The production of Al-Mg alloy/SiC metal matrix composites by pressureless infiltration

Metal matrix composites have been produced by pressureless infiltration of Al-Mg alloys into SiC preforms at 900°C under N₂ for different infiltration times. The wettability of the ceramic reinforcement by the Al-Mg alloy is crucial in determining whether an MMC can be produced by pressureless infiltration. Sessile drop results show that Al alloys with Mg contents greater than 8 wt% had a contact angle lower than 90°C after 5 minutes contact time. This was in agreement with the pressureless infiltration results as MMCs have been produced after 30 minutes with these alloys. Sessile drop experiments also show that SiC is similarly wetted by Al-Mg alloys under both N₂ and Ar. It is concluded that the infiltration process does not involve the intermediate nitride phase suggested by other authors.     

Fabrication and characteristics of AA6061/SiCp composites by pressureless infiltration technique

The tensile properties and microstructures of AA6061/SiC_p composites fabricated by the pressureless infiltration method under a nitrogen atmosphere were examined. Since the spontaneous infiltration of molten AA6061 into the powder bed containing SiC_p occurred at 800 °C for 1 hour under a nitrogen atmosphere, it was possible to fabricate composites reinforced with SiC_p. Reaction product (Al₄C₃) was formed at the interface between SiC_p and Al alloy matrix. In addition, the amount and size of the Al₄C₃ is increased significantly by increasing the infiltration temperature. The reaction product (AlN) was formed as a result of the in situ reaction in both the control alloy and the composite. A significant strengthening even in the control alloy occurred due to the formation of in situ AlN particle even without an addition of SiC_p. While a further strengthening of the composite was produced by the reinforced SiC_p, strain to failure of the composite fabricated at 800 °C showed the lowest value (1.3%) in the T6 condition due to the formation of the severe reaction product (Al₄C₃). The grain size of the control alloy significantly decreased to about 20 m compared to 50 m for the commercial alloy. In addition, the grain size in the composite reinforced with SiC_p further decreased to about 8.0 m. This grain refinement contributed to strengthening of the control alloy and composite.     

Numerical simulation of metal matrix composites and polymer matrix composites processing by infiltration: a review

The injection of a liquid metal through a fibrous preform is one of the techniques used to manufacture metal matrix composites (MMCs). The flow of metal through fibrous preform is a problem of fluid mechanics in porous medium. Numerical simulations of this process were developed in particular for non-isothermal infiltrations which take into account the phenomena of phase change. In addition, numerical models were developed to predict the appearance of defects in the end product and to study the evolution of the deformation of the fibrous preform during metal infiltration. After pointing out the analogous numerical studies devoted to the Resin Transfer Moulding (RTM) process, we give a progress report on the models developed to date for MMCs.     

Aluminium-matrix silicon carbide whisker composites fabricated by pressureless infiltration

Al-matrix SiC whisker composites were fabricated by pressureless infiltration of liquid Al-Mg or Al-Si-Mg alloys at 830–950°C in the presence of N₂ into a preform of nickel coated SiC whiskers. The nickel coating on the whiskers was obtained by electroless plating and made pressureless infiltration possible. The composite made by pressureless infiltration exhibited slightly lower tensile strength and modulus and slightly higher coefficient of thermal expansion than the corresponding composite made by pressure infiltration. However, the differences were small in spite of the lack of prior evacuation in the pressureless infiltration case. On the other hand, the hardness decreased with increasing distance from the preform-melt interface much more significantly in composites made by pressureless infiltration than those made by pressure infiltration. The hardness decrease, which was attributed to a porosity increase, was larger for composites made by pressureless infiltration without prior evacuation than those made by pressureless infiltration with prior evacuation. The Al-SiC reactivity was larger for composites made by pressureless infiltration than those made by pressure infiltration, because the infiltration time was longer in pressureless infiltration.[/p]     

Fabrication and tribological properties of carbon nanotubes reinforced Al composites prepared by pressureless infiltration technique

Aluminum composites reinforced with CNTs were fabricated by pressureless infiltration process and the tribological properties of the composites were investigated. Al has been infiltrated into CNTs–Mg–Al preform by pressureless infiltration in N₂ atmosphere at 800 °C. By means of scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDS), it was found that CNTs are well dispersed and embedded in the Al matrix. The friction and wear behaviors of the composite were investigated using a pin-on-disk wear tester under unlubricated condition. The tests were conducted at a sliding speed of 0.1571 m/s under an applied load of 30 N. The experimental results indicated that the friction coefficient of the composite decreased with increasing the volume fraction of CNTs due to the self-lubrication and unique topological structure of CNTs. Within the range of CNTs volume fraction from 0% to 20%, the wear rate of the composite decreased steadily with the increase of CNTs content in the composite. The favorable effects of CNTs on wear resistance are attributed to their excellent mechanical properties, being well dispersed in the composite and the efficiency of the reinforcement of CNTs.     

