LOCALIZED CORROSION MECHANISMS OF AL-LI-CU ALLOY AF/C458 AFTER INTERRUPTED QUENCHING FROM SOLUTIONIZING TEMPERATURES

摘要

The effect of slow or delayed quenching on localized corrosion mechanisms for the Al-2.05Li-2.70Cu-0.6Mg-0.3Zn-0.08Zr alloy AF/ C458 was assessed. Alloy samples were subject to a series of systematic interrupted quenching experiments conducted at temperatures ranging from 480℃-230℃ for times ranging from 10 to 1000 seconds. Samples were then exposed to an oxidizing aqueous chloride environment to induce localized attack. The alloy exhibited pitting, intersubgranular attack (ISGA), or intergranular attack (IGA), depending on the time at temperature. Detailed micro-structural characterization by means of transmission electron microscopy was employed, which clearly showed that ISGA and IGA were related to the precipitation of a Zn-modified T_1(Al_2(Cu,Zn)Li) at high and low angle boundaries respectively. In situations where the T_B(Al_7Cu_4Li) phase was present on boundaries instead of T_1, IGA and ISGA susceptibility was comparatively diminished.