Corrosion Characteristics of Raw and Anodized Aluminium

Abstract

Corrosion resistance of aluminium and its alloys in different media can be improved by many procedures. One of the most used methods is anodisation or anodic oxidation, which is commonly known as anodising. Solutions of: NaCl, w = 3 %, HCl, w = 3 %, H 2 SO 4 , w = 10 %, NaCl + NaOH (pH = 10.09), NaOH (pH = 10.17), and seawater taken from Ploče were used as corrosive media. Anodisation enables higher potentials in all corrosive environments, indicating that a protective oxide film has been formed. This oxide layer is the most stable in a solution of sulphuric acid, and has the lowest protective role in 3 % HCl solution, 3 % NaCl solution and seawater. By increasing the thickness of anodising from 10 to 20 micrometres, no improvement of the corrosion protection was achieved, except in the NaOH solution. Anodising also reduces the polarization resistance by a similar dependence of the corrosive environment. An even greater and similar protective effect is exhibited by anodised aluminium with a thickness of 20 micrometres. Anodising decreases the corrosion rate by several orders of magnitude, which confirms that aluminium anodising protects against corrosion. Values are from 3.57 to 2699.00 mm a-1 .

Keywords

• Corrosion
• Aluminium