41 00... Materials Science
1. Aluminum
1.1 Chassis/suspension components
READ and observe the Notes on chassis/suspension components before handling aluminum.
1.2 Material influences
| Causes | Effects/remedies |
|---|---|
| A galvanic element is created under the effects of moisture by contact with materials such as copper, tin, nickel, iron and zinc. | This plating process causes aluminum to be removed from the connection point. This results in surface corrosion or pitting. New parts and accessory parts which have been approved by the BMW Group for aluminum (screws, washers, nuts etc.) have undergone special surface treatment. Such parts must not be replaced by conventional parts.
NOTE:
Damaged parts lose this protection and must be specially coated or replaced. Damage caused by contact corrosion is excluded from the warranty. |
| Tools also used for work on steel components can implant steel particles in the softer surface of an aluminum component. | Surface corrosion or pitting occurs. A separate tool set is available for processing/machining aluminum. |
| Surfaces are attacked when fluxing agents are used. | Soldering is not permitted for joining aluminum components. Risk of corrosion from chemical factors. |
| Aluminum/steel grinding dust from adjoining working areas. | This results in surface corrosion. Erection of protective barriers. |
1.3 Machining properties
| Properties of aluminum compared with steel | Effects |
|---|---|
| Aluminum parts are magnetically neutral. | Attachment with magnetic tools/working aids is not possible. |
| Elasticity is only 1/3 as high. | Convertibility is limited in comparison with steel. |
| Elongation failure is approx. 50 % slighter. | Overstretching the material results in strain-hardening and an increased tendency of cracking. |
| Electrical conductivity is almost 4 times higher. | Electric welding methods require different equipment (MIG welding). |
| Material expansion during heating is twice as high. | The material expands more markedly. Shorter heat treatment is necessary for removing dents. |
| Thermal conductivity is 3 times higher. | Heat is drained more quickly. Adjoining working areas are affected more heavily e.g. during welding. |
| Structural transformation between 200°C and 250°C | Elongation characteristics and thus plasticity are improved. Strength is reduced.
IMPORTANT:
No heat treatment during repair work on the vehicle structure! Workshop operation doesn't make it possible to control the temperature to sufficiently exact levels.
|
| Aluminum shows no annealing colors. | The melting point is 650 °C. Once the melting temperature has been reached, the material begins to flow without any further indications. The temperature can only be estimated by means of the paint coloring and the surface warpage.
IMPORTANT:
Do not use thermo crayons. Not suitable for workshop operation because the paint runs too quickly.
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1.4 Storage
| Characteristic features of aluminum | Special measures |
|---|---|
| Corrosion (ageing) in damp environments. | Store aluminum components in a dry place. |
| Contact corrosion in event of contact e.g. with steel components. | Always store aluminum components separately or in isolation from steel components. |
| Susceptibility to paint infiltration. | Do not damage factory protective layer of the surface since this would cause oxidation. Failure to comply with this requirement would result in more painting work. |