Effect of predeformation and preaging at room temperature in Al-Zn-Mg-(Cu,Zr) alloys

The effect on yield stress of predeformation and natural aging prior to a t wo-stage artificial hardening treatment has been investigated for the 7xxx series alloys AA7108 and AA7030. It was found that 10% predeformation in te nsion reduced the yield stress measured in the T6-state by 7-10%. About hal f of this reduction could be regained when a preaging period was inserted b etween the deformation and the artificial aging treatment. The natural agin g response was followed also by measurement of electrical conductivity and hardness. Precipitate phases and GP (Guinier-Preston)-zones occurring durin g the aging treatments were investigated by transmission electron microscop y. The lower yield stress in predeformed samples is explained by early nucl eation of the equilibrium phase eta on the dislocation network, leaving les s solute for formation of the main hardening phase eta' The reduction in yi eld stress was partly offset by the preaging, due to recovery processes in the dislocation network. (C) 2001 Elsevier Science B.V. All rights reserved .