Dry Sliding Behavior of an Aluminum Alloy after Innovative Hard Anodizing Treatments
Abstract
:1. Introduction
2. Materials and Methods
2.1. Microstructure and Mechanical Properties
2.2. Wear Tests
3. Results
3.1. Microstructure and Mechanical Properties
3.2. Wear Tests
4. Discussion
5. Conclusions
- All AAO layers show the typical microstructure of anodic aluminum oxides with very fine-scale and Ag-rich dendrites that appear only at the coating/aluminum substrate interfaces of G- and GP-treated surfaces. In agreement with the phase compositions analysis, all AAO layers exhibit amorphous structures with some boehmite deriving from the sealing in hot deionized water;
- The HA treatment generates the hardest anodic aluminum oxides, while GP produces the softest. The examination of scratches reveals two main failure modes: wedge spallation for the coatings 25 μm thick and conformal cracking for those 50 and 100 μm thick. Finally, all anodic aluminum oxides with a thickness of 25 μm display the lowest adhesion strength, whereas the GP-treated surfaces show the highest one;
- The friction coefficient variations with sliding distance are influenced by changes in wear morphology and the extent of oxidation. The GP-treated surfaces with a thickness of 50 μm exhibit the lowest friction coefficients and wear rates. Their improved wear resistance may be related to the increased adhesion strength compared to those of the other anodized surfaces;
- In any case, a well-adherent tribofilm consisting of iron oxide is observed on the wear tracks as a result of tribochemical reaction and metal transfer between the mating materials. During sliding, its detachment leads to delamination of the underlying anodic aluminum oxides and to the subsequent abrasion of the aluminum substrate. Despite the presence of abraded surfaces, the best tribological performance of G- and GP-treated surfaces may be related to the existence of a thin Ag-rich film at the coating/aluminum substrate interfaces.
Author Contributions
Funding
Acknowledgments
Data Availability Statement
Conflicts of Interest
References
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Types of Anodizing Treatment | Designation | Thicknesses of AAO Layers (μm) | Samples |
---|---|---|---|
Hard anodizing treatment | HA | 25 | HA_25 |
50 | HA_50 | ||
100 | HA_100 | ||
Golden hard anodizing treatment | G | 25 | G_25 |
50 | G_50 | ||
100 | G_100 | ||
Golden hard anodizing treatment_plus | GP | 25 | GP_25 |
50 | GP_50 | ||
100 | GP_100 |
25 | 50 | 100 | |||||||
---|---|---|---|---|---|---|---|---|---|
Ra (μm) | Rz (μm) | HV0.01 | Ra (μm) | Rz (μm) | HV0.01 | Ra (μm) | Rz (μm) | HV0.01 | |
HA | 0.18 ± 0.02 | 2.09 ± 0.40 | 450 ± 20 | 0.22 ± 0.02 | 1.98 ± 0.33 | 458 ± 10 | 0.17 ± 0.01 | 1.81 ± 0.27 | 438 ± 11 |
G | 0.19 ± 0.01 | 2.13 ± 0.37 | 427 ± 18 | 0.19 ± 0.05 | 2.06 ± 0.53 | 435 ± 12 | 0.17 ± 0.02 | 1.65 ± 0.13 | 398 ± 15 |
GP | 0.23 ± 0.02 | 2.16 ± 0.35 | 374 ± 31 | 0.21 ± 0.05 | 2.14 ± 0.53 | 412 ± 17 | 0.18 ± 0.05 | 2.09 ± 0.48 | 356 ± 30 |
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Soffritti, C.; Fortini, A.; Nastruzzi, A.; Sola, R.; Merlin, M.; Garagnani, G.L. Dry Sliding Behavior of an Aluminum Alloy after Innovative Hard Anodizing Treatments. Materials 2021, 14, 3281. https://doi.org/10.3390/ma14123281
Soffritti C, Fortini A, Nastruzzi A, Sola R, Merlin M, Garagnani GL. Dry Sliding Behavior of an Aluminum Alloy after Innovative Hard Anodizing Treatments. Materials. 2021; 14(12):3281. https://doi.org/10.3390/ma14123281
Chicago/Turabian StyleSoffritti, Chiara, Annalisa Fortini, Anna Nastruzzi, Ramona Sola, Mattia Merlin, and Gian Luca Garagnani. 2021. "Dry Sliding Behavior of an Aluminum Alloy after Innovative Hard Anodizing Treatments" Materials 14, no. 12: 3281. https://doi.org/10.3390/ma14123281