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. 2023 Mar 14;16(6):2327.
doi: 10.3390/ma16062327.

Effect of Plasma Argon Pretreatment on the Surface Properties of AZ31 Magnesium Alloy

Cecilia Montero  1 , Cristián Gino Ramírez  1 , Lisa Muñoz  2 , Mamié Sancy  3 , Manuel Azócar  4 , Marcos Flores  5 , Alfredo Artigas  1 , José H Zagal  4 , Xiaorong Zhou  6 , Alberto Monsalve  1 , Maritza Páez  4
Affiliations

Effect of Plasma Argon Pretreatment on the Surface Properties of AZ31 Magnesium Alloy

Cecilia Montero et al. Materials (Basel). .

Abstract

Climate change has evidenced the need to reduce carbon dioxide emissions into the atmosphere, and so for transport applications, lighter weight alloys have been studied, such as magnesium alloys. However, they are susceptible to corrosion; therefore, surface treatments have been extensively studied. In this work, the influence of argon plasma pretreatment on the surface properties of an AZ31 magnesium alloy focus on the enhancement of the reactivity of the surface, which was examined by surface analysis techniques, electrochemical techniques, and gravimetric measurements. The samples were polished and exposed to argon plasma for two minutes in order to activate the surface. Contact angle measurements revealed higher surface energy after applying the pretreatment, and atomic force microscopy showed a roughness increase, while X-Ray photoelectron spectroscopy showed a chemical change on the surface, where after pretreatment the oxygen species increased. Electrochemical measurements showed that surface pretreatment does not affect the corrosion mechanism of the alloy, while electrochemical impedance spectroscopy reveals an increase in the original thickness of the surface film. This increase is likely associated with the high reactivity that the plasma pretreatment confers to the surface of the AZ31 alloy, affecting the extent of oxide formation and, consequently, the increase in its protection capacity. The weight loss measurements support the effect of the plasma pretreatment on the oxide thickness since the corrosion rate of the pretreated AZ31 specimens was lower than that of those that did not receive the surface pretreatment.

Keywords: AZ31 alloy; argon plasma; corrosion; magnesium alloy; surface treatment.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Figure 1
Figure 1
AFM images of AZ31 alloy (a) before and (b) after 2 min of pretreatment.
Figure 2
Figure 2
(a) Survey spectra for AZ samples, (b) survey spectra for AZ + Ar-P samples, (c) high-resolution XPS of O 1s spectra for AZ samples, (d) high-resolution XPS of O 1s spectra for AZ + Ar-P samples, (e) high-resolution XPS of Mg 2p spectra for AZ samples, and (f) high-resolution XPS of Mg 2p spectra for AZ + Ar-P samples.
Figure 3
Figure 3
Open circuit potential of AZ31 surfaces (before and after pretreatment) as a function of immersion time in Na2SO4 0.1 M. (■) AZ and (●) AZ + Ar-P samples.
Figure 4
Figure 4
Potentiodynamic polarization curves of AZ31 alloy immersed in 0.1 M Na2SO4, (a) AZ surface, (b) AZ + Ar-P surface. All potentials refer to MSE electrode.
Figure 5
Figure 5
Evolution of anodic current density at +50 mV vs. EOC, in the pseudo-passive range for AZ and AZ + Ar-P samples.
Figure 6
Figure 6
Nyquist diagrams evolution of (a) AZ and (b) AZ + Ar-P samples in 0.1 M of Na2SO4, (○,◊) 3 h, (○,◊) 24 h, (○,◊) 72 h, (○,◊) 120 h, (○,◊) 168 h, and (○,◊) 240 h.
Figure 7
Figure 7
(a) A representative Cole-Cole plot of AZ samples after 3 h of immersion, as an example for the determination of Cox; (b) Evolution of complex capacitance (Cox) for the differently pretreated AZ31 alloy immersed in 0.1 M of Na2SO4.
Figure 8
Figure 8
Evolution of the layer thickness (δox) for the differently pretreated AZ31 alloy immersed in 0.1 M of Na2SO4.
Figure 9
Figure 9
Proposed equivalent circuit and physical model representing the impedance responses of samples AZ and AZ + Ar-P after exposure in 0.1 M Na2SO4 solution.
Figure 10
Figure 10
Corrosion rate vs. immersion time determined by weight loss experiments.
Figure 11
Figure 11
Schematic illustration of the cross-section view of the oxide/hydroxide film formed on the AZ31 alloy surfaces, before and after the pretreatment.
See this image and copyright information in PMC

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