Study on Processing Conditions of Aluminum Matrix Composites Reinforced with Boron Carbide Particles

Different pre-heating of boron carbide particles for reinforcement and different processing conditions were studied in this work. Being one of the most cost-effective industrial methods, conventional melt stir-casting route was utilized.Result showed that the boron carbide particles distributed well for a suitable pre-heating temperature and processed in air.No reaction product was found at the A1-B4C interfaces at the resolution limit of SEM used in that way.

Diffusion Bonding of Silicon Carbide Particulate Reinforced 2024 Al Composites

A study has been made on diffusion bonding of SiCp/2024Ai composites by means of pure Al interlayer. In the condition of TB=843 K, PB=16 MPa, tB= 60 min, the diffusion bonded joint, with a shear strength of 235 MPa, was obtained when a 15 μm thick interlayer was used. The results of the shear testing and SEM indicate that fracture of the joint presented characteristics of ductile rupture.

Machining studies of die cast aluminum alloy-silicon carbide composites

Metal matrix composites （MMCs） with high specific stiffness, high strength, improved wear resistance, and thermal properties are being increasingly used in advanced structural, aerospace, automotive, electronics, and wear applications. Aluminum alloy-silicon carbide composites were developed using a new combination of the vortex method and the pressure die-casting technique in the present work. Machining studies were conducted on the aluminum alloy-silicon carbide （SiC） composite work pieces using high speed steel （HSS） end-mill tools in a milling machine at different speeds and feeds. The quantitative studies on the machined work piece show that the surface finish is better for higher speeds and lower feeds. The surface roughness of the plain aluminum alloy is better than that of the aluminum alloy-silicon carbide composites. The studies on tool wear show that flank wear increases with speed and feed. The end-mill tool wear is higher on machining the aluminum alloy-silicon carbide composites than on machining the plain aluminum alloy.

Microstructure and properties of electronic packaging shell with high silicon carbide aluminum-base composites by semi-solid thixoforming

The electronic packaging shell with high silicon carbide aluminum-base composites was prepared by semi-solid thixoforming technique. The flow characteristic of the Si C particulate was analyzed. The microstructures of different parts of the shell were observed by scanning electron microscopy and optical microscopy, and the thermophysical and mechanical properties of the shell were tested. The results show that there exists the segregation phenomenon between the Si C particulate and the liquid phase during thixoforming, the liquid phase flows from the shell, and the Si C particles accumulate at the bottom of the shell. The volume fraction of Si C decreases gradually from the bottom to the walls. Accordingly, the thermal conductivities of bottom center and walls are 178 and 164 W·m-1·K-1, the coefficients of thermal expansion(CTE) are 8.2×10-6 and 12.6×10-6 K-1, respectively. The flexural strength decreases slightly from 437 to 347 MPa. The microstructures and properties of the shell show gradient distribution.

Fabrication and densification enhancement of SiC-particulate-reinforced copper matrix composites prepared via the sinter-forging process

The fabrication of copper （Cu） and copper matrix silicon carbide （Cu/SiCp） particulate composites via the sinter-forging process was investigated. Sintering and sinter-forging processes were performed under an inert Ar atmosphere. The influence of sinter-forging time, temperature, and compressive stress on the relative density and hardness of the prepared samples was systematically investigated and subsequently compared with that of the samples prepared by the conventional sintering process. The relative density and hardness of the composites were enhanced when they were prepared by the sinter-forging process. The relative density values of all Cu/SiCp composite samples were observed to decrease with the increase in SiC content.

Exploration of Al-based matrix composites reinforced by hierarchically spherical agents

Al-based composites reinforced with A1-Ti intermetallic compounds/Ti metal hierarchically spherical agents were successfully fabricated by powder metallurgy. This kind of structure produces strongly bonded interfaces as well as soft/hard/soft transition regions between the matrix and reinforced agents, which are beneficial to load transfer during deformation. As expected, the resultant composites exhibit promising mechanical properties at ambient temperature. The underlying mechanism was also discussed in this paper.

