A Mass Reduction Potential Study (see Related Documents), conducted by fka, investigated the mass reduction claims made by the steel and aluminium industries compared with results of many design projects and specific vehicle programmes.
The steel industry documents that vehicle mass can be reduced by 25% through the application of modern high-strength and Advanced High-Strength Steels (AHSS). Aluminium advocates sometimes claim up to 50% mass savings by replacing steel with aluminium.
The study documents some specific simplified scenarios where aluminium provides a 50% reduction over conventional mild steel, however, it requires a 40% increase in package space requirements. The study also demonstrates that in alternative simple load cases using high-strength steels (Figure 1), the reverse actually can be true — mass can be reduced by 25% by replacing aluminium with high-strength steel applications, while favourably reducing package space requirements by 60%.
Unfortunately, fundamental load cases using mild-strength steels and unconstrained package space has very little to do with actual automotive structural designs.
Automotive applications do not lend themselves to such simple load scenarios. They are structures with multiple and complex loading conditions that are vital to vehicle handling and performance, strength, durability and safety. These design criteria create extreme demands on the material that are not easily satisfied. In addition, package space is rigidly constrained by the need to maximize the space for powertrain and passengers. These combined conditions result in significant barriers when trying to reduce mass with lower density materials like aluminium.
Data cited in the study indicates that actual aluminium body structures demonstrate mass savings between 16 and 40% relative to the conventional steel designs they replaced.
However, the replaced conventional steel body structures were outdated, non-optimized designs constructed using traditional manufacturing techniques and conventional automotive steels. In comparison, optimized AHSS designs have demonstrated 21 to 25% mass savings relative to the conventional steel designs they replace.
This achievement is reflected in the ULSAB family of research, as well as in automakers’ own body structure designs in recent years. These projects and vehicles feature designs that make extensive use of AHSS and holistic design optimization and improve performance and crash safety along the way. Automakers have embraced these steel-intensive solutions and have established clear material strategies for their future that reflect the benefits of using these advanced steels.
Overall, when looking at the evidence and the current state of the art in technology, the fka study concludes that aluminium designs provide 5 to 20% mass savings compared to an advanced steel design (Figure 2). In fact, the average mass reduction advantage of aluminium is only 11%, far less than the 40-50% reduction often communicated.