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 predeformation reduces the time required for the alloy to reach peak hardness during aging at 120 degrees 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 degrees 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 A1* and A2* textures, but reduces texture intensity. After aging treatment, the primary intragranular precipitates are eta' phases, and dislocations generated by pre-deformation stimulate the heterogeneous nucleation of eta' phases and their transformation to eta 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 eta phase content, and expanded PFZ width. Predeformation 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.