Microstructure and Mechanical Properties of AZ80 Magnesium Alloy by Cyclic Expansion-extrusion Processing

AZ80 magnesium alloy billets of 100 mmx50 mmx170 mm in size were extruded by cyclic expansion-extrusion process in two orthogonal planes (CEEOP). The effect of 1 similar to 4 pass deformation of CEEOP on the equivalent strain, microstructure and mechanical properties of AZ80 magnesium alloy was investigated by simulation, OM, tensile test and hardness test. The results show that with the increasing of CEEOP pass, the grain size beco,es smaller and more uniform; the grain size can be refined from 200 to 6 mu m after one-pass; after four-pass, the size of equal-axial grain is reduced to approximately 1.5 mu m and the distribution is uniform. Furthermore, the mechanism of grain refinement is mechanical fragmentation and dynamic recrystallization. However, the grain refinement effect is not obvious after two-pass. Their mechanical properties have been greatly improved compared with those of the annealed alloy. One-pass deformation of CEEOP can significantly improve the hardness (HB) of the annealed alloy from 615 to 830.7 MPa. Similarly, four-pass deformation can also obviously improve that from 615 to 862.7 MPa. The ultimate tensile strength and yield strength via one-pass can be improved from 230.9, 115 MPa to 262.7, 155 MPa, respectively. And after four-pass, they can increase to 294 and 170 MPa, respectively. At the same deformation temperature and strain accumulation, CEEOP can refine grain and improve the tensile strength and yield strength of the material better than ECAP.