AGEING AND PLASTIC DEFORMATION OF AN AL-MG-ZN ALLOY

The ageing kinetics of an Al-5.75% Zn-1.95% Mg-alloy has been followed by hardness measurements. The results indicate a two-stage process, which has been interpreted as the consecutive formation of two types of GP-zones. The variation of the dislocation distribution with degree of deformation was studied as a function of ageing time at room temperature using thin foil technique. It is found that while the distribution is fairly homogeneous in the as-quenched condition, the distribution becomes increasingly more heterogeneous with increasing annealing time. The dislocations in the latter case were found to be confined to the {111}-planes and in the form of greatly elongated loops and dipoles. With increasing deformation, the dislocations are gathered in rather narrow bands, within which they are extensively tangled. This special dislocation arrangement is discussed in terms of a short range interaction between dislocations and zones. © 1969.