Aluminum Versus Steel: Ferrous Fights Back with AHSS

Advanced high-strength steel goes toe-to-toe with aluminum in a strength/weight automotive challenge.

My recent video about the success of aluminum in Ford’s F-150 program struck a nerve with the steel community. They were quick to let me know that the metal is far from dead in automotive applications.

The folks at the Steel Market Development Institute (SMDI) dropped me a line to point out that advanced high-strength steels (AHSS) are responsible for significant performance improvements and weight reductions in current vehicle platforms.

The 2016 Chevrolet Malibu for example uses AHSS to allow a four-inch wheelbase stretch while cutting 300 pounds of weight compared to the 2015 model.

The 2016 Hyundai Tucson and the 2016 Kia Optima both use significantly more AHSS than the models they replace, making the current versions both lighter and stiffer. The 2016 Nissan Maxima has even dropped 82 pounds with greater torsional rigidity using high-strength steels.

Does this mean that steels can compete toe-to-toe with aluminum in automotive body construction? The short answer is yes, but in the long run the situation is a little more complicated.

A major advantage of steel is its formability, and the new high-strength grades promise this along with sufficient strength to allow down gauging for weight reduction. The new steels are not lighter than the old carbon grades, they’re stronger, allowing thinner panels than before.

Adding strength while maintaining enough ductility when stamping sheets into complex forms is a factor in mass production body stamping. Tailored, laser welded blanks put the thickness just where it’s needed in a large and complex die, and high-strength steels can be spot welded using conventional equipment.

It’s also significantly cheaper than aluminum sheet.

Overall process cost, however, is difficult to measure. Those tailored blanks, for example, might compete with thicker section single-gauge aluminum blanks, which might be strip or coil fed, lowering costs. And if plastic flow in tooling is thoroughly simulated before metal is cut, the formability issues that made aluminum notoriously difficult to stamp are no longer a major cost obstacle.

Advanced welding technologies, notably lasers, can be used with both processes, although it’s further developed with steels.

So, here’s the bottom line:

  1. Advanced high-strength steels are new materials with different properties to conventional carbon steels, so there is a learning curve with both AHSS and aluminum.
  2. Ferrous materials are easier to weld. Mechanical fastening is about the same in terms of complexity, although galvanic corrosion is an issue if aluminum must be joined to a steel substructure.
  3. Aluminum is lighter, and can be formed from relatively thick sheets. High-strength steels can match aluminum parts application-for-application by part redesign and thinner gauge sheet.
  4. Both steel and aluminum are 100 percent recyclable. However, steel is easier to handle in the recycling process.
  5. What may decide the future of automotive bodies: aluminum is cool. Aluminum is the material of aircraft and space vehicles, as well as exclusive luxury vehicles and sports cars. Aluminum has cachet, ironically, because of its limited use to do forming difficulties and high costs before Ford’s mass production breakthrough.

So, in the end, this may be less about an engineering breakthrough and more of a marketing one.

Dollar for dollar, who wouldn’t want a vehicle made from the stuff of rockets and fighter planes? And by dollar for dollar, I mean that literally. Ford’s F-150 is currently priced similarly to GM and Fiat Chrysler’s models, which are Ford’s primary competitors in the light truck market.

I suspect that Ford is eating some margin to keep pricing in line. Would buyers pay a 10 to 15 percent price premium for aluminum bodies? For mainstream vehicles, I suspect the answer is “no,” especially if advanced steel vehicles are not significantly heavier.

Should aluminum vehicles demonstrate superior corrosion resistance and no additional cost in collision insurance, however, high residual values on trade-in may tip the balance in aluminum’s favor. This remains to be seen, especially as the steel community is working hard on improved corrosion resistance as well.

In a sense, I have skin in this game. I drive an older F-150, whose steel body I’m slowly replacing with advanced composites, namely Bondo and fiberglass. I’m going to have to replace it at some point, and the aluminum structure of the F-150 may be a factor in that decision. But not as much as the price and towing specs, and I’m sure that’s the metric with a lot of buyers.

When reliable sales numbers are out, we’ll follow up.

Written by

James Anderton

Jim Anderton is the Director of Content for Mr. Anderton was formerly editor of Canadian Metalworking Magazine and has contributed to a wide range of print and on-line publications, including Design Engineering, Canadian Plastics, Service Station and Garage Management, Autovision, and the National Post. He also brings prior industry experience in quality and part design for a Tier One automotive supplier.