Fabrication And Pore Structures Of GASAR Aluminum-Copper Alloys

In recent years, GASAR (the metal-gas eutectic method) has received considerable attention as a new process for preparation of porous metal. As a kind of porous metals, GASAR metal shows high specific strength/stiffness, energy absorption, damping vibration, sound absorption and insulation, electromagnetic shielding and many other excellent properties. In addition, because of its unique directional pore structures, GASAR metal has the characteristics of stress anisotropy. Based on its unique structure and good performance, GASAR metal will have a good application prospect in aerospace, automobile manufacturing, transportation, medical industry and many other fields.In this work Al-Cu alloys were fabricated by the directional solidification technique at the hydrogen atmosphere. The influence of temperature and hydrogen pressure on the porosity of GASAR Al-5%Cu alloy was investigated. The result shows that:the improvement of the temperature and hydrogen pressure can increase the hydrogen solubility in the liquid aluminum copper alloy and make the porosity increase in GASAR Al-5%Cu alloys. The compressive properties of GASAR Al-5%Cu alloys with different porosity were investigated and stress-strain curves with three stages of deformation were showed, i.e. elastic deformation stage, collapse deformation stage and densification stage. With the increasing of porosity, the "platform areas" of stress-strain curves are more obvious.The influence of the copper content (5,10,15,20,25,30 and 33 wt.%) on the pore structure and porosity was investigated. The results show that both the porosity and the average pore diameter of the specimens increase with the increasing of the copper content when the copper content is between 0-25%. When copper content is between 25%-33%, the porosity and average pore diameter decrease with the increasing of copper content. It is revealed that pores are almost absent in the alloys with copper content 33 wt.%which is the eutectic composition of Al-Cu alloys. Meanwhile, it is noticed that the shape of pores gradually transforms from elongate to a spherical one with the increasing of copper content. Such results can be explained as following:the pores are affected by the primary-precipitated phase and the width of the mushy zone. The diffusion of hydrogen atoms is affected by the width of mushy zone. The porosity and diameter of pores increase with the decreasing of the width of mushy zone. The lamellar structure of eutectic composition is not conducive to the porosity formation, so there are no pores in Al-33%Cu alloy. The development of the pores is limited by the primary-precipitated phase. Thus, with the decrease of the primary-precipitated phase, the pores change from elongate to spherical. The compressive properties of GASAR Al-Cu alloys with different Cu content were investigated. The result shows that with the increasing of copper content, the strength of GASAR Al-Cu alloys increases while the plasticity decreases.