Recent fuel economy requirements have driven chatter about automotive materials, with some people postulating that pickups will soon be built of aluminum. After seeing an acquaintance's expensive aluminum car sit in a body shop for months,
I am confident it won't happen soon.
Aluminum may be the darling of light-weighting structures, especially given Range Rovers' crash diets and road car adoption by the likes of Audi, Aston Martin, and Jaguar. Ferrari's carbon F50 and Enzo have become aluminum road cars. McLaren, BMW, and Corvette are leaning toward carbon-fiber composites. But the steel industry isn't going to roll over and let those beer-can and wheel people steal a big chunk of their business.
All those cars are pricey and low-volume, exactly counter to a pickup. Like the BMW M's carbon-fiber roof and the boron steel on Porsches, Mercedes-Benzes, and Volvos, the lightness-versus-strength payoff is more easily justified on expensive vehicles. As with many commodities and technologies, prices will come down over time. A carbon-fiber-composite Boeing 787 costs little more than the 767 it's replacing, but an aluminum pickup won't be on the market in 2015.
Stiff and light, carbon fiber is expensive, labor-intensive, and time-consuming to make, hence BMW's investment in carbon facilities and methods for its electric i3 and i8. Magnesium, while also strong and light, is brittle and can't be bent back if you crash it. They're great for parts like dashboard stiffeners and console mounts, but no one wants a $150,000 pickup even if it does get 30 mpg.
Big-truck builders have offered aluminum frame rails for years. They are still optional on some trucks where absolute payload rules, but the operator determines the payoff. These are straight rails and often are "repaired" by simply replacing the rail.
Aluminum is lighter than steel but costs more, perhaps running another $1000 for a crew cab or big SUV. It's very recyclable, but so is most automotive steel. Aluminum advocates cite life-cycle CO2 emissions superior to magnesium and steel, and better crush characteristics in impacts. A GM supplier is said to have developed a manufacturing method that saves 5 kg on a 20-kg aluminum wheel without a significant cost increase.
But bonded and riveted structures require significant repair tools and expertise investments, more so than even the latest steels. Audi and Jaguar sell many of the aluminum or mixed content cars in North America, but Jaguar has fewer than 60 authorized body repair places and Audi about 35. If your insurance company has to ship a truck 500 miles for repair, premiums will cost more.
There are more than 3500 types of steel, most developed in the last 20 years. Any new vehicle sports 5-10 grades in the body structure alone, with more in components. Some automakers that are no stranger to volume production (including Volkswagen) have gone back to steel, replacing what were once aluminum parts for the best-case weight-versus-cost benefit.
Hot-stamped and very high-strength steels are up to six times stronger than conventional steels. ArcelorMital's hot-stamped nano steel is lighter and more expensive, but not to the degree of aluminum or costlier materials. As with many materials, its maximum benefit comes with purpose-built designs, but manufacturing processes don't require big change and components can benefit immediately.
While fuel economy is a singular target, in 2007, the Minerals, Metals, and Materials Society studied CO2 emissions over a vehicle lifetime for steel or aluminum. Aluminum production costs 2-5 times that of steel, a 10 percent weight reduction was assumed to net a 5 percent improvement in fuel efficiency, and the steel BIW rated 20 mpg compared with the aluminum BIW 22 mpg.
Total CO2 emissions ended up at 8988 kg for steel and 8923 kg for aluminum. However, at 10 percent better fuel economy over a 14-year, 174,000-mile lifetime, the aluminum vehicle would save 791 gallons of gas. That's a savings of $3200, but can a pickup currently costing $22,000-$60,000-plus be built with an aluminum body and frame for $3200?
Last year, Lotus Engineering completed phase two of a mass reduction study for a crossover based on the dimensions of a Toyota Venza. Computer analysis of a body-in-white constructed with aluminum, magnesium, composites, and high-strength steels took 311 pounds off. Since a lighter structure requires less power and lighter parts, the model crossover built on that BIW weighed 1162 pounds less, nearly a third of the lightest 3760-pound Venza. It had the potential to meet federal impact requirements including side, belt, and LATCH loading and buckling stability, among others; used a third fewer components; and was 20 percent torsionally stiffer. Lotus pegged the additional body costs at $723, but overall the vehicle was cheaper by $239.
Meanwhile, hybrids such as aluminum mixed with ceramic or carbon fiber keep materials execs calculating how to save fuel and make profit, but steel will remain the dominant pickup truck material near-term, and as with powertrains, there is no single right answer.