Microstructure and Strength of Laser Welds of Sub-micron Particulate-reinforced Aluminum Matrix Composite Al_2O_(3p)/6061Al

The microstructure of laser welds of sub-micron particulate-reinforced aluminum matrix composite Al_2O_(3p)/6061Al and the weldability of the material were studied. Experimental results indicated that because of the huge specific surface area of the reinforcement, the interfacial reaction between the matrix and the reinforcement was re- strained intenslvely at elevated temperature and pulsed laser beam. The main factor affecting the weldability of the com- posite was the reinforcement segregation in the weld resulting from the push of the liquid/solid interface during the soli- dification of the molten pool. The laser pulse frequency directly affected the reinforcement segregation and the reinfor- cement distribution in the weld, so that the weldability of the composite could be improved by increasing the laser pulse frequency. On the basis of this, a satisfactory welded joint of sub-micron paniculate-reinforced aluminum matrix com- posite Al_2O_(3p)/6061Al was obtained by using appopriate welding parameters.

Pseudo-in-situ stir casting: a new method for production of aluminum matrix composites with bimodal-sized B_4C reinforcement

A new method was applied to produce an Al-0.5wt%Ti-0.3wt%Zr/5vol%B_4C composite via stir casting with the aim of characterizing the microstructure of the resulting composite. For the production of the composite, large B4 C particles（larger than 75 μm） with no pre-heating were added to the stirred melt. Reflected-light microscopy, X-ray diffraction, scanning electron microscopy, field-emission scanning electron microscopy, laser particle size analysis, and image analysis using the Clemex software were performed on the cast samples for microstructural analysis and phase detection. The results revealed that as a consequence of thermal shock, B_4 C particle breakage occurred in the melt. The mechanism proposed for this phenomenon is that the exerted thermal shock in combination with the low thermal shock resistance of B_4 C and large size of the added B_4 C particles were the three key parameters responsible for B_4 C particle breakage. This breakage introduced small particles with sizes less than 10 μm and with no contamination on their surfaces into the melt. The mean particle distance measured via image analysis was approximately 60 μm. The coefficient of variation index, which was used as a measure of particle distribution homogeneity, showed some variations, indicating a relatively homogeneous distribution.

Effect of Silicon Carbide and Titanium Hydride on the Foamability of Aluminum Alloy (6061)

Aluminum foam is a light weight material with good mechanical and energy absorption properties. In this study, aluminum foam composite was fabricated using aluminum powder 6061 and silicon carbide (SiC) powder. Titanium hydride (TiH2) was used as the foaming agent. Cold compact followed by hot pressing (sintering) was used to produce the composite precursor. Foaming was carried out, following the sintering process, by heating the aluminum composite precursor to a temperature above the melting point of aluminum (Al). The linear expansion of the foam and the percent porosity were found to increase as the SiC percentage decreased from 10 to 4%, whereas the density got lower. The percent porosity and linear expansion were both found to increase as the percentage of the foaming agent was increased from 0.5 to 1.5%. Compression stress was evaluated for two different porosity values (40% and 47%), and found to be higher for the samples with lower percent porosity at the same strain value. Effect of shape memory alloy fiber, made of nickel and titanium (NiTi), on the mechanical properties was also investigated. The compression stress was higher, in the densification region, for the samples in which NiTi was used.

Pulse-Impact on Microstructure of Liquid-Phase-Pulse-Impact Diffusion Welded Joints of Particle Reinforcement Aluminum Matrix Composites at Various Temperatures

Investigation was to study the influence of pulse-impact on microstructure of Liquid-Phase-Pulse-Impact Diffusion Welding (LPPIDW) welded joints of aluminum matrix composite SiCp/A356, SiCp/6061Al, Al2O3p/6061Al. Results showed that under the effect of pulse-impact: 1) the interface state between reinforcement particle (SiC, Al2O3) and matrix was prominently;2) the initial pernicious contact-state of reinforcement particles was changed from reinforcement (SiC, Al2O3)/reinforcement (SiC, Al2O3) to reinforcement (SiC, Al2O3)/matrix/ reinforcement (SiC, Al2O3);3) the density of dislocation in the matrix neighboring to and away from the interface in the matrix was higher than its parent composite;and 4) the intensively mutual entwisting of dislocation was occurred. Studies illustrated that: 1) deformation was mainly occurred in the matrix grain;and 2) under the effect of pulse-impact, the matrices around reinforcement (SiC, Al2O3) particles engendered intensive aberration offered a high density nucleus area for matrix crystal, which was in favor of forming nano-grains and improved the properties of the successfully welded composite joints.

