Investigation of carbon nanotube reinforced aluminum matrix composite materials

We have increased the tensile strength without compromising the elongation of aluminum (Al)–carbon nanotube (CNT) composite by a combination of spark plasma sintering followed by hot-extrusion processes. From the microstructural viewpoint, the average thickness of the boundary layer with relatively low CNT incorporation has been observed by optical, field-emission scanning electron, and high-resolution transmission electron microscopies. Significantly, the Al–CNT composite showed no decrease in elongation despite highly enhanced tensile strength compared to that of pure Al. We believe that the presence of CNTs in the boundary layer affects the mechanical properties, which leads to well-aligned CNTs in the extrusion direction as well as effective stress transfer between the Al matrix and the CNTs due to the generation of aluminum carbide.     

An aluminum borate whisker-reinforced aluminum matrix composite with high plasticity

A pure aluminum matrix composite reinforced by ZnAl₂O₄-coated Al₁₈B₄O₃₃ whiskers was fabricated by a squeeze casting technique. The effect of ZnAl₂O₄ coating content on the wettability between whiskers and matrix, the ultimate tensile strength and elongation to fracture of the composite were investigated. The results show that the interface wettability and the ultimate tensile strength increase with increasing the coating content. The coating content remarkably affects the elongation to fracture of composites. When the mass ratio of ZnO and ABOw is 1:30, the elongation to fracture of the composite can reach 7.9% at room temperature.     

Wear behaviour of aluminium matrix composite materials

Wear behaviour of aluminium matrix composites is characterized by the dry spindle wear test under various conditions (volume fractions of reinforcements, sliding distances and speeds). Wear resistance of composites is improved due to the presence of reinforcements, but no noticeable improvements are observed in the wear resistance with more than 20% addition of reinforcements. To analyse wear mechanisms, wear surfaces are examined by scanning electron microscopy (SEM). The major wear mechanisms of discontinuous metal matrix composites (MMC)s are strongly dependent on sliding speeds. Dominant mechanism is the adhesive-abrasive wear at low and intermediate sliding speeds, and melt wear at high sliding speeds. Weight loss is linearly increased with the sliding distance. The effect of reinforcements' orientations on wear behaviours is also discussed.     

Polymer matrix,polymer ribbon-reinforced transparent composite materials

Composites of a polymer–matrix reinforced by polymer ribbon monofilaments are investigated as mechanically robust, transparent composite materials. Transparent nylon monofilaments are mechanically worked to form flattened nylon ribbons, which are then combined with index-matched epoxy resin to create transparent composites. A range of optical and mechanical experiments are performed on composites and surrogate systems in order to quantify properties and guide system design. The results show that these polymer–polymer composites provide good transparency over a wide temperature range, and superior ballistic penetration resistance compared to monolithic transparent polymers.     

Properties of high reinforcement-content aluminum matrix composite for electronic packages

Aluminum matrix composites reinforced by a high volume fraction of ceramic particles provide a novel solution to electronic packaging technology, because of their high thermal conductivity, compatible and tailorable coefficient of thermal expansion (CTE) with chips or substrates, low weight, enhanced specific stiffness, and low cost. In this paper, SiC-particle-reinforced aluminum matrix composites are fabricated by the cost-effective squeeze-casting technology, and their microstructure characteristics, thermo-physical, and mechanical properties are investigated. The reinforcement volume fraction is as high as 70% and composites with linear CTE of 6.9–9.7×10^–6 °C^–1 and thermal conductivity of 120–170 W m^–1 °C^–1 are produced. The composites can be electric-discharge machined, ground, and electric-spark drilled. An electroless nickel layer is plated on the composite by the conventional procedures. Finally, their potential applications in electronic packaging and thermal management are illustrated via prototype examples.     

含锂霞石颗粒和硼酸铝晶须的铝基复合材料

为了制备具有低热膨胀系数和较高强度的复合材料，选用具有负体膨胀系数的β-锂霞石颗粒和高强度的硼酸铝晶须作为复合材料组分，用挤压铸造法制备了6061铝基复合材料，并对该复合材料的显微结构、拉伸性能和热膨胀性能进行了研究，结果表明，该复合材料能同时获得较低的热膨胀系数和较高的强度；通过改变复合材料中β-锂霞石和硼酸铝的体积分数，在较大的范围内可以对复合材料的强度和热膨胀系数进行设计和调节。     

A boundary element analysis of metal matrix composite materials

The numerical modelling of metal matrix composites is an important part of the research now being conducted on these materials. Due to the numerical complexity of a fully three-dimensional analysis, two-dimensional approximations are normally used with finite element methods. While these analyses are informative, they cannot treat complex particle shapes or examine three-dimensional effects in the composite. The use of boundary element methods in place of the more widely used finite element methods significantly reduces the computing power necessary to obtain a solution to a given problem, making it possible to simulate fully three-dimensional geometries. In the present paper a two-dimensional form of the BEM is applied to the study of metal matrix composite materials, and its performance compared with that of similar FEM stadies. We also compare the predicted composite properties with existing and new experimental results. We conclude that the BEM is an effective tool for the analysis of this class of problems.     

