Influence of equal-channel angular pressing on the acoustic emission behaviour of magnesium alloy AZ31 under compression

To investigate the effect of severe plastic deformation on the acoustic emission behaviour of the magnesium alloy AZ31, equal channel angular pressing (ECAP) was carried out at 200 °C up to four passes following route BC. Acoustic emission was measured during compression tests at various temperatures from room temperature up to 300 °C. The compression tests at room temperature of undeformed specimens revealed a significantly higher activity of acoustic emission as compared to that of material that had been pressed four times through the ECAP die. At elevated temperatures the acoustic emission vanished for ECAP processed specimens, as opposed to the case of the undeformed material. In the case of undeformed specimens, the high acoustic emission activity can be explained in terms of collective dislocation motion and mechanical twinning. ECAP processed AZ31 exhibits a recrystallized microstructure with a grain size of approximately 800 nm. It was found that during compression tests, the concomitant acoustic emission is significantly reduced.