Aluminum School

Almost half the weight of steel, the most abundant metallic element on earth has made significant inroads into the automotive industry.

There's a lot of noise being made right now about aluminum use inproduction (and concept) vehicles. And justifiably so, this element that makes rubies rubies is also making vehicles lighter, more fuel efficient, and—in some cases—safer. With this in mind, we thought perhaps a little "schooling" was in order.

Course I—The Basics

Aluminum is: A metallic chemical element
Symbol: Al
Atomic Number: 13
Atomic Weight: 26.9815
Characteristics: Silvery-white in color; in its pure form, it's soft and pliable; but it becomes quite hard when alloyed.
History: Compounds used by ancient Romans as astringents (alums); Identified as a metallic element by scientists early in the 19th century; Isolated by Hans Christian Oersted in 1825. Now produced commercially using the Hall-Héroult method.

 

Course II—The Car Story

Since the early 70's, aluminum has been growing in acceptance and use in the automotive industry. From 1976 to 1996, the amount of aluminum in the average vehicle grew from 87 lb. to over 250 lb. per vehicle. By the year 2000, the Aluminum Association(Washington, DC) expects there to be nearly 350 lb. of aluminum in the average vehicle. Of course, in cars like the Plymouth Prowler, Audi A8, or any of the EVs, there is significantly more.

There are several reasons behind automakers' interest in aluminum. Not only is it almost half the weight of steel, but it doesn't rust and is infinitely recyclable. Weight and environmental issues aside, there are a few other reasons aluminum is turning heads.

 

car and house

For instance, the metal's strength to weight ratio is higher than that of steel. So by using strategic increases in material thickness and section size, as well as effective joining (welding, fastening, etc.), body structure strength and stiffness requirements can be met while still reducing vehicle weight.

In terms of "crashability," aluminum structures absorb energy in the exact same manner as steel. In fact, in September, the National Highway Traffic Safety Administration gave the Audi A8 a five-star safety rating in frontal crash testing. Aluminum responds to high stress in a predictable manner, so engineers can assert fold, break, and collapse zones with confidence. They can also engineer larger crash zones since aluminum is so much lighter than steel.

And the A8 isn't the only car to meet government safety standards. Production cars like the Prowler and the GM EV-1 have both received the thumbs up, as well as the all-aluminum Mercury Sable concept vehicle. The most aluminum-intensive vehicle on the road right now has also passed Big Brother's tests. At around 1,000 lb., the Honda Acura NSX reigns supreme in the aluminum content game. According to Honda, the NSX shed about 450 lb. of weight, which has not only improved fuel economy, but overall performance in terms of acceleration, braking, and handling as well.

Course III—Alloys

As mentioned previously, aluminum is rather pliable in its pure form. For this reason, most commercially used aluminum is combined with other metals (see table). Some metal producers, however, are breaking out beyond the well-used series alloys to come up with new combinations. One such alloy is Boralyn from Alyn Corp. (Irvine, CA). Consisting of an aluminum alloy and boron carbide particulates, the alloy is actually lighter and stronger than both steel and aluminum.

GM's Advanced Technology Vehicles Group is using Boralyn for suspension, crossmember, and control arm structures (12 parts in all) in a new development program. The material was initially used by the group for the EV-1 engine cradle.

When compared to steel, titanium and plain old aluminum, the Boralyn composite was about 40% stiffer, a statistic that is magnified by the fact that it is less dense than any of the comparative metals. In terms of strength, testing showed Boralyn to have stress-strain limits to titanium and greater than both steel and 6000- and 7000-series aluminum alloys. And last, but not least, the composite wears well. When kept properly lubricated, it has a very low friction coefficient, as does its mating surface.

Boralyn isn't the only aluminum alloy making waves with carmakers. There are new alloys, a spray forming process for aluminum sheet (a DOE-driven project), and aluminum foams (Karmann's already using one for body applications) being tested for everything from oil pans to door beams.

Course IV—Self-Guided Study

As always, the best way to learn is through self-discovery.

 

THE ALUMINUM ALLOY SERIES
Here's a list of aluminum alloys, their characteristics, and their typical automotive
applications as listed by the Aluminum Association.
Series Characteristics Uses
1000 Series Using 99% or higher purity aluminum, the compositions in this series are usually strain hardened. They resist corrosion well, and have high thermal and electrical conductivity. Trim, nameplates, and appliques, as well as extruded condenser tubes and fins.
2000 Series Copper is the alloying element of choice here. Heat treating yields properties similar to mild steel. Sometimes they are artificially aged for even higher strength. Sometimes combined with 6000 or 7000 series alloys to increase corrosion resistance. Outer/inner body panels; screw machine parts; mechanical fasteners
3000 Series Alloys in this series are coupled with manganese. They have good corrosion resistance and formability. NOT heat treatable. Trim, nameplates, appliques; radiator and HVAC components; interior panels and components; extruded condenser tubes.
5000 Series Magnesium, one of the few metals lighter than aluminum, is used here. The resulting non-heat treatable alloys feature moderate to high strength. Extremely weldable, they are also very corrosion resistant. Trim, nameplates, appliques; interior panels and components; truck bumpers and body panels; inner body panels, heat shields, structural and welded parts; wheels; engine brackets and mounts.
6000 Series Both magnesium and silicon enter the mix for this series, making them heat treatable and extremely versatile (especially the 6061 alloy). Formability, corrosion resistance, and high strength top the list of desirable characteristics. Body panels; bumper face bars; fasteners; body components (both extruded and sheet); driveshafts and driveshaft yokes; bumper reinforcements; brake housings; fuel delivery systems; luggage racks; and more
7000 Series Zinc is the main ingredient, although small amounts of magnesium and/or copper can be thrown in for special applications. All alloys in this series are heat treatable and have extremely high strength. Seat tracks; bumper reinforcements and face bars; condenser and radiator fins; headrest bars.