Post-yield deformation characteristics in Al–Li alloys

New insights into plastic instability in precipitation strengthened Al–Li alloys

“…It has been shown, on the basis of detailed experimental investigations of instability behavior of AA2198, that dynamic strain aging (DSA) cannot sufficiently account for the occurrence of plastic instability in Al-Li based systems as is often assumed [21][22][23][24][25]. This observation is consistent with conclusions made recently for solution strengthened alloys that exhibit plastic instability.…”

“…This observation explains why several authors [21][22][23][24][25] argue for DSA as the origin of plastic instability in Al-Li alloys. Proponents of this view associate the disappearance of instabilities in these alloys to the depletion of Li from the matrix as a result of the precipitation of d 0 (Al 3 Li) phase.…”

“…Their model however suggests that since forest hardening is insignificant in precipitation strengthened alloys, plastic instability is not expected to occur in such materials unless a solute aging effect on the precipitate strengthening mechanism exists. These theoretical models [18][19][20] question the widely accepted view that DSA by Li atoms alone governs plastic instability in precipitation strengthened Al-Li based alloys [21][22][23][24][25]. The plausibility of DSA by Li to activate nSRS in Al-Li alloys is further undermined by the rather weak binding energy of Li atoms to dislocation cores [26].…”

“…Nonetheless, the disappearance of plastic instability in these alloys usually occurs in the underaged states [22,38,62] and can be attributed to the precipitation of more potent strengthening precipitates such as T 1 and S 0 . When strengthening from these phases becomes dominant, the order hardening mechanism and the pseudo-locking mechanism described above will be suppressed.…”

“…The slightly higher volume fraction of d 0 phase in OA in comparison with NA, in addition to a high density of other precipitates, including Li bearing precipitates such as T 1 phase in PA and T 2 and T B phases in OA affirms this fact. In other words, if DSA by Li exclusively governs the occurrence of plastic instability in Al-Li based alloys, as suggested by several authors [21][22][23][24][25], then this phenomenon should ordinarily occur in the NA temper. Our analyses however show that this is not the case; the absence of plastic instability in the NA temper is clearly not associated with a deficiency of Li atoms.…”