Abstract
Impact of applied current density during the plasma electrolytic oxidation (PEO) process on corrosion resistance of AZ31 magnesium alloy was studied. The PEO coatings were prepared using four different current densities with values of 0.025 A/cm2, 0.05 A/cm2, 0.1 A/cm2 and 0.15 A/cm2 in electrolyte consisting of 10 g/l Na 3PO4.12H2O and 1 g/l KOH. Morphology and chemical composition of the coatings was examined using the scanning electron microscopy and EDS analysis respectively. Electrochemical characteristics of ground and coated samples were measured by means of electrochemical impedance spectroscopy (EIS) in 0.1M NaCl solution. Obtained data in form of Nyquist diagrams were analysed by equivalent circuit method. Results of experiments showed that value of applied current density had significant effect on protective performance of the PEO coatings prepared on AZ31 magnesium alloy surface.
Highlights
The main reason, which impedes the wider usage of magnesium alloys in technical applications is their high reactivity and the resulting low corrosion resistance in most of the practical environments
It can be assumed that applied current density does not have marginal impact on the chemical composition of plasma electrolytic oxidation (PEO) coatings
It is clear that PEO coatings are consisting of elements present in the electrolyte (P, Na, O) and elements, which came from Mg substrate (Mg, Al)
Summary
The main reason, which impedes the wider usage of magnesium alloys in technical applications is their high reactivity and the resulting low corrosion resistance in most of the practical environments. A perspective technique called plasma electrolytic oxidation is getting a lot of scientific attention as it is a method for preparation of protective coatings on Mg alloy in a non-expensive way In this process, unlike conventional anodic oxidation, much higher voltages are reached/applied and the obtained coatings have a ceramic-like character. The advantage of the PEO is that there is a variety of environmentally acceptable electrolytes and secondly it is possible to use both DC and AC power sources The preparation of such layers is relatively complicated in terms of the obtained coating properties as there is a number of variables in the PEO process such as the value of applied current/voltage, time of preparation, optimal composition of the electrolyte and the applied frequency in the case of alternating power sources. This paper is focused on the effect of applied current density on the morphology and chemical composition of prepared layers and on corrosion protective function in an aggressive chloride containing environment
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