Comparative characterisation of damping behaviour of aluminium alloy composites produced by different fabrication techniques

Abstract

There is limited information currently available on the damping behaviour of silicon carbide reinforced metal matrix composites for aerospace structural applications. Dynamic mechanical analysis is one of the thermal analysis techniques which can be used to study the damping properties. In the present investigation, a dynamic mechanical thermal analyser is used to investigate the dynamic mechanical properties as a function of temperature for aluminium alloy 2124 + 5%SiC particle reinforced composites. The formation and dissolution of precipitate phases as a function of temperature have also been characterised by the technique of differential scanning calorimetry. It was observed that in all composites, the complex modulus, loss modulus, and damping capacity increased whereas the storage modulus decreased with increasing temperature.     

Mechanical damping and dynamic modulus measurements in alumina and tungsten fibre-reinforced aluminium composites

Simultaneous measurements of mechanical damping, or internal friction (Q ^–1 ), and dynamic Young's modulus (E) were made near 80 kHz and at strain amplitudes () in the range 10^–8 to 10^–4 on small specimens of continuous or chopped fibre-reinforced metal matrix composites (MMCs): 6061 aluminium reinforced with alumina (Al/Al₂O₃) and 6061 aluminium reinforced with tungsten (Al/W). Baseline experiments were also done on 99.999% aluminium (pure Al). The strain amplitude dependence of damping and the temperature dependence of dynamic modulus were of particular interest in this study. The temperature (T) dependence of the modulus from room temperature up to 475° C was determined for the Al/Al₂O₃ and pure Al specimens and a highly linear decrease in modulus with increasing temperature was observed. The rate of modulus loss (dE/dT –80 M Pa° C^–1 ) was the same for both materials and the reduction in modulus of the Al/Al₂O₃ was attributed to the reduction in modulus of the alu minium matrix, not the alumina fibres. The size, type, and amount of fibre reinforcement were found to have a significant effect on the strain amplitude dependence of the damping in both MMCs. Unreinforced aluminium exhibited classical dislocation damping trends with a region of strain amplitude independent damping at low strains (less than 10^–5) followed by a non linear, strain amplitude dependent region at higher strains. The addition of alumina fibres (chopped or continuous), while increasing stiffness, resulted in a significant reduction in damping capacity for the MMC relative to that for aluminium and near complete suppression of the amplitude dependent response. The damping levels increased as the volume fraction of fibre, and therefore, the amount of fibre/matrix (FM) interface decreased, indicating that the matrix, not factors such as increased dislocation densities at the FM interface, was the dominant influence on the damping. Analysis of the Al/Al₂O₃ results by Granato-Lücke (GL) theory indicated that dislocation densities were increased relative to those in aluminium, but the dis locations were well pinned and unable to increase damping levels effectively. Analysis of the Al/W results by GL theory also revealed high dislocation densities, but, unlike the Al/Al₂O₃ specimens, the Al/W specimens (continuous fibres) exhibited strong amplitude dependent damping (starting near strain levels of 2 × 10^–6) with damping levels approximately twice those of pure aluminium. Trends showed increased damping with increased fibre diameter, not with increased FM interface area. There was some evidence that it was the tungsten fibre itself that dominated the damping behaviour in Al/W composites, not the aluminium matrix or the FM interface.     

A new cladding technology to bond aluminium on magnesium

ABSTRACT

An in situ hot press bonding technology has been developed to clad aluminium on magnesium. Followed by regular hot rolling, magnesium sheets, covered by ductile and corrosion-resistant aluminium without detectable oxides in the interface, are produced. The new technology requires no welding, vacuum, protective atmosphere or barrier layer, and it makes good interfacial strength and rollability. Aluminium–magnesium intermetallic phases are formed along the clad–core interface at elevated temperatures. They are not detrimental under compression but may cause clad-core delamination in tensile strain. However, the tensile failure is more dependent on the formability of magnesium core than on the strength of interface.     

