Effect of Process Parameters on the Corrosion Resistance Properties of PEO Coatings Produced on AZ31B Magnesium Alloy
Bibliographic record
Abstract
The automotive sector is particularly interested in magnesium alloys, which can decrease the weight of the vehicle leading to improved fuel efficiency and decreased emissions. However, poor corrosion resistance, especially in solutions containing chlorides, is a major limitation for its widespread exploitation in exposed automotive applications. Plasma electrolytic oxidation (PEO) coatings have been shown as a promising technology to improve the corrosion resistance of magnesium alloys 1 . The properties of PEO synthesized coatings have been shown to significantly dependent on the process parameters employed to produce them 2,3 . Understanding the influence of process parameters on the overall corrosion resistance of AZ31 is essential if PEO technology is to be used in an industrial application. The present investigation examines the effect of processing time, current density, and electrolyte temperature on structural morphology of PEO coatings made on AZ31B linked to their corrosion resistance. PEO coatings were produced using a sodium silicate basic electrolyte using current densities ranging between 10 mA/cm 2 and 20 mA/cm 2 . The temperature of the electrolyte was varied between 10-40ºC, while the processing time was varied between 15 and 30 minutes. The overall corrosion rate of PEO-coated samples was evaluated using mass loss testing and electrochemical impedance spectroscopy (EIS), while the composition and morphology of the PEO coatings were analyzed using a combination of x-ray diffraction (XRD), electron microscopy, and white light profilometry. The phase composition of the synthesized PEO coatings was analysed using XRD, see Figure 1. Spectra indicated that the PEO coating comprised two main phases, namely magnesium oxide (MgO) and forsterite (Mg 2 SiO 4 ). The ratio between magnesium oxide and magnesium silicate was estimated via the reference intensity ratio (RIR) analysis. The mass ratio (MgO/Mg 2 SiO 4 ) for PEO coatings made on AZ31B decreased from 0.63 (10 mA/cm 2 ) to 0.11 (20 mA/cm 2 ). The observed increase in the weight fraction of forsterite when higher current densities were is related to polymerization of silicate ions during the deposition process. It has been previously reported that the extremely high energy generated by the plasma discharges promote polymerization of the silicate 4 . Increasingly favorable polymerization resulted in greater incorporation of silicates into the coating, ultimately leading to higher weight fraction of forsterite and lower weight fraction of magnesium oxide. The corrosion rates of the two coated specimens (10 mA/cm 2 and 20 mA/cm 2 ) in addition to the bare metal AZ31 substrate were measured by 5-day mass loss testing in a 0.086M NaCl solution, see Figure 2. Both PEO coatings exhibited significantly improved corrosion resistance properties compared to as-received AZ31. The corrosion rates of coatings produced using an applied current density of 10 mA/cm 2 were significantly lower than those of coating produced using a current density of 20 mA/cm 2 . The current research effort is focusing on providing explanations for observed differences in corrosion resistance properties of PEO produced when applying different current density values. The effect of changes in processing time and electrolyte temperature is also under investigation. References: T. Chen, W. Xue, Y. Li, X. Liu, J. Du, Mater. Chem. Phys. 144, 3 (2014): p. 462. H. Chen, G. Lv, G. Zhang, H. Pang, X. Wang, H. Lee, S. Yang, Surf. Coat. Technol . 205 (2010): p. S32. A. Ghasemi, N.Scharnagl, C. Blawert, W. Dietzel, K. U. Kainer, Surf. Eng. 26, 5 (2010): p. 321. H. Guo, M. An, H. Huo, S. Xu, L. Wu, Appl. Surf. Sci. 252, (2006): p. 7911. Figure 1
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".