Investigation of thermal properties of Al–Si matrix reinforced fine SiCp composites

Abstract

The characterisation of thermal expansion coefficient and thermal conductivity of Al–Si matrix alloy and Al–Si alloy reinforced with fine SiC_p (5 and 20 wt-%) composites fabricated by stir casting process are investigated. The results show that with increasing temperature up to 350°C, thermal expansion of composites increases and slowly reduces when the temperature reaches to 500°C. The values of both thermal expansion and conductivity of composites are less than those for Al–Si matrix. Microstructure and particles/matrix interface properties play an important role in the thermal properties of composites. Thermal properties of composites are strongly dependent on the weight percentage of SiC_p.     

Processing and properties of Al–Li–SiCp composites

Al–Li–SiC_p composites were fabricated by a modified version of the conventional stir casting technique. Composites containing 8, 12 and 18 vol% SiC particles (40 mm) were fabricated. Hardness, tensile and compressive strengths of the unreinforced alloy and composites were determined. Ageing kinetics and effect of ageing on properties were also investigated. Additions of SiC particles increase the hardness, 0.2% proof stress, ultimate tensile strength and elastic modulus of Al–Li–8%SiC and Al–Li–12%SiC composites. In case of the composite reinforced with 18% SiC particles, although the elastic modulus increases the 0.2% proof stress and compressive strength were only marginally higher than the unreinforced alloy and lower than those of Al–Li–8%SiC and Al–Li–12%SiC composites. Clustering of SiC particles appears to be responsible for reduced the strength of Al–Li–18%SiC composite. The fracture surface of unreinforced 8090 Al-Li alloy (8090Al) shows a dimpled structure, indicating ductile mode of failure. Fracture in composites occurs by a mixed mode, giving rise to a bimodal distribution of dimples in the fracture surface. Cleavage of SiC particles was also observed in the fracture surface of composites. Composites show higher peak hardness and lower peak ageing time compared with unreinforced 8090Al alloy. Macroand microhardness increase significantly after peak ageing. Ageing also results in considerable improvement in strength of the unreinforced 8090Al alloy and its composites. This is attributed to formation of δ^' (Al₃Li) and S^' (Al₂CuMg) precipitates during ageing. Per cent elongation, however, decreases due to age hardening. Al–Li–12%SiC, which shows marginally lower UTS and compressive strength than the Al–Li–8%SiC composite in extruded condition, exhibits higher strength than Al–Li–8%SiC in peak-aged condition.     

Thermal expansion behaviour of plasma sprayed Al–SiCp composites

Abstract

Al with 55 and 75 vol.-%SiC powders were free mechanically mixed or ball milled as feedstock. The powder feedstock was deposited onto a graphite substrate to form near net shape of Al/SiC composites by air plasma spraying. The pores and the gaps at the Al/SiC interface as well as at the boundary of Al grains exist extensively in the as sprayed composites. Coefficient of thermal expansion (CTE) of the sprayed composites was measured in the temperature range of 25–300°C. The composites plasma sprayed with Al–75SiC powder feedstock can reach a low CTE value of 8 × 10^?6 °C^?1. The effect of pore on the CTE of the composites has been discussed. The gap at Al/SiC interface has an influence on thermal expansion behaviour only at lower test temperatures. Reduction and elimination of the gap with temperature can offset the thermal expansion of the as sprayed composites, resulting in lower CTE at the beginning of the CTE test. Roughly quantitative consideration of the effect of the interfacial gaps between Al and SiC on CET was given. Linear rule of mixture (ROM), Turner and Kerner's models were used to estimate the CTE of the sprayed composites. It was found that ROM and Kerner's model give closer CTE prediction for the present composites.     

Mechanical alloying process and mechanical properties of Cu–SiCp composite

Abstract

A composite of copper powder and SiC particle reinforcement was prepared by mechanical ball milling and subsequent sintering. Proper choice of processing parameters ensured a homogenous distribution of SiC particles in the copper matrix. Microstructure, powder morphology and mechanical properties of the composite were investigated as a function of milling time. With increasing milling time, the dentritic copper powder became flattened, which subsequently became spherical shaped. Mechanical properties of the composites change with the distribution of SiC.     

