Fabrication, Properties Of Entangled Metallic Wire Materialand Its Strengthening Effect Onaluminum Matrix

Both porosity and metallicity are integrated into the porous metals, which havecomprehensive applications in various fields of industry such as filtration and separation,heat transfer, flame retardant, catalyst carrier, energy absorption and damping, andbiomedical implants. The weaknesses of complex fabrication processes, high cost, andinferior toughness, however, always limit the ever-increasing applications of porousmetals. In order to overcome the bottleneck of conventional porous metals, new kinds ofporous metals referred to as entangled metallic wire materials (EMWMs) have beenfabricated by using commercial metallic wires and following a simple three-step route, i.e.,'preparing coil-like springs-entangling stretched springs-volumetric compression'. Thestructures, quasi-static mechanical behaviors, energy absorption and auxetic of EMWMshave been researched systematically. On the other hand, A356aluminum alloy liquidphase was squeezed into the pores of EMWMs consisting of the through-connected poresby squeezing casting. The microstructures, mechanical properties of aluminum alloyreinforced with EMWMs, and their strengthenging effect on aluminum alloy have beeninvestigated.The structures indicate that EMWMs are kinds of three-dimensional (3D)through-connected networks and that they consist of lots of coil-like springs assembled byentangling, interconnecting, interlocking, and overlapping. The morphology and size of the pores in EMWMs are very complicated, and non-bonding cross-points are formed bythe physical contact of the wires' surface. The samples show obvious anisotropy in3Dspace, but present 'global homogeneity while local inhomogeneity'in all solo sections.Entangled aluminum alloy wire materials (EAWMs) with57~77%porosity preparedby using5052Al wires with0.28mm in diameter exhibit a typical three-stage stress-strainbehavior under uniaxial compressive loading, i.e., initial nonlinear quasi-elastic stage,strain-hardening pseudo-platform stage, and the final densifying stage. The nonlinear andstrain-hardening behaviors are ascribed to the structural elastic deformation and structuralplastic deformation, respectively. The loading/unloading curves indicate the significantstrain-hysteresis effect which results from the irreversible rearrangement of the wires inspace. Both the yield strength and elastic modulus decrease with the increasing porosity.The data of the yield strength obeys the power law relationship suggested by G-Aequation,and a larger exponent2.1is obtained. Compared with that of conventional porous metals,it indicates that the yield strength of EAWMs is more sensitive to the porosity. And theenergy absorption of EAWMs decreases as porosity increases at the same strain level, andthe maximum efficiency of energy absorption is about55~67%and appears in the range of10~35%strain level.Entangled stainless steel wire materials (ESWMs) with45~80%porosity prepared by304stainless steel wires with0.10mm in diameter exhibit a novel three-stage stress-strainbehavior under uniaxial tensile loading, i.e., nonlinear elastic stage, quasi-platform steadydeveloping stage, and continuing loosing stage. This kind of material shows a very largetension strain level, e.x., a260%strain has been obtained for ESWMs with45%porositywhen just considering the early two deformation stages, which can be attributed to theconcurrent role of coil-like springs and non-bonding joints. And stress increases abruptlywith the strain at the third stage, which is quite different from that for conventional porousmetals and is attributed to the strectching of coil-like springs. The yield strength andelastic modulus decrease as the porosity increases. And the data accord by a power-law relationship, but all the values are obviously lower than that predicted by G-Aequation.ESWMs, noticeably, exhibit significant auxeticity in a large range of tensile strainlevel. The samples with60%and45%porosity show the Poisson's ration of-1.3and-1.5at the out-of-planes at5%tensile strain. Bashed on the observation of both entangledstructures and tensile evolution, a new auxetic mechanism named as 'network unclosing'has been proposed, which includes three sub-mechanisms, i.e.,'stretching of wire','enlarging of pore', and 'decreasing of cross-points'. The result of semi-quantitativecalculation indicates that the initial entangled structure is extremely important for theauxeticity of ESWMs.The microstructures indicate that the interface between the aluminum alloy matrixand304stainless steel wires shows fair cohesion without any reaction products, and thedensity indicates the pores of ESWMs were fully filled without any micro-pores or otherdefects. The uniaxial compression tests show that the yield strength of aluminum alloyreinforced with entangled structure of35.4vol.%comes up to318MPa which is abouttwice higher than that of A356alloy (about164MPa). Noticeably, the yield strength ofaluminum alloy reinforced with entangled structure is sensitive to the volume fraction ofentangled structure: the yield strength is reasonably low and appears below the Voigtupper bound when the volume fraction of entangled structure is lower than26.5vol.%; butthe yield strength increases significantly beyond the upper bound when the volumefraction of entangled structure becomes larger than26.5vol.%. This phenomenon can beattributed to the structure-strengthening role of the entangled wire preforms.