Fabrication,Microstructure And Properties Of Nanocrystalline Foamed Magnesium

Due to their extremely efficient energy absorption,heat exchange,shock absorption,shock resistance and noise absorption properties,metallic foams have been considered the promising materials used in the area of aerospace lunar exploration,railway vehicles,household noise reduction,engine exhaust noise reduction,biomedicine,etc.Moreover,foamed Mg has become one of the research hotspots because of its extremely low densities and unique combination of excellent mechanical properties.Commonly,blowing agents are necessary to create the cellular structures in the preparation technologies of foamed Mg which use powders as the raw materials.However,the size,shape and distribution of pores introduced by blowing agents are usually uncontrollable.Moreover,the residual blowing agents and their reaction products with the matrix metals are not easy to remove completely and inevitable to weaken the properties of foams.The purpose of the present study is to develop a simple route to prepare Mg foam with higher mechanical properties but without using blowing agents.In this paper,we synthesized porous Mg through powder metallurgy（TPM）and hydrogen-dehydrogen（HD）+spark plasma sintering（SPS）techniques,respectively.By comparison,the pore size of foam Mg prepared by HD+SPS method was smaller and more distributed.The compressive yield strength of the two foams have no significant difference,but the platform strength of the HD+SPSed Mg foam was higher（9MPa）.In addition,the HD+SPSed Mg foam has better energy absorption performance of 14.9 MJ/m³,which is closer to the ideal energy absorption material.Since HD+SPS technique is effective to prepare nano-foamed magnesium without using pore-making agent,the effect of the HD+SPS parameters on the porosity and energy absorption properties of Mg foam were analyzed systematically.By changing the content of Mg H₂in the original powder and the sintering temperature,foamed Mg with a porosity of 8.7%～34.5%was prepared.With the increase of the sintering temperature the density of foamed Mg increased,and the porosity decreased from 34.5%to 17.8%.Meanwhile,the compressive yield strength of Mg foam increased from 21MPa to 43MPa,the platform strength also increased from 5MPa to 21MPa,and the corresponding energy absorption capacity increased（9MJ/m³to 41MJ/m³）.On the other hand,when the content of Mg H₂in the original powder increased from 0 to 100%,the density of magnesium foam decreased,the porosity increased from 8.7%to28.7%,the platform length in compression stress-strain curve increased,and the platform stress and compressive yield strength first decreased and then increased（from 21MJ/cm³reduced to 4MJ/cm³and then increased to 15MJ/cm³）.