| As a new foam material in the field of porous metal materials,steel foams have much higher strength and toughness,high temperature resistance and impact energy absorption than low-melting porous metals such as aluminum foam,and steel foams can be compatible with steel structure.The steel foam filled tube combines the characteristics of thin-walled metal tube and steel foam,with high bending resistance,high plateau stress and wide plastic platform,which has become a structural-functional material with excelent mechanical and energy absorption properties.It has a broad application prospect in machinery manufacturing,construction,shipping,packaging,transportation,aerospace.CaCl2 is used as space holders and 400 series ferrite stainless steel powder as the matrix raw material.Steel foam was prepared by powder metallurgy.The effects of different process parameters on the porosity of foam steel and the relationship between porosity and mechanical properties are discussed,and the microstructure and properties of 410L and 430L foam steel were compared.The steel foam filled tubes were fabricated by the bonding of steel foam core and metal tubes by physical method.The axial compression deformation behavior of foam filled tubes,and the effect of height,wall thickness,tube materials on its compression performance,energy absorption,and the compression deformation mechanism of the foam filled tubes were discussed and analyzed.The steel foam filed tubes with the best structure,mechanics,absorption properties were obtained.The main research contents and conclusions summarized as follows:（1）The effects of different processing parameters（volume fraction of space holders,compacting time,sintering temperature,and holding time）on the properties of steel foams were investigated.The porosity of steel foams increases with the increase of the volume fraction of the mixture.The overall performance of the steel foam is the best while the volume fraction of space holder is 75%.During the compacting process,metal powder particles are mechanically bonded,and the holding time has little effect on the porosity of the foam steel.The porosity of steel foams decreases with the increase of sintering temperature,and decreases slowly with the increase of holding time.The optimum sintering temperature is 1150℃and the optimal holding time 120min.（2）410L and 430L steel foam through high temperature sintering,the metal powder particles forming metal urgical combination,the microstructure of them isɑferrite.The bonding of 430L bond strength is better than 410L steel foam.410L steel foam is more prone to corrosion,and the surface of its cell forms a large number of FeCr mixed oxides,which distributed in the shape of fishbone.In the process of quasi-static axial compression,410L steel foam presents brittle collapse deformation,while430L steel foam collapse layer by layer.（3）Porosity is the main factor affecting the mechanical properties and energy absorption of steel foams.When the porosity of 410L steel foam is 73.01～83.40%,its yield stress is 5.45～22.06MPa,and the energy absorption value per unit volume is 2.5～6.2MJ/m3 at 50%strain.When the porosity of 430L steel foam is 73.01～83.40%,its yield stress is14.75～56.77MPa,and the energy absorption value per unit volume is11.6～40MJ/m3 at 50%strain.（4）Comparing the stress-strain curves of 430L,410L foam steel and aluminum foam,the plateau stress of 430L foam steel is up to 52MPa,which is obviously higher than that of 410L steel foam（11MPa）and aluminum foam（6.76MPa）.The energy absorption value of 430L steel foam is also significantly higher than that of 410L foam steel and aluminum foam.When the strain is 50%,the energy absorption value of 430L foam steel is 31.19MJ/m3,which is 5.16 times of 410L foam steel and 7.83 times of aluminum foam sample.Therefore,430L foam steel has better energy absorption performance.（5）During quasi-static axial compression,thin-walled aluminum tubes and steel foam-filled aluminum tubes show axisymmetric deformation mode,thin-walled steel tubes show non-axisymmetric deformation mode and steel foam tubes show mixed deformation modes.When strain in the region of 5%to 50%,the plateau stress of 430L steel foam-filled aluminum tubes is higher than the sum of aluminum tubes and steel foam.When the strain is 50%,the energy absorption value of the steel foam-filled aluminum tube is 40%higher than the sum of steel foam and aluminum tube.The plateau stress and energy absorption value of the steel foam-filled steel tube are slightly higher than the sum of steel foam and steel tube.（6）During quasi-static axial compression,the effect of height of steel foam-filled tubes on their mechanical properties and energy absorption is not obvious.When the wall thickness of the foam filled aluminum tube increases from 1mm to 2mm,the plateau stress of steel foam-filled aluminum tubes and aluminum foam-filled aluminum tubes increases about 1.3 and 1.7 times.When the strain is 45%,their energy absorption value increases about 1.32 and 3.03 times.Thicker the wall thickness of the metal foam filled tubes is,the higher mechanical properties and energy absorption performance of the foam filled tubes.The steel and aluminum foam filled steel tube samples with similar porosity,the 430L steel foam filled steel tube samples have the best mechanical properties and energy absorption properties. |
