The Influence of Potassium Hexafluorophosphate on the Morphology and Anticorrosive Properties of Conversion Coatings Formed on the AM50 Magnesium Alloy by Plasma Electrolytic Oxidation
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials and Coatings Preparation
2.2. Coatings Characterization
3. Results and Discussion
3.1. Plasma Electrolytic Oxidation Process
3.2. Thickness and Roughness of PEO Coatings
3.3. Corrosion Resistance of PEO Coatings
3.4. Morphological and Composition Characteristics of PEO Coatings
4. Conclusions
- The anticorrosive properties of the obtained coatings increase when the KPF6 concentration is increased to 2.5 g/L. The addition of larger amounts of KPF6 causes damage to the coating (a large increase in its roughness), probably due to the local formation of HF during the PEO process.
- The addition of KPF6 allows for better anticorrosive properties of the synthesized coating to be obtained, compared to a mixture of NaF and Na3PO4 with an equimolar content of fluorine and phosphorus.
- XPS measurements have shown that in coatings obtained in the presence of KPF6, as well as a mixture of NaF and Na3PO4 in the baths, the coating components derived from these additives are the same [MgF2 and Mg3(PO4)2]. Mg(PF6)2 was not present in the formed coatings, which is in contrast to the formation of Mg(BF4)2, when the silicate bath contained NaBF4 [46].
- The surface morphology of the PEO coatings produced in the KPF6-containing baths was more uniform and showed a sponge-like structure, in contrast to commonly reported crater-like structures. The sponge-like structure is similar to bone structure, and in combination with the presence of phosphates, it can increase the biocompatibility and the possibility of self-healing of this coating.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Al | Mn | Zn | Si | Fe | Cu | Ni | Mg |
---|---|---|---|---|---|---|---|
4.40–5.50 | min. 0.1 | max. 0.02 | max. 0.1 | max. 0.005 | max. 0.01 | 0.002 | balance |
Concentration of KPF6, g/L | Time to Reach Critical Voltage, min | Final Voltage, V |
---|---|---|
0.0 | 8.8 | 455 |
0.5 | 8.3 | 461 |
1.0 | 8.0 | 465 |
1.5 | 7.0 | 466 |
2.0 | 5.9 | 467 |
2.5 | 5.0 | 470 |
3.0 | 9.5 | 453 |
4.0 | - | 346 |
Concentration of KPF6, g/L | ECORR, V | jCORR, µA/cm2 | RP,kΩ∙cm2 |
---|---|---|---|
0.0 | −1.630 | 33.01 | 1.04 |
0.5 | −1.606 | 23.11 | 1.46 |
1.0 | −1.596 | 9.35 | 3.81 |
1.5 | −1.595 | 4.55 | 7.88 |
2.0 | −1.593 | 3.91 | 9.41 |
2.5 | −1.587 | 1.76 | 21.09 |
3.0 | −1.555 | 2.94 | 13.09 |
4.0 | −1.453 | 5.94 | 7.25 |
Concen. of KPF6, g/L | RS, Ω·cm2 | QOL, µFn/cm2 | nOL | ROL, Ω·cm2 | QIL, µFn/cm2 | nIL | RIL, kΩ·cm2 | Cdl, mF/cm2 | Rct, kΩ·cm2 | L kH·cm2 | RL kΩ·cm2 | Rtotal kΩ·cm2 | Χ2 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
0 | 155.5 | - | - | - | 5.713 | 0.877 | 3.296 | 0.469 | 1.533 | 25.5 | 0.75 | 3.80 | 5.12 × 10−4 |
0.5 | 146.8 | 1.032 | 0.905 | 37.9 | 4.189 | 0.917 | 3.476 | 0.516 | 1.927 | 53.8 | 3.87 | 4.80 | 2.88 × 10−4 |
1.0 | 147.9 | 0.784 | 0.913 | 42.5 | 3.347 | 0.926 | 4.971 | 0.348 | 2.928 | 24.2 | 18.64 | 7.54 | 4.25 × 10−4 |
1.5 | 135.9 | 0.814 | 0.858 | 79.1 | 2.051 | 0.922 | 5.728 | 0.178 | 4.361 | 200.7 | 21.60 | 9.44 | 3.31 × 10−4 |
2.0 | 153.9 | 0.803 | 0.873 | 74.2 | 1.974 | 0.922 | 6.222 | 0.180 | 4.550 | 233.1 | 15.92 | 9.84 | 2.74 × 10−4 |
