Bimetal cans are really a combination of steel that is coated with a very thin layer of tin. It can be produced by dipping sheets of steel in molten tin or by electroplating.
Tin is used as a coating because it has a much slower chemical reaction with food than steel does. The tin coating not only protects the metal from corrosion by food, but also protect the foods from metal contamination.
They usually have a seam along the side and at the tops of the cans. They are magnetic due to the iron in the steel. Aluminum cans are not magnetic.