Particle Removal Mechanism of High Volume Fraction SiCp/Al Composites by Single Diamond Grit Tool

Particle removal mechanism was presented during machining particle SiC/Al composites with diamond grinding tool. The relevant removal modes and their mechanisms were discussed considering the impact and squeezing effect of diamond grit on the SiC particle. The experimental results show that the aluminum matrix has larger plastic deformation, so the aluminum mixed with the surplus SiC particles is cut from the surface. The SiC particles can be removed in multiple ways, such as broken/fractured, micro cracks, shearing and pulled out, etc. More particles removed by shearing, and less particles removed by fractured during material removal progress can produce a better machined surface.

Optimization of Machining Characteristics for Al/SiCp Composites using ANN/GA

The present work is focused on optimization of machining characteristics of AI/SiCp composites. The machining characteristics such as specific energy, tool wear and surface roughness were studied. The parameters such as volume fraction of SiC, cutting speed and feed rate were considered. Artificial neural networks (ANN) was used to train and simulate the experimental data. Genetic algorithms (GA) was interfaced with ANN to optimize the machining conditions for the desired machining characteristics. Validation of optimized results was also performed by confirmation experiments.

Near-net shaped Al/SiCP composites via vacuum-pressure infiltration combined with gelcasting

To solve the problem of difficult machining, the near-net shaped Al/SiCP composites with high volume fraction of SiC particles were fabricated by vacuum-pressure infiltration. The SiCP preform with a complex shape was prepared by gelcasting. Pure Al, Al4Mg, and Al4Mg2Si were used as the matrices, respectively. The results indicate that the optimal parameters of SiCP suspension in gelcasting process are pH value of 10, TMAH content of 0.5 wt.%, and solid loading of 52 vol.%. The Al matrix alloyed with Mg contributes to improving the interfacial wettability of the matrix and SiC particles, which increases the relative density of the composite. The Al matrix alloyed with Si is beneficial to inhibiting the formation of the detrimental Al4C3 phases. The Al4Mg2Si/SiCP composite exhibits high relative density of 99.2%, good thermal conductivity of 150 W·m^-1·K^-1, low coefficient of thermal expansion of 10.1×10^-6 K^-1, and excellent bending strength of 489 MPa.

Preparation and characterization of different surface modified SiCp reinforced Al-matrix composites

The effects of SiCp surface modifications(Cu coating,Ni coating and Ni/Cu coating)on the microstructures and mechanical properties of Al matrix composites were investigated.Surface modification of SiC particles with Cu,Ni and Cu/Ni,respectively,was carried out by electroless plating method.SiCp/Al composites were prepared by hot pressed sintering followed by hot extrusion.The results show that the surface modification of SiC particles plays an effective role,which is relative to the type of surface coating,and the interfacial bonding become stronger in the following order:untreated SiCp<Ni(Cu)-coated SiCp<Ni/Cu-coated SiCp.The Ni/Cu-coated SiCp/Al composites exhibit the best comprehensive mechanical properties,with ultimate tensile strength(σUTS)and fracture strain(εf)of 389 MPa and 6.3%,respectively.Compared with that of untreated-SiCp/Al composites,theσUTS andεf are enhanced by 19.3%and 57.5%.

Effect of a Slight Interfacial Reaction on Mechanical Properties of SiCp/Al Composites

A slight interfacial reaction in squeeze-cast SiCp/6061AI composites has been studied. It is found that this kind of reaction has a particular effect on the mechanical properties of the composites. The results of fie-cure tests show that this reaction in the composites obviously increases the elastic properties, but is not beneficial to the fracture strength and ductility.This phenomenon can be interpreted in terms of two different micromechanisms which have been analyzed using TEM and HREM observations, acoustic emission (AE) technique and SEM fractography. In addition, a new method of SiC surface modification which can control the interface state is initially presented.

