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Steel
vs. Aluminum: The
Basic Facts
- Elastic modulus
Steel at 210
GPa, has three times the elastic modulus compared to aluminum's 70 GPa.
Steel has three times the elastic modulus as aluminum.
Related to stamping performance, aluminum will possess higher
springback than mild steels. Even compared to high strength
steels, strength level to strength level, aluminum will still
possess higher springback.
Advantage: Steel
- Density
Aluminum
is approximately 1/3 the density of steel,
2.72 Mg/m3 versus steel's 7.85 Mg/m3.
|
Criterion |
Stiffness
Relation |
Comments |
| Bending
Specific Stiffness of Hollow Sections |
|
Steel
with a specific stiffness value of 26.75 vs. aluminum at 25.64
places steel at a slight advantage for structures such as front
crash rails, b-pillars, etc, or virtually any hollow section. |
| Bending
Specific Stiffness of flat plates |
|
This
relation pertains to surfaces such as hood outer
applications. Aluminum will have an advantage for outer skin
surfaces if only elastic material properties are considered.
When dynamic material effects are taken into consideration, steel
often shows an advantage. |
Advantage: Application
Dependent
- Strain rate
sensitivity
Steel is strain rate sensitive, many aluminum structural
grades are not. It is well known that steel displays positive strain rate
performance. That is, at the higher rates of strain
typically associated with crash events, steel has
higher strength increases and consequently higher energy
absorption at a given part weight. The figure bellow show's
results from a study conducted at the University of Michigan and the
Ford Scientific Research Lab on the effects of high speeds on aluminum
5754-O, DQSK (Mild Steel), Dual Phase 600, and TRIP 600 Materials;
grades that are proposed for tomorrow's body structures.
(click
for bigger picture)
(source:
J. McGuire & E. Wilson, 2001)
Advantage: Steel
- Fatigue
Aluminum fatigue performance is less than ½ that of steel.
This is a very important advantage for steel in terms of vehicle life durability.
Automotive steel grades also possess an endurance limit. From
testing, it was found that structural aluminum grades (5XXX series)
will not reach an endurance limit, but continually degrade at higher
cycles. The following figure indicates this pictorially:
Source: Autosteel
Partnership, Dofasco Co.
Advantage: Steel
- Formability
Aluminum's Formability is approximately 2/3 that of steel (less forming range).
This is a very important advantage for steel for vehicle styling and overall
manufacturing robustness.
Advantage: Steel
- Hardness
Aluminum's hardness is lower than steel's. Stone
chips and surface quality
are harder to maintain for an aluminum body over a vehicle's lifecycle.
Advantage: Steel
- Damping
Noise, Vibration, and Harshness (NVH). The
ability of any material to attenuate airborne noise is directly
proportional to its mass. Regarding airborne noise, steel
clearly has an advantage in most cases.
Advantage:
Steel
- Magnetic
Steel is magnetic, aluminum is not; very important in
recycling end of life vehicles. Steel is easily recycled
because of its magnetic properties versus other nonferrous
materials such as lead, copper, zinc, and aluminum. Thus,
Steel separates extremely efficiently, but the nonferous scrap
will possess all the unwanted residual materials as well
(polymers, glass, adhesive, ceramics, etc.).
Advantage: Steel
- Galvanic
potential
Aluminum's galvanic potential is high, while steel's is low. On an auto body, when aluminum and steel are in direct contact,
accelerated corrosion is evident. There are barrier technologies available
to help with this condition when mixing metals, but at a
significant cost impact.
Advantage: Steel
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