Microstructure Characteristics of