Overall micro-arc oxidation treatment for AZ31B–6061 magnesium–aluminium dissimilar metal connecting parts

Abstract

The magnesium-aluminium connecting parts are important application form for lightweight structural materials. But the conductive connect of magnesium and aluminium will cause serious galvanic corrosion problems. Therefore, the overall corrosion protective treatment is necessary. A ceramic coating was prepared via overall micro-arc oxidation to wrap the magnesium-aluminium connecting part integrally. The surface morphologies and compositions of the coatings were analysed by scanning electron microscopy and X-ray energy dispersive spectroscopy. The corrosion behaviour of the coatings was investigated with potentiodynamic polarisation tests in 3.5 wt-% NaCl solution. The growth process of ceramic coating on aluminium and magnesium surface was investigated, which showed the micro-arc oxidation reaction priority and the balanced growth process of ceramic coating under unbalanced micro-arc distribution. The results demonstrated that the overall micro-arc oxidation treatment improved the corrosion resistance and reduced the corrosion potential difference of each metal of magnesium-aluminium connecting part.

The Study on the Overall Plasma Electrolytic Oxidation for 6061–7075 Dissimilar Aluminum Alloy Welded Parts Based on the Dielectric Breakdown Theory

“…They consisted of Al, O, Si, and P. However, the dense basal layer on the welding area was made up of O and Al, as shown in Figure 8 d, and the main composition was inferred as Al 2 O 3 . The difference reflected that a time sequence or growth priority existed during the growth process of the overall ceramic coating: the dense basal layer formed first on the surface of base metal, and the porous layer then grew on the dense basal layer [ 15 , 20 , 21 ].…”

“…Accordingly, it would significantly reduce the service life of the dissimilar metal welded/connected parts. The overall micro arc oxidation could improve the corrosion resistance of each material as well as reduce the corrosion potential difference between different metals i [ 15 , 36 ]. Furthermore, the insulated integral ceramic coating isolated the 6061–7075 welded parts from corrosion media and broke the electronic circuit of corrosion, which meant the generation and extension of the corrosion were curbed effectively and it was the key technology to reduce the galvanic corrosion for lightweight alloys [ 15 ].…”

“… The sealed and insulated fixture for electrochemical test. ( a ) The schematic of three-electrode system; ( b ) the schematic of working electrode [ 15 ]. …”

Efficient Micro-Arc Oxidation Technology for As-Cast AZ80 Magnesium Alloy

“…The working electrode was set in a custom-made Teflon holder, which had a circular 1 cm window exposed to the electrolyte solution, and the exposed circular area is 0.785 cm 2 as Fig. 1(b) shows [16]. Besides, the Tafel curves were obtained after the electrodes were placed in the NaCl solution for 60s in order to made the electrolytes fully infiltrated by the solution and the obtained curves were used to deduce the equilibrium potential E corr and i corr .…”

Analysis on corrosion of aluminum-based micro-arc oxidation coating

“…MAO has been gaining increased attention as a novel and unique technique for depositing thick, dense and ultra-hard ceramic coatings on AAs (Chen et al , 2017). The MAO process on AAs has been studied to optimize the MAO coating properties.…”