Effect of alcohol addition on the structure and corrosion resistance of plasma electrolytic oxidation films formed on AZ31B magnesium alloy

Abstract

Alcohol used as an additive could act not only as a leveler for the formation of compact film but also as an enhancer for film qualities, such as corrosion resistance and withstand voltage.

Optimization of Surface Properties of Plasma Electrolytic Oxidation Coating by Organic Additives: A Review

“…Similar findings were reported during PEO treatment of Mg alloys using other organic additives, such as starch [39,40], benzotriazole (BTA) [41], sodium oxalate (SO x ) [42], and phytic acid [43]. However, the effect of organic additives on the voltage response during PEO was still controversial [44][45][46]. For instance, Zhu et al [44] reported that the breakdown and final voltages during PEO treatment of AZ31B Mg alloy in electrolytes containing 10 g/L ethylene glycol (EG) and polyethylene glycol (PEG) as organic additives were almost identical to the counterparts obtained in electrolytes without organic additives.…”

“…Sun and co-workers [45] also reported that only minor changes in the voltage-time curves of PEO processes conducted in silicate electrolytes without or with an addition of 10 g/L of either halloysite nanotubes (HNT) or BTloaded HNT. According to Asoh et al [46], the PEO treatment of AZ31B Mg alloy using a phosphate electrolyte (0.25 M Na 3 PO 4 ) containing 5 vol.% EtOH as an organic additive had no obvious increase in voltage after reaching the value of breakdown voltage (Figure 1a), suggesting that ethanol was not desirable for coating formation presumably due to its somewhat low pH (12.65) and weak base compared with that comprising only Na 3 PO 4 (12.73). This result indicated that ethanol could suppress the dissociation of the electrolytes during PEO.…”

“…Voltage-time curves of AZ31 Mg alloy coated via plasma electrolytic oxidation (PEO) in electrolytes without and with organic additives, such as ethanol (EtOH), ethylene glycol (EG), and glycerol (GLY). [46] (b) Voltage-time curves of 6061 Al alloy coated in the electrolytes without and with NaBz. Reprinted from permission from [47].…”

“…To sum up, the organic additives could affect the characteristics of the PEO process by increasing the voltage. However, controversial results can be found in the literature that are ascribed to differences in the pH, conductivity, concentration, composition, and viscosity of the electrolytes, as well as electrical parameters, used during PEO [1,[44][45][46].…”

Forming Hard Anodic Films on Aluminum by Anodization in Oxalic Acid and Alcohol

“…In addition to aluminum, other studies have considered how adding alcohol can improve the film formation process and film properties of magnesium and its alloys. [32][33][34][35] Therefore, further research is needed to clarify the role of alcohol in the electrolyte during anodization.…”