自渗透制备SiCp／Al复合材料及其耐磨性

研究了以Ｋ２ＺｒＦ６为助渗剂，用自渗透法制备ＳｉＣｐ／Ａｌ复合材料的技术，全面考查了Ｋ２ＺｒＦ６的配比，ＳｉＣｐ粒度，温度，保温时间等工艺参数对自渗透过程的影响。借助于复合材料金相组织的分析，认为粉体预热温度６５０℃，铝合金液浇注和保温温度７８０－８００℃，保温２ｈ后随炉冷却是本试验的最佳工艺参数。     

Role of Mg and Mg+Si as external dopants in production of pure Al–SiC metal matrix composites by pressureless infiltration

Abstract

Metal matrix composites have been produced by pressureless infiltration of pure Al into Mg doped SiC preforms after 1 h at 900°C. Aluminium has been found to infiltrate preforms containing between 2 and 14 wt-%Mg, however Al did not infiltrate a preform containing 1 wt-%Mg. Preforms doped with 1 wt-%Mg and Si did result in infiltration. Increasing the Mg content or increasing the Si content in the preform resulted in more extensive infiltration. The effect of Mg and Mg mixed with Si on pressureless infiltration of pure Al, microstructure of MMC as well as mechanical properties are discussed. Although the dopant was uniformly distributed throughout the preform microstructural analysis and hardness measurements indicate that the resultant composite may not be uniform due to infiltration inwards from the edge to the centre of preform.     

无压渗透法制备Al／AlN复合材料及其性能

在常压下通过熔渗工艺将AlSi7Mg合金渗入由AlN粉末模压成形、预烧所获得的预烧结坯中,得到了不同Al含量的Al／AlN复合材料。采用X射线衍射仪对复合材料的相组成进行了测试,采用金相显微镜和SEM对其显微组织进行了观测,并对不同Al含量的Al／AlN复合材料的维氏硬度、抗弯强度、热膨胀系数及导热系数等进行了测试分析...     

无压浸渗法制备Al/70vol%Sip复合材料

采用无压浸渗工艺,成功制备出Al/70vol%Sip复合材料,对Al-Si体系进行了自发浸渗的热力学及动力学分析,并分析了组织中残留微细孔隙的形成机理.研究表明:由于存在冶金润湿,在毛细压力作用下,Al合金液能较好浸渗Si多孔预制体,浸渗深度与时间成抛物线关系;采用饱和成分的Al合金浸渗,可有效抑制对Si预制体的溶解浸蚀;对复合材料浸渗组织观察表明,Si颗粒发生钝化,相邻颗粒融合连接,呈连续三维网状.     

Fabrication and infiltration kinetics analysis of Ti-coated diamond/copper composites with near-net-shape by pressureless infiltration

The Ti-coated diamond/copper composites with near-net-shape are manufactured by pressurelessly infiltrating liquid copper into porous Ti-coated diamond preforms. The contact angle between diamond and copper, relative density, thermal conductivity (TC), coefficient of thermal expansion (CTE), leak rate and microstructure are evaluated and characterized. In addition, the numerical analysis of the pressureless infiltration kinetics is also discussed. The results indicate that the relative density, TC and CTE of composites are 99.3%, 385 Wm⁻¹ k⁻¹ and 3–8 × 10⁻⁶ K⁻¹, respectively. It can meet heat-sink package requirement of high-power electronic devices as LED, insulated gate bipolar transistor (IGBT), etc. The liquid copper exhibits a turbulent flow with the Reynolds number in the range of 27.83–49.7. The porosity ? and the pressure drop Δp are the main influence factors controlling the velocity of liquid copper. Moreover, under vacuum condition of 8.7 × 10⁻³ Pa, the maximum theoretical infiltration length L_max of Ti-coated diamond/copper composites is found to be 552 mm.     

