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.     

Dual-nanoparticulate-reinforced aluminum matrix composite materials

Aluminum (Al) matrix composite materials reinforced with carbon nanotubes (CNT) and silicon carbide nanoparticles (nano-SiC) were fabricated by mechanical ball milling, followed by hot-pressing. Nano-SiC was used as an active mixing agent for dispersing the CNTs in the Al powder. The hardness of the produced composites was dramatically increased, up to eight times higher than bulk pure Al, by increasing the amount of nano-SiC particles. A small quantity of aluminum carbide (Al(4)C(3)) was observed by TEM analysis and quantified using x-ray diffraction. The composite with the highest hardness values contained some nanosized Al(4)C(3). Along with the CNT and the nano-SiC, Al(4)C(3) also seemed to play a role in the enhanced hardness of the composites. The high energy milling process seems to lead to a homogeneous dispersion of the high aspect ratio CNTs, and of the nearly spherical nano-SiC particles in the Al matrix. This powder metallurgical approach could also be applied to other nanoreinforced composites, such as ceramics or complex matrix materials.     

高阻尼铝基复合材料在海水中的腐蚀行为

研究了高阻尼铝基复合材料在海水中的腐蚀行为,本实验所用高阻尼铝基复合材料是以6061铝合金为基体,加入SiC颗粒和石墨粉,用粉末冶金方法制备的。测定了高阻尼铝基复合材料在海水中的腐蚀速率度、电极电位和极化曲线,并通过与基体金属的对比来描述它的腐蚀特性。实验表明,在海水介质中,高阻尼铝基复合材料的耐蚀性能比6061铝合金差,孔蚀倾向大。在海水介质中使用高阻尼铝基复合材料必须加以保护。     

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.     

Fabrication and characterization of aluminum nitride polymer matrix composites with high thermal conductivity and low dielectric constant for electronic packaging

Polymethyl methacrylate (PMMA) composites filled with Aluminum Nitride (AlN) were prepared by powder processing technique. The microstructures of the composites were investigated by scanning electron microscopy techniques. The effect of AlN filler content (0.1–0.7 volume fraction (vf)) on the thermal conductivity, relative permittivity, and dielectric loss were investigated. As the vf of AlN filler increased, the thermal conductivity of the specimens increased. The thermal conductivity and relative permittivity of AlN/PMMA composites with 0.7 vf AlN filler were improved to 1.87 W/(m K) and 4.4 (at 1 MHz), respectively. The experimental thermal conductivity and relative permittivity were compared with that from simulation model.     

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。     

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.     

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.     

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.     

电子封装用聚苯硫醚高性能复合材料的研制

微电子工业的快速发展迫切需要性能更为优异的封装材料.采用聚苯硫醚复合材料作为电子封装材料,具有使用温度高、热膨胀系数低、介电损耗低、电绝缘性能好等优异的性能,应用于现代微电子领域的前景良好.本文用国产商品PPS树脂经纯化处理后,与其它材料复合,成功制备出了聚苯硫醚高性能电子封装材料,制备的PPS电子封装材料具有低吸水性、低热膨胀系数、高强度以及优异的介电性能等综合性能,优于目前常用的环氧类电子封装材料.     

Friction stir welding of thick plates of aluminum alloy matrix composite with a high volume fraction of ceramic reinforcement

The microstructure and mechanical properties of joints conducted by friction stir welding, FSW, at different rotational speeds in thick plates of a composite material with a high volume fraction of reinforcement, namely 2124Al/25vol%SiC_p, are studied. Original particle-free regions vanish during the stirring process, leading to a homogeneous particle distribution. Occasional breakage of some large particles occurs. Tunnel defects appear at low rpm, and disappear at high rotational speeds. The size of the thermo mechanically affected zone, TMAZ, increases with increasing rpm. Ductility of the welds in the range of 10–15% is achieved in compression tests whereas a rather brittle behavior is obtained in tension. A strength difference, SD, effect between compression and tensile test is obtained. This accounts for the little detrimental effect of the FSW process on the matrix–reinforcement interface. The SD effect is attributed to the presence of a microscopic residual stress.     

Adiabatic shear failure of high reinforcement content aluminum matrix composites

Dynamic failure behaviors of high reinforcement content TiB₂/Al composites were experimentally investigated using split Hopkinson pressure bar (SHPB). The TiB₂/Al composites showed high flow stresses and good plastic deformation ability at high strain rates. Adiabatic temperature rise decreased the flow stresses of TiB₂/Al composites, which was verified by the prediction of Johnson–Cook model. While the predictions by Cowper–Symonds model exhibited obvious strain hardening characteristic, the values of which were much higher than those of the Johnson–Cook model and the experimental. The composites were failed macroscopically in brittle fracture and some phase transformation bands were found on the shearing surfaces. The dynamic failure behavior of TiB₂/Al composites was predominated by the formation of adiabatic shear bands.     

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。     

Intelligent process design system for the transfer moulding of electronic packages

Currently, mould design and the setting of the process parameters of transfer moulding for electronic packages are done manually in a trial-and-error manner. The effectiveness of the setting of parameters is largely dependent on the experience of engineers. The paper describes an intelligent process design system for transfer moulding of electronic packages that is used to determine optimal mould design parameters and the setting of the process parameters mainly based on case-based reasoning, artificial neural networks and a multiobjective optimization scheme. The system consists of two modules: a case-based reasoning module and a process optimization module. The former module is used to determine initial mould design parameters and the setting of the process parameters while the latter module is used to determine optimal mould design parameters and the setting of the process parameters. Implementation of the intelligent system has demonstrated that the time for the determination of optimal mould design parameters and the setting of the process parameters can be greatly reduced, and the setting of parameters recommended by the system can contribute to the good quality of moulded packages.     

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.