2. LIGHT METAL AGE, OCTOBER 2015 39
stant cross section parts like the lower sill (rocker) seems
the evident choice, since its linear aspect coupled with
the need of complex cross sections for the part are all at-
tributes of extruded products. On the other side, center
tunnel sections or floor pans fall squarely in the sheet
stamping column, as they require a variable section along
the part and a number of added fasteners.
Several of the parts in the aluminum-intensive 2015
Ford F-150 are formed from extrusions, where the bound-
aries of design and manufacturing have been extended
to incorporate the attributes of extrusions into what have
historically been sheet components. This transformation
resulted in the consolidation of several traditionally steel
stampings into single aluminum parts,6
such as the wind-
shield header, roof bow, and rocker, with exceptional
stiffness and strength.
High Strength Aluminum Sheet vs. Steel
As mentioned, there are areas in the structure of a ve-
hicle that are strength rather than stiffness dominated.
In those cases, increasing the material strength will result
in weight savings, as it will allow a thinner component to
handle the same load. Although aluminum has a high
strength-to-density ratio, the parts normally produced with
ultra-high-strength steels in current steel structures do not
find a corresponding aluminum offering in the current
market. As indicated in Figure 2, alloys with strength in
excess of 450 MPa are needed to cover that range.
To close that gap, Constellium is working to develop
high strength alloys of the 7xxx series, specifically de-
signed for stampings that are currently produced via the
hot forming process. Figure 3 is a schematic representa-
tion of the production processes involved, from the sheet
mill to the OEM, to produce and assemble hot formed
parts. Logically, since 7xxx series alloys are heat treatable,
the high temperature processes are key to successfully
manufacturing the finished part.
This process yields parts of very high strength, excellent
ductility, and robust corrosion resistance. The mechani-
cal properties were measured from actual parts, such as
B-pillar stampings (Figure 4), produced at Constellium’s
Technical Center. The strength-to-density ratio resulting
from the combination of alloy and stamping processes, is
equivalent to those of hot stamped steels. This develop-
ment should result in significant thickness reduction in
high stress areas of a car body, achieving not only weight
reduction but also packaging improvements and overall
section optimization.
References
1. “Corporate Average Fuel Economy for MY 2017-MY
2025 Passenger Cars and Light Trucks,” NHTSA, August
2012, p. 1,014, www.nhtsa.gov/staticfiles/rulemaking/
pdf/cafe/FRIA_2017-2025.pdf
2. Lund, A., “The Relative Safety of Large and Small
Passenger Vehicles,” NHTSA Workshop on Mass-Size-
Safety Symposium, Washington, DC, February 2011.
3. “VENZA Aluminum BIW Concept Study,” Sce-
naria, Inc. for the Aluminum Association, 2012,
www.drivealuminum.org/research-resources/PDF/
Research/2013/venza-biw-full-study.
4. Peckham, R., “Reviewing Challenges and Identifying
Opportunities with Integration of Lightweight Materi-
als into High Volume Automotive Production – an OEM
Perspective,” Global Automotive Lightweight Materials
conference, Detroit, MI, 2015.
5. Pope, Byron, “Ford No Stranger to Aluminum,”
WardsAuto, March 19, 2015.
6. “Aluminum Extrusions and the 2015 Ford F-150,
Chief Engineer Dr. Bruno Barthelemy” (video), The
Aluminum Channel, April 2015, www.thealuminumchan
nel.com/videos/view/aluminum-extrusions-and-the-
2015-ford-f-150.
Raw Material Form Extrusion Sheet
Cross Sections
Easy to implement
closed sections
Open, close sections
need subassembly
Cross Section Type
Complex, multiple
chambers
Multi-piece sections
necessary
Longitudinal Section Constant along part Variable along part
Component
Thickness
Variable Constant
Features and
Fasteners
Additional cost Easy to implement
Cycle Time 2-10 spm 5-25 spm
Table I. Decision making factors when considering raw material forms
for aluminum components.
Figure 2. Strength and ductility of aluminum alloys compared with
equivalent strength-to-weight ratio in steel.
Sheet manufacturing process
Part manufacturing process OEM assembly
Process
Temperature
Hot rolling Cold Rolling
Blanking
Blanking
Solution Heat
Treatment
Stamping and
press-quenching
Ageing
~500 °C ~180 °C
Assembly Paint-bake
Figure 3. Schematic of the manufacturing route for hot formed parts.
Figure 4. B-pillar trial parts produced at Constellium’s Technical Center.
Dr. Alex Graf is director of Engineering at Constellium, a world-
wide manufacturer of aluminum products that utilizes cutting-
edge technologies to supply innovative aluminum material and
components required by today’s car manufacturers.