Influence of microstructure on acoustic emission during deformation of aluminium alloys

Abstract

Acoustic emission (AE) has been measured during the deformation of pure aluminium and aluminium alloys with a range of microstructures. In polycrystalline aluminium ‘continuous’ emission activity was observed which increased with grain size to approach that of single crystal aluminium. The data were consistent with dislocation glide as the source of emission. In the binary solid solution, Al–1·3Mg, ‘burst’ emission activity was observed which increased rapidly with grain size to a peak value at 80 μm before decreasing at larger grain size. The cooperative escape of dislocations from solute atoms is proposed as the source of emission. In the binary age-harden able alloy, Al–4Cu, there was a peak in burst emission activity in underaged samples (2 h at 170°C). Here the proposed source of emission was the formation of coarse slip bands induced by the shear of weak Guinier–Preston zones. Studies of Al–5·5Zn–2·5Mg and Al–5·5Zn–2·5Mg–1·6Cu alloys indicated a similar source. Large burst emissions were detected after aging at 120°C that correlated with the appearance of transgranular slip bands. Broad-band measurements of emission from the quaternary alloy tested in the peak-aged condition have been made and a model for AE during dislocation motion is proposed to interpret the results.