Exploring the effect of alkaline silicate solution composition on the ac/dc spark anodization of Al–Cu Alloys

Plasma Electrolytic Oxidation of Valve Metals

“…Obviously, the milder mullite better fills pores in the oxide layer than harder oxides do. Somewhat similar results were obtained by another research group [7] for another Al alloy (2219) and also demonstrated that higher silicate contents in silicate-alkaline electrolytes increase the corrosion resistance of PEO coatings.…”

“…Although PEO layers have a relatively high porosity [2], they can effectively protect the base metal against corrosion because the pores formed by a discharge can subsequently "heal" by molten oxides due to high local temperatures in the vicinity of plasma discharge channels [3] and are therefore impermeable to corrosion media. The improved corrosion stability of PEO-treated metals as compared to bare metals has been reported for aluminum [4][5][6][7][8] and magnesium alloys (see, for instance, [9,10]). Both direct and alternating current can be used for PEO.…”

“…The production of oxide layers by PEO was most often studied for aluminum and its alloys (for example, in [5][6][7][8], [12][13][14][15][16][17]), magnesium and its alloys ( [9,10] and others), titanium and its alloys (for example, in [18][19]). Studies of PEO on other metals (zirconium [20], zirconium alloys [21] and steel [22]) are scarce.…”

“…The most frequently used electrolytes for the PEO processing of aluminum and aluminum alloys are aluminate [23,24], phosphate [24,25] and, most often, alkaline silicate solutions (for example, [7,11]). Magnesium and its alloys are normally PEO processed in alkaline phosphate [26][27][28] or alkaline silicate electrolytes [10,29,30] often containing fluorides [27][28][29][30].…”

An investigation of the characteristics of Al2O3/TiO2 PEO nanocomposite coating

“…For the coatings, the semicircle at high frequencies could be attributed to the coating structure [46]. It is well known that the medium frequency semicircle and the inductive loop in all EIS curves represent the corrosion process [46,47] and the adsorption/desorption of aluminum ions [44] or electrochemical active species [47,48] on the surface, respectively. Although, the low-frequency capacitive loop appeared after a mediumfrequency inductive loop may misinterpret as the presence of an oxide barrier layer, Brett [49] has proved this could not be a valid assumption.…”