Precipitation strengthening and its influence on the mechanical behaviour of cyclically deformed Al-Li alloys

Abstract

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 underaged specimens the experiments show a plateau in the stress response for the first 10–100 cycles which is 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 ƒ and the mean particle radius r were the variables. Results of monotonic tests collected from the literature were also included in the analysis. Good agreement between theory and experimental results obtained from both cyclic and monotonic testing can be reached by assuming a specific antiphase boundary energy of 165 mJ/m² for the (111) planes