26.10.1997

Alfa 156: Materials


Introduction
How to reduce the car's weight in order to obtain sparkling performance, while at the same time, increasing the bodyshell's toughness and rigidity in a way that would guarantee the Alfa 156 superlative active and passive safety, as well as eliminating vibration in order to minimise cabin noise? That was the complex equation Alfa Romeo engineers had to solve as soon as the new project reached the drawing board.
They found the answer in a careful selection of the materials used in building the car and in rethinking the ways those materials were used: in some cases that meant abandoning traditional techniques and blazing new trails in search of innovative new engineering methods. The result is a car that looks much the same size as that of the model it replaces, but is up to 50 kilograms lighter, depending on the version and assuming identical engines. And that despite the fact that the Alfa 156 incorporates many standard features that were only available as options on the earlier model.
This was achieved by using advanced metals like laminated, high strength steel sheet, aluminium and magnesium.
The entire 'skeleton' of the Alfa 156 was re-thought, point by point. It was a question of deciding where thinner steel sheet could be used to reduce weight without detriment to the build quality of the car.
A car door for example, needs more strength near the hinges than around the lock. Similarly, the central pillar needs to be very thick at the bottom for protection in the event of side-on collisions, but can be thinner at the top.

Steel
Alfa engineers decided to use laminated steel sheet to manufacture the front doors, roof beams and centre pillars of the Alfa 156. Known as 'tailored blanks', these steel sheets are obtained by laser-welding two sheets of different thicknesses together for pressing.
From 'skeleton' to 'skin'; sheet metal that is highly resistant to knocks (bake hardened), laminated and HSLA steel. In fact most of the steel sheet employed on the Alfa 156 is of the latter type. HSLA stands for High-Strength, Low-Alloy and gives enhanced resistance to denting assuming the same thickness. Or in the case of the Alfa 156 identical resistance to mechanical stresses from thinner steel sheet (from 0.9 to 0.7 mm).

Aluminium and magnesium
Steel was combined with much lighter materials for which new forming methods were sometimes invented. We're talking about aluminium and magnesium. Aluminium is used on three of the suspension components (the upper trailing arm, the damper support fork and the support for the upper suspension link). It is also used for the rear suspension cross-member, all rear brake calipers and the front brake calipers on the 1.6 T. Spark, 1.8 T. Spark and 1.9 JTD. Magnesium alloy is used for the seat frames, steering wheel armature and the facia cross-member.
The rear suspension cross-member was produced by a high pressure vacuum casting method called 'Vacural' which involves injecting the aluminium into one side of the die while extracting air to create a vacuum on the other side in order to optimise the geometry of the component. Other components were produced by 'thixoforming', a special type of pressure die casting. The procedure involves injecting fine grain aluminium in a semi-solid state into the die at a temperature of about 550ºC, rotating it in a cylinder to keep it homogeneous. This operation is performed while a vacuum is created inside the die. The result is thixoformed aluminium components which are lighter than those produced by any other method. Finally, all exhaust pipes are made of stainless steel for a longer life and enhanced resistance to corrosion.


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