The fracture behavior of recrystallized Al-2.8% Li-0.3% Mn sheet

Abstract

The fracture behavior of recrystallized Al-2.8wt.% Li-0.3wt.% Mn was investigated as a function of artificial aging conditions. Isothermal aging resulted in the growth of coherent Al 3Li metastable precipitates. The growth process followed a (time) 1 3 dependence. Together with the growth of the matrix precipitates, a preferential coarsening of the precipitates near grain boundaries occured. To accomodate the accelerated growth in the grain boundary regions, a precipitate-free zone (PFZ) developed; the change in the width of the PFZ also followed a (time) 1 3 behavior. The shearable nature of the Al 3Li precipitates, the coarse grain boundary precipitates and the PFZ all helped to localize deformation and to promote intergranular failure. In the early stages of aging, before the PFZ had had an opportunity to grow significantly, the fracture process was due to dislocation pile-ups at the grain boundaries. Continued aging resulted in the growth of the PFZ and the deformation process localized in the grain boundary region, leading again to intergranular failure.