The Research Of AZ31 Magnesium Alloys Directional Sllidification Macrograph Structure And Property

It is well known that magnesium alloys have many excellent and unique properties, such as low density, high specific strength and stiffness, perfect damping capacity and shock energy absorption capacity, easy processing, as well as a good recycling capacity and compatibility with environment, and the resource of the magnesium is very abundant in the nature. Therefore, it is believed that magnesium alloy can be the most promising green material of the 21st century. But because of its poor plastic deformation ability, low yield stress and fracture toughness, the use of magnesium alloys is limited for a long time. AZ31 magnesium alloy is one of the most useful deformation magnesium alloys. In the present work, AZ31 based alloys. The aim is that control the proof sample microstructure and grain orientation, in order to improve the formability by directional solidification.In this thesis is adopted the vacuum directional solidification of AZ31 magnesium alloys and produced AZ31 magnesium alloys proof sample of continuous columnar crystals structure successfully. Using examine microstructure is observed this proof sample, the influence of directional solidification and proof sample microstructure of AZ31 were analyzed. And then compression test was processed in gleeble-1500D. The relationship about the thermal parameter and the flow stress is researched. At the same time the characteristics of room temperature and high temperature compression behavior of directional solidification of AZ31 magnesium alloys are analyzed. The result showed: (1) AZ31 magnesium alloys have coarse columnar crystals structure prepared by the directional solidification process. At the beginning of the stage there are a few small tenuous ball of the second phase distribute in crystals grain. As the proceeding of tension, the second phase entrances the basal corpuscle after the growing is stable. Crystals have a regular and directional growth and show the obvious preferred orientation which is parallel to thermal flow orientation of directional solidification.(2) The number of crystal grain is increasing as the speed of tension accelerates, and the declination between crystal grain direction and axial becomes bigger. When pulling rate > 50μm/s, columnar crystals are not continuous and tend to the equiax grain and develop. The number of crystals is increasing obviously and columnar crystals distribute more evenly as temperature rises.(3) Under the temperature of room compression strength of proof sample of directional solidification of AZ31 magnesium alloys is higher than the common proof sample of AZ31 magnesium alloys. Proof sample of directional solidification of AZ31 magnesium alloys has good performance of crush as the temperature rises. But when the temperature raises to 400℃, proof sample of directional solidification of AZ31 magnesium alloys hardens again which has the performance of super-plasticity and good high temperature.