Improvement of the Corrosion Resistance of Aluminium Alloys Applying Diff erent Types of Silanes - Advanced Materials for Agriculture, Food and Environmental Safety - page 57

fact that a small portion of bis-amino silane makes the mixture solution
hydrophilic enough to increase the wettability of the aluminium oxide,
which facilitates the formation of a homogeneous i lm. A large portion of
bis-sulfur silane enhances the hydrophobicity of the mixture i lm, which is
the basis for the good protective performance of the mixture.
h e bis-sulfur silane i lm is neutral and it is not expected to promote the
penetration depth of Cl - , but the mixture bis-sulfur:bis-amino (3:1) con-
tains some -NH 3 + group, but not too many, due to the fact that this mixture
ensures very good corrosion resistance of AA2024. From the contact angle
values observed it could be concluded that the surface i lm is hydrophobic
and therefore somehow blocks the chlorine transport.
From the results obtained from the SST (840 h) tests it could be observed
that the corrosion protection of AA 2024 TSA anodized, HTS sealed and
conversion coatings with dif erent silanes varied in this way:

Bis-sulfur silane:bis-amino silane > bis-sulfur silane >

bis-amino silane:VTAS

Taking into account the obtained results, pretreatment using silanes rep-
resents a promising alternative to the Cr(VI)-based solution for AA 2024.

Acknowledgements

Financial support from the Seventh Framework Programme (FP7) (ECO-
design) is gratefully acknowledged. h e authors would like to acknowledge
Dr. Jaroslaw Wosik (CEST GmbH) for SEM characterization.

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