Characteristics of Oxide Layers on 2021 Al Alloys by Plasma Electrolytic Oxidation in Aluminate Fluorosilicate Electrolyte

Oxide layers were prepared on 2021 Al alloys substrate under a hybrid voltage of AC 200V (60Hz) combined with DC 260V value at room temperature within 5~60min by plasma electrolytic oxidation (PEO). An optimized aluminate-fluorosilicate solution was used as the electrolytes. The surface morphology, thickness and composition of layers on 2021 Al alloys within different reaction times were studied. The results showed that it is possible to generate good property oxide layers on 2021 Al alloys in aluminate-fluorosilicate electrolytes. Analysis show that the double-layer structure oxide layers consist of different states of Al2O3 such as α-Al2O3 and γ-Al2O3. For short treatment times, the formation process of oxide layers follows a linear kinetics, while for longer times the formation process slows down and becomes a steady stage. During the PEO processes, the average size of the discharged channels increase gradually as the treatment time increased.