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|
|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.
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.
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
Generally, when OEMs produce aluminum engine blocks (aluminum rather than cast iron because cast iron weighs like cast iron), they insert sleeves into the piston bores—cast iron sleeves.
While aluminum vs. steel is getting more contentious in the world of light-duty trucks, when it comes to creating structures, the heavy-duty truck people know something important about strength and mass.
A young(ish) guy that I’ve known for a number of years, a man who spent the better part of his career writing for auto buff books and who is a car racer on the side, mentioned to me that his wife has a used Lexus ES Hybrid.