Deformation and fracture behavior of a RSP Al–Li alloy

Abstract

The deformation and fracture behaviors in a rapid solidification processed (RSP) Al–Li alloy have been studied by tensile tests, transmission electron microscope (TEM) and scanning electron microscope (SEM) observations. The results show that the interaction mechanism between dislocations and δ′ precipitates is shearing in underaged, peak aged and some overaged conditions. In the early stage of deformation ( δ<1%) δ′ precipitates are sheared by moving dislocations in one direction, showing that planar slip is predominant. However, in the later stage of deformation ( δ>5%) of the alloy, δ′ precipitates are cut into pieces by dislocations from different directions, suggesting that cross slip is predominant. In severely overaged conditions, the deformation is mainly concentrated on the precipitate-free zones (PFZs), and only smaller δ′ precipitates near PFZs are sheared. The fine grain size (2–3 μm) produced by rapid solidification cannot change the inherent intergranular fracture mode of Al–Li alloys. TEM observations show that the nominal intergranular fracture in the alloy is actually caused by the cracking of PFZs but not by the fracture of grain boundary. Therefore, it is suggested that in alloys with PFZs in their microstructure, PFZ is the main reason that results in the intergranular fracture, and the width of PFZ is not an important factor in controlling the fracture mode. Tensile tests show that the peak strength of the alloy does not correspond to the transition stage of dislocations’ shearing to bypassing of δ′ precipitates. The high volume fraction of PFZ and the small spacing of δ′ precipitates are thought to be reasons for such a phenomenon.