Influence of strain amplitude on damping property of aluminum foams reinforced with copper-coated carbon fibers

Aluminum foams containing 0.35, 1.0, 1.7 vol.% copper-coated carbon fibers were fabricated by a melt route. The room temperature damping property of Al/C_f foam was studied at different strain amplitude in two directions. The experimental results show that the critical strain amplitude decreases and the damping capacity of Al/C_f foam increases with the copper-coated carbon fibers contents. It can be attributed to the interfacial micro-slip increasing with the C_f contents and the microplasticity deformation arises from the micro-crack among the C_f–Al interface. Moreover, the damping property in the transverse direction is higher than that in the longitudinal direction. The ratio of longitudinal loss factor to transverse loss factor is almost independent of the C_f contents and strain amplitude.     

Investigation on interface of Al/Cu couples in compound casting

Abstract

The joining of Al and Cu commercially pure metals using the compound casting process has been investigated where an aluminium melt is cast onto a solid cylindrical copper insert. The microstructure of the interface between copper core and surrounding aluminium was characterised by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and Vickers hardness tests. Results showed that five separate reaction layers are formed in the reaction interface of core and surrounding Al. These layers included Cu₉Al₄, AlCu and Al₂Cu intermetallic compounds; a eutectic layer; and a eutectic α-Al dendritic structure layer. Owing to the presence of hard and brittle intermetallic compounds within reaction layers, microhardness profile showed a peak of 300 HV where both parent metals have hardness <50 HV. Microhardness profile also showed that hardness decreases from the copper to the aluminium side.     

Damping characterisation of aluminium containing interconnected wire reinforcement using a novel frequency domain based method

Abstract

In this study, an aluminium alloy, AA 1050, was reinforced with an interconnected, axisymmetrical, galvanised iron wire preform. The composite was synthesised using a conventional casting technique followed by hot extrusion. The composite was tested in a free - free type suspended beam arrangement, coupled with circle fit approach to determine damping characteristics. This testing method is based on classical vibration theory, by which the geometry and material properties of the metal matrix composites are related to the resonant frequency and structural damping of the test specimen. Using the fact that the ratio of the vibration response to the applied force fits to a circle in the Argand plane for each resonant frequency of the test specimen, the damping factor and natural frequency is predicted accurately for the test specimen. To demonstrate the accuracy of the test method, test results of a pure aluminium sample are compared against results from other test methods from published literature. Results of this study show that addition of about 5% of interconnected reinforcement increases the overall damping capacity of the aluminium matrix by ~ 17%. An attempt is made to correlate the increase in damping with the reinforcement associated microstructure variation of the aluminium matrix.     

退火工艺对Al/Mg/Al复合板界面结合与阻尼性能的影响

研究了Al/Mg/Al三明治结构复合板的退火热处理工艺,探讨了退火温度、时间对复合界面和阻尼性能的影响。结果表明:退火使得Mg层中的孪晶及变形组织消失,晶粒明显长大,且可以促进Al-Mg界面原子的相互扩散。随着退火温度的升高,界面效应对复合板的阻尼性能影响由不利转变为有利,在250℃下随着退火时间的延长,复合板的阻尼性能有一定的提高。综合复合板的组织与性能要求,得到Al/Mg/Al复合板的最佳退火工艺为250℃×2h,在应变振幅为5×10~(-4)下复合板的阻尼值Q~(-1)达0.045。     

Friction welding process of 5052 aluminium alloy to 304 stainless steel

Abstract

Type 5052 aluminium alloy was joined to type 304 austenitic stainless steel via a continuous drive friction welding process. The joint strength increased, and then decreased after reaching a maximum value, with increasing friction time. Joint strength depended on the size and shape of the tensile testpiece. Friction weldability could be estimated by electrical resistmetry. The process of friction welding between the aluminium alloy and the stainless steel is proposed to evolve as follows: welding progresses from the outer to the inner region; an unbonded region is retained at the centre of the weld interface with shorter friction time; longer friction time causes the formation of an intermetallic reaction layer at the weld interface; and the reaction layer grows as the friction time increases. When the thickness of the reaction layer increased above a critical value, the joint was brittle and fractured at the weld interface. The joint was sound when there was no unbonded region and a thin reaction layer formed along the entire weld interface.     

