Abstract
AZ91 magnesium alloy exhibits jerky flow when deformed a short time after solution heat treatment and quenching. The occurrence of stress drops and discontinuous plastic deformation has been observed at temperatures in the vicinity of ambient temperature in tension as well as compression. The alloy exhibits some degree of negative strain rate sensitivity. Acoustic emission accompanies the stress drops. It is concluded that successive deformation bands propagate along the gauge length as soon as the material develops gross plastic deformation, regardless of the applied strain rate. The results are discussed in terms of current theories for the Portevin-LeChâtelier effect.

Key words
serrated yielding, dislocations, solid solution, diffusion, collective motion of dislocations, acoustic emission

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