Evolution of active species and discharge sparks in Na2SiO3 electrolyte during PEO process

For the plasma electrolytic oxidation (PEO) of Mg alloy in Na2SiO3 electrolyte, optical emission spectroscopy (OES) was adopted to identify the active plasma species at the four stages and the evolution of the discharge sparks in the PEO process was analyzed. At the conventional anodic oxidation stage the emitting-light was correlated to the “flaws” in the oxide films. At the transition stage the active species were O2 and H2O. At the transition stage, the collapse and ionization of the bubble layer happened. At the plasma discharge stage, the active plasma species transited and emitted light. The main active plasma species of the micro-discharges were Na, K, Mg, Hα, O2+ and OH. At the arc discharge stage, the energy was not uniform and the discharge was uneven, the light intensity increased sharply, O+ and O were excited.

► The emitting-light mechanisms were different at different stages.
► At conventional anodizing stage the emitting-light correlated to the “flaws”.
► At transition stage the active species were mainly O2 and H2O.
► At discharge stage the active plasma species transited and emitted light.
► The active plasma species were Na, K, Mg, Hα, O2+ and OH.
► Active plasma species influence the appearance of the sparks significantly.