XPS Analysis of the Cerium Conversion Coatingon the Anodized A16061／SiCp

A method of concentration analysis based on X-ray photoelectron spectroscopy (XPS) results was introduced.The concentration of Ce-rich conversion coating on the anodized Al based metal matrix composites Al6061/SiCp was then studied according to this method.The results revealed that the Ce conversion coating on the anodized Al6061/SiCp consisted of Al oxide,Ce oxide and Ce hydroxide.The state of Ce element exhibited the mixture of Ce^3 and Ce^4 .Some of Cell was oxidized to be CelV in the outer layer coating.     

SiCp表面化学镀对SiCp/Al复合材料微结构及热性能影响

为了改善SiCp与Al基体之间的界面,在碱性条件下,甲醛作为还原剂,采用化学镀的方法在SiCp表面沉积铜层,然后采用无压渗透方法制备SiCp/Al复合材料。采用X射线衍射仪、3D立体视频显微镜、扫描电子显微镜来分析化学镀后SiCp和复合材料的表面、界面形貌、组织结构及物相,并通过EDS能谱对复合材料表面元素成分分析,利用激光闪光法测定复合材料导热系数。结果表明,相比酒石酸钾钠单一络合剂,采用酒石酸钾钠和EDTA-2Na组成的双络合剂的SiCp镀层更致密,且镀层未被氧化,复合材料界面结合良好,界面厚度为2.5~3μm,有AlCu2相生成,无Al4C3脆性相存在。室温下,镀铜后的复合材料热导率达到181 W/(m·K),远高于没有表面改性的复合材料热导率102 W/(m·K)。     

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

The present work is focused on optimization of machining characteristics of Al/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(NN) 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.     

Enhanced thermal conductivity of SiCp/PS composites by electrospinning–hot press technique

Silicon carbide particle/polystyrene (SiCp/PS) electrospun mats are firstly prepared by electrospinning technology, then to be fabricated the corresponding thermally conductive SiCp/PS composites by the method of “laminating-hot press”. The mass fraction of SiCp and laminating mode of SiCp/PS electrospun mats affecting on the thermal conductivities, dielectric and thermal properties of the composites are investigated. The addition of 32.8 vol% SiCp improves the thermally conductive coefficient λ of pure PS from 0.182 to 0.566 W/m K and thermal diffusivity of pure PS from 0.169 to 0.376 mm²/s, whereas the dielectric constant values still remain at relatively low levels. The thermal stabilities of the SiCp/PS composites are increased with the increasing addition of SiCp. For a given SiCp loading, the SiCp/PS composites from warp–weft arrangement of SiCp/PS electrospun mats possess relative higher thermally conductive coefficient λ and dielectric constant values than those of SiCp/PS composites from warp–warp arrangement of SiCp/PS electrospun mats.     

SiCp/Fe复合材料断口分析

应用SEM和EDS等分析技术对SiCp／Fe金属基复合材料的断口形貌进行了研究。结果表明，SiCp／Fe在l100℃烧结时发生界面反应生成硅铁和石墨而恶化界面结构和材料性能；在1050℃烧结能避免界面反应，其界面结构为机械啮合型，复合材料呈韧性断口形貌特征，以基体撕裂为主，产生撕裂棱；裂纹易沿SiCp／Fe界面扩展，SiCp涂覆金属镀层通过镍与铁基体扩散结合来改善SiCp／Fe界面结合，提高材料的强度、韧性及耐磨性。     

Corrosion behavior of Al–60 vol.% SiCp composites in NaCl solution

In this study, corrosion behavior of pure Al and Al–4 wt.% Mg alloy matrix composites, comprising 60 vol.% SiC particles, has been investigated. Composites were produced by pressure infiltration technique at 750 °C. The corrosion tests were carried out in 3.5 wt.% NaCl environment up to 28 days. The weight loss of the composites increased with increasing duration time up to 3–5 days then remained constant. Scanning electron microscopy (SEM) analysis showed that Al–4 wt.% Mg alloyed matrix composite exhibited higher corrosion resistance than pure Al matrix composite although potentiodynamic polarisation measurements showed higher i_corr values of Al–4 wt.% Mg alloyed matrix composites than pure Al matrix composites. Experimental results revealed that precipitation of Mg₂Si as a result of reaction between Al–Mg alloy and SiC particle has a beneficial effect on corrosion resistance of Al–4Mg alloy matrix composites due to interruption of the continuity of the matrix channels within the pressure infiltrated composites.     