Processing of nanostructured metallic matrix composites by a modified accumulative roll bonding method with structural and mechanical considerations

Particulate reinforced metallic matrix composites have attracted considerable attention due to their lightweight, high strength, high specific modulus, and good wear resistance. A1/B4C composite strips were produced in this work by a modified accumulative roll bonding process where the strips were rotated 90° around the normal direction between successive passes. Transmission electron microscopy and X-ray diffraction analyses reveal the development of nanostructures in the Al matrix after seven passes. It is found that the B4C reinforcement distribution in the matrix is improved by progression of the process. Additionally, the tensile yield strength and elongation of the processed materials are increased with the increase of passes.

INVESTIGATION ON THE FORMATION MECHANISM OF TITANIUM CARBIDE PREPARED BY IN SITU REACTION IN MOLTEN ALUMINUM

A novel technique in which TiC particulate are prepared by an in situ reaction in molten aluminum was introduced for producing TiC/Al composite. In order to reveal the characteristics of the technique, the formation mechanism of TiC particulate prepared by this method was studied. Both theoretical and experimental results show that the TiC particulate is formed by a diffusion mechanism when the molar fraction of aluminum in the preforms is higher than 20.02%. On the contrary, the TiC particulate is formed by a solution-precipitation mechanism when the fraction of aluminum in the preforms is lower than 20.02%.

Improvement of SiC_p Reinforced Cast AluminiumComposites by the ROC Method

The process of rapid omnidirectional compaction (ROC) of SiCp/cast Al composites was investigated. An apparatus for ROC process was established. Full compactibility of various SiCp/cast Al composites was accomplished. Defects in the materials were eliminated. It is found that after ROC, the tensile strength of the 30% SiCp/Z1109 composite increased by 35%. It is demonstrated that the ROC process is an effective method for improving the performance of SiCp/Al composites.

CRYOGENIC PROPERTIES OF AI-SiC COMPOSITES AND EFFECT OF MATRIX CHARACTERISTICS AND REINFORCEMENT TYPE

The tensile tests on the silicon carbide whisker and paniculate reinforced 2124A1 and 2024Al alloy composites fabricated by P/ M technique were carried out at the temperatures ranging from room temperature to - 196C . and the fracture surfaces were examined. The cryogenic strength of the composites increases with the decreasing test temperature. Clean interface is beneficial to the improvement in cryogenic strength of the composites. The effect of the interface characteristics on the paniculate composite is less than that on the whisker composite. With the decreasing temperature, the increase in strength of the whisker composite is more than that of the paniculate composite, which could be attributed to different strengthening mechanism.

Fabrication and Characterization of Glass Fiber with SiC Reinforced Polymer Composites

Glass Fiber Reinforced Polymeric (GFRP) Composites are most commonly used as bumpers for vehicles, electrical equipment panels, and medical devices enclosures. These materials are also widely used for structural applications in aerospace, automotive, and in providing alternatives to traditional metallic materials. The paper fabricated epoxy and polyester resin composites by using silicon carbide in various proportions along with GFRP. The hand lay-up technique was used to fabricate the laminates. To determine the properties of fabricated composites, the tensile, impact, and flexural tests were conducted. This method of fabrication was very simple and cost-effective. Their mechanical properties like yield strength, yield strain, Young’s modulus, flexural modulus, and impact energy were investigated. The mechanical properties of the GFRP composites were also compared with the fiber volume fraction. The fiber volume fraction plays a major role in the mechanical properties of GFRP composites. Young’s modulus and tensile strength of fabricated composites were modelled and compared with measured values. The results show that composites with epoxy resin demonstrate higher strength and modulus compared to composites with polyester resin.

