Microstructure evolution and mechanical properties of AZ80 magnesium alloy during high-pass multi-directional forging

Severe plastic deformation (SPD) was carried out on AZ80 alloy by high-pass multi-directional forging (MDF). Results showed that AZ80 alloy was effectively refined through MDF, and average grain size was refined to 0.73 mu m after 24 passes of forging. Its tensile strength, yield strength and elongation reached 333.8 MPa, 233.7 MPa and 17.8%, respectively, which were 1.22 times, 1.35 times and 2.54 times of those before the forging. When the MDF was less than 6 passes, the coarse grains were mechanically divided and refined, and a small amount of recrystallized grains appeared in the deformation band and its cross zone. When the MDF was more than 6 passes, grain division, recrystallization nucleation and grain growth occurred simultaneously, the microstructure refinement was slowed, and the uniformity was improved continuously. The heating between forging passes mainly caused restoration in the early forging, and the static recrystallization refinement in the middle of forging. In the later stage of forging, the grain growth caused by static recrystallization and the grain refinement caused by the deformation canceled out, and the microstructure no longer continued to refine with the increase of the forging pass.