Luminescence during anodization of magnesium alloy AZ31

In this paper, we have presented our recent investigation of luminescence during anodization of magnesium alloy AZ31 at 100 mA/cm2 in water solution containing 4 g/L Na2SiO3·5H2O + 4 g/L KOH. Spectral characterization of anodic luminescence (galvanoluminescence GL) showed that there are wide GL bands in the range from 375 nm to 875 nm, with three spectral peaks around 430 nm, 600 nm and 780 nm. As the anodization voltage approaches the breakdown voltage, a large number of microdischarges appear superimposed on the GL. The microdischarges characteristics above breakdown (so-called plasma electrolytic oxidation PEO) were studied using real-time imaging. The spatial density of microdischarges is the highest in the early stage of PEO, while the percentage of oxide coating area covered by active discharge sites has maximum after about 120 s from the beginning of PEO and then stays almost constant. The elements present in PEO microdischares were identified using optical emission spectroscopy technique.

► Anodization of AZ31 magnesium alloy in water solution Na2SiO3·5H2O/KOH.
► Spectral characterization of anodic luminescence showed wide GL bands in the range from 375 nm to 875 nm.
► Analysis of PEO emission spectra reveals spectral lines both from the substrate and from the electrolyte.
► Spatial density of microdischarges is the highest in the early stage of PEO process.