From the engine block to the fenders and everything in between, today’s automobiles are an amalgamation of traditional and space-age materials. The push for more efficient vehicles has necessitated the use of new methods and technologies to produce the lightest, strongest components possible.
This article will discuss some of the most commonly used materials in the modern automotive world, where they are found within a car and the properties that make them suitable for each specific application.
The most commonly used material in the automotive industry, mild steel (aka plain-carbon steel) is cheap, malleable and readily available. Its properties are well-understood and it is simple to produce; it can be hardened by increasing the carbon content and responds well to standard welding processes, making it easy to repair. Improved galvanizing and painting techniques have made it more resistant to corrosion, one of the biggest problems with mild steel. Factory exhaust systems are typically built using mild steel, as well as the body panels on the vast majority of vehicles.
Primarily used in cylinder blocks for its strength, cast iron is one of the oldest alloys known to man and also one of the cheapest to produce. While cast iron blocks are superior for performance applications with higher cylinder pressures, aluminum is much lighter with better thermal conductivity. Modern vehicle design has seen a sharp decline in the use of cast iron.
While more expensive to manufacture and more difficult to work with, aluminum is lightweight, corrosion-resistant and can be used for all elements of a vehicle’s body, from induction piping to wheels to frames and unibodies. Manufacturers have also begun using aluminum for engine blocks.
Like the name implies, stainless steel will not readily oxidize like mild steel due to the higher percentage of chromium in the alloy. Stainless steel is heavy and therefore not ideal for body panels; it is typically found in performance exhaust systems and exhaust manifolds.
The most common applications of titanium in cars include valves, valve springs, valve retainers, rocker arms, exhaust systems, connecting rods, wrist pins, drive shafts and high-strength fasteners. Titanium has extremely high strength, low density, excellent resistance to corrosion and ductility; it is 60 percent denser than aluminum but twice as strong. The firewall in the new Dodge Viper is made completely of titanium.
Fibers, Plastics & Polymers
Polypropylene (PP) has begun to replace metal bodywork and is commonly found in bumpers due to its excellent elastic and plastic deformation characteristics, which make it ideal for use in impact areas. Unfortunately, it is unstable under temperature changes and expands and contracts too much to be useful in areas where tight tolerances are a concern.
Fiberglass-reinforced plastic, also known as glass-reinforced plastic (GRP) is a fiber-reinforced polymer; lightweight and strong, although not as strong as carbon fiber, FRP is less brittle and the materials involved in production are much cheaper. It is easily formed using molding processes and is used primarily for custom body panels and aerodynamics.
Extremely strong and lightweight, carbon fiber is comprised of super-thin strands of carbon woven together to make a “fabric,” which is then laid into a mold and coated with a stiff resin or epoxy so it retains its shape. The properties of carbon fiber are truly amazing: it can be up to 10 times stronger than steel and eight times stronger than aluminum, while being five times lighter than steel and 1.5 times lighter than aluminum. Due to its high relative cost, carbon fiber has not been put into mass production thus far and is typically found only on high-end performance vehicles and racecars. It is typically used to make body panels and aerodynamic parts such as hoods, fenders, lips, splitters, wings and trunk lids, as well as instrumentation panels.
Tires are by far the biggest use of rubber in automotive applications; however, window and door seals, windshield wiper blades, belts, gaskets, bushings and motor mounts are also made from rubber.
Also called toughened glass or safety glass, tempered glass is designed to crumble into small, granular chunks instead of dangerous, jagged shards. All automotive glass has been tempered for passenger safety; the downside is it must be pre-cut to shape before being tempered. Any polishing or drilling must also be performed before the glass is toughened.
The Big Picture
Here's a video showing how the Audi R8 is constructed. This provides a great illustration of how different automotive materials are used together to create a complete package.