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Silicon (Si) has a significant influence on the cellular structure and microstructure of the aluminum (Al) foams, which in turn will notably affect their mechanical responses. Herein, the Al–Si foams are fabricated via a novel powder metallurgy foaming approaches with multiple Si contents to investigate the role of Si concentrations on the structural and mechanical properties. The results show that the certain contents of Si can not only delay the expansion process, but also increase the maximum expansion rate to improve the cellular structure. Specifically, the AlSi7 foams process the optimal comprehensive compressive properties of yield stress (4.36 MPa), plateau stress (6.02 MPa), and energy absorption capacity (3.47 MJ m−3) with the relative density of 0.15. However, excessive Si can decrease the expansion rate and deteriorate the cellular structure. Moreover, the deformation mode of the Al foams during compressive process converts from plastic mode to brittle mode by the adding of Si. Generally, the AlSi7 foams possess an excellent trade‐off between toughness and brittleness and exhibit the optimal mechanical responses. [ABSTRACT FROM AUTHOR]

Performance of a mechanical buffer can be significantly improved by strengthening the materials and optimizing its structure. Manufacturing of high-strength and light-weight foam-filled tubes (FFTs) has been proved to be an ingenious strategy. In this work, the in situ grown carbon nanotubes (CNTs) were used to reinforce aluminum (Al) foams. The FFTs were prepared by inserting CNT/Al composite foams (CFs) into 6061 Al alloy empty tubes (ETs). The crushing behavior and energy absorption property of the as-prepared CNT/Al FFTs (C-FFTs) were evaluated using uniaxial compressive tests. The results show that the adopted CFs can effectively interact with outside tubes in C-FFTs. The C-FFTs significantly improve the compressive performance and energy absorption property, but only slightly increase the structure weight compared to single ETs. The plateau stress and energy absorption capacity of C-FFTs are nearly 3.5 and 3.7 times higher than those of ETs, respectively. This phenomenon is ascribed to the stable support of CFs and the excellent load transfer ability of CNTs. [ABSTRACT FROM AUTHOR]

A free-standing covalently bonded CNTs/graphene foam (LPM-3D rebar GF) is developed by using an in-situ loose powder metallurgy templates method for high-performance dendrite-free Li metal anodes. The LPM-3D rebar GF possesses a macroporous structure with interconnected porous pipelines. The homogeneously dispersed CNTs can induce an in-situ growth for covalently bridging graphene sheets, resulting in the increase of electrical conductivity, structural stability, and active Li nucleation sites. With the guidance of CNTs, Li metal deposit preferentially on the junctions of CNTs and graphene to achieve a uniform deposition and avoid the formation of Li dendrites effectively, which is verified by both experiments and first-principle calculations. As the anode of Li metal battery, the LPM-3D rebar GF shows outstanding cycling stability even at 20 mA cm−2 for 20 mA h cm−2. Notably, this anode can still operate 90 cycles at 30 mA h cm−2 with a Coulombic efficiency (CE) of >98%. These properties indicate promising prospects of LPM-3D rebar GF as a new and dendrite-free anode with large areal capacity for high-performance Li metal batteries, and in other fields requiring 3D carbon monoliths including fuel cells and sodium-ion batteries. Image 1 • Covalently bonded CNTs/graphene foam (LPM-3D rebar GF) wasdeveloped through an in-situ loose powder metallurgy approach. • Li was uniformly deposited under the guidance of CNTs by nucleating preferentially at the covalent junctions. • The LPM-3D rebar GF shows excellent performance at high current density of 20 mA cm−2 for areal capacity of 20 mA h cm−2. [ABSTRACT FROM AUTHOR]

• The carbon nanotubes (CNTs) reinforced closed-cell Al-Si composite foams (C-ASCFs) with CNTs content of 0.50 wt% have fatigue strength of 0.697 σ s (7.40 MPa), showing a superior improvement of the fatigue properties. • The appropriate incorporation of CNTs can change the fatigue failure mode, reduce the crack growth rate, and delay the fracture, hence raising the fatigue life. • The microstructure optimization of C-ASCFs influenced by CNT and its content was deeply investigated to interpret the influences on the fatigue properties of C-ASCFs. • The load transfer effect of CNTs in composite foams was firstly revealed, the contribution of which exhibits the largest of 2.07 MPa in 0.50 wt% C-ASCFs accounting for 22.5 % of its yield strength. As the requirement of compressive fatigue loading on the mechanical properties of aluminium foams increase rapidly, the limited fatigue performance of them significantly restricts their engineering applications. In this study, the compression-compression fatigue properties of carbon nanotubes (CNTs) reinforced closed-cell Al-Si composite foams (C-ASCFs) were investigated. The fatigue strength of C-ASCFs with 0.50 wt% CNTs increased by 54% than that of Al-Si foams, where the CNTs contributed to decrease the crack expansion rate, transfer the fatigue load and hence change the fatigue failure mode, causing a combination of plastic and brittle deformation in them. Meanwhile, the appropriate incorporation of CNTs decreased pore nucleation threshold, optimized the pore morphology, and promoted the formation and refinement of eutectic Si. Such inhibited the probability of fatigue cracks initiation, resulting in the enhancement of fatigue life. This work provides theoretical and practical basis of design strategy of Al-Si composite foams and broadens their application prospect. [ABSTRACT FROM AUTHOR]

