Advances in Automotive Conversion Coatings during Pretreatment of the Body Structure: A Review
Abstract
:1. Introduction
2. The Automotive Coating Stack
3. The Automotive Conversion Coating Timeline and Purpose
4. The Foundation of Zinc Phosphate Conversion Coatings
Steel | |
Pickling | Fe + 2H3PO4 → Fe (H2PO4)2 + H2 (g) Fe + 2H+ → Fe2+ + H2 (g) |
Coating | 3Zn2+ + 2H2PO4− + 4H2O → Zn3 (PO4)2·4H2O (s) + 4H+ Hopeite 2Zn2+ + Fe2+ + 2H2PO4− + 4H2O → Zn2Fe (PO4)2·4H2O (s) + 4H+ Phosphophyllite Zn2+ + 2Mn2+ + 2H2PO4− + 4H2O → Mn2Zn (PO4)2·4H2O (s) + 4H+ ZnMn-Phosphate |
Sludge | Fe2+ + H+ + Ox → Fe3+ + HOx Fe3+ + H2PO4− → FePO4 + 2H+ |
Zinc-Coated Steel | |
Pickling | Zn + 2H3PO4 → Zn (H2PO4)2 + H2 (g) Zn + 2H+ → Zn2+ + H2 (g) |
Coating | 3Zn2+ + 2H2PO4− + 4H2O → Zn3 (PO4)2·4H2O (s) + 4H+ Zn2+ + 2Mn2+ + 2H2PO4- + 4H2O → Mn2Zn (PO4)2·4H2O (s) + 4H+ |
Aluminum | |
Pickling | Al2O3 + 6H+ → 2 Al3+ + 3 H2O Al + 3H+ → Al3+ + 1 ½ H2 (g) |
Complexing | Al3+ + 6F− → AlF63− |
Coating | 3Zn2+ + 2H2PO4− + 4H2O → Zn3 (PO4)2·4H2O (s) + 4H+ Zn2+ + 2Mn2+ + 2H2PO4− + 4H2O → Mn2Zn (PO4)2·4H2O (s) + 4H+ |
Sludge | Al3+ + 6F− + 3Na+ → Na3AlF6 Al3+ + 6F− + 2K+ + Na+ → K2NaAlF6 |
4.1. Phosphoric Acid
4.2. Jernstedt Salt
4.3. Oxidizing Agents
4.4. Chromate Rinse
4.5. Environmental Terminology
5. The Evolution of Conversion Coatings
5.1. Conversion Coating [23]—Bender et al. (approx. 1970–1980)
- Water;
- Phosphoric Acid;
- A mixture of salts of zinc phosphate;
- Oxidizers.
5.2. Conversion Coatings [24]—Narayanan (approx. 1980–2005)
5.3. Conversion Coatings [12]—Milosev and Frankel (approx. 2000–2018)
5.4. Connecting The Nearly 50 Years of Progress in Conversion Coatings: Approximately 1970–2018
6. Magnesium
7. Tri-Cationic Phosphate Pretreatment Process
8. Zirconium Oxide Pretreatment Process
9. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
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Doerre, M.; Hibbitts, L.; Patrick, G.; Akafuah, N.K. Advances in Automotive Conversion Coatings during Pretreatment of the Body Structure: A Review. Coatings 2018, 8, 405. https://doi.org/10.3390/coatings8110405
Doerre M, Hibbitts L, Patrick G, Akafuah NK. Advances in Automotive Conversion Coatings during Pretreatment of the Body Structure: A Review. Coatings. 2018; 8(11):405. https://doi.org/10.3390/coatings8110405
Chicago/Turabian StyleDoerre, Mark, Larry Hibbitts, Gabriela Patrick, and Nelson K. Akafuah. 2018. "Advances in Automotive Conversion Coatings during Pretreatment of the Body Structure: A Review" Coatings 8, no. 11: 405. https://doi.org/10.3390/coatings8110405