Research On Microstructure And Compression Characteristics Of Glass Cenospheres/Al Foam Composites

With the rapid development of tank armor and human protective equipment,low density and high energy absorption capacity are required for impact protection materials and their structures.In this paper,glass cenospheres/Al foam composites with 1100 Al,Al-3Mg,and Al-6Mg matrix were designed and studied for shock resistance in the application of military explosion protection and transportation.The influences of Mg content and cenosphere wall thickness/radius ratio(t/R ratio)on the quasi-static compression properties,damage evolution,and dynamic compression properties of Al matrix foam composites have been systematically investigated.A sandwich structure with glass cenospheres/Al foam composite core was designed,and its stress wave propagation characteristic was discussed.By means of designing the Mg content in Al matrix,MgAl2O4 interface coating was formed in the interface between cenospheres and matrix,leading to the improvement of cenospheres' compression capacity.Based on the interface strengthening and the mechanical properties of the corresponding matrix,Al-3Mg and Al-6Mg alloys were selected as the matrix,and 1100 Al matrix was used for comparative study.The microstructure and pore structure of glass cenospheres/Al foam composites were studied.The interface of 1100 Al matrix composite was clean and no interface product.In Al-3Mg matrix foam composite,the interface reaction led to the formation of MgAl2O4 interface coating and Si.No Mg element was observed in matrix due to the complete interface reaction.The corresponding matrix composition was Al and Si.In Al-6Mg matrix foam composite,the remaining Mg reacted with Si leading to the forming of Mg2 Si after interface reaction,so the corresponding matrix composition was Al,Si and Mg2 Si.The pore structure characterizations for glass cenospheres/Al foam composites were investigated by two-dimensional image technology and ?-CT three-dimensional analysis.The cenospheres distributed uniformly in composites.The two-dimensional and three-dimensional porosity quantification results agreed well with calculations by density method.With the increase of cenospheres t/R ratio and Mg content,the quasi-static compression properties of glass cenospheres/Al foam composites were improved.The compressive strength of cenospheres enhanced with the increase of t/R ratio,resulting in the improvement of composites' compressive properties.The strengthening mechanism of Mg content on the composites' compressive properties was as follows: first,the forming of strong MgAl2O4 interface coating strengthened the cenospheres;secondly,the forming of Si and Mg2 Si reinforced the matrix.Al-3Mg matrix foam composite exhibited great energy absorption capacity due to its suitable interface tailor and good plasticity matrix.The specific energy absorption capacity of Al-3Mg matrix foam composite with 0.064 cenospheres t/R ratio was 50 J · g-1.The compressive peak stress model of Al matrix foam composites was established,and the prediction was in agreement with the experimental results.The quasi-static compression damage evolution of Al matrix foam composites was studied through digital image correlation method.From the later stage of elastic region to the peak stress,a strain concentration zone was forming at 45o tangential direction,followed by the formation of shear band.In shear band,the failure behavior of cenospheres could be concluded as: cracks initiation and propagation in cenosphere's wall,then cenosphere's wall buckling and folding,finally collapse.In the stress plateau region,the shear deformation zone expanded,and finally the composite was densified.The compression damage evolution of glass cenospheres/Al foam composite was related to the characteristic of matrix.With the increasing of Mg content in matrix,the transverse strain at the formation of shear band decreased,the deformation state of the composite in the vicinity of peak stress transformed from drum shape deformation to shear fracture,and the stress plateau region was fluctuated.The dynamic compression properties and strain rate sensitivity of glass cenospheres/Al foam composites have been discussed.The compression stress increased with the increasing of strain rates.The strain rate sensitivity was declined with the increase of Mg content.The dynamic damage behavior of Al-3Mg matrix foam composite has been studied.With low impact velocity,deformation first occurred at the core and the corner area,followed by shear bands forming and propagation.When the impact velocity was high,each parts of composite simultaneously deformed.The cenospheres in deformation zone collapsed due to shear failure.The composite significantly expanded in a lateral direction and finally compacted as disk shape.Based on the design principle of hard/soft/hard armor sandwich structure,a sandwich structure with Al-3Mg matrix foam composite core was investigated.The stress wave propagation characteristics of sandwich structure were discussed by using a combine method of experiment and simulation.The results showed that the stress wave attenuation rate of the 27 SiMn/foam composite/2024 Al structure was 0.86 at 11m/s impact velocity,which was 3.4 times as high as the double-layer structure,and was higher than the 0.76 of AZ31/foam composite/2024 Al structure.The back-plane stress of 27 SiMn/foam composite/2024 Al structure was small and stable.Glass cenospheres/Al foam composites attenuated stress wave through large plastic deformation.