The incorporation of nano carbon reinforcement is a useful strategy to broaden the engineering applications of metal foams. In this work, carbon nanotubes (CNTs) reinforced aluminum (Al) matrix composite foams (CNTs/Al composite foams) with different CNTs content are prepared by combining ball-milling technique with powder metallurgy method. The result shows that the appropriate content of CNTs can reduce the pore size, improve the circularity, and enhance the compressive properties. Especially, the 1.0 wt% CNTs/Al composite foams possess the optimal compressive properties of yield stress (7.90 MPa), plateau stress (8.75 MPa) and energy absorption capacity (5.19 MJ/m3), which have an enhancement of 23.24%, 98.41% and 84.70%, respectively. Composite foams undergo shear deformation throughout the quasi-static compression process, and the failure mode performs as the brittle mode combined with ductile mode. Meanwhile, the incorporation of CNTs can contribute to the inhomogeneous distribution of the Si phase, provide more nucleation sites, and significantly refine the pore size. It is confirmed that the CNTs in composite foams contribute the grain refinement and the formation of micro stacking faults, making the mechanical properties of CNTs/Al composite foams outperform the counterpart of Al-Si foams. Moreover, due to the weak interfacial reaction, the low content of aluminum carbide is formed, which can promote the load transfer between CNTs and Al. The present finding provides a theoretical and practical design strategy to the future preparation of CNTs/Al composite foams. • The CNTs/Al composite foams with CNTs content of 1.0 wt% show a superior improvement of the compressive properties. • The incorporation of CNTs can contribute to the inhomogeneous distribution of the Si phase and refine the grain size. • The deformation and failure mode of CNTs/Al composite foams are affected by the content of CNTs. • The formation of aluminum carbides and micro stacking faults benefit to promote the compressive properties of composite foams. [ABSTRACT FROM AUTHOR]

The controllable design of composition and structure makes incorporating reinforcements to be a promising way to fabricate aluminum (Al) composite foams. In this work, graphene nanosheets (GNSs) decorated with copper (Cu) nanoparticles reinforced Al composite foams are successfully synthesized via shift-speed ball-milling and space-holder method. The compressive properties and energy absorption capacity of composite foams increase first and then decrease with the increase of the GNSs@Cu content. Unexpectedly, the introduction of the GNSs@Cu has not changed the ductile failure mode of pure Al foams. The strengthening mechanisms of composite foams include load transfer strengthening and dispersion strengthening, and the toughening mechanism of composite foams is considered as crack bridging. The 0.75 wt% GNSs@Cu/Al composite foams possess the optimal yield stress (24.7 MPa), plateau stress (41.3 MPa) and energy absorption capacity (22.8 MJ/m3), which has an improvement of 104.7%, 113.7% and 115.1% in comparison with that of pure Al foams. Image 1 [ABSTRACT FROM AUTHOR]

This study presents the results of quasi-static compressive tests of aluminum (Al) foam-filled tubes (A-FFTs) and Carbon Nanotubes (CNTs)/Al composite foam-filled tubes (C-FFTs) prepared by in-situ filling space-holder method. The effects of processing parameters and interface interaction between foam fillers and tubes on mechanical properties and deformation behaviors of the C-FFTs are analyzed, through both the macro- and micro-scopic characterizations. The results show that both cold pressing and sintering can improve the interface connection between foam fillers and tubes. Besides, the addition of CNTs not only increases the strength of foam fillers, but also changes the deformation mode of foam fillers from layer-by-layer shear failure to overall shear failure, which in turn influences the mechanical properties of foam-filled tubes (FFTs). Meanwhile, the interface between foam fillers and tubes (macro interface) of the A-FFTs shows a metallurgical bonding because of the atom diffusion during cold pressing and sintering processes, and as a result, the energy absorption capability of the A-FFTs and 2.5 wt% C-FFTs are increased by 51.3% and 45.8%, respectively. Based on the current findings, a distinctive deformation behavior associated with the interaction effect is proposed. [ABSTRACT FROM AUTHOR]

• Effect of strength of tubes on performance of aluminum foam-filled tubes. • Crush behavior of aluminum foam-filled tubes at elevated temperatures. • A new criterion to predict the deformation mode of aluminum foam-filled tubes. In this paper, two types of the foam-filled tubes (FFTs), including O-FFTs and T6-FFTs, were prepared by directly inserting Al foams (AFs) into 6061-O Al alloy empty tubes (O-ETs) and 6061-T6 Al alloy empty tubes (T6-ETs), respectively. Quasi-static compression tests of studied specimens were carried out using an environmental chamber under the temperatures ranging from 25 °C to 250 °C. The results show that the mechanical properties of FFTs decrease with temperature increasing. The T6-FFTs show better energy absorption capacities while the deformation modes are less stable than the O-FFTs. The T6-ETs and T6-FFTs change the deformation mode when the temperature is higher than 150 °C. Both of the number of defects and the lengths of cracks decrease for the T6-FFTs with the increment of temperature. A couple of criteria are proposed to effectively describe and predict the deformation mode of FFTs under quasi-static compression. [ABSTRACT FROM AUTHOR]