December 1

When aluminium reacts with its environment, this often causes pre-corrosion. Different, mostly barely visible changes on the surface of the aluminium are the result. But what are the effects of pre-corrosion?

If pre-corrosion occurs on the material, this often leads to unsaleable goods. This is because the pre-corrosion on the raw material is usually only noticed after pickling, as the structure of the pre-corrosion remains as a visible relief.

What causes pre-corrosion?

The most common cause of pre-corrosion is incorrect storage. For example, if the raw material is exposed to a very corrosive atmosphere or is stored in a room with too much humidity, this enhances pre-corrosion. Pre-corrosion can also occur if condensation occurs under the foil in the case of foiled raw profiles. Further examples are:

  • Exposure of the aluminium surface to aggressive substances,
  • Touching aluminium without gloves (hand perspiration = corrosion),
  • Use of corrosive additives when sawing and cutting,
  • Unsuitable spacers used between aluminium profiles (e.g. acid containing or humid cardboard strips),
  • Storage of aluminium raw material close to marine climates (humid, salty).
Pre-corrosion due to acidic, moist cardboard strips as spacers

Pre-corrosion due to humid storage
Pre-corrosion due to exposure to aggressive liquids

How can pre-corrosion be avoided?

To avoid pre-corrosion and the resulting unsaleable goods, some rules should be observed when handling the raw material. For example, the aluminium should be stored in a dry place and contact with aggressive liquids should be avoided. The right packaging also prevents the formation of condensation. When transporting the raw material, gloves should also be worn to avoid corrosion through hand perspiration.

In most cases of pre-corrosion, however, only mechanical treatment can help . This can be done by grinding, of the pre-corroded raw material for example. Pickling alone is not always sufficient to avoid the visible consequences of pre-corrosion in anodising operations.

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