2.5 | 141.1 | 0.392 | 0.847 | 218.2 | 0.819 | 0.892 | 13.400 | 0.093 | 9.271 | 231.5 | 28.51 | 20.61 | 5.13 × 10−4 |
3.0 | 151.1 | 0.425 | 0.867 | 129.4 | 1.431 | 0.894 | 7.921 | 0.189 | 7.069 | 293.1 | 16.92 | 13.04 | 3.30 × 10−4 |
4.0 | 144.9 | 1.115 | 0.896 | 64.9 | 2.818 | 0.903 | 5.975 | 0.345 | 5.035 | - | - | 11.07 | 6.37 × 10−4 |
Sample | Composition of Electrolyte, g/L | Molar Contents of Fluorine, mM/L | Molar Contents of Phosphorus, mM/L |
---|---|---|---|
Base | Na2SiO3·5H2O: 10 | - | - |
NaOH: 4 | |||
2.5PF6 | Na2SiO3·5H2O: 10 | 81.5 | 13.6 |
NaOH: 4 | |||
KPF6: 2.5 | |||
FPO4 | Na2SiO3·5H2O: 10 | 81.5 | 13.6 |
NaOH: 4 | |||
NaF: 3.42 | |||
Na3PO4·12H2O: 5.17 |
Sample | ECORR, V | jCORR, µA/cm2 | RP,kΩ∙cm2 |
---|---|---|---|
Uncoated AM50 | −1.607 | 140.10 | 0.22 |
Base | −1.630 | 33.01 | 1.04 |
2.5PF6 | −1.587 | 1.76 | 21.09 |
FPO4 | −1.501 | 2.75 | 13.41 |
Sample | RS, Ω·cm2 | QOL, µFn/cm2 | nOL | ROL, Ω·cm2 | QIL, µFn/cm2 | nIL | RIL, kΩ·cm2 | Cdl, mF/cm2 | Rct, kΩ·cm2 | L kH·cm2 | RL kΩ·cm2 | Rtotal kΩ·cm2 | Χ2 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Base | 155.5 | - | - | - | 5.713 | 0.877 | 3.296 | 0.469 | 1.533 | 25.5 | 0.75 | 3.80 | 5.12 × 10−4 |
2.5PF6 | 141.1 | 0.392 | 0.847 | 218.2 | 0.819 | 0.892 | 13.400 | 0.093 | 9.271 | 231.5 | 28.51 | 20.61 | 5.13 × 10−4 |
FPO4 | 130.6 | 0.828 | 0.890 | 63.7 | 2.411 | 0.910 | 10.270 | 0.016 | 5.271 | - | - | 15.60 | 5.73 × 10−4 |
Sample | RS,Ω·cm2 | QC,µFn/cm2 | nC | RC,kΩ·cm2 | Cdl,mF/cm2 | Rct, kΩ·cm2 | L kH·cm2 | RL kΩ·cm2 | Rtotal kΩ·cm2 | Χ2 | |||
Uncoated AM50 | 122.9 | 0.302 | 0.873 | 0.073 | 7.627 | 0.029 | 1.53 | 0.153 | 0.061 | 2.50 × 10−4 |
Sample | Layer | Elements Content, at.% | |||||
---|---|---|---|---|---|---|---|
Mg | O | Si | Al | F | P | ||
Base | outer | 49.1 | 37.3 | 11.2 | 2.4 | - | - |
inner | 53.8 | 37.4 | 6.4 | 2.5 | - | - | |
2.5PF6 | outer | 39.6 | 43.0 | 10.1 | 3.7 | 2.6 | 1.1 |
inner | 39.6 | 40.5 | 9.1 | 3.3 | 6.3 | 1.1 | |
FPO4 | outer | 45.0 | 41.3 | 7.6 | 3.1 | 1.7 | 1.4 |
inner | 38.9 | 42.8 | 7.4 | 3.7 | 5.2 | 1.9 |
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Florczak, Ł.; Kościelniak, B.; Kramek, A.; Sobkowiak, A. The Influence of Potassium Hexafluorophosphate on the Morphology and Anticorrosive Properties of Conversion Coatings Formed on the AM50 Magnesium Alloy by Plasma Electrolytic Oxidation. Materials 2023, 16, 7573. https://doi.org/10.3390/ma16247573
Florczak Ł, Kościelniak B, Kramek A, Sobkowiak A. The Influence of Potassium Hexafluorophosphate on the Morphology and Anticorrosive Properties of Conversion Coatings Formed on the AM50 Magnesium Alloy by Plasma Electrolytic Oxidation. Materials. 2023; 16(24):7573. https://doi.org/10.3390/ma16247573
Chicago/Turabian StyleFlorczak, Łukasz, Barbara Kościelniak, Agnieszka Kramek, and Andrzej Sobkowiak. 2023. "The Influence of Potassium Hexafluorophosphate on the Morphology and Anticorrosive Properties of Conversion Coatings Formed on the AM50 Magnesium Alloy by Plasma Electrolytic Oxidation" Materials 16, no. 24: 7573. https://doi.org/10.3390/ma16247573
APA StyleFlorczak, Ł., Kościelniak, B., Kramek, A., & Sobkowiak, A. (2023). The Influence of Potassium Hexafluorophosphate on the Morphology and Anticorrosive Properties of Conversion Coatings Formed on the AM50 Magnesium Alloy by Plasma Electrolytic Oxidation. Materials, 16(24), 7573. https://doi.org/10.3390/ma16247573