May 28, 2003

More aluminum being used in cars
by Jim Kerr

Aluminum, or aluminium if you prefer, was first discovered in the early 1800's and produced in quantity in 1824. By the turn of the century, aluminium was being reliably cast, rolled and formed. Automakers quickly discovered its attributes and it has played an important roll in automobile construction ever since.

Aluminum has been used for doors skins, hoods, trunk lids, engines, radiators, suspension components and interior trim. The weight saving and attractive appearance aluminum provides are definite benefits, but steel has been the more traditional material used in automobile body and frame construction because of low cost and easy joining methods. That is gradually changing.

Racecars use aluminum extensively to save weight, although carbon fibre composites have now replaced it in some areas. High performance sports cars like the AC Cobra used aluminum bodies for low weight, although steel frames were often still used.

Ettore Bugatti used aluminum extensively in his cars and his son, Jean Bugatti, built a couple cars in the 1930's almost entirely of an aluminum-magnesium alloy. Even the frame of the car used aluminium alloy sections riveted together. Many other European car builders such as Ferrari and Aston used aluminum in the 1920's and 30's. Aluminum was easy to shape by hand and was well suited to limited production runs.

The use of aluminum in automobiles has increased over the years. According to the Aluminum Association in the 2002 North American Light Vehicle Aluminum Content Study, for 2002 the average aluminum content for passenger cars and light trucks combined is 274 pounds. This reflects a 23-pound increase over the average of 251 pounds of aluminum estimated for all vehicles sold in 1999. Although aluminum plays an important roll in automobile construction, it hasn't been until recently that modern assembly techniques have supported mass production of vehicles.

A few modern cars are built with complete aluminum bodies as well. The Plymouth Prowler used an aluminum body on an aluminum frame. The Honda Insight and Acura NSX have aluminum unibodies that utilize construction methods similar to steel cars: panels are spot welded together. The Audi A8 and the Audi A2 use aluminum space frame construction that is welded, and riveted for structural strength. The A2 aluminum body is 43% lighter than a comparable steel body and Audi claims the resulting lightweight body is stronger than steel and cheaper to repair.

2004 Jaguar XJ8. Click image to enlarge

Jaguar's new XJ8 is the latest aluminum car to hit the showrooms and it has a Canadian connection: Alcan, the aluminum supplier, was a key technical partner in the development of construction techniques. This flagship sedan weighs almost 92 kg less than the previous model yet is larger and incorporates more features. According to Jaguar's XJ Chief Program Engineer, David Scholes, customers "may not care whether the body structure is aluminum or steel, but the Jaguar customer does care very much about performance, dynamics, emissions and safety. The choice was clear." To take full advantage of aluminum's properties, Jaguar has adopted construction techniques used in the aerospace industry.

2004 Jaguar XJ aluminum monocoque body. Click image to enlarge

The XJ8 uses several different types of aluminum parts to construct the car's monocoque body. High-pressure vacuum aluminum die-cast parts are used as mounting points for the suspension and driveline components. High strength "green sand" aluminum castings are used to provide mounting points for the XJ's bolt-on front end. This allows parts damaged in low speed accidents to be easily replaced. Hydroformed aluminum alloy tubular components are used to produce complex shapes that are stronger than welded assemblies. Aluminum alloy extrusions are used in door structures for enhanced security. Bake-hardened aluminum sheet is used for exterior panels, providing a tough surface resilient to dents that can occur in parking lots.

Over 3200 self-piercing rivets and 120 meters of adhesives are used to assemble the inner body structure, while many exterior panels are bolted on. The result is a body that is 40 percent lighter and 60 percent stiffer than the previous model XJ8. Improved handling, superior ride comfort, and better fuel economy are but a few of the benefits.

Pound for pound, aluminum can be up to two-and-a-half times stronger than steel and can absorb twice as much crash energy. Vehicles made lighter with aluminum can have improved acceleration, braking, handling and better fuel economy. Finally, aluminum is easily repaired but it takes special techniques, so have your aluminum car repaired by a knowledgeable bodyman.

Jim Kerr is a master automotive mechanic and teaches automotive technology. He has been writing automotive articles for fifteen years for newspapers and magazines in Canada and the United States, and is a member of the Automotive Journalist's Association of Canada (AJAC).

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