Design of Scanning Micro-Arc Oxidation Forming Ceramic Coatings on 2024 Aluminium Alloy

Abstract

Micro-arc oxidation (MAO), also called plasma electrolytic oxidation (PEO), anodic spark deposition (ASD), or micro-arc discharge oxidizing (MDO), is an effective surface treatment technique which come from anodic oxidation technology. Via increasing the anodic voltage breaking through faraday area to a high stage accompanied by micro-arc discharge phenomenon, It indicated the ceramic coatings thickness increase along with the scanning times increase, while the thickness increment reduces. The phase composition, morphology and element distribution was studied by X-ray diffraction, scanning electron microscopy and line scanning. The morphology of the ceramic coatings shows it divided into compact layer and loose layer. And it composes of α-Al2O3 and γ-Al2O3.

The influence of phase gradient within the micro arc oxidation (MAO) coatings on mechanical and tribological behaviors

“…Further, the mechanism explained above clearly supports the reported phenomenon that the -Al 2 O 3 content increases with increasing MAO treatment time. [30] If the above mechanism is true, then the central column of the discharge channel as it appear on the coating surface at the centre of the pancake should have its trace throughout the coating thickness. However, as can be seen from the coating cross section shown in Fig.1, the dense coating structure does not leave any such trace indicating the history of discharge channel's presence.…”

“…Further, Number of researchers has explicitly pointed out that the relative proportion of -and -Al 2 O 3 phases in the coating depends upon the MAO processing conditions, substrate and electrolyte compositions. [7][8][9][29][30] However, there is no single study carried out so far to establish the quantitative inter-relationship between microhardness, proportion of -and -Al 2 O 3 phases across the coating thickness vis-à-vis the tribological performance of the MAO coating. In addition, since -Al 2 O 3 is a metastable phase, which in general is not obtained through bulk ceramic processing, its mechanical properties such as hardness and modulus are not well known.…”

A study of the phase-structural engineering possibilities of coatings on D16 alloy during micro-arc oxidation in electrolytes of different types

“…Towards the outer surface of the modified layer, the amount of low-temperature modifications of aluminum oxide increases. It is assumed that the latter is associated with the conditions of electrolysis at the initial stages of anode-spark treatment, since the temperature of the metal sections adjacent to the discharge craters is only 400-500 °C [40].…”

The influence of the conditions of microplasma processing (microarc oxidation in anode­cathode regime) of aluminum alloys on their phase composition

“…As a rule, the phase composition of coatings varies throughout the thickness of the MAO layer [28]. With MAO of aluminum-based alloys, it has been found that high-temperature modifications of aluminum oxide are in its internal layers.…”