DISCONTINUOUS YIELDING AND ACOUSTIC-EMISS ION IN AL-LI-CU-MG-ZR ALLOY

Yielding behavior of an aged Al-Li-Cu-Mg-Zr alloy was studied by the t ensile test and acoustic emission and transmission electron microscopi c observations, and the yield mechanism was discussed in detail. The c ontinuous-type acoustic emission which can be related to the accelerat ing motion of dislocations was affected by the precipitates of a metas table delta' phase and a metastable Al3Zr phase, and had its maximum v alue when the mean diameter of the delta' phase was 12 nm. The reason was discussed in accordance with the frictional forces to the dislocat ion motion in the matrix and the delta' phase, and the misfit strain o f the Al3Zr phase in the delta' phase. On the other hand, the burst-ty pe acoustic emission which can be related to the shearing of the delta ' precipitates was also detected to be piled up above the continuous-t ype acoustic emission. Consequently, it was indicated that this alloy was plastically deformed by the dislocation motion with large planar s lip and the shearing of the coherent ordered precipitates as the delta ' phase at the same time. Finally, it was shown that the burst-type ac oustic emission also included the effect of the solute atom as the sou rce of serration in addition to the shearing of the delta' precipitate s.