Microstructure And Mechanical Properties Analysis Of Bimadal-grained Mg Fabricated By HDDR-SPS-Extrusion Technique

In order to improve the overall performance of magnesium alloys,the researches have proposed a number of methods in which grain refinement is a commonly used efficient technology.However,with the reduction of grain size,the grain boundary will hinder the generation and movement of dislocations,and then reduce the processing hardening ability,plastic deformation and ductility of ultra-fine crystalline material.Bimodal microstructures have been proposed to solve this problem by balancing the strength and mechanical properties of materials.Bulk magnesium materials with bimodal grain size distributions comprised of nanograined(NG)regions and coarsegrained(CG)regions were produced using atomized spherical pure magnesium powders via hydriding and dehydriding followed by spark plasma sintering and hot extrusion.In this study,one basic preparation method,hydrogenation and dehydrogenation technology(HD),and two different preparation paths were applied.We have prepared Nanostructured Mg by using HD technology.The first path is preparing Mg powders with bimodal structures by incomplete hydrogenation.The second path is mixing complete HD powders and the original powders to acquire bimodal structured powders.The results are shown as follows:1.For path 1,with the increasing of hydrogenation rate and the fraction of nanostructured grains,the higher the tensile strengths are,and the lower theelongations are.The sample with 92.3% nanostructured grains has better comprehensive properties with 287 MPa of tensile strength and 6.1% of elongation.2.For path 2,with the increasing of the fraction of HD powders,the tensile strengths increase but the elongation decrease.The sample with 70 wt.% fraction of HD powders has best comprehensive properties.The yield strength,the ultimate tensile strength and the elongation are 246 MPa,291 MPa and 5.8%,respectively.