Effect of Extrusion Preforming Process on Microstructure and Mechanical Properties of AZ81 Magnesium Alloy Die-Forged Net Forming Specimen

With semi-continuous casting AZ81 magnesium alloy as the carrier, the evolution of microstructure and properties in different deformation processes was analyzed and discussed by means of SEM, EBSD, XRD and metallographic microscope. The results show that the microstructure of as-cast AZ81 magnesium alloy is composed of alpha- Mg matrix, Mg-32(Al, Zn)(49) and MnAl6 phases, with coarse dendrite morphology. After die-forged net-final forming of the extrusion perform, the tensile strength, yield strength and elongation are increased by 95.8%, 138.8% and 353%, respectively, compared with that of as-cast AZ81 magnesium alloy. After solution treatment 400celciusx0.5 h + 200celciusx20 h, the internal stress was eliminated and the microstructure was more uniform. The tensile strength and yield strength were increased by 0.9% and 9.1% respectively compared with the untreated sample, but the elongation decreased by 48.5%. The fracture mechanism of as-cast AZ81 magnesium alloy is mainly brittle cleavage fracture, while the fracture characteristics of as-extruded and die-forged AZ81 magnesium alloy are the mixed fracture characteristics of cleavage and quasi cleavage fracture. After solution and aging treatment at 400celciusx0.5 h + 200celciusx20 h, the cleavage steps and cleavage patterns in the fracture surface increase, and the quasi-cleavage characteristics decrease, which makes the tensile strength and yield strength properties of the alloy slightly improve, but its plasticity decrease.