Effects of optimizing continuous forging extrusion process on the microstructure and mechanical properties of AZ31 magnesium alloy

Continuous forging extrusion (CFE) is a newly developed extrusion process to refine grains of wrought magnesium alloys. However, at lower extrusion temperatures, CFE also easily leads to material failure during extrusion, resulting in poor mechanical properties. In this paper, a high-pressure holding stage was added to the CFE process to effectively heal cracks in Mg-3Al-1Zn (AZ31) alloy. Meanwhile, the high-pressure holding leads to a large number of {10-12} tensile twinning, which acts as potential recrystallization nucleation points and promotes grain refinement during extrusion. By optimizing CFE process with this high-pressure holding, the strength and ductility of AZ31 alloy are greatly improved. AZ31 alloy specimens with a diameter of 60 mm before extrusion exhibit good mechanical properties with a tensile yield strength (TYS), ultimate tensile strength (UTS), compressive yield strength (CYS), fracture elongation (FE), and tensile compressive yield asymmetry (aCYS/aTYS) of 327 MPa, 365 MPa, 303 MPa, 23.5%, and 0.93, respectively. Deformation mechanism and microstructure evolution during the high-pressure holding stage are discussed in detail.