Influence Of Impact Deformation On Microstructure Evolution Of Magnesium Alloy

The magnesium alloy has a series of excellent physical and mechanical properties, such as low density, high specific strength and so on, which shows extensive application prospect in aspects of aerospace, communication and the lightweight of weapon equipment. The article focuses on factors which affecting the deform behavior of magnesium alloy and its deformation mechanism, develops series of experimental studies and theoretical analyses, and gets series of meaningful results.The thesis chooses the typical extruded AZ31 magnesium alloy as studying object, using the split Hopkinson pressure bar to make impact and compression experiment, and with the help of testing devices such as metallographic microscope, X ray diffraction, back scattering diffraction to analyze the microstructure evolution of magnesium alloy impact deformation, studying influence rules and mechanism of macro mechanical behavior and micro deformation mechanism by loading direction, strain rate, temperature and other technological conditions on AZ31 magnesium alloy. Important conclusion is gained as below:Dynamic mechanical behavior of material is close to loading direction. When the impact compression direction is perpendicular to the c axis, on the initial stage, stretch twin is on a favorable orientation and could easily be activated and started-up, the yield point is lower and shape of stress strain curve is concave, the yield strength is not sensitive to strain rate, which is about 70 Mpa, and with the increase of temperature, the yield strength shows a downward trend. When the impact compression direction is parallel to the c axis, the grain orientation is not conducive to activate { 2110 } tensile twin, the yield point is higher and shape of stress strain curve is convex, deformation mechanism is mainly non-basal slipping, { 1110 } compression stress of the twin in a favorable state was also involved in coordination deformation, but that’s not a main plastic deformation mechanism.Under high strain rate, for both samples that paralleled to ED and perpendicular to ED, adiabatic temperature rises under room temperature increases along with the increase of strain rate, due to the strain rate is small, impact deformation under room temperature is not enough to make the organization internal temperature reach to occur dynamic recrystallization, deformation is mainly { 2110 } twin.With the increase of impact temperature, adiabatic temperature rise declines under same dependent variable. Although the adiabatic temperature rise declines, but energies provided externally can make the critical shear stress of material reach to the status required by cylindrical, conical slipping in the process of deformation, which makes the way of plastic deformation switching mainly from twinning to slipping, and occurs the phenomenon of dynamic recrystallization. Besides, the higher the temperature is, the easier this phenomenon occurs, the influence of adiabatic temperature rise in the process of deformation is decreased.Extruded AZ31 magnesium alloy has a strong {0002} basal texture. Due to the existence of texture caused large difference of the mechanical properties in different directions, which shows anisotropy. In the process of thermal shock, the thermal softening effect can make the strain rate strengthening effect of material get weakened. In high temperature deformation, showing features of continuous, discontinuous and rotational dynamic recrystallization and texture is obviously weakened.