A lot has been written about Ford’s switch to sheet aluminum for the 2015 F150 light truck line and it’s been a notable success.
Aluminum has been used in automotive applications since the 1920s, but forming aluminum sheet into car bodies has been expensive, difficult and, as a result, limited to high-cost, low-volume vehicles such as sports cars and heavy trucks.
Why? Because aluminum sheets are notoriously difficult to form and fasten, compared to sheet steel.
In stamping, spring back is an issue, and aluminum’s property of quick passivation in air leaves an oxide layer that complicates many welding and finishing processes. Mostly, it’s a lack of experience with the material.
Forming and spot welding of sheet steel into unitized body and frame construction took off in the 1960s. In over half a century, any manufacturing process can mature to the point where it’s a low-risk choice when developing new products. It will be no different with aluminum.
The mass media claims that the shift to aluminum is driven by the need to reduce weight and improve fuel efficiency, but that’s not entirely the case. High-strength, low-alloy steels have allowed significant down gauging of steel sheet and a lot of weight reduction, plus they’re easy to form and fasten with conventional technologies.
Most modern aluminum automotive body production however is hybrid — not in powertrains, but in that steel is still used in critical applications, specifically to support the passenger compartment for crashworthiness reasons.
Atlanta-based Novelis has introduced what the firm calls its Advanz 7000 series aluminum sheet that’s two to three times stronger than current high-volume sheet aluminum alloys.
These new alloys allow aluminum into safety-critical structural components such as bumper systems, door intrusion beams, B pillars and other safety-cage components. Novelis claims that the additional strength comes without sacrificing formability.
Novelis is a supplier to Ford for the F150 program as well as to Range Rover and the Jaguar XE model. The firm developed the current generation of high-volume aluminum sheet alloys, 6111, 6016 and 5754.
Simplified Assemblies with New Aluminum
The reduction or elimination of mixed-metal construction in automotive bodies significantly reduces the fastening and assembly challenges in current mass production.
For example, Cadillac uses flow drive screws for significant portions of their small car platform. Although robotics has dramatically reduced the cost of mechanical fastening, the old axiom in the automotive industry, “never use a screw where a spot weld will do,” is still true today.
Even advanced structural adhesives work best when gluing together materials with similar coefficients of thermal expansion. And galvanic corrosion can never rear its head between bonded metals of the same material.
Stamping aluminum sheet has never been easy, but the combination of Ford’s successful experience with the F150 program and modern simulation software makes it work. This software reduces the number of iterations of tooling needed to accommodate spring back and the unique flow properties of light alloys under pressure.
It’s now possible to spend $1 billion to launch a new vehicle platform, and much of that price tag is in tooling. The simulation software gives designers the ability to specify new materials with confidence.
Just as importantly, the cost reductions associated with simplified assemblies should push aluminum construction down from larger, high-margin vehicles into the mainstream. This could put even more pressure on the steel community to down gauge even further with advanced high-strength alloys.
The major loser in this battle may in fact be carbon fiber composites. Composites are currently the ultimate in high strength and low weight, but even with automated layup and prepreg sheet and strip, it’s expensive. With mass producible all-aluminum structures, the weight advantage of carbon fiber is lower when compared to steel structures.
It’s likely that for all but specialty luxury vehicle applications, composite construction will be delayed for years and may never go mainstream.
So is there a long-range threat to aluminum in auto manufacturing? If so, I suspect it will come from thermoplastics, not composites or HSS.