Strength analysis of random short-fibre-reinforced metal matrix composite materials

A theory to analyse the strength of composite materials with randomly oriented short fibres has been developed. The short fibres are assumed to be uniformly distributed and randomly oriented in three dimensions. The non-homogeneous deformation within the composite has been taken into account in the strength calculation. The influences of thermal stress in the short fibres, the short-fibre dispersion hardening and the dislocation density in the matrix on the composite strength have all been estimated, and the strengthening mechanisms involved are discussed. A comparison with previous strength theory suggests that the present theory gives a better agreement with experimental data, and can be used to explain some experimental phenomena that remain unsolved.     

6061铝颗粒层增强7075铝基复合材料的微观结构及阻尼性能

采用热轧法制备出具有颗粒层状结构的6061p/7075铝基复合材料以改善7075铝合金的阻尼性能。通过OM、SEM、EDS和XRD分析6061p/7075层状铝基复合材料的微观组织,分别采用万能力学试验机和动态热机械分析仪分析其力学性能和阻尼行为。研究表明,6061铝颗粒层存在大量的颗粒间界面和微小孔隙,6061铝颗粒层与7075铝基体之间界面结合良好,没有发生界面反应;6061p/7075层状铝基复合材料最大抗拉强度为370.5 MPa,比7075铝基体提高了30%;6061p/7075层状铝基复合材料和基体材料的内耗值分别随着温度和应变量的升高而增大,复合材料的阻尼性能明显优于7075铝基体,在360℃时,复合材料的内耗值高达0.117,比7075铝基体提高了149%;6061p/7075层状铝基复合材料和基体材料的储能模量分别随着温度和应变量的升高而降低,在30℃时,复合材料的储能模量为38601 MPa,比7075铝基体高16%。      

Cavitation resistance of powder metallurgy aluminum matrix composite with AlN dispersoids

The cavitation erosion resistance of P/M aluminum alloy sintered composite with AlN dispersoids, prepared via the in situ synthesis and the conventional premixing process, was evaluated by using a magnetostrictive-vibration type equipment. In situ synthesized AlN particles were effective for the improvement of the erosion resistance of the composite because of their good bonding with the aluminum matrix. The additive AlN by the premixing process were easily detached from the specimen surface due to the insufficient coherence with the matrix, and caused the poor resistance. The cavitation resistance also depended on the porosity of the sintered composite. The continuously opened pores accelerated the wear phenomena by the cavitation due to the high pressure attack on the primary particle boundaries of sintered materials in the collapse of the bubbles.     

Structure and properties of modified compocast microsilica reinforced aluminum matrix composite

A356 aluminum alloy reinforced with 7 wt.% microsilica composites was produced by the three different processing routes viz. liquid metal stir casting followed by gravity casting, compocasting followed by squeeze casting and modified compocasting route and their properties were examined. Microstructure of liquid metal stir cast Al MMC shows agglomeration of particles leading to high porosity level in the developed material. Adopting new route of compocasting followed by squeeze casting process prevents the agglomeration sites with uniform distribution and dispersion of the dispersoids in the matrix metal. Modified compocasting process reduces the segregation of particles in the final composites thus enhancing the mechanical, tribological and corrosion properties of the composites. Superior wear-resistance properties were exhibited by the modified compocast composite compared to the unreinforced squeeze cast alloy and abrasive type wear mechanism was observed in the case of composite. Increasing the sliding speed resulted in the quick evolution of tribolayer and the wear rate of composite gets reduced. The presence of intermetallic phases like MgAl₂O₄, NaAlSi₃O₈ and KAlSi₃O₈ has a favorable effect on increased corrosion resistance of the composite. Microsilica particles significantly enhanced the compressive strength of modified compocast composites compared to the unreinforced squeeze cast Al alloy.     

