Hot Deformation On Continuous Casting Microstructure And Mechanical Properties Of Az31b Magnesium Alloy

AZ31B Mg alloy plate blanks which were fabricated by twin-roll casting technology has been homogenized, and then hot compression tests and hot-rolling tests were carried out to analyze the hot deformation behavior of AZ31B Mg alloys. The flow stress constitutive equations for high temperature and low temperature were established respectively, and the performance and microstructure of the alloy as well as its dynamic recrystallization mechanisms have been analyzed by Vickers hardness testing, optical microscope, transmission electron microscope, X-ray diffraction, and Electronic Back Scattering Diffraction. Finally, the conclusions were obtained are as follows:1. The true stress-strain curves of AZ31B magnesuim alloy which have a characteristc of dynamic recrystallization are composed of four different stages, i.e., work hardening, transition, softening and steady stages. The peak stress increases with the decrease of deformation temperature and the increase of strain rate. The specimens cracked when the temperatures lower than 100℃and strain rates higher than 0.1s-1.2. The flow stress constitutive equations for high temperature and low temperature can be described by the Arrhenius equation which is ameliorated by hyperbolic sine fuction and Z parameter, and the equations are obtained as follows: Low temperatureε=5.6288[sinh(0.029667σ)]4.5430 exp(-94352/RT) High temperatureε=5.7195×107[sinh(0.029667σ)]2.658 exp(-127524/RT)3. Through OM observing, it was found that the main mechanisms for low temperature of AZ31B alloy are basal plane slip and twinning, while dislocation slip, cross slip and climb for high temperature; the dynamic recrystallization mechanism is twining dynamic recrystallization at low temperature. However, continuous dynamic recrystallization mechanisum is operating when the temperature is higher.4. Twins intersected with each other and tangled dislocations located on twins-intersected zone, further more, a few DRX nuclei and tiny DRX grains were observed in the twinning band and twins-intersections, these imply that the main places where DRX nuclei formed are in twin boundaries and twins-intersection zones.5. The hot-rolled experiments represented that the AZ31B alloy sheet has good hot-rolled property that it can reduce by 60% one pass when be rolled at 375℃. With the increase of reduction, the scale of as-annealing grains decrease gradually, and the grains were only 4.3μm, when the reduction reached up to 60%.6. When the grain size is large, the main deformation mechanism of the AZ31B alloy is twinning during the low reduction stage. In pace with the increase of the reduction, the dislocation gliding become the dominant mechanism instead of twinning.7. The grain size is 8μm when the 60%-reduction AZ31B alloy sheet has annealed at 375℃for 30min. The small grain size hindered the twinning, so the dominant mechanism during 10% reduction stage becomes the dislocation gliding. However, changing the annealing conductions to enable the grain size to grow up to 20μm then the dominant deformation mechanisms go back to twinning again, these explain that twinning is easier than dislocation gliding in coarse grains while the opposite in tiny grains.8. Influenced by{1012} twins, the texture of (0001) plane get down suddenly during small deformation, and then get up slowly with the increase of deformation.