Aluminium as a material tends to 'absorb' more light than it 'reflects', due to surface oxidation (unless it has been recently cut or polished) - A little light oiling with a vege oll/vaseline type wax or similar (applied just before shooting, so that the surface is also dust free!) may be a quick way to enhance the surface enough to catch and refract more (directionable) light, to provide a little lift to the shots.

Whatever substance you apply should be tested first, as some chemicals can increase surface oxidation or leave unwanted marks. - You can buy me a pint one day. Happy shooting