Cast iron and iron alloys known as steel were the basic metal components of the first cars. Lighter and stronger metals such as aluminum and magnesium are used for many parts in the early 21st century. Specialty metals include platinum, rhodium and palladium in catalytic converters and copper for wiring. Sheet metal exteriors panels are being shed in favor of lightweight plastic and composite panels.
Combustion engines were first made with cast iron blocks and cylinder heads. Aluminum blocks have evolved through problems such as higher wear and shorter life span with the advent of advanced lubricants, finer machining and more precise bearings. Most engines are now made out of aluminum alloys. Magnesium is also used for engine parts, usually alloyed with aluminum. Aluminum is lighter but has higher wear properties than steel or iron.
Early cars were built on a frame or chassis, similar to the foundation of a house. Steel, a class of alloys that have greater strength properties than cast iron, was predominantly used for car frames throughout the 20th century. But as of the turn of the 21st century, the frame is no longer as integral a part of most modern vehicles. Components of the vehicle are designed to fit together structurally, giving the car much more strength and stiffness and making the frame somewhat obsolete.
Car bodies were typically stamped and cut out of sheet steel. Lighter-weight aluminum is used for interior portions of modern car bodies. Because aluminum is softer than steel and more prone to damage, it is not a common exterior sheet material. Vehicles save weight by making some exterior body panels out of plastic, fiberglass, or other composite materials.
Wiring is typically copper or aluminum. Lead is used in car batteries. Catalytic converters rely on special beads that are coated with "platinum-group metals" such as rhodium, palladium and of course, platinum. These metals help burn unwanted combustion products, converting them to cleaner carbon dioxide and water.