Characterization of coatings formed on AZX magnesium alloys by plasma electrolytic oxidation

Abstract

Abstract. Plasma Electrolytic Oxidation (PEO) is an electrochemical anodization process which involves the application of a high voltage to create intense plasma on a metal surface to form a ceramic type of oxide. The resulted coating exhibits high wear resistance and good corrosion barrier which are suitable to enhance the performance of biodegradable Mg alloys. In this work, the role of alloying element Ca in modifying the characteristics of PEO layer formed on AZ61 series magnesium alloys was investigated. PEO treatment was conducted on AZ61, AZX611, and AZX612 alloys in 0.5 M Na3PO4 solution at a constant current of 200 A/m 2 at 25°C for 8 min. The resulted coatings were characterized by field emission-scanning electron microscope (FESEM), X-ray diffraction spectroscopy (XRD), and X-ray fluorescence spectroscopy (XRF), as well as hardness test. The presence of alloying element Ca in the AZ61 alloys accelerated the PEO coatings formation without altering the coating properties significantly. The coating formed on AZX specimen was slightly thicker (~14-17 μm) than that of formed onthe AZ specimens (~13 μm). Longer exposure time to plasma discharge was the reason for faster thickening of the coating layer on AZX specimen. XRD detected a similar crystalline oxide phase of Mg3(PO4)2 in the oxide formed on all of the specimens. Zn was highly incorporated in the coatingswith a concentration in the range 24-30 wt%, as analyzed by XRF. Zn compound might exist in amorphous phases. The microhardness test on the coatings revealed similar average hardness ~124 HVon all of thespecimens.

Degradation Behavior of Coatings Formed by the Plasma Electrolytic Oxidation Technique on AZ61 Magnesium Alloys Containing 0, 1 and 2 wt% Ca

“…The anodization curves reported earlier (Anawati & Gumelar, 2017) indicated that for an identical anodization time there was a tendency for the coating thickness to increase slightly in line with the Ca concentration in the alloys, owing to the extension of fine plasma life-time during anodization, but the increment was insignificant. Figure 1 shows the PEO coating appearance and the thickness formed on the AZ61, AZ61-1Ca and AZ61-2Ca specimens.…”

“…We have previously reported the characterization results of the PEO coatings formed on AZ61, AZ61-1Ca and AZ61-2Ca specimens (Anawati & Gumelar, 2017). The coatings had an uneven structure decorated with micrometer sized voids and cracks.…”