Design of μ-CNC machining centre with carbon/epoxy composite–aluminium hybrid structures containing friction layers for high damping capacity

The focus of this paper is on the design of machine tool structures, such as columns and spindle holders, for a 3-axis μ-CNC machining centre. Carbon/epoxy composite–aluminium hybrid structures with friction layers were used to increase structural damping. Two types of hybrid column structures were proposed. Finite element analyses were carried out to calculate both the static deflection of columns due to deadweight and also the first natural frequency of machine tool structures as a function of the stacking angle and thickness of the carbon/epoxy composites. To increase damping capacity, a friction layer was inserted between the aluminium-composite interface. For the design of the structures the stacking angle and the thickness ratio of the composites were considered as major design variables. And the most appropriate stacking sequence of the composite–aluminium hybrid structure employing a friction layer was determined using finite element analyses and vibration tests.     

Effect of the interface bonding on the mechanical response of aluminium foam reinforced steel tubes

Aluminium foams have been recently proposed as filling reinforcements to improve impact behavior of hollow components used as protection systems in vehicles. In this study, aluminium foam filled stainless steel tubes have been prepared by directly foaming metal powder compacts inside the tubes. Attention was concentrated on the interface phenomena that characterize the core–shell interaction and the process parameters determining the metallurgical reactions between the two alloys. The formation of binary and ternary intermetallic compounds was observed at the aluminium/steel interface whenever the growth of the oxide layer on the foam surface in foaming was constrained. Compression tests of the reinforced tubes confirmed a maximized energy absorption in coincidence with the formation of the interface bonding. In those cases, extended foam intrusions into compressed tube folds were observed. The microstructural investigation revealed that in the transition zone the intermetallic layer strength was comparable to that of the foamed matrix.     

Damping properties of open cell microcellular pure Al foams

Abstract

Damping behaviours of the open cell microcellular pure Al foams fabricated by sintering and dissolution process with the relative density of 0·31–0·42 and the pore size of 112–325 μm were investigated. The damping characterisation was conducted on a multifunction internal friction apparatus. The internal friction (IF) was measured at frequencies of 1·0, 3·0 and 6·0 Hz over the temperature range of 298–725 K. The measured IF shows that the open cell pure Al foam has a damping capacity that is enhanced in comparison with pure Al. At a lower temperature (～400 K), the IF of the open cell pure Al foams increases with decreasing relative density, with decreasing pore size and with increasing frequency. The IF peak was found at the temperature range of 433–593 K in the IF curves. It is clear that the IF peak is relaxational type and the activation energy associated with the IF peak is about 1·60 ± 0·02 eV. Defect effects can be used to interpret the damping mechanisms.     

Factors affecting the damping capacity of cast aluminium-matrix composites

The damping capacity of stir-cast aluminium-matrix composites containing graphite and silicon carbide particles, were studied using a cantilever beam specimen and an HP 5423A Structural Dynamics Analyser. Damping data were determined in the first mode of vibration. Aluminium-matrix composites containing 5–10 vol % graphite particles and 10 vol % silicon carbide particles were prepared by the stir-casting technique and die cast to obtain standard samples (6 mm×25 mm100 mm). Graphite particles were found to be more effective in enhancing the damping capacity of composites compared to silicon carbide particles. The damping capacity of composites increased with the volume percentage of graphite within the range studied. However, no notable improvements in damping capacity were observed by dispersion of silicon carbide in aluminium alloy. The results have been analysed in terms of the effect of size, shape, nature and volume fraction of particles on the damping capacity of the aluminium matrix particulate composites and compared with the damping capacity data available in the literature. The effects of frequency, strain amplitude, temperature and processing on damping capacity of the aluminium matrix composites are reviewed.     

The characterisation of the interfacial chemistry of adhesion of rigid polyurethane foam to aluminium

