Corrosion resistance and polarization characteristics of Al-Zn alloys

Abstract

Corrosion resistance of Al-Zn alloys was studied by potentiodynamic method.Specimens used were Al-0%Zn, Al-0.1%Zn, Al-0.3%Zn, Al-0.7%Zn, Al-1%Zn and Al-5%Zn alloys. Experiments were conducted in 0.1N HCl, 0.1N NaOH, 5wt% NaCl aqueous solution and city water. The results obtained by potentiodynamic method and immersion tests were summarized as follows:(1) When immersed in the acid, there was correlation between the weight loss by corrosion and current intensity for corrosion obtained from the cathodic polarization curves of Al-Zn alloys by overvoltage-intercept method. The corrosion resistance of the alloys containing Zn of more than 0.7% was lower.(2) When immersed in the alkali, the electrochemical behavior of the alloys exhibited a typical transition between active and passive states. The critical current for passivation and the current for keeping passivity as well as the weight loss by dissolution were decreased with the increase in Zn content of the alloys.(3) When immersed in naturally aerated 5% solution of NaCl, the current for limiting diffusion calculated from the cathodic polarization curves of the alloys as well as the weight loss by corrosion was increased with the increase in Zn content of the alloys.(4) When immersed in city water, the polarization curves of the alloys were nearly identical with those in 5wt% solution of NaCl. The diffusion current in cathodic regions as well as the weight loss by corrosion was increased with the increase in Zn content of the alloys.