THE DEPENDENCE OF PITTING CORROSION MORPHOLOGY ON THE PRECIPITATED PHASES FOR 7020 AL-ALLOY

Abstract

AbstractAl-alloy type 7020 was heated at different temperature (from 100 to 500) ºc to observed the shape of precipitated phases. Pitting corrosion of this alloy was also study by using immersion in 3.5% NaCl and polarization techniques. The aim of this paper is to find the dependence of pitting corrosion morphology on the precipitated phases for 7020 Al-alloy.The results are confirmed that, at low heating temperatures between (100-200) °C dendrite structures were observed. These zones suffered dendrite pitting corrosion, when the alloy was exposed to corrosive medium of 3.5% NaCl. At the intermediate temperatures range (250-350) °C, different shapes precipitated phases are obtained. As heating temperature was increased these shapes converted from dendrite to spherical shapes. This transition in shapes was also observed for developed pit. At heating temperature up to 500 °C most of the formed pitting has the spherical overall shapes corresponded with the phases shape, precipitated at these range of temperatures.