Microstructure and mechanical properties of graphite fiber-reinforced high-purity aluminum matrix composite

Industrial pure aluminum (0.5 wt% impurity elements) was utilized in many investigations of aluminum matrix composites at home and abroad. However, impurity elements in industrial pure aluminum may influence the interface during fabrication of composite at high temperature. Thereby, it is necessary to use high-purity aluminum (impurity elements less than 0.01%) as matrix to enable study the interface reaction between reinforcement and matrix. In this study, stretches of brittle Al₄C₃ at the fiber/matrix interfaces in Gr_f/Al composite were observed. The fracture surface of the composite after tensile and bending tests was flat with no fiber pull-out, which revealed characteristic of brittle fracture. This was related to Al₄C₃, as this brittle phase may break before the fiber during loading and become a crack initiation point, while the corresponding crack may propagate in the fiber and the surrounding aluminum matrix, finally resulting in low stress fracture of composites.     

Research on laser welding of aluminum matrix composite SiCw/6061

Effects of laser welding parameters on strength of welded joint were studied. Mechanism of loss of joint strength was analyzed. It was pointed out that an important factor affecting joint strength is the reaction between matrix and reinforced phase. On the basis of this, the concept of critical Si activity was proposed. In appropriate welding parameters and Si activity, welded joint with high quality for aluminum matrix composite SiCw/6061Al subjected to laser welding could be successfully obtained.     

Manufacture of one-piece automotive drive shafts with aluminum and composite materials

The natural bending frequency of a torque transmission shaft can be increased without reducing the torque transmission capability if the shaft is made using both carbon fiber composite and aluminum: the former increases the natural bending frequency and the latter sustains the applied torque. The high natural bending frequency of a shaft makes it possible to manufacture the drive shaft of passenger cars in one piece.

In this work, a hybrid one-piece drive shaft composed of carbon fiberepoxy composite and aluminum tube was manufactured by co-curing the carbon fiber on the aluminum tube.

The fabricational thermal residual stresses due to the coefficient difference of thermal expansions of aluminum and carbon fiber composite were eliminated by applying a compressive preload to the aluminum tube before the co-curing operation.

From the dynamic tests, it was found that the first natural bending frequency and the minimum static torque transmission capability of the hybrid shaft were 9000 rpm and 3550 Nm, respectively, and the shaft did not fail until 10⁷ cycles under a dynamic load of ± 500 Nm.     

晶须增强铝基复合材料的热压缩变形行为研究

采用试验和数值模拟相结合的方法研究了纵向、横向和倾斜分布的晶须增强铝基复合材料热压缩变形行为.研究表明:SiCw/6061Al复合材料300℃压缩的应力-应变行为与晶须取向角密切相关;在热变形过程中,纵向分布晶须折断严重,导致复合材料表现为应变软化行为;而倾斜于压缩方向30°的晶须折断和转动明显,引起相应复合材料应变软化;横向分布晶须没有转动而折断程度很小,使复合材料呈现出加工硬化行为.     

颗粒增强铝基功能梯度复合管研究

对强化颗粒进行了预处理,通过控制搅拌条件及感应炉供电功率等参数,使颗粒直接加入到基体铝合金中,并在浆体中呈现不同的分布,再通过调整其它的工艺参数,利用水平式离心铸造机制了三种具有不同强化部位和不同颗粒分布的功能梯度复合管,外层强化,内层强化以及内外层同时强化,结果表明：功能梯度复合管的显微硬度与颗粒分布具有良好的对应关系,而且显微组织也呈呈现梯度变化,强化部位的多样化可为功能梯度厚壁复合管的应用开辟新的领域。     

Transient liquid-phase bonding of alumina and metal matrix composite base materials

Transient liquid-phase (TLP) bonding of aluminium-based metal matrix composite (MMC) and Al2O3 ceramic materials has been investigated, particularly the relationship between particle segregation, copper interlayer thickness, holding time and joint shear strength properties. The long completion time and the slow rate of movement of the solid–liquid interface during MMC/Al2O3 bonding markedly increased the likelihood of forming a particle-segregated layer at the dissimilar joint interface. Preferential failure occurred through the particle-segregated layer in dissimilar joints produced using 20 and 30 μm thick copper foils and long holding times (≥20 min). When the particle-segregated layer was very thin (<10 μm), joint failure was determined by the residual stress distribution in the Al2O3/MMC joints, not by preferential fracture through the particle-segregated layer located at the bondline. Satisfactory shear strength properties were obtained when a thin (5 μm thick) copper foil was used during TLP bonding at 853 K. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of reinforcement size and matrix microstructure on the fracture properties of an aluminum metal matrix composite

The effects of systematic changes in reinforcement size and matrix microstructure on the crack initiation and growth toughness of a 7091 aluminum alloy reinforced with SiC particulates were studied. It is shown that changes in matrix microstructure have a significant effect on both initiation and growth toughness. The effect of reinforcement size on these properties is far less marked. These observations have been related to local microstructural parameters and the nature of the distribution of the reinforcement.