Influence of Technological Parameter on Boehmite Sol Sealing Anodized Al 2024 Alloy

Abstract

The boehmite sol is prepared with cheap inorganic salt Al(NO3)3and NH3H2O. The anodized aluminum alloy was sealed with the boehmite sol. Influences of concentration of Al3+, pH and temperature of sol on the properties of sol and the sealed film were studied. The results shows that the viscosity of sol increases and the stability becomes lower with the increase of Al3+concentration and pH of sol. The viscosities of sol become lower with the rises of its temperature. The thickness of anodized film increases when sealed with boehmite sol. The thickness value of sealed film increases with the increase of the sol viscosity. The properties of sealed film are better while the color of sol is azury. The corrosion resistance of sealed film was enhanced with the pH rising from 5.5 to 7 at the same concentrate and temperature of sol. The corrosion resistance in acidic solution is improved remarkably for sol sealed film as the sol temperature rises up to 60°C. The time of changing colour for sol sealing film is longer than that of the film sealed by distilled water.

Effect of Process Parameters on Anodization of AA7075

“…During anodization process, air bubbles were passed through the electrolyte to cause agitation to make the process effective. After the anodization was over, it was necessary to properly seal the porous coating of aluminium oxide in order to provide good corrosion resistance [3]. The anodic coating was placed in boiling water for 15 to 30 minutes.…”

“…The specimens anodized with various process parameter combinations were viewed under FE-SEM (Field Emission Scanning Electron Microscope). The images obtained were used for calculating the porosity index as depicted in Equation 1where, D p is the pore diameter and D i is the interpore distance [3]. After calculating porosity index and mean thickness, grey relation analysis was carried out and grade order was found out [4].…”