive paint on alum. We always rough up the surface slightly with 220 grit or scotchbright in order to get the paint to "grab onto" if you will. I'm not shur with an arrow, but I would assume since it's alum. the concept to get the paint to hold would be the same. we also use a good sealer/primer to help the bonding. If you don't, it ends up flaking off, are you guys roughing the surface prior to painting it? just a thought..