增强体表面改性在高导热金属基复合材料中的应用

随着电子技术的高速发展和电子器件的更新换代,电子封装材料的性能需求越来越高。金属基复合材料,尤其是铝基和铜基复合材料具有高导热、低膨胀、高稳定性等特点,是具有广阔应用前景的电子封装材料。然而,金刚石、石墨烯、硅等增强体与基体的润湿性差,或者在高温下与基体发生有害的界面反应,限制了此类高导热金属基复合材料的开发和应用。本文简述了金属基复合材料的界面研究进展,结合影响金属基复合材料界面结合的因素,提出了几种改善界面结合的方法。增强体表面改性是改善金属基复合材料界面的重要途径之一,常用工艺有磁控溅射法、化学气相沉积法、溶胶凝胶法、化学镀法等;最后,对增强体表面改性在高热导金属基复合材料中的应用进行分析和展望。

铝酸盐体系中氧化时间对碳化硅颗粒增强铝基复合材料微弧氧化膜层的影响

[目的]探究氧化时间对碳化硅颗粒增强铝基(SiC_(p)/Al)复合材料微弧氧化膜层的影响。[方法]选用铝酸盐体系作为电解液,对SiC_(p)/Al复合材料进行微弧氧化处理,分析氧化时间对膜层组织结构、物相、厚度、粗糙度、结合力、电绝缘性及耐蚀性的影响。[结果]随着氧化时间延长,膜层逐渐变得连续均匀,厚度增加。若氧化时间过长,膜层会出现层叠现象,形成大尺寸微孔及裂纹,且生长速率越来越低。膜层结合力随氧化时间延长先增大后减小,在60 min时最大,达到39.85 N。氧化时间为10 min时,膜层的电绝缘性及耐蚀性最优,100 V和500 V电压下的绝缘电阻分别达到3.11×10^(12)Ω和1.41×10^(12)Ω,腐蚀电位为-0.6298 V,腐蚀电流密度为1.332×10^(-7)A/cm^(2)。[结论]SiC_(p)/Al复合材料表面微弧氧化膜层的连续性、均匀性及生长速率均与氧化时间有关。需选择合适的氧化时间,才能制备出连续、均匀且综合性能优异的膜层。

球磨方式对CNTs/Al复合材料显微组织与力学性能的影响

采用湿法球磨和干法球磨两种方式制备碳纳米管(carbon nanotubes,CNTs)和铝的复合粉体,再使用放电等离子烧结结合热挤压的工艺制备碳纳米管增强铝基(CNTs/Al)复合材料,系统研究了制备工艺-组织结构-材料性能之间的关系。结果表明,相较于干法球磨,湿法球磨可以更好地分散碳纳米管,且显著减少对其结构的破坏;乙醇球磨介质具有冷却作用,在减少粉体冷焊的同时有助于细化Al基体晶粒,从而使复合材料获得出色的力学性能。乙醇湿法球磨6 h后烧结并热挤压的2%CNTs/Al复合材料抗拉强度达到207 MPa。

电压对15%SiC_(p)/2009铝基复合材料微弧放电析出气体成分的影响

在硅酸盐溶液中,对15%SiC_(p)/2009铝基复合材料进行不同电压下的微弧氧化试验。通过分析微弧放电过程中复合材料析出气体的组成,评估电压对阳极析出气体成分的影响,并阐释其产生机制。结果表明:不同电压下阳极析出的气体均由H_(2)、O_(2)及少量CO组成,不同于传统电化学理论认为的阳极析出氧气。在360~440 V范围内,随着电压的升高,放电火花强度增大,微弧氧化膜生长速率加快,H_(2)含量随之增加,O_(2)含量相应降低;电压超过440 V后,H_(2)含量约为80%(体积分数),O_(2)含量约为20%,两者含量保持稳定。阳极火花放电区水热分解释放大量H_(2)和O_(2),且放电越剧烈,水分解量越多。放电区中铝和水氧化反应及高能电子轰击电离水分子也是过量H_(2)析出的重要原因。此外,SiC增强体参与成膜过程,并在放电区高温环境中被氧化,生成了少量的CO气体。

SiC复合陶瓷增韧研究现状

SiC陶瓷具有优良的性能,被广泛应用于各领域,但因韧性不足而制约其作为结构材料的应用,故提升其韧性已成为研究热点和焦点。因此,综述了颗粒、晶须、纤维和低维纳米材料(碳纳米管和石墨烯)等不同增强相增韧SiC复合陶瓷的研究现状,期望为今后SiC陶瓷的增韧研究提供参考。