Initial stages of multi-phased aluminium alloys anodizing by MAO: micro-arc conditions and electrochemical behaviour

Abstract

International audienceThe electrochemical behaviour of AA1050 and AA2214 alloys was studied in a KOH/silicate in order to investigate the first stages of the coating formation during MAO process (by SEM and electrochemical measurements). Before the sparking initiation, occurring around 300 V for both alloys, a thin inner layer of aluminium oxide grows by a classical anodizing mechanism, and induces a great enhancement of the electrochemical resistance. Then, the micro-arc regime beyond 300 V leads to the formation of a dense, thicker but cracked external aluminium oxide layer. Afterwards, from 400 V, a sharp increase of current density named ``current wall'' and due to an increase of oxide conductivity, leads to a significant oxygen release and the occurrence of large and energetic sparks. Microscopic analyses reveal that the presence of copper-rich intermetallic phases in the multi-phased alloy (AA2214) induces the incorporation of copper nanoparticles in the gamma-alumina layer formed by the sparking phenomenon. These copper particles increase the reaction of water oxidation during the classical anodizing stage, and result in a delay of the sparking initiation during the galvanostatic anodizing and in a lower electrochemical resistance of the anodized layers

The effect of applied voltages on the structure, apatite-inducing ability and antibacterial ability of micro arc oxidation coating formed on titanium surface

“…With the increase of the applied voltage, the average micropore size on the MAO coating increased, while the micropore intensity on the MAO coating decreased ( Fig. 1 ) [ 26 , 27 ]. Meanwhile, the thickness of the MAO coatings continuously increased ( Fig.…”

Discharge Characteristic of Micro-Arc Oxidation on Aluminum Alloy under the Changing Electrolyte Temperature

“…Immediately after the dielectric breakdown occurred on the barrier layer, fine and short-lived sparks were observed, which moved and were homogeneously distributed on the anode surface. Then, the MAO process was considered in the micro-arc oxidation regime, which was simultaneously controlled by the ionic and electric currents, instead of the traditional anodizing regime like the first stage [15].…”

In situ spectroelectrochemical ellipsometry using super continuum white laser: Study of the anodization of magnesium alloy

“…We have previously monitored, by in situ SE, the wet anodization of AZ91D Mg alloy in 3 M KOH medium 12 in order to enhance the understanding of the subsequent sparking regime initiation of the plasma electrolytic oxidation surface treatment, [13][14][15][16][17] beyond other established literature. [18][19][20] In this former study only the low voltage range i.e.…”