Production and characterization of the anodic film on Al-6%Zn-1%Mg alloy

The newly developed high strength aluminum alloy Al-6wt.%Zn- 1wt.%Mg was anodized in acids by direct current to produce a protective anodic coating against abrasion and corrosion. Mechanical properties of the anodized finish, including microhardness, abrasion resistance and fatigue strength were evaluated in terms of the composition and temperature of the electrolyte, applied voltage, current density, duration of anodizing and sealing temperature. Pitting is destructive of the anodized finish particularly in a marine environment and thus can also serve as a direct measure of the efficacy of sealing procedures.The optimum conditions for anodizing Al-6wt.%Zn-1wt.%Mg are a bath of 5 wt.% oxalic acid with 3 wt.% formic acid as an additive, a current density of 4 A dm^-2 for 30 min at 20 °C and sealing in boiling deionized water for 30 min. Results show that this anodized finish possesses good mechanical properties and corrosion resistance.