Effect of Na3AlF6 Addition and Surface Modification of SiCp on the Microstructure and Mechanical Properties of SiCp/Al Composites

Al-matrix composites reinforced with 56.5 vol% SiC were prepared by powder metallurgy with different amounts of additives and surface modifications of SiCp. The crystalline phase, morphology, elements on the surface of SiCp and the interface between SiCp and Al were characterized by XRD, SEM, EDS and EPMA. The results show that it is favorable for the reaction between TiO2-C on the surface of SiCp and Al at the SiCp-Al interface at 1 050 ℃. Besides, the process of Na3 AlF6 melting, dissolving and then contacting with Al2 O3 formed the NaF-AlF3-Al2 O3 system, which generated OAlF2-, promoting the dessolution of Al2 O3 film on the surface of Al powder. Na3 AlF6 meets the needs of chemical reaction in TiO2-C-Al system at the SiCpAl interface in the way of offering more molten Al. After 0.75 wt% Na3 AlF6 was added into raw materials, the whole TiO2-C film and most SiO2 film were destroyed and the interfacial bonding between SiCp and Al was keeping good, in which no obvious void and crack were observed. Meanwhile, no brittle Al4 C3 phase formed in the system. At this time, the flexure strength and density of samples presented optimal values, reaching up to 106.5 MPa and 90.77% respectively.

Experimental Study of Machinability in Millgrinding of SiCp/Al Composites

An attempt was made to investigate the machinability of Si Cp/Al composites based on the experimental study using mill-grinding processing method. The experiments were carried out on a high-speed CNC machining center using integrated abrasive cutting tool. The effects of combined machining parameters, e g, cutting speed（vs）, feed rate（vf）, and depth of cut（ap）, with the same change of material removal rate（MRR） on the mill-grinding force and surface roughness（Ra） were investigated. The formation mechanism of typical machined surface defects was analyzed by SEM. The experimental results reveal that with the same change of material removal rate, lower mill-grinding force values can be gained by increasing depth of cut and feed rate simultaneously at higher cutting speed. With the same change of MRR value, lower surface roughness values can be gained by increasing the feed rate at higher cutting speed, rather than just increasing the depth of cut, or increasing the feed rate and depth of cut simultaneously. The machined surface of Si Cp/Al composites reveals typical defects which can influence surface integrity.

Investigation on Material Response of 55% SiCp/Al Composites Induced by Pulsed Laser

Silicon carbide particle reinforced aluminum matrix composites(SiCp/Al composites)are widely used in aviation,aerospace and electronic package.However,low machining efficiency,severe tool wear and poor surface quality are severe during the machining of SiCp/Al composites.Laser-induced oxidation is capable to improve the machinability of SiCp/Al composites.The material response of 55%(volume fraction)SiCp/Al composites induced by a nanosecond pulsed laser is studied.A metamorphic layer which is composed of an oxide layer and sub-layer is produced.The effects of reaction surrounding and laser average power on the microstructure and thickness of the oxide layer and sub-layer are investigated.Experimental results show that:A thicker oxide layer and a sub-layer are formed in an oxygen-rich atmosphere.The oxides are mainly composed of 2Al2O3·SiO2(mullite).A positive correlation between the laser average power and thicknesses of oxide layers and sub-layers is found.A loose oxide layer of 138μm and a sub-layer of 21μm are formed at the laser average power of 6 W,laser scanning pitch of 10μm,and laser scanning speed of 1 mm/s under an oxygen-rich atmosphere.The high efficient machining of Si Cp/Al composites can be realized by laser-induced oxidation.

Spark Effect on the Densification of SiCp/Al Composites by SPS

SiCp/ Al composites containing high volume fraction of SiC particles were fabricated by spark plasma sintering （SPS）. and their thermophysical properties, such as thermal conductivity （TC） and co.lent of thermal expansion （CTE）, were characterized. The electric field in the vacuum column was calculated and the generation condition of the spark was analyzed. Spark can be generated by a low current if the cavity in the green body is large enough. A high relative density of the composites was successfully achieved through the optimization of sintering parameters. The measured TCs of the SiCp/ Al composites fabricated by SPS are higher than 195 W/m ·K.

Reactive Diffusion Bonding of SiCp/Al Composites by Insert Powder Layers with Eutectic Composition

Mixed Al-Si and Al-Cu powders were investigated as insert layers to reactive diffusion bond SiCp/6063 metal matrix composite （MMC）. The results show that SiCp/6063 MMC joints bonded by the insert layers of the mixed Al-Si and Al-Cu powders have a dense joining layer of high quality. The mass transfer between the bonded materials and insert layers during bonding leads to the hypoeutectic microstructure of the joining layers bonded by both the mixed Al-Si and Al-Cu powders with eutectic composition. At fixed bonding time （temperature）, the shear strength of the joints by both insert layers of the mixed Al-Si and Al-Cu powders increases with increasing the bonding temperature （time）, but get maxima at bonding temperature 600℃ （time 90 min）.

