Influence Of Extrusion Forming On Microstructure And Mechanical Properties Of AZ31B Magnesium Alloy

This article took AZ31B Magnesium Alloy as the research object, Through designing extrusion dies which is simple and applied, did extrusion experiment with two kind of AZ31B Magnesium Alloy bar which were cast and uniform annealed condition under the 6300KN hydraulic machine, and tested the sample on the microstructures and mechanical properties. The results of the study were as following:During the extrusion process, the extrusion pressure increased and the plastic deformation degree of metals raised with the knock-down of temperature and the accretion of extrusion ratio.By a variety of heat treatment and extrusion, the dynamic recrystallization happened to the product's microstructure. The grains distinctly get smaller than what before extrusion. Direct extrusion with no heat treatment, when the grain of structure was lesser then extrusion with heat treatment, but the second phases were more, and structures were asymmetry. It's seen that the second phases were squeezed along the extrusion direction, formed thermal processing streamline. The grains after heat treatment and extrusion were bigger, but the structures were uniformity. Through heat and extrusion, the products'tensile strength could be 303MPa, and the prolongation ratio was 17.8%. Compared to the performance of direct extrusion with no heat treatment, the mechanical properties of AZ31B Magnesium Alloy could increased effectively after uniform treatment.When the alloy extrusion temperature increased from 250℃to 450℃, grain grew up after extrusion, the volume fraction of second phase decrease, the recrystallized grains got full deformation and more evenly distributed. At the same time, tensile strength reduced, prolongation ratio lowered.With the extrusion ratio increasing, alloy grain could be refined. When the extrusion ratio was 20, grain looked rough, the average size was 4μm. When the extrusion ratio was 35, grain got thinner, but because some have not been refinement, grain looked uneven. When the extrusion ratio got to 50, the grains become more compact and smaller, and distributed evenly. By the extrusion ratio increasing, metal deformation increased, deformation streamline got more compact, grain got more smaller, the tensile strength and prolongation rate of Magnesium Alloy got improvement. When the extrusion ratio was 35, temperature was 250℃, the alloy prolongation rate reached 25% after heat treatment and extrusion, it showed that with the low temperature and large extrusion ratio, the toughness of Magnesium Alloy could effectively improved.In a word, the paper has studied the influence of different deformed temperature and extrusion ratio to the microstructure and mechanical property in the processing of the AZ31B Magnesium Alloy, the law and mechanisms of Magnesium Alloy grain refinement and performance changes were discussed, what supply the basis for the extrusion technology establishment of Magnesium Alloy parts with high performance.