Aluminum use for performance structures

Why use aluminum?

Vehicle makers use aluminum because it:

• is lightweight. Lighter weight material can contribute to quicker vehicle acceleration and shorter stopping distances.
• has excellent corrosion resistance.
• is almost 100 percent recyclable.
• can be formed multiple ways for part construction.

Aluminum also has excellent strength for a lighter weight metal. Part of the strength bonus of aluminum is that it has high torsional rigidity, or more resistance to twisting. This quality is even further enhanced in a multi-celled aluminum extrusion (see Figure 1). A multi-celled extrusion with inner reinforcements designed into the part greatly increases the strength and rigidity. This can contribute to better cornering stability and better wheel-to-road power distribution.

Safety is one of the main reasons for using aluminum in performance vehicles. Performance vehicles are designed to perform at higher speeds, which may lead to more severe damage to the vehicle in the event of a collision. Aluminum is very predictable in the way it reacts to collision forces. Vehicle designers can use this predictability for designing vehicles that absorb collision energy and transfer collision energy around and away from the vehicle occupants. Certain vehicle parts, such as front crush tubes or single-cell, extruded lower rails are designed to compress and absorb collision energy, while larger, multi-celled extruded inner rockers will transfer collision energy around the occupants.

2008 Audi R8

Audi released the new R8 with a space frame structure built of 69 percent extruded aluminum. Some of these extrusions are multi-celled, including a five-celled inner rocker and an eight-celled inner B-pillar (see Figure 2). Different than previous Audi space frame vehicles, the R8 only uses six castings for construction. Parts that would typically be made of cast aluminum are made from extruded 6000 series aluminum to streamline production (see Figure 3).

The R8 has a rear-mounted, 4.2-liter V8 engine, capable of producing 420 horsepower. The R8 engine uses a dry sump oil system with an external oil tank, similar to conventional race car applications, that holds 15 quarts of engine oil.

The R8 structure is primarily GMA (MIG) welded together, but does use some rivet-bonding and threaded fasteners for joining. Audi has complete front and rear structural assemblies available for collision damage repairs (see Figure 4). When replacing damaged structural parts, the factory joining method is typically duplicated. Welded sectioning is only allowed in a few areas, such as the outer A-pillar, the outer rocker panel, and select extruded parts pointed out in the body repair manual. All sectioning joints are made using inserts. All welding is done using GMA (MIG) welding using pulsed-spray arc transfer.

2006-Current Jaguar XK

Jaguar released the redesigned XK with a new aluminum-intensive structure, replacing the outgoing steel unibody design (see Figure 5). The new advanced monocoque construction of the XK consists of twice as many castings as the Jaguar flagship model, the XJ sedan, and three times the extruded parts. The use of more castings and extrusions led to building a vehicle with a more torsionally rigid structure, with fewer parts. The rocker panels are an open extrusion design, which makes them a C-channel shape with mating flanges. The XK does use a combination of 5000 and 6000 series aluminum, similar to the current XJ design.

The XK has two engine options available, a 4.2-liter V8 capable of 300 horsepower and a 4.2-liter supercharged V8 capable of 420 horsepower. The XK also is available as a coupe or a convertible body style.

The XK has a unique structural design, which mostly uses rivet bonding and threaded fasteners for joining. The front structure has a bolted-on front crush tube for low-speed impacts. If damage transfers past the front crush tube, the lower front rail also is attached with bolts near the cowl. Other than threaded connections, the XK coupes and convertible use mostly rivet bonding for part replacement procedures, while limiting the amount of welding and sectioning. Rivets used for repairs include self-piercing rivets, blind rivets, and monobolts. Monobolts differ from blind rivets in that rather than compressing the rivet body down onto the backside panel, the stem of the monobolt flares the body out, creating a wedge effect. The body repair manual will indicate which rivet type to use for specific locations.

2006-current Chevrolet Corvette Z06

The Z06 comes with a 7.0 liter V8 engine, capable of producing 505 horsepower. The Z06 also uses a dry sump oil system.

The Z06 aluminum structure is primarily GMA (MIG) welded. Self-piercing rivets are used for assembling some stamped pieces together, for example the B-pillar.

The Z06 side frame rails can be sectioned in five locations. General Motors recommends that Z06 repairs involving GMA (MIG) aluminum welding be done using pulsed-spray arc welding equipment.