The Portevin-LeChatelier (PLC) effect was investigated in Mg-Zn (0.3, 0.4, 1, 2, and 3 at% Zn) binary alloys and ternary Mg-Al-Zn (AZ61, AZ91, AZ92) alloys.
Previous work  indicated that the PLC effect does not occur in Mg-Al alloys. Tensile testing of the Mg-Zn compositions shows that the PLC effect does not occur in that system either, under the experimental conditions. In the Mg-Zn-Al system, the only alloy to display PLC was the AZ91. This suggests that both Zn and Al are needed, but within a narrow composition.
A mechanism based on Korbel’s dislocation dynamics model is suggested to account for the need of both Al and Zn in solid solution. Korbel's model is based on two mechanisms, one regarding the dynamics of pile up formation, and the other regarding the role of secondary slip as a means of stress relaxation.
Aluminium is thought to control the dislocation dynamics as dislocations move on the basal planes towards grain boundaries. It is postulated that the stress exponent of dislocation velocity m value is reduced with increasing aluminium content, enabling the development of plastic bursts.
The zinc, in turn, acts by lowering the critical resolved shear stress on the prismatic planes and allowing secondary slip to relax the stress at the head of the dislocation pileups. This produces forest dislocations on “alien” slip planes relative to the glide plane. This forest of dislocations initially hinders dislocations on the glide plane, but when the stress increases enough to cut through the forest, an avalanche of dislocations can move through the forest with little strain hardening, initiating PLC bands.