The interfacial interactions between a rigid polyurethane foam (RPUF) and aluminium have been studied to understand the mechanisms of adhesion. Three different blowing systems are used in the production of the foam: chemical blowing, physical blowing and a mix of chemical and physical blowing systems. In addition an unfoamed system has been examined for comparison of the catalysts behaviour with and without blowing agents and the surfactant. Peeled failure surfaces have been examined by X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF–SIMS). To examine the intact interfacial regions of the RPUFs cured against aluminium, samples have been sectioned by microtomy. The failure surfaces of the aluminium sides exhibit relatively clean aluminium surfaces with RPUF residues observed for all three foamed systems; such thin RPUF layers (ca. 1 nm) indicate good adhesion (and a cohesive failure) between foam and substrate and that the interfacial adhesion is higher than the cohesive strength of the foam. The unfoamed system behaves in a similar manner but has a higher peel strength. A fragment indicative of covalent bond formation between isocyanate and aluminium (nominal mass at 102 u: AlCHNO₃ ⁻) is observed on the failure surface of aluminium side, where RPUF/aluminium interface region is present, for all foams. The catalyst used in these formulations, pentamethyldiethylenetriamine (PMDETA), is concentrated at the interface area. Whilst examination of the sectioned specimens shows that the silicone surfactant is concentrated within the cell area fulfilling its role on cell formation and stabilisation, and is not segregated at the RPUF/aluminium interface.     

Microstructure of Al/Al bimetallic composites by lost foam casting with Zn interlayer

A novel method named the lost foam casting (LFC) liquid–liquid compound process with a Zn interlayer was proposed to prepare the Al/Al bimetallic composites, and the microstructure of the Al/Al bimetallic composites was investigated in the present work. The results showed that the Al/Al bimetallic composites were successfully produced using the novel process. The Zn interlayer prevented different liquid metals from directly mixing. A uniform and compact metallurgical interface was obtained between the Al and the A356 aluminium alloy, which consisted of the η-Zn, α-Al rich, α?+?η eutectoid, and primary silicon phases. The microhardness of the interface layer was significantly higher in comparison with those of the Al and A356 matrixes.     

Effect of graphite addition on martensitic transformation and damping behavior of NiTi shape memory alloy

In this investigation, the effect of graphite addition on martensitic transformation and damping behavior of Ni₅₀Ti₅₀ (at.%) shape memory alloy has been studied. It is found that martensitic transformation temperature decreases obviously with the addition of graphite. Microstructural observation shows that TiC precipitates and forms whiskers when the carbon content is increased beyond ~ 0.6%. With the increase of graphite content, the damping capacity during reverse transformation increases initially and then decreases while the damping capacity of full martensite is remarkably improved by the addition of graphite particles. It is proposed that the enhancement of damping capacity can be ascribed to the high damping capacity of graphite itself, as well as, the increase of the amount of interface between martensite and austenite can be beneficial to the damping capacity.     

稀土氧化物填充丁基发泡橡胶阻尼性能的研究

制备了一种具有较好阻尼性能的丁基发泡橡胶,研究了发泡、补强剂种类、稀土氧化物种类对丁基橡胶阻尼性能的影响,并对其泡孔形貌进行了表征。结果表明,发泡后丁基橡胶的阻尼性能优于未发泡的丁基橡胶;加入白炭黑后丁基发泡橡胶的损耗峰明显高于加入炭黑后丁基发泡橡胶的损耗峰,但加入炭黑的丁基发泡橡胶具有较宽的有效阻尼温域;稀土氧化钆(Gd_2O_3)由于具有磁性,其作为填料时,丁基发泡橡胶的阻尼性能较好,泡孔形貌均一、分布均匀,且多为闭孔。     

Analysis of coating layer formedon steel strips during aluminising by hot dipping in Al-Si baths

Abstract

Aluminising of low carbon (0.19 wt-%C) steel was carried out using AI-0, 4, 8, and 12 wt-%Si melts. Different dipping times and melt superheat were used. In all cases, a coating layer was formed which is composed of an intermetallic layer and an aluminium top coat layer. The thickness of the intermetallic layer increased with bath temperature, especially in pure aluminium baths, and decreased with increasing silicon content. Addition of more than 8 wt-%Si to the bath had no detectable effect on the thickness. This thickness X increased with time following the parabolic relationship X =KTⁿ, where the growth rate constant K decreased with silicon content. Energy dispersive X-ray analysis revealed that the intermetallic layer is composed of a thick layer of AI₅Fe₂ followed by a much thinner one of Al₃Fe on the aluminium side. In the case of a silicon containing bath, different Al_xFe_ySi_z compounds were identified. The kinetics of the reaction between solid steel and liquid aluminium were studied. In AI-Si baths, the growth rate of the intermetallic layer was lower and its dissolution rate higher compared with a pure aluminium bath. Separation of parts of the layer was also found. Iron loss from the steel strip, especially in the case of AI-Si baths, was partly used in the formation of both the measured and the dissolved layer and partly dissolved in the melt. The growth rate of the layerwas evaluated and the activation energy was found to be 138.46 and 106.65 kJ mol^-1, for pure aluminium and Al-8Si baths respectively.     

