Hydro Aluminium Deutschland GmbH, R&D, D-53014 Bonn, Germany
The European automotive industry is known world wide as the technically most advanced and innovative. Based on economical and political pressure to reduce fuel consumption and CO2 emission the efforts for light weighting in automobile design and constructions have increased significantly and specific solutions based on the intensive use of aluminum as modified or new alloys have been developed in the last decades.
The European automotive industry has more than doubled the average amount of aluminum used in passenger cars during the last decade (Figure 1) and will do even more so in the coming years. In the year 2000 an average of 102kg aluminum was used in automotive parts in Western Europe, with 59kg in engine parts, 11kg in structural parts, 6kg chassis applications and 5kg for body-in-white (21 kg others). Based on current developments in new model generations with innovative aluminum concepts it can be estimated that the use of this material in European passenger cars will more than double in the next decade.
A more detailed analysis is shown in Figure 2. The range of aluminum use today for modern small and medium size models lies between 50 and 200 kg per car, in some cases, such as the AUDI A2 and the top class model A8 (Figure 3) up to 300 and even 550 kg are used, respectively. However, aluminum is heavily competing with other light weight materials (new steel grades, magnesium, fibre-reinforced-plastics "FRP") which also demonstrate their potentials. But it is maintaining a preferred position due to it’s advantages like good availability, good recyclability and mass production capabilities at a reasonable price.
Figure 1: Average use of aluminum per car in Western Europe [EAA].
Several novel concepts in light weight solutions and applications help to strengthen this position and support even further evolution, e.g. the for flexible space frames, chassis components like axles and wheels and body-in-white applications. Here the diversity in solutions based on the large variety of semi-finished products, such as castings, extrusions and sheet with their specific advances of functional integration and tailored properties contribute to the great success of aluminum, in spite of its sometimes specific requirements in handling, forming and joining and related production costs and higher material costs - compared to conventional steel.
Figure 2: Relative and absolute shares of Aluminum in some European cars.
One of the main advances of aluminum is its availability in a large variety of semi-finished forms, such as shape castings, extrusions and sheet. Such semis are very suitable for mass production and innovative solutions in the form of compact and highly integrated parts that meet the high demands for performance, quality and cost efficient manufacturability.
The main challenges involved here are joining and surface treatment issues for which many suitable solutions have been developed as indicated by numerous examples and cars made with aluminum as the preferred light weight material. Aluminum semis are applied as castings, extrusions and sheet increases, e.g. in engine blocks and power train parts, space frames (e.g. Audi A2, A8, BMW Z8, Lotus Elise), sheet structures (Honda NSX, Jaguar) or as closures and hang-on parts (e.g. DC-E-class, Renault , Peugeot) and other structural components.
The highest volume of aluminum components in cars are castings, such as engine blocks, cylinder heads (Figure 3) and chassis parts. The substitution of cast iron engine blocks continues. Even diesel engines, which continue to gain a substantial increase in market share in Europe now are being cast in aluminum (Figure 3b) where, due to the high requirements on strength and durability, cast iron has generally been used.
However progress in aluminum alloy development (Al-Si-Cu-Mg-Fe - type) and new casting techniques came up with improved material properties and functional integration that enables aluminum to meet the requirements. This trend is driven by the needs of the automotive manufacturers to substantially reduce weight of the power train and chassis components. Additional features for achieving a better car performance would otherwise produce an unacceptable increase in car weight. Already well established in high class automobile engines, aluminum is gaining a significant share in the smaller but high volume compact-size cars (e.g. Ford Fiesta).
Figure 3: Production of cylinder heads in Europe [Hydro].
The evolution of Magnesium as engine block material is a further step in weight reduction as shown by BMW for the new 6 cylinder engine. If manufacturing processes are developed to be more cost efficient, the price level for magnesium cast alloys decreases further and engine design is developed appropriately to the available level of properties, magnesium will achieve a significant market share for light weight engine applications.
Aluminum castings are also gaining acceptance for many parts and innovative applications in the construction of space frame, axle parts and structural components. Complex parts are produced by special casting methods that ensure optimal mechanical properties and allow enhanced functional integration (Figure 4).
Though the piece price may be higher, total cost for the components may be reduced due to the avoiding of joining efforts and the high degree of integration of several functions in only one part.
Figure 4: Development of Al die-castings for multifunctional integration [AUDI].