Influence Of Pre-deformation And Frustum Shearing Extrusion Deformation On Microstructure And Mechanical Properties Of AZ31 Magnesium Alloy

This paper selects the commercial AZ31 magnesium alloy as studing subject, with a new pre-deformation and frustum shearing extrusion on the deformation of AZ31 magnesium alloy,throug detection means such as metallographic microscope, X ray diffraction, scanning electron microscopy and electron backscatter diffraction analysis, focusing on the effects of pre-compression deformation and extrusion temperature on grain refine, texture weakening,mechanical properties and fracture mode of AZ31 magnesium alloy after the deformation and frustum shearing extrusion, The conclusions are as follows:1. After pre-deformation and frustum shearing extrusion, grain of AZ31 magnesium alloy has been significantly refined from the initial 213 ?m (as-cast) to 6.4 ?m; The yield strength and tensile strength of alloy have also been significantly improved, even the maximum can reach 234 Mpa and 304.9 Mpa; The elongation has increased with the grain refine in room temperature, the elongation rate can reach up to 24.9%. It represents that after adopting the method of pre-deformation and frustum shearing extrusion, strength and toughness of magnesium alloy has been improved comprehensively.2. Compared with the pre-compression epsilon of ?=0%, through pre-compression of 3%and 6%, the degree of dynamic recrystallization microstructure of magnesium alloys has gradually increased, and the uniformity has improved, while the texture intensity has gradually weakened. The yield strength and tensile strength with texture have decreased,while the elongation has increased. When the pre-compression epsilon ?=6%, the extension rate of magnesium alloy has been significantly reach up to 24.9%, the tensile fracture shows a typical ductile fracture characteristic.3. When the pre-compression epsilon was ?=6%, with extrusion temperature increasing,the grain has grown gradually, and the texture intensity has increased. The experimental data shows that the yield strength of magnesium alloy has increased with the increase of grain refinement, which conforms to the Hall-Petch relationship. When the extrusion temperature was 290 ?, the average size of grain in magnesium alloy sheet was 6.4 ?m, and the grain was distributed equably, yield strength and tensile strength were as high as 288.4 Mpa and 189.6 Mpa. Under different methods of cooling, after water-cooling, the grain of magnesium alloy sheet was more fine and well-distributed, and the yield strength and tensile strength were 165.2 Mpa and 283.4 Mpa respectively, which has been increased than the plate after air-cooling,4. The grain refinement mechanism of AZ31 magnesium alloy during pre-deformation and frustum shearing extrusion can be attributed to the following points:?Pre-compression deformation provided billet with twin structure, which makes the grain stored more deformation and dislocation, which provides more nucleation for the dynamic recrystallization during the subsequent process of frustum shearing extrusion. ? The interaction between deformation of overstriking area of the die and deformation of cone angle shear caused coarse grain crushing, and the continuous dynamic recrystallization occurred in the whole process of extrusion deformation, resulting in that the grain refine and structural homogenity in magnesium alloy has significantly improved.