化学沉积SiCp陶瓷复合镀层

采用化学沉积方法，实现ＳｉＣｐ与Ｎｉ（Ｐ）合金复合，形成ＳｉＣｐ陶瓷复合镀层，研究表明，ＳｉＣｐ均匀地分布于Ｎｉ（Ｐ）合金中，显著地起强化作用，与Ｎｉ（Ｐ）合金层相比，ＳｉＣｐ陶瓷复合镀层具有更高的硬度，热稳定性和抗氧化性能。     

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。     

Effect of sliding distance on the wear and friction behavior of as cast and heat-treated Al–SiCp composites

The present investigation aims to evaluate the effect of sliding distance on the wear and friction behavior of as cast and heat-treated Al–SiCp composites using pin-on-disc wear testing machine, giving emphasis on the parameters such as wear rate and coefficient of friction as a function of sliding distance (0–5000 m) at different applied pressures of 0.2, 0.6, 1.0 and 1.4 MPa, and at a fixed sliding speed of 3.35 m/s. Characterizing the alloy and composites in terms of microstructure, X-ray diffraction analysis, microhardness and wear surface analysis. The results revealed that the heat-treated composite exhibited superior wear properties than the base alloy, while the coefficient of friction followed an opposite trend. Moreover, the wear rate of the composite is noted to be invariant to the sliding distance and increased with applied pressures. Microstructure of composite shows fairly uniform distribution of SiC particles in the metallic matrix. The hardness value of heat-treated composite increased 20–30% by addition of SiC particles to the alloy, intermetallic phases like Al₂Mg₃ and Al₂CuMg, etc., were obtained from X-ray analysis. The wear mechanism of the investigated materials was studied through worn surfaces examination of the developed wear tracks.     

Tensile behaviour of powder metallurgy processed (Al–Cu–Mg)/SiCp composites

Abstract

The tensile behaviour of Al–Cu–Mg alloy matrix composites produced by a powder metallurgy process was investigated as a function of particle size in the as extruded, homogenised, and peak aged conditions. The tensile behaviour of the corresponding matrix alloy which was produced in a similar manner, designated as Control, was also studied. There was a significant increase in the 0.2% yield strength of Control and all the metal matrix composites (MMCs) after homogenisation treatment (53–68%) and peak aging (93–109%), as compared to their values in the as extruded condition. The ultimate tensile strength (UTS) of Control as well as the MMCs also increases considerably after homogenisation treatment (39–70%), however, subsequent peak aging did not result in any further increase in UTS in case of any of the MMCs. It was found that the finer the reinforcement size, the higher the 0.2% yield strength and UTS in all the conditions. On the other hand, ductility decreased considerably after homogenisation treatment and subsequent peak aging. The results are discussed in the light of dislocation strengthening as well as reinforcement damage.     

Corrosion Behavior of SiCp／2024 Al Matrix Composites in 3.5 wt pct Sodium Chloride

The influences of volume fraction and particle size of SiC particulate reinforcements on the corrosion characteristics of SiCp/2024Al metal matrix composites in aerated 3.5wt pct NaCl aquecus solution were investigated.The electro-chemical behavior was investigated by prtentiodynamic polarization and electrochemical impedance spectroscopy, the general corrosion behavior of the composites was studied further by immersion tests.The results showed that pitting susceptibility was about the same for the composites and the alloy.The corrosion potentials were also independent of SiC phase.The corrosion resistance for the composites decreased as the volume fraction increased or particle size decreased.     

