Aluminium

Assignment

If ever a light metal was able to conquer the automobile sector, it is the material aluminium. It has, for a long time now, been the favorite for cylinder heads, intake systems, and gearbox- and final drive casings etc. However, the final breakthrough was recently achieved through using it for engine blocks (see picture) and particularly, for chassis parts. Then, there are the areas where the use of aluminium cannot be seen (e.g., seat-racks and dashboard support etc.). In addition (brushed) aluminium is now also often used, e.g., on the dashboard as a surface material.

Function

The silver-coloured aluminium is the the most abundantly found metal in the world. Of all the chemical elements, it is the 3rd most prolific. In it's pure form, because of the lack of stability, it is hardly ever found in technology. It is nearly always alloyed with silicon and/or magnesium. Once it has developed an oxide layer, it doesn't corrode any further. On the contrary, the oxide layer (anodization) even strengthens the component.

Aluminium is extracted from Bauxite. This is a material which is mixed with, among other things, iron and titanium, it's name comes from the now insignificant, first site of discovery, Le Baux, in the south of France. In the manufacturing process it is ground, dried and thus made into powder form, whose aluminium parts are then disolved in sodium lye. Pressure and heat accelerate this process.

In the first process, aluminium is is separated from all substances found in the ore except for iron. Now the, through the iron, slightly reddish solid components are extracted in containers with sloping floors. Once the last red mud portion has been removed through additional filtering, the aluminium oxide is coagulated in gigantic mixers by adding small amounts of alluminium hydroxide.

Aluminium hydroxide is developed, which, after once more being filtered and heated in a rotary kiln at just under 1300°C, is freed from it's water portions. Large amounts of Direct-Current are then necessary, to separate the aluminium from it's oxygen through electrolysis in a temperature sinking cryolite-bath.

Due to the high energy input necessary, the aluminium-technology only makes sense in combination with a functioning recycling process (returning the materials into the production process). If one compares the density of aluminium (2,7 kg/dm3) with that of steel (7,85 kg/dm³), the targeted of using as much as possible in vehicles, becomes understandable.

For it to be cast, aluminium must of course be heated. Whereby, it is important to repeatedly remove any dross, e.g., the oxides. Aluminium appears exclusively as an alloy with 10- to 20% silicon and other manufacturer specific components, which, among other things, distinctly improve the strength and hardness of the material. Cylinder-blocks are produced in a low pressure process (at 0,8 bar, from the bottom upwards).

Good running characteristics, when paired with pistons (also made of aluminium) are obtained, when they glide on the silicon crystals. These can be chemically exposed, or prefabricated as a special silicon containg alloy, then recast with the otherwise normal mixture. Before being further processed, the components are X-rayed to ensure a continuous quality standard. The last part of the process, is the deburring, turning and the milling. Particularly thin iron- or ceramic layers can also be applied through laser- or spraying technology. 09/11