Microstructure and Mechanical Properties of Unidirectional W Filament Reinforced Al-6 Ti-6 Nb and SiCp-Al-6 Ti-6 Nb Matrix Composites

Unidirectional Tungsten filament (W_f) reinforced pure Al,Al-6Ti-6Nb and SiC_p-Al-6Ti-6Nb matrix composites were prepared by hot-pressing in vacuum atmosphere,their microstructure and room temperature mechanical properties were investigated. It was indicated that no reaction products appeared at W_f/Al interfaces in pure Al matrix composites. While, in W_f/Al-6Ti-6Nb and W_f/SiCp-Al-6Ti-6Nb,intermetallic WAl_4 interfacial reaction products formed. Much better strengthening effect from W filament was shown in the W_f/Al-6Ti-6Nb and W_f/SiCp-Al-6Ti-6Nb composites than in the pure Al matrix composite. Their strength reached 319 and 339MPa, respectively, with only a small content of W_f(<5Vol.%). The excellent reinforcement effects could be predominantly attributed to the strong W_f/Al interfacial bonding strength due to the interfacial reaction.

Pressureless infiltration processing and thermal properties of SiCp/Al composites with high SiC particle content

SiCp/1060Al, SiCp/ZL101,SiCp/ZL102 composites with SiCp volume fraction of 55% were fabricated by pressureless infiltration. The microstructure was examined and thermal properties were characterized for SiCp/Al composites. The results show that the composites are dense and macroscopically homogeneous. With the increase of temperature, the mean linear coefficient of thermal expansion(CTE) at 25-200℃of the composites increases and ranges from 7.23×10-6 to 10.4×10-6K-1, but thermal conductivity declines gradually at the same time. With the increase of Si content in the Al matrix, CTE of the composites declines and thermal conductivity also declines but not linearly, when Si content is up to 7%, the average thermal conductivity is 140.4 W/(m·K), which is close to that of the SiCp/1060Al composite (144.6 W/(m·K)). While Si content is 11.7%, the average thermal conductivity declines markedly to 87.74 W/(m·K). The annealing treatment is better than the solution aging treatment in reducing CTE and improving thermal conductivity of the composites. Compared with conventional thermal management materials, SiCp/Al composites are potential candidate materials for advanced electronic packaging due to their tailorable thermo-physical properties.

Wear Behaviour of Al-SiCp Metal Matrix Composites and Optimization Using Taguchi Method and Grey Relational Analysis

Aluminium metal matrix composite is a relatively new material that has proved its position in automobile, aerospace and other engineering design applications due to its wear resistance and substantial hardness. Need for improved tribological performance has led to the design and selection of newer variants of the composite. The present investigation deals with the study of wear behaviour of Al-SiCp metal matrix composite for varying reinforcement content, applied load, sliding speed and time. Aluminium metal matrix composites reinforced with SiC particles are prepared by liquid metallurgy route using LM6 aluminium alloy and silicon carbide particles (size ~ 37 μm) by varying the weight fraction of SiC in the range of 5% - 10%. The material is synthesized by stir casting process in an electric melting furnace. The materials are then subjected to wear testing in a multitribotester using block on roller configuration. A plan of experiments based on L27 Taguchi orthogonal array is used to acquire the wear data in a controlled way. An analysis of variance is employed to investigate the influence of four controlling parameters, viz., SiC content, normal load, sliding speed and sliding time on dry sliding wear of the composites. It is observed that SiC content, sliding speed and normal load significantly affect the dry sliding wear. The optimal combination of the four controlling parameters is also obtained for minimum wear. The microstructure study of worn surfaces indicates nature of wear to be mostly abrasive.

