Experimental modeling and multi-objective optimization of Micro Arc Oxidation process parameters of aluminium alloy joints

Abstract

Abstract Micro Arc Oxidation (MAO) is an advanced electrochemical surface-processing technique capable of producing hard, dense and adherent ceramic coatings on aluminium alloys, exhibiting superior wear and corrosion properties than traditional anodizing. This research project produced MAO coating on CMT-welded AA6082-T6 aluminium alloy joints and the effect of current density, the oxidation time and the distance in between the electrodes on the coating characteristics were systematically studied using Response Surface Methodology (RSM) based parametric mathematical modelling (PMM). The PMMs generated very accurate predictions of the porosity and hardness of the aluminium alloy joints with an error margin less than 2% and 99% confidence level. Detailed characterization was done to test model predictions. The analysis of the SEM showed how the crater-type discharge channels, micropores, and the patterns of molten-oxide resolidification changed, and optimal parameters resulted in homogeneous and compact structures. The thickness variation between about 58 μm to 110 μm with current density was established by cross-sectional SEM. The XRD patterns showed that, γ-Al 2 O 3 , θ-Al 2 O 3 and α- Al 2 O 3 phases existed and were transformed with α- Al 2 O 3 enrichment at moderate current density (0.19 A/cm 2 ) that increased peak hardness. High density of current (0.25 A/cm 2 ) inhibited the formation of α- Al 2 O 3 and high porosity. Optimized MAO conditions of 0.19 A/cm 2 current density, 20 min oxidation time, and 6-cm spacing between electrodes gave minimum porosity (2.07 vol) and maximum hardness (1459.36 HV). The coatings also exhibited positive wear behaviour, and decreased friction coefficient was observed due to high density of ceramic phase. The overall results of modelling and characterization offer a solid system of application of MAO coating on welded aluminium structures in the high-performance engineering applications.