HIGH-RESOLUTION ELECTRON-MICROSCOPY STUDY OF A HIGH-COPPER VARIANT OF WELDALITE 049 AND A HIGH-STRENGTH AL-CU-AG-MG-ZR ALLOY

A high-resolution electron microscopy study was preformed on two high-strength aluminium alloys, an Al-6.2Cu-0.4Ag-0.4Mg-0.2Zr alloy and a similar alloy but having a low lithium addition (1.25 wt%), named Weldalite 049, in order to identify their principal strengthening phase. The lattice images of the principal strengthening phase in these alloys were found to be different. The former alloy had the so-called OMEGA phase, which agrees with previous publications, whereas Weldalite 049 had a phase similar to, but not exactly like, the so-called T1 phase which is the principal strengthening phase of some high lithium (greater-than-or-equal-to 2 wt%) AlCuLi allays.