2.1.2. Materials: Notes
A modern vehicle body has to fulfill many different requirements. Despite small exterior dimensions, it is to provide the largest possible passenger compartment. In the event of an accident, it must provide the passengers with the best possible protection. All assemblies, such as the engine and transmission, are supported by the body against the torque they generate. Futhermore, the body must have high static and, above all, dynamic rigidity to guarantee the excellent driving characteristics typical of BMW vehicles.
In addition, the supporting structure of the vehicle must have high fatigue strength and be able to be repaired with reasonable effort and cost in the event of an accident.
To fulfill all these requirements, BMW applies a manufacturing strategy that produces each part from the material that is best suited for its function.
The two terms "aluminum" and "steel" are only the generic terms for the wide variety of alloys used in the construction of the body.
These different alloys have quite different properties.
| Index | Explanation |
|---|---|
| 1 | Multiphase steels (> 300 MPa) |
| 2 | Hot-formed steels (> 900 MPa) |
| 3 | Aluminum |
| 4 | Other steels (< 300 MPa) |
Multiphase steels are steels with a structure that consists of multiple phases. Advanced-strength multiphase steels with a yield strength Rp0.2 of 300 to 600 MPa include, for example, dual-phase steels and TRIP steels. Advanced-strength multiphase steels with a yield strength Rp0.2 over 600 MPa include, for example, complex-phase steels and martensite-phase steels.
The hot-formed manganese-boron steels are ultra-high-strength steels with a yield strength Rp0. 2 of over 900 MPa.