The evaluation of the critical electrochemical potentials influencing environmentally assisted cracking of Al-Li-Cu alloys in selected environments

Abstract

The electrochemical behavior of aluminium has been determined as a function of copper content using potentiodynamic polarization and scratching electrode techniques. This information has been correlated to trends in environmental cracking of Al-Li-Cu alloys in inhibited sodium chloride environments. Scratching electrode-constant extension tests of stressed tensile samples have revealed a change from no failures to rapid failures due to a 10 mV change in applied potential. The potentials ( E CRIT-EAC) where these transitions occur appear to be linked to the electrochemistry of a copper depleted region along microstructural boundaries. Similar values for E CRIT-EAC were observed for both Li-containing and Li-devoid Al-Cu-X alloys, and for a given alloy the values were a function of temper. These observations are used to support the theory of Cu-depletion controlling crack-tip electrochemistry as opposed to an active precipitate phase as the dominant feature.