Remove the door from its hinges by tapping the pins up through the hinge with a screwdriver and hammer. Lay out a plastic drop cloth to protect your floor. Set up a pair of heavy-duty sawhorses. Lay the door with the painted side up on top of the sawhorses.
Spread a thick coat of gel-type paint remover rated for metal surfaces onto the face of the door with a fine bristle paintbrush. Cover the entire surface, paying special attention to any detail areas. Allow the stripper to sit for the time recommended on the label.
Scrape the stripper and spray paint from the surface of the door with a chemical resistant nylon scraper. Work from the inside of the door out, scraping the stripper and old paint into a metal container with a lid for safe disposal. Scrape the entire surface of the door. Use fine steel wool to remove the paint from the detail areas. Rinse the door with warm water and a sponge to remove any remaining stripper. Allow the door to dry thoroughly before continuing.
Sand the surface of the door with a power sander. Use a fine grit bi-metal paper, 150 grit or finer works best. Work from the inside of the door out. Keep the sander moving, and work in a small section at a time until the aluminum is clean of any paint. Random orbit finish sanders work best. Work across the entire surface of the door. Sand the detail areas by hand or with a sanding sponge.
Brush the dust from the door with a dry, fine bristle brush. Rinse the surface of the door with clear water and a sponge. Allow the surface to dry thoroughly before proceeding to apply a new finish. Repeat the entire process on the reverse side of the door and the edges, if desired.