The elevated temperature strengths of alumina-aluminium and magnesium-aluminium samples

Pairs of alumina cones were soldered with aluminium at 1000° C and tested in tension at 20 to 500° C. The fracture strengths of the samples fell between the ultimate tensile strength of aluminium and the fracture strength of alumina, reaching a maximum at a temperature that depended on the thickness of the aluminium solder layer. The sample fracture surfaces produced by room temperature strength tests were entirely ceramic but became increasingly metallic at higher test temperatures. In contrast, the fracture strengths of magnesia cones soldered with aluminium did not peak between 20 and 500° C, and the location of the fracture surfaces could not be related to the testing temperature or sample strengths. It is argued that the effects observed with alumina-aluminium samples are due to the conflicting influence of the testing temperature on relaxation of residual stresses within the ceramic and the ability of the metal solder layer to deform. In the case of the reactive magnesia-aluminium system, strengths seemed to be largely determined by the formation of a MgO.Al₂O₃ spinel layer at the ceramicmetal interface during soldering and by the fragility of the porous ceramic.     

Effect of high energy ball milling on solid state reactions in Al–25 at.-%Ni powders

Abstract

The effect of high energy ball milling on the solid state reactions between aluminium and nickel in Al–25 at.-%Ni powders has been investigated using scanning electron microscopy, thermal analysis techniques, and X-ray diffractometry. It has been observed that the microstructure of the powder particles evolves in three stages: stage I is the formation of entrapped nickel particles in the aluminium matrix structure; stage II is the formation of an Al–Ni multilayered structure; and stage III is the formation of Al₃Ni single phase. The temperature required to activate the reaction between aluminium and nickel during heating decreases by more than 200 K as the powder particle microstructure evolves from the entrapped particle structure to the multilayered structure, and then it decreases gradually with decreasing nickel layer thickness. The nucleation and lateral growth of Al₃Ni phase at the Al/Ni interfaces occurs at much lower temperatures than those required for the transverse growth of Al₃Ni. The fraction of Al₃Ni formed through nucleation and lateral growth at the interface is almost linearly proportional to the interfacial area. The activation energy for nucleation and lateral growth of Al₃Ni at the Al/Ni interfaces is independent of nickel layer thickness, but the activation energy for transverse growth of Al₃Ni decreases substantially with decreasing nickel layer thickness. The latter is attributed to the observation that the nickel layers are thinned by plastic deformation and thus contain an increasingly higher density of dislocations.     

Harnessing Three Dimensional Anatomy of Graphene Foam to Induce Superior Damping in Hierarchical Polyimide Nanostructures

Graphene foam‐based hierarchical polyimide composites with nanoengineered interface are fabricated in this study. Damping behavior of graphene foam is probed for the first time. Multiscale mechanisms contribute to highly impressive damping in graphene foam. Rippling, spring‐like interlayer van der Waals interactions and flexing of graphene foam branches are believed to be responsible for damping at the intrinsic, interlayer and anatomical scales, respectively. Merely 1.5 wt% graphene foam addition to the polyimide matrix leads to as high as ≈300% improvement in loss tangent. Graphene nanoplatelets are employed to improve polymer–foam interfacial adhesion by arresting polymer shrinkage during imidization and π–π interactions between nanoplatelets and foam walls. As a result, damping behavior is further improved due to effective stress transfer from the polymer matrix to the foam. Thermo‐oxidative stability of these nanocomposites is investigated by exposing the specimens to glass transition temperature of the polyimide (≈400 °C). The composites are found to retain their damping characteristics even after being subjected to such extreme temperature, attesting their suitability in high temperature structural applications. Their unique hierarchical nanostructure provides colossal opportunity to engineer and program material properties.