The effect of G.P. zones on the dislocation structure and on the work-hardening process in an Al-3,2wt.%Zn-2,2wt.%Mg alloy has been studied by tensile testing, transmission electron microscopy and X-ray small angle scattering investigations. The results show that the dislocations cut through the G.P. zones formed during R.T. aging after quenching as well as after l min reversion heat treatment at 80 and 200°C. A tendency towards oriented dislocation structure can be observed with increasing volume fraction of G.P. zones. When the volume fraction of G.P. zones reaches about 0.6% the dislocation structure attains a definitely oriented character even after relatively small deformations. The flow stress of the alloy was found to depend linearly on the square root of the strain for both the solution heat treated and R.T. aged, as well as the reversion heat treated and reaged samples. The energy needed to cut a unit area of a G.P. zone by the dislocations was found to be 0.350 Nm/m2.
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