AbstractAcoustic emission was monitored and analysed during tensile tests of pure Mg and Mg alloys of the AZ series in order to study the influence of alloy composition on plastic deformation. The Kaiser effect was used to determine the stability of the microstructure. During the tests at room temperature, repeated stress relaxations were performed. The solute–dislocation interaction in the alloys leads to ageing phenomenons, which manifest themselves in a post-relaxation effect and subsequent serrated flow (Portevin–Le Chatelier effect). The post-relaxation effect was sensitive to alloy composition and the strain at which the stress relaxation was performed.