An aluminium-2% magnesium alloy solidified to a pronounced sub-structure shows, when tested in tension, at approximately 300°C an abrupt change in the mode of plastic deformation. Above this ‘transition’ temperature, where the flow stress maintains a steady value up to high strains, restoration is suggested to occur by means of a ‘stress-induced’ knitting process combined with dislocation annihilation, when vacancies created in the process are rapidly destroyed at high temperatures. The structure remains all the time polygonal, consisting of cells separated by two-dimensional dislocation networks which have a remarkable regularity.