SiCp增强泡沫铝制备工艺研究

对熔体发泡法制备SiCp增强泡沫铝基复合材料的制备工艺进行了探索，通过正交试验研究了SiC的粒度、发泡剂TiH2的加入量、发泡温度、保温时间等工艺参数对泡沫铝孔隙率及孔结构的影响，确定了制备SiCp增强泡沫铝基复合材料的最佳工艺参数：掺入10％（质量分数）1000目的SiC颗粒增粘，在发泡剂TiH2加入量为2％（质量分数），搅拌时间2min，保温温度700℃以及保温时间3min的工艺条件下，制得的泡沫铝的孔隙率达到80％，平均密度达到了0．5g／cm^3，且基本没有无泡层。最后对泡沫铝的产业化生产的可行性作了讨论。     

SiCp/Al复合材料抗弯性能研究

利用空气气氛下的无压渗透法制备了高体积分数的SiCp/Al复合材料,研究了颗粒粒径、基体合金成分、预处理工艺对复合材料抗弯性能的影响,并采用SEM观测了复合材料抗弯断口形貌.结果表明,SiCp/Al复合材料的抗弯强度随着SiC颗粒粒径减小而增大;基体材料的强度越高,复合材料的抗弯强度越高;复合材料整体上表现出脆性断裂的特征.     

SiCp/Al复合材料的化学镀镍

采用化学镀技术对高体分SiC颗粒增强铝基复合材料(SiCp／Al)表面进行改性以改善其焊接性能和抛光性能。本文探索了在SiCp／Al表面化学镀镍的预处理工艺及条件,系统分析并阐述了除油、粗化、活化等工序对化学镀镍的作用和影响,同时在最优的条件下成功地制备出光亮、均匀、完整且与基体结合良好的镍磷合金镀层。利用扫描电子显微镜(SEM)、能谱(EDAX)对镀层微观结构和成分进行表征。结果表明,预处理可以改变基体表面的结构形貌,影响镍磷合金镀层在其表面的分布,从而对镀层质量、结合强度及沉积速度起决定性作用。     

SiCp/Al复合材料界面调控研究进展

SiCp/Al复合材料具备一系列优异的物理性能,是航空航天、电子封装、装备、核电、汽车、轨道交通等国家重大需求和国民经济装备制造所需的关键材料.但是,工业精密仪器关键零部件对SiCp/Al复合材料的性能要求相对较高,导致复合材料在诸多高端领域的应用受到了严重限制,因而提升SiCp/Al复合材料的整体性能是当前亟需解决的重要难题.对于给定的增强体与基体,界面相具有的微观结构和物化性质是影响SiCp/Al复合材料性能的决定因素.然而,界面相在形成过程中通常会出现润湿性差、结构缺陷多以及生成不良界面产物等问题,对SiCp/Al复合材料的性能产生了严重的负面影响.因此,有效实现界面的可控设计成为提升复合材料性能的关键.根据近几年关于SiCp/Al复合材料界面调控的研究工作来看,增强体颗粒表面改性在抑制增强体与基体之间的相互扩散以及减缓化学反应速率等方面发挥着重要作用,而表面改性处理的方式通常包括酸洗、高温氧化和添加涂层等.在基体中添加合金元素能够有效降低铝液的表面张力,改善SiCp/Al复合材料界面相的润湿性,同时可抑制不良界面反应的发生.目前合金化处理添加的元素通常包括Mg、Si、Cr、Ti、Fe等.在SiCp/Al复合材料的制备过程中,烧结温度、保温时间、冷却速率、成型压力、球磨时间以及烧结气氛等成型工艺参数均会影响界面的反应程度,因而对成型工艺的优化改进同样能够有效调控复合材料的界面信息,以实现对SiCp/Al复合材料性能的提升.本文结合SiCp/Al复合材料界面相具有的微观结构和物化性质,从增强体颗粒表面改性、基体合金化和成型工艺优化改进三个角度综述了SiCp/Al复合材料界面调控的研究现状,并对其未来发展的整体趋势进行了展望.     

Evolution of Thermoplastic Shear Localization and Related Microstructures in Al／SiCp 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 g