The fracture resistance of 1420 and 1421 Al-Mg-Li alloys

The resistance to stable crack growth in 1420-T6 (Al-5Mg-2.1Li-0.1Zr-0.01Sc, less than 0.06Fe, in wt pct) and 1421-T6 (Al-4.7Mg-1.9Li-0.09Zr-0.2Sc, less than 0.06Fe) Al-Mg-Li alloys was investigated, based on the R curves generated in accordance with ASTM E561-86 and fractography analyses. The crack resistance of 1420 and 1421 alloys was found to be comparable to that of the conventional Space Shuttle External Tank Al alloy, 2219-T87. The main differences in the fracture behaviors arose from differences in the alloys' microstructures. In the case of 1420 alloy, a slightly enhanced toughness behavior was observed, due to the T-phase precipitates, which may have promoted more homogeneous deformation and enhanced microvoid coalescence. In the case of 1421 alloy, the addition of Sc led to a refined grain size and resulted in slightly reduced toughness.