Fabrication And Properties Of Hollow Spheres/Aluminum Matrix Composite Foams

Hollow Sphere/Aluminum matrix composite foam（H/M MCF）is a new type of porous material foamed by combining the advantages of metal matrix composite and metal composite foams.It has a number of good performance characteristics such as mechanical properties,energy absorption characteristic and sound insulation performance.In this thesis,316L stainless hollow spheres and 7075 aluminum alloy were used as raw materials to prepare Hollow Sphere/Aluminum matrix composite foams at different sintering temperatures by vacuum hot-pressing sintering technology（powder metallurgy method）and T7 heat treatment.The influence of sintering temperature and heat treatment on the microstructure and properties of materials was investigated to determine the appropriate sintering temperature.Based on that,Hollow Sphere/Aluminum matrix composite foams with different porosity were also prepared,meanwhile,their mechanical and acoustic properties were studied by us.Research was carried out to explore the influence of heat treatment,porosity,stain rate on mechanical properties.And the effect of heat treatment,porosity on the performance of sound insulation was investigated.The results are given as follows:（1）With the sintering temperature increasing,the thickness of intermetallic layer in the H/M MCF increases gradually.The intermetallic layer was consisted of discontinuous lingual phase at lower temperature,then it gradually grows into an layer consisted of Fe-rich layer,non-uniform layer,Al-rich layer and a intermetallic phase extending to the aluminum matrix.After heat treatment,the grain of matrix tends to be round and the definition on the grain boundary was increased.The total thickness of intermetallic layer was increased.In addition,some defects in the intermetallic phase caused by the excessive cooling rate in solid solution treatment appear.（2）With increasing sintering temperature,part of the matrix aluminum was piled into the porous of hollow spheres by the pressure during sintering.This situation was most serious when sintering temperature arrived 570℃.Therefore,minimum porosity and maximum density are appeared under this sintering temperature.With increasing sintering temperature,the compressive strength,plateau stress and the absorption of energy increase gradually.Considering the results discussed above,550℃is the appropriate sintering temperature with better comprehensive performance in these setting temperatures.（3）The result of compression test of H/A MCF with different porosity under pre-heat treatment or heat treatment showed that the true compressive stress-stain curve of composite foam is mainly divided into three stage:linear elastic stage,stress plateau stage and densification stage.After heat treatment,the peak compressive strength,plateau stress and energy absorption were increased significantly.With increasing porosity,the peak compressive strength of samples increase firstly,then decrease gradually.The relationship of H/A MCF with different porosity was as follow:（Pre-heat treatment）_0.57<_0.30<_0.49<_0.39;（Heat treatment）_0.57<_0.49<0.30<0.39.（4）The result of sound insulation properties of H/A MCF with different porosity under pre-heat treatment or heat treatment indicated the sound insulation properties of H/A MCF would be changed to different degrees after T7 heat treatment.With increasing porosity,the increase of transmission loss decreases gradually.When the porosity of H/A MCF is 0.57,there is no increase of transmission loss after T7 heat treatment.And with increasing porosity,the transmission loss decreases gradually because of the negative influence of pores on the sound insulation performance.