Investigation on longitudinal weld seams during porthole die extrusion process of high strength 7075 aluminum alloy

Abstract

In this study, the porthole die extrusion experiments were carried out to study the welding quality of longitudinal weld seams (L-seam) of high-strength 7075 aluminum alloy. The differences in microstructure and mechanical properties of L-seams under various extrusion temperatures and at different positions along extrusion direction were discussed. Moreover, three-dimensional transient numerical modeling was employed to have a better understanding on experimental findings. Based on the results, it was firstly proposed that the cross section of the profile can be divided into welding zone, transition zone, and matrix zone. Dynamic recrystallization completely occurred in the welding zone, while its fraction gradually decreased in transition and matrix zones, and this phenomenon was also verified by simulated results. The welding quality of L-seams near the front of the profile was relatively poor, while it was enhanced along the opposite direction of extrusion. Moreover, higher extrusion temperature was beneficial to enhance the welding quality of L-seams. Finally, the evolution of dynamic recrystallization and the evaluation of L-seam quality were analyzed based on simulated results and J criterion, all of which showed good agreement with the experimental findings.