Abstract
Plasma Electrolytic Oxidation (PEO) is a surface treatment, similar to anodizing, that produces thick oxide films on the surface of metals. In the present work, PEO coatings were obtained on zinc-aluminized (ZA) carbon steel using a solution containing sodium silicate and potassium hydroxide as electrolyte, and working with high current densities and short treatment times in Direct Current (DC) mode. The thickness of the coating, as well as the surface morphology, were strongly influenced by the process parameters, with different dissolution grades of the ZA layer depending on the current density and treatment time. A compromise between thickness and porosity of the coating was found with low current density/long treatment time or high current density/short treatment time. The PEO layer was mainly composed of aluminum oxides and silicon compounds. The corrosion resistance increased remarkably in the samples with the PEO coating. These PEO coated samples are suitable for sealing treatments that further increase their corrosion properties or will be also an ideal substrate for commercial painting, assuring improved mechanical adhesion and protection even in the presence of damages.
Highlights
Steel is often employed in engineering applications due to its good mechanical properties, good machinability, and low cost
The surfaces and the cross sections of the samples were analyzed at scanning electron microscopy (SEM) and the results are presented in Figure 1 and Figure 2
The surface analysis showed the typical morphology of Plasma electrolytic oxidation (PEO) coatings with the presence of nodular structures and with the evidence of a lot of pores and micro-cracks of different dimensions, coming from the discharge phenomena
Summary
Steel is often employed in engineering applications due to its good mechanical properties, good machinability, and low cost. Corrosion problems often affect carbon steels and the substitution with stainless steels is often not possible due to their higher cost. Plasma electrolytic oxidation (PEO) of metals is an electrochemical process that produces an oxide ceramic layer on the surface. PEO is similar to traditional anodic oxidation but works with higher voltages and current densities. The high voltage (that has to be above the dielectric breakdown potential of the oxide layer) forms anodic micro-discharges that moving randomly over the processed surface produce the growth of the coating [1,2]. The corrosion and wear properties depend on current density, voltage, treatment time, and electrolyte composition employed during PEO treatment [3]. The process has been widely studied on aluminum and magnesium alloys and many results are reported in the literature, especially about the increased corrosion and wear performances of light alloys after
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