Research On Deformation And Fracture Behavior Of AZ31 Magnesium Alloy Under Different Strain Rates

Magnesium alloys have a broad application prospect in the field of aerospace for its light weight, high strength and high shock resistance. This topic studies the deformation behavior of extruded AZ31 magnesium alloys under the condition of static, medium and high strain rate, using the universal material testing machine, thermal simulation testing machine and split Hopkinson pressure bar to realize the low strain rates of 10-3s-1, 10-1s-1 and 101s-1, the high strain rates of 103s-1, we get the deformation mechanisms of the material under different strain rates by analyzing the corresponding mechanical behavior and the microstructure evolution under different strain rates by OM, SEM, EBSD and TEM.The material shows different mechanical behavior along the extrusion and transverse direction—twinning-dominated and slip-dominated respectively. The increase of strain rate will increase the degree of strain hardening of material. The deformation mechanical behavior of material show big difference under high strain rate and low strain rate: with the increase of strain rate, the change of mechanical properties show the increase of strength and decline of plasticity under low strain rate; but the increase of strength and plasticity under high strain rate.Materials have a low sensitivity of the strain rate and the deformation processes are basically the same under low strain rate: twins began to nucleate and grow up gradually, the number rises, crystal orientation changes continually, part of the slip system open, dislocation and twin deformation coordination and transformation, density of dislocation increases gradually, in the late stage of deformation twins saturated(~80%), the stress level is higher, so there are strong stress concentration on the grain boundary, the twin boundary and dislocation plug which induces cracks and the last breaking. It can be found that with the increase of strain rate, twin effect become more apparent. Fracture size near the fracture of crack increase, we can find ASB under the strain rate of 101s-1. Under high strain rate, when strain rate increase from 2200 s-1 to 4300 s-1,there are the adiabatic shear band in the deformation zone, its size increase gradually, throughout the entire sample, and cause the sample fracture as a whole. After deformation under high strain rate, there are long and thin strips throughout large grains which evolved from the compression twins and are easy to become cracks. There are actives of twin and slip in the sample, the twin types are tensile twin and compression twin, there are high density of dislocation inside and around twins under high strain rates, interface of twins bent and shift quantity of twins increase gradually and the interaction between twin and dislocation become more intense with the increase of strain rate.