超声振动辅助切削SiCp/Al复合材料的加工机理及试验

切削加工过程中材料损伤形式对加工表面质量会产生较大影响,现有仿真分析难以模拟真实颗粒失效行为,通过建立二维微观多相有限元模型能够深入了解材料损伤与表面质量的关系。基于常规切削(Conventional cutting,CC)与超声振动辅助切削(Ultrasonic vibration-assisted cutting,UVAC)两种加工方式,通过有限元仿真软件Abaqus对20%SiCp/Al复合材料的切削过程进行仿真模拟,阐释加工过程中刀具与工件的相互作用机理,并在同一参数下验证有限元仿真的准确性。通过设计单因素试验,对比两种加工方式及不同加工参数对切削力和表面粗糙度的影响规律,得出最佳加工参数组合,并对最佳加工参数下表面形貌进行分析。模拟和试验结果表明,SiC颗粒断裂、颗粒耕犁、颗粒拔出以及Al基体撕裂是影响SiCp/Al复合材料加工质量的主要原因,刀具与颗粒不同的相对作用位置会产生不同的损伤形式。与常规切削相比,施加超声振动后可以有效抑制颗粒失效和基体损伤,使加工中的平均切削力(主切削力)降低33%,工件已加工表面粗糙度值最大减小量为531 nm,显著提高了表面质量。所建立的二维微观多相有限元模型,能够有效模拟铝基复合材料的加工缺陷和裂纹损伤问题,对提高难加工材料的高质量表面制备有重要借鉴意义。

SiCp/Al复合材料纳米压痕/划痕下的脆塑性行为研究

为探究SiCp/Al复合材料中两相材料相互作用引起的力学性能差异,研究微观尺度下法向载荷变化对SiCp/Al复合材料形变和去除的影响。采用纳米压痕实验,基于Oliver-Pharr法测得其硬度和弹性模量,并对其压痕表面进行观察,结合有限元仿真分析产生力学性能差异的原因;同时,根据纳米压痕实验所得力学参数进行变载荷纳米划痕仿真,并配合实验后划痕表面观察结果分析材料的形变和脆塑性行为。结果表明:当金刚石压头作用于SiC颗粒时,颗粒出现破碎和二次压入现象,所测硬度与弹性模量小于单晶SiC的理论值;当金刚石压头作用于基体相时,由于SiC颗粒阻碍基体压入,复合材料的硬度与弹性模量测量结果偏大。在纳米划痕过程中,复合材料的去除形式随载荷变化体现为划擦、耕犁和切削阶段,其中的基体相通过塑性流动产生塑性脊堆积并伴随有涂覆现象,SiC颗粒则以脱黏、断裂破碎和拔出等脆性机制而去除,且SiC颗粒的二次压入、断裂、破碎和拔出是导致复合材料力学性能与单晶SiC的力学性能产生巨大差异的主要原因。随着划痕载荷增加,SiC体积分数为45%的SiCp/Al复合材料的去除机制更多取决于以塑性去除为主的基体相,而SiC颗粒则主要表现为脆性去除。

纵扭超声辅助铣削SiCp/Al复合材料表面质量研究

高体积分数SiCp/Al复合材料具有高比强度、高比模数和良好的耐磨性等优异性能。然而,它们的高硬度和脆性会导致精密制造过程中应力分布更为复杂,这会使材料中产生过大的力和过多的热,从而影响加工精度和工件耐久极限寿命。目的通过分析切削过程中颗粒的去除机理和表面缺陷类型,利用纵扭超声辅助铣削(longitudinal-torsional ultrasonic assisted milling,LTUAM)技术,改善高体积分数SiCp/Al复合材料的加工表面质量。方法利用ABAQUS和PYTHON软件,建立考虑颗粒断裂过程的两相随机分布颗粒SiCp/Al复合材料模型,并采用Johnson-Cook模型和Brittle Cracking模型对SiCp/Al复合材料纵扭超声辅助铣削过程进行有限元模拟仿真。针对不同加工参数,进行SiCp/Al复合材料纵扭超声辅助铣削和常规铣削(conventional milling,CM)试验,评估有限元仿真模拟与试验结果的一致性。结果模拟结果表明,损伤和裂纹主要产生在SiC颗粒(SiCp)中上部的切削线上,凹坑缺陷主要产生在颗粒下部的切削线上。试验结果显示,表面缺陷的类型主要包括颗粒的损伤和拔出、颗粒的损伤和断裂形成凹坑、未损伤的颗粒形成凸起、破损颗粒与刀具在已加工表面上挤压摩擦形成犁沟、铝基体涂覆、表面微裂纹和表面空穴等,并且当加工速度120 m/min,超声振幅3μm时,最大裂纹深度最小,表面缺陷最小,表面质量最好。结论对比有限元仿真结果与试验结果发现,二者的表面质量变化趋势基本具有一致性。纵扭超声辅助铣削技术的应用对提高SiCp/Al复合材料的表面质量有较好效果。

