Aluminum Pickling
The Foundation for Adhesion and Corrosion Protection
Degreasing alone is not sufficient to ensure high-quality coatings. Only a controlled pickling process creates a uniformly active surface as the basis for optimal adhesion and long-term corrosion protection.
Why Is Pickling Necessary?
Aluminum has a natural oxide layer. In addition, rolling, annealing, or extrusion processes create a so-called microcrystalline deformation layer. This layer contains:
- Metal oxides
- Intermetallic phases
If these layers remain, they can impair adhesion and promote corrosive processes.
Only controlled material removal through pickling results in a homogeneous and reactive surface.
Key Factors in the Pickling Process
To achieve reproducible results, the following parameters are critical:
- Aluminum concentration in the bath
- Chemical concentration
- Temperature
- Pickling time
- Plant design and process control
Precise coordination of these parameters is essential for uniform material removal and process reliability.
Typical Sources of Error
Insufficient process control may lead to:
- Filiform corrosion
- Uneven pickling results (“etching marks” / pickling shadows)
- Zinc deposition on mixed materials
- Adhesion problems
- Incomplete removal of the deformation layer
Exposed environments (e.g. coastal or industrial areas) are particularly sensitive to pretreatment deficiencies.
Safety and Environmental Aspects
Acidic and alkaline pickling solutions are highly corrosive. Appropriate safety measures and personal protective equipment (PPE) are essential. Formulations containing hydrofluoric acid >1% are classified in accordance with Regulation (EC) No. 1272/2008 (GHS).
Conclusion
Properly controlled pickling provides the ideal foundation for: