Microstructure and mechanical properties of an Al-Mg-Si tube processed by severe plastic deformation and subsequent annealing

This study is aimed to realize evolution of microstructure and mechanical properties of aluminum 6061 alloy tube subjected to Severe Plastic Deformation (SPD) and subsequent annealing. For this purpose, the tube is initially processed by different passes of an SPD process called Tube Channel Pressing (TCP) and then subjected to a subsequent annealing at 473 °K for 2 h. Afterwards, tension test is used for the evaluation of mechanical properties while Electron Back-Scattered Diffraction (EBSD) equipped Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) are utilized for the microstructural characterizations. Results show that the Continuous Static Recrystallization (CSRX) is the main restoration phenomenon during annealing of aluminum 6061 alloy, even after imposing a moderate plastic strain. For instance, CSRX has been observed during annealing treatment after imposing an equivalent plastic strain as low as 1. However, the used annealing treatment causes different microstructural variations in specimens depending on the pass number of TCP. As an illustration, while the average grain size impressively decreases due to annealing of 1 pass TCPed specimen, it moderately increases after annealing of 5 passes TCPed specimen. This is due to development of a bimodal microstructure after 5 pass of TCP which leads to a different evolution of microstructure during successive annealing. It is also notable that TCPed and annealed specimens show higher strength and ductility compared with as TCPed specimens which is attributed to the occurrence of precipitation hardening besides restoration phenomenon during the annealing treatment.