Discontinuous Yielding and Acoustic Emission in Al-Li-Cu-Mg-Zr Alloy

Abstract

Yielding behavior of an aged Al-Li-Cu-Mg-Zr alloy was studied by the tensile test and acoustic emission and transmission electron microscopic observations, and the yield mechanism was discussed in detail. The continuous-type acoustic emission which can be related to the accelerating motion of dislocations was affected by the precipitates of a metastable δ^′ phase and a metastable Al₃Zr phase, and had its maximum value when the mean diameter of the δ^′ phase was 12 nm. The reason was discussed in accordance with the frictional forces to the dislocation motion in the matrix and the δ^′ phase, and the misfit strain of the Al₃Zr phase in the δ^′ phase. On the other hand, the burst-type acoustic emission which can be related to the shearing of the δ^′ precipitates was also detected to be piled up above the continuous-type acoustic emission. Consequently, it was indicated that this alloy was plastically deformed by the dislocation motion with large planar slip and the shearing of the coherent ordered precipitates as the δ^′ phase at the same time. Finally, it was shown that the burst-type acoustic emission also included the effect of the solute atom as the source of serration in addition to the shearing of the δ^′ precipitates.