Fabrication And Compressive Property Of In-Situ Grown Carbon Nanotubes Reinforced Aluminum Composite Foams Based On Rapid Powder Metallurgy Foaming Method

Owing to the characteristics of light weight,high energy absorption,damping and electromagnetic shielding properties,aluminum?Al?foam has been widely used in the fields of automotive and aerospace industries.However,the relatively low matrix strength is difficult to meet the needs of high-performance applications.Carbon nanotube?CNT?is expected to be an ideal reinforcement due to its excellent mechanical,physical and chemical properties.Unfortunately,CNTs are easily to agglomerate to clusters owing to the large aspect ratio and strong Van der Waals force,and the poor dispersity is a serious hindrance for the development of composite Al foams.Usually,Al foams are fabricated by melting method and powder metallurgy.Powder metallurgy foaming method developed in recent years is a promising approach combined of both the two usual fabrication means.Howbeit,the preparation for composite Al foams is still in its infancy.In this study,a high-efficiency manufacture of homogeneous dispersed CNT/Al alloy composite foams was achieved based on the combination of an in-situ chemical vapor deposition and the powder metallurgy method.The content of silicon?Si?and the pretreatment of titanium hydride?TiH₂?were studied while the matching relationship between the melting point of the matrix and the decomposition temperature of TiH₂ was established.The effects of powder metallurgy on the foaming process were investigated,including TiH₂ content,mixing time?Al powders,Si powders and TiH₂ powders?,cold pressure and foamable blank height.The foaming temperature and foaming time were systematically studied and chosen.In addition,the influences of CNTs on the bubbles in melt during foaming process as well as the effects of CNTs content on the improvement of compressive properties were discussed.Furthermore,the strengthening mechanism was revealed.The research results are as follows:The introduction of Si can lower the melting point of the matrix,and the pre-oxidation treatment of TiH₂ can delay the decomposition temperature,so that the balanced matching was achieved between the melting point of the matrix and the decomposition temperature of TiH₂.The pore size increased with the increment of TiH₂content while the optimal mixing time could guarantee the uniform distribution of pores.The foamable blanks are supposed to be dense as far as possible in case of the escape of H₂ decomposed from TiH₂.The moderate height of foamable blank could not only guarantee adequate expansion,but also avoid the serious gravity drainage.The foaming temperature and time should be appropriate,so that the driving force is enough and the viscosity is suitable to prevent the collapse of bubbles in the foaming process.The introduction of CNTs could provide more nucleation sites in bubbles nucleation stage and hinder the aggregation of the bubbles in growth stage.Besides,the CNTs could enhance the viscosity and improve the surface tension to avoid the collapse of the bubbles.Hence,CNT/Al composite foams possess smaller pore size and more homogenous pore distribution.The compressive results of the composites show the properties increase with the introduction and increment of CNTs.Compared with Al foams without CNTs,the plateau stress and the energy absorption capacity of 1.5 wt.%CNT/Al composite foams are enhanced by approximately 93%and 94%,respectively.The improvement of compressive properties is attributed to the load transfer and crack bridge of CNTs as well as the modification of pore morphology.