Effect of large pre-deformation on the microstructure, texture and mechanical properties of Al-Zn-Mg alloy extruded profiles

The effect of large pre-deformation on the microstructural evolution and mechanical property anisotropy of large-sized Al-Zn-Mg alloy extruded profiles with thin-walls and high-ribs was investigated. The increase in pre-deformation reduces the time required for the alloy to reach peak hardness during aging at 120 °C, but leads to a decrease in peak hardness. The undeformed alloy exhibits the highest ultimate tensile strength (UTS) of 527 MPa and yield strength (YS) of 497 MPa in the 90° direction, accompanied by a low elongation (EL) of 12.7 %, highlighting significant anisotropy. At a large pre-deformation of 38 %, UTS, YS, and EL dramatically fall, with IPA values of 2.43 %, 3.77 %, and 11.96 %, respectively. Increased pre-deformation promotes the formation of substructures without altering the texture type, which remains predominantly A ₁* and A ₂* textures, but reduces texture intensity. After aging treatment, the primary intragranular precipitates are η` phases, and dislocations generated by pre-deformation stimulate the heterogeneous nucleation of η` phases and their transformation to η phases. Additionally, increased pre-deformation leads to the growth and uneven distribution of precipitates and an increase in the width of the precipitate-free zones (PFZ). The reduced anisotropy is attributed to decreased texture intensity, increased dislocation substructures, higher η phase content, and expanded PFZ width. Pre-deformation between 8 % and 18 % effectively maintains mechanical properties while reducing anisotropy. These findings provide insights into optimizing pre-deformation treatments to balance mechanical properties and anisotropy in Al-Zn-Mg alloy profiles.