SiCp/Al-Si基复合材料界面结构调控及强化机制的研究进展

SiCp/Al-Si基复合材料具有高的比强度、比刚度、比模量,良好的导热、导电、耐磨性及尺寸稳定性等优点,作为结构功能性材料应用于空间工程、电子封装、交通运输和精密仪器等领域。其研究热点主要集中在界面结构调控、强化机制及性能调控等方面。在SiCp/Al-Si复合材料中存在着增强体与基体界面、析出相与基体界面、析出相与增强体界面,这些界面受各种因素影响,会出现多种界面反应和界面产物,界面结构和结合状态复杂而多样。基于此,本文综述了制备工艺、基体合金成分和SiCp表面改性等方面对SiCp/Al-Si基复合材料界面结构的影响及调控,并总结了影响其力学性能的因素及强化机制的研究现状,最后对复合材料未来的发展及研究方向进行了展望。

基于单颗磨粒磨削的SiCp/Al材料去除机理研究

基于单颗磨粒磨削的仿真和实验,研究了SiCp/Al复合材料的去除机理,并对体积分数为20%和55%的SiCp/Al材料加工表面/亚表面质量进行对比研究。通过建立单磨粒磨削SiCp/Al材料的有限元仿真模型,对材料的去除过程进行仿真模拟,研究了不同磨削深度对表面/亚表面质量的影响;通过单磨粒磨削实验验证了仿真结果的准确性,并深入研究体积分数分别为20%和55%的SiCp/Al材料的表面形貌,分析了Al基体与SiC颗粒的去除方式,此外,还研讨了SiC颗粒的塑性去除条件。最后,通过对磨屑形貌的分析,进一步研究了材料的去除机理。

SiCp/Al复合材料焊接综述

为实现SiCp/Al复合材料的高质量可靠焊接,推广SiCp/Al复合材料在各领域的应用,调研了国内外SiCp/Al复合材料不同焊接方法的研究现状。在熔化焊方面,国内外学者通过调整工艺参数、在焊缝中加入Ti元素发生诱发反应等方法,抑制了焊缝中Al4C3针状脆性相的形成,从而提高了焊接接头的力学性能。在搅拌摩擦焊方面,国内外学者针对不同材料设计了专用的焊接搅拌头,以保证它们具备高耐磨性与足够的冲击韧性,在焊接过程中不出现破损情况;关注了焊接过程中焊接头转速、焊接速度、轴向力与热输入等因素,以获得力学性能优秀、晶粒细小均匀的焊接接头。在扩散焊方面,国内外学者探究了中间夹层对焊缝界面间原子相互扩散的促进作用;采取不同工艺参数,以外加超声或电子束表面加热等方式促进了原子间的相互扩散,以获得力学性能优异的焊接接头,提高焊接效率。在钎焊方面,国内外学者通过探究钎料与SiCp/Al复合材料之间的润湿性来组合钎料与钎剂,通过化学腐蚀处理表面暴露颗粒增强相、在复合材料表面电镀金属等方法来增大钎料与增强相的润湿性、解决钎料铺展受阻的问题,以进一步提高钎焊焊接接头质量。

Evolution of Thermoplastic Shear Localization and Related Microstructures in Al/SiC_p Composites Under Dynamic Compression

The localized shear deformation in the 2024 and 2124 Al matrix composites reinforced with SiC particles was investigated with a split Hopkinson pressure bar (SHPB) at a strain rate of about 2.0×103 s-1. The results showed that the occurrence of localized shear deformation is sensitive to the size of SiC particles. It was found that the critical strain, at which the shear localization occurs, strongly depends on the size and volume fraction of SiC particles. The smaller the particle size, the lower the critical strain required for the shear localization. TEM examinations revealed that Al/SiCp interfaces are the main sources of dislocations. The dislocation density near the interface was found to be high and it decreases with the distance from the particles. The Al matrix in shear bands was highly deformed and severely elongated at low angle boundaries. The AI/SiCp interfaces, particularly the sharp corners of SiC particles, provide the sites for microcrack initiation. Eventual fracture is caused by the growth and coalescence of microcracks along the shear bands. It is proposed that the distortion free equiaxed grains with low dislocation density observed in the center of shear band result from recrystallization during dynamic deformation.