Microstructure evolution and mechanical properties of Mg-3Al-3Sn-1Zn alloy during multi-pass high-speed rolling

The microstructure evolution and mechanical properties of as-homogenized Mg-3Al-3Sn-1Zn (ATZ331) alloy with an initial grain size of ∼126.7 µm are studied during multi-pass high-speed rolling (HSR) process. The main deformation mechanism governing the microstructure is comprised of twinning and dislocation migration, Firstly, high dislocation density and twinning generated during HSR. Then, the dislocations are rearranged and incorporated as subgrain boundaries (sub-GBs), leading to a reduction of grain size with an increase in rolling pass. Results show that a fine and uniform microstructure (1.1 µm) of HSRed ATZ331 is achieved after the sixth pass, with a yield strength (YS), ultimate tensile strength (UTS), and elongation to failure (FE) of 319 MPa, 360 MPa, and 5.9 %, respectively. After being subject to HSR, low-temperature short-time annealing is carried out in order to improve ductility, which has proven to bring about sufficient static recrystallization (SRX). The SRX mechanism of ATZ331 alloy after HSR processing is found to consist of the classical recovery followed by recrystallization. Subgrains are formed by the realignment and absorption of the accumulated dislocations, which is followed by the migration of low angle grain boundaries (LAGBs) and their transformation into high angle grain boundaries (HAGBs). Finally, the sample with fine average grain size (1.7 µm) is achieved. Furthermore, the YS, the UTS, and the FE of ATZ331 are 253 MPa, 313 MPa, and 9.8 %, respectively.