Atmospheric corrosion of Zn–Al coatings in a simulated automotive environment^*

* This paper was presented at Interfinish 2016.

ABSTRACT

Accelerated NVDA (VDA 233-102) tests were performed on bare Zn and Al sheets, Galfan coating (Zn–5 wt-% Al) and Galvalume coating (Zn–55 wt-% Al) on steel. ZnO, Zn(OH)₂ and Zn₅(OH)₈Cl₂·H₂O were the main corrosion products identified on both bare Zn sheet and Galfan. AlOOH and Al(OH)₃ were preferentially formed on bare Al sheet and Galvalume. In addition, Zn–Al–containing corrosion products, Zn₆Al₂(OH)₁₆CO₃·4H₂O and/or Zn₂Al(OH)₆Cl·2H₂O were identified on both Galfan and Galvalume. Corrosion products of Zn₆Al₂(OH)₁₆CO₃·4H₂O with a platelet morphology were preferentially formed in the zinc-rich interdendritic regions of the Galvalume surface. Galfan revealed a similar corrosion behaviour as bare Zn sheet, whereas Galvalume exhibited similar behaviour as bare Al sheet. Deposition of chlorides highly influenced the corrosion of both Galvalume and Al rather than Galfan and Zn due to the rapid local damage of the compact native thin film of Al₂O₃.

KEYWORDS:

• Atmospheric corrosion
• NVDA tests
• Zn
• Al
• Galfan
• Galvalume
• chloride
• microstructure

Acknowledgements

The full report is entitled ‘Corrosion of heterogeneous metal–metal assembling in the automotive industry’, authored by C. Allély, A. Coffigny, G. Luckeneder, S. Reiter, S. Krebs, W. Friedhoff, F. Beier, K. Ogle, P. Volovitch, C. Leygraf, I. Odnevall Wallinder, Arcelor Research Maizières-les-Metz, VASL Linz, DOC Dortmund, SZMF Salzgitter, ENSCP Paris, KTH Stockholm, 2013. Gerald Luckeneder, VoestAlpine, Austria, is highly acknowledged for enabling the possibility to run the NVDA test and Ping Qiu, KTH, Sweden is highly appreciated for her help to run the test.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Christofer Leygraf http://orcid.org/0000-0002-9453-1333

Notes

* This paper was presented at Interfinish 2016.

Additional information

Funding

This work was supported by the European Union's Research Programme under the Research Fund for Coal and Steel (RFCS) (No. RFSR-CT-2009-00015).