Fabrication and thermal conductivity of near-net-shaped diamond/copper composites by pressureless infiltration

Near-net-shaped diamond/copper composites with a relative density of over 99% and thermal conductivity of over 350 Wm⁻¹ K⁻¹ are successfully fabricated by powder press-pressureless infiltration processing. The effects of infiltration temperature, infiltration time, interfacial thickness, and type of protective atmosphere on the thermal conductivity of the diamond/copper composites were investigated. The results showed that the diamond-copper composites with complicated shape exhibited better thermal properties, which can be widely used in electronic packaging field. It was found that the properties of diamond-copper composites infiltrated in high vacuum atmosphere were better than that of composites infiltrated in other atmospheres. The thickness of interface showed great effects on the properties of composites. The carbide interfaces were attributed to the decrease of interfacial thermal resistance and enhancement of wetting properties between the diamonds and copper.     

Activated pressureless infiltration of metal-matrix composites with graded activator content

Metal-matrix composites (MMCs) were produced by activated pressureless infiltration of porous Al₂O₃ compacts with the presence of elemental titanium as an activator and steel (X38CrMoV5-1) as the metal matrix. The quality of infiltration was subsequently investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The results show that poor quality of infiltration is associated with blocking of infiltration channels due to the formation of Ti-rich phases which are accumulated over infiltration depth. To prevent the pores blocking, a layer-graded activator green body in which the activator quantity is decreased with infiltration depth was used. Furthermore, it could be shown that the mechanism based on evaporation/condensation of metal onto activator particles is in agreement with the results of this study.     

Microstructure and thermo-mechanical properties of SiCp/Al composites prepared by pressureless infiltration

In this paper, SiCp/Al composites with high reinforcement content are fabricated by pressureless infiltration with aluminum alloy into porous SiC preforms obtained by cold press forming. Microstructures and particulate distributions are analyzed with scanning electron microscope, X-ray diffraction and energy dispersive spectrometer. The reinforcement volume fraction reaches 65 % by using bimodal particle distributions. The bending strength ranges from 320 to 342 MPa, depending on particle sizes. Due to the intrinsically low thermal conductivity of the matrix, the thermal conductivity of SiCp/Al composites are in the range of 121–143 W m^?1 K^?1.     

Particulate metal matrix composites and their fabrication via friction stir processing – a review

Particulate-reinforced metal matrix composites are of particular interest because of their ease of fabrication, low cost, and isotropic properties. Friction stir processing offers a promising alternative in the fabrication of surface as well as bulk metal matrix composites. Its very nature aids in the microstructural refinement of the matrix material, avoids the formation of detrimental phases and provides flexible control of the process. Over the period, the technique was successfully applied in the synthesis of various composites. This paper conducts a critical review of the current trends and strategies used to enhance friction stir process efficiency during fabrication of particulate metal matrix composites. It discusses a few of the key underlying principles necessary for making the right combination of matrix and reinforcement. The exhaustive comparative study presented in this article helps in identifying matrix/reinforcement combinations that are yet to be addressed. In the end, a few crucial observations are summarized and important suggestions are provided for future work.     

Ultrasonic assisted fabrication of particle reinforced bonds joining aluminum metal matrix composites

This paper presents a method of producing uniform particle strengthened bonds between pieces of aluminum metal matrix composite (Al-MMCs), of strength equal to that of the substrate material. SiC particle reinforced Zn-based filler metals were fabricated by mechanical stir casting and ultrasonic treatment, and then used to join pieces of SiC_p/A356 composite with the aid of ultrasonic vibration. The filler metals made by mechanical stirring were porous and contained many particle clusters. Ultrasonic vibration was used to disperse the agglomerates and prevent further coagulation of SiC particles during joining, but the method failed to eliminate the porosity, resulting in a highly porous bond. The filler metal treated by ultrasonic vibration was free of defects and produced a non-porous bond strengthened with uniform particles between pieces of SiC_p/A356 composite. The presence of surface oxide films at the bonding interface significantly degraded the performance of SiC particle reinforced bond. Removal of this oxide film by at least 4 s of ultrasonic vibration significantly increased the bond strength, reaching a value equal to that of the substrate metal.