The strengthening contribution of δ' precipitates in Al-Li alloys was determined from low-cycle fatigue tests under plastic strain control performed on single- and polycrystalline specimens. For under-aged specimens the experiments exhibited a plateau in the stress response, for the first 10 to 100 cycles, which was independent of the plastic strain amplitude. These stress levels were compared with theoretical estimates of particle strengthening due to internal order where the volume fraction and the mean particle radius were the variables. Literature results of monotonic tests were also included in the analysis. Good agreement between theory and experimental results obtained from both cyclic and monotonic testing was possible by assuming a specific antiphase boundary energy of 165mJ/m2 for the (111) planes.

Precipitation Strengthening and its Influence on the Mechanical Behaviour of Cyclically Deformed Al-Li Alloys. H.J.Gudladt, J.Lendvai, J.Schneider: Acta Metallurgica, 1989, 37[12], 3327-33