Understanding the Compromise between Strength and Exfoliation Corrosion in High Strength 7000 Alloys

Abstract

The microstructural evolution has been investigated in three alloys of the 7000 series possessing increasing zinc contents by combining small-angle X-ray scattering, differential scanning calorimetry and transmission electron microscopy, in order to gain understanding on the evolution of the compromise between yield strength and corrosion resistance. We show that the three materials show qualitatively identical precipitation sequences; however the precipitated volume fraction is shown to increase in parallel to the Zn content. Moreover, the precipitate size evolution is faster in the high Zn alloy. The precipitate composition is inferred to vary in the three materials, and this difference is shown to explain the differences in calorimetric behavior, precipitation kinetics and corrosion resistance.