Generally, the film produced by the chemical film process is not as corrosion-resistant as that produced by the anodizing process, and that is why the chemical film process can only be used for the surface treatment of aircraft skins and non-structural parts.
Unlike the chemical film process, the anodizing process can produce a dense and thick porous oxide layer with excellent corrosion resistance performance. For a thicker and denser oxide layer on the aluminum sheet surface, an aluminum sheet should be immersed in a treatment tank with suitable electrolyte and a direct current or an alternating current should be applied to it. The porous oxide layer provides a large wetting area for adhering, thus enhancing the bonding strength of the aluminum sheet.
Chromic anodizing, sulfuric anodizing, hard anodizing and hot etching are the most commonly used surface treatments of aluminum sheets.
Kim Nam Il, a researcher at the Faculty of Materials Science and Technology, has found the most suitable surface treatment by studying the effect of the four different surface treatments on AlMgSi aluminum sheets when they are bonded with an epoxy-based film adhesive.
He performed four different surface treatments on aluminum sheets that were then bonded with an epoxy-based film adhesive in an autoclave to achieve good adhesion. He examined the microstructure of the porous oxide layer on the aluminum sheet surface and its effect on the bonding performance.
The analysis of the failure modes of the bonded surfaces, the peeling strength and the microstructure of the porous oxide layer showed that chromic anodizing of aluminum sheets have the best bonding performance, whereas sulfuric anodizing and hard anodizing exhibit the worst bonding performance.
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