Anodizing - interplay between bath aging and oxide formation and properties

The present study investigates the interplay between ongoing bath aging during the anodizing process and the formation and properties of the anodic formed oxide layers on AA 1050 in sulfuric acid. The change in the bath over the time of use is studied by controlling the conductivity of the bath. The pH value and the concentration of Al3+ ions in the bath are simultaneously measured. The kinetic of the oxide formation depending on the bath aging is electrochemically investigated by repetitive potential controlled anodizing of reference samples. Supplementary material diagnostics by SEM and infrared reflection–absorption spectroscopy show a significant decrease of the oxide film thickness as well as the molecular composition with ongoing bath aging

An FT-IRRAS-study of anodic oxide films on aluminum alloys and the impact of bath aging

This present work studies the influence of the anodizing bath aging on the oxide formation and the oxide layer structure. The ongoing bath aging was mainly monitored by measurements of the electrolyte conductivity and concentration of Al3+ concentration in the electrolyte. SEM measurement clearly shows the changing of the oxide thickness as well as the porosity with ongoing bath aging. The molecular structure of the oxide film studied by FT-IRRAS shows that SO42- and PO43- are incorporated in the oxide layers. With ongoing bath aging the part of incorporated amount of sulfate decreases, whereas the amount of phosphates increases as confirmed by EDX analysis. No significant incorporation of copper or copper oxides were detected inside the anodic oxide layer

Particle reinforced open porous anodizing layers on AA5005

The present work deals with the target aimed design of anodic oxide films on AA5005 by modified phosphoric acid anodizing and reinforcement by subsequent impregnation with nanosized silicon dioxide by chemical nanotechnology. The authors show the influence of the anodizing time on the oxide layer thickness, the pore diameter and the morphology. It is revealed that silicon dioxide nanoparticles are successful when incorporated into the open structure pores of the layer. The anodizing and the incorporation process were carried out wet on wet. Complementary electrochemical measurements show the potential of the modified oxide layer in view of corrosion protection despite their deliberated open porosity

Nanoparticle-based impregnation of chromate-free anodizing layers for corrosion protection and adhesive bonding

The present work suggests a new approach of chromate-free surface pretreatment of aluminum alloy AA 1050 by using a modified phosphoric acid anodizing process, followed by an impregnation with a commercial SiO2-nanoparticle dispersion (Levasil® 300/30%) by dip-coating technique. The nanoparticles constitute an additional barrier layer against corrosion without closing the pores completely. The open porous oxide layer is a suitable promoter of adhesive bonding. The influence of withdrawing speed, the dipping time, solid content, temperature and pH-value in respect to the filling height in the pores of the anodized oxide layer were investigated. Surface morphology of the impregnated anodic oxide layers as well as their cross-section microstructure were investigated by scanning electron microscopy (SEM). Corrosion properties were investigated by electrochemical impedance spectroscopy (EIS) and adhesion was evaluated by single lap shear tests

Plasma Electrolytic Oxidation on Magnesium AZ31 with Sepiolite as Inhibitor Carrier for Improved Corrosion Protection

Plasma electrolytic oxidation (PEO) in an alkaline silicate electrolyte containing nanosized sepiolite fibers was carried out on magnesium alloy AZ31. The mineral fibers were loaded with different corrosion inhibitors and incorporated in situ during the PEO treatment. The composition and microstructure of the PEO coatings were investigated by SEM. It was shown that the fibers are located on the surface as well as inside the “weak spots” of the coating, i.e., pores and discharge channels. The fixation of the particles is caused by sintering due to the heat developed during the PEO treatment. Investigations using electrochemical impedance spectroscopy and linear sweep voltammetry in 0.01 M NaCl solution confirmed an improvement of the corrosion protection. The use of the inhibitors shifts the critical pitting potential in the anodic direction. Regarding efficiency, cerium-loaded sepiolite showed the best behavior by shifting the pitting potential by +0.9 V