Effect of different cyclic expansion–extrusion processes on microstructure and mechanical properties of AZ80 magnesium alloy

Abstract

In this work, cyclic expansion–extrusion process in the same plane and cyclic expansion–extrusion process in two orthogonal planes have been employed, and the isothermal finite element simulations of both processes have been carried out. The equivalent plastic strains of AZ80 magnesium alloy billets produced by cyclic expansion–extrusion process in the same plane and cyclic expansion–extrusion process in two orthogonal planes were analyzed. Furthermore, the distinction between the accumulated equivalent plastic strains of both processes was also explored. The AZ80 magnesium alloy samples machined from the deformed billets were tested by tensile test machine, hardness tester, and optical microscope. This work also discussed the relationships between the microstructure and mechanical properties of deformed billets. The research results show that the average equivalent plastic strain of deformed billet is larger caused by two-pass cyclic expansion–extrusion process in two orthogonal planes than that by two-pass cyclic expansion–extrusion process in the same plane, and furthermore, the deformation uniformity after two-pass cyclic expansion–extrusion process in two orthogonal planes is far superior to that after two-pass cyclic expansion–extrusion process in the same plane. Cyclic expansion–extrusion process in the same plane can partly refine the grain size of annealed alloy from 190 to around 10 µm; however, cyclic expansion–extrusion process in two orthogonal planes can substantially refine that from 190 to approximately 3 µm. Two-pass cyclic expansion–extrusion process in the same plane can significantly improve the Brinell hardness of annealed alloy from 61.5 to 88.5 HB. Similarly, two-pass cyclic expansion–extrusion process in two orthogonal planes can also obviously improve that from 61.5 to 86.6 HB. Ultimate tensile strengths via two-pass cyclic expansion–extrusion process in the same plane and cyclic expansion–extrusion process in two orthogonal planes increase by 60 and 40 MPa than the annealed alloy, respectively. With the identical strain accumulation and deformation temperature, cyclic expansion–extrusion process in two orthogonal planes might look to be attractive when compared with equal-channel angular pressing for improvement of ultimate tensile strength and hardness as well as for grain refinement.