ACOUSTIC EMISSION DURING DEFORMATION OF Al-Li ALLOYS

The relationship between tensile elongation and acoustic emission (AE) detected during compressive deformation of 81-Li and Al-Li-Zr alloys has been investigated for a range of microstructure. For comparison, AE measurements have been carried out for A1-Cu and commercial 7050 alloys. In the polycrystalline binary A1-Li alloys, the most pronounced AE was detected in the underaged condition during the onset of plastic deformation. The AE increased with increasing Li content, attained a maximum emission at 3-4.5% Li and decreased by further addition over the maximum solid solubility of Li in Al. The strong burst AE was detected in the A1-Li single crystal with a multi-slip orientaion. In contrast, the AE in the sample with a single slip orientation was appreciably small. The AE in the binary A1-Li alloys was much greater than those in the A1-Cu and 7050 alloys. The addition of 0.1-0.5% Zr to the polycrystalline A1-Li alloy greatly lowered the AE and improved the ductility appreciably. The proposed sources of burst AE in the binary A1-Li alloys during the onset of plastic deformation are the formation of coarse slip bands induced by shearing of L1 -ordered coherent 6'-particles and the intersection of slip bands with each other an8 with grain boundaries. The intersection of coarse slip bands and weak grain boundaries are considered to be responsible to the loss of ductility in the binary A1-Li alloys. Transmission electron microscope observations of the interaction between deformation induced dislocations and precipitate particles revealed that the dispersion of fine metastable A1 Zr particles changed the mode of dislocation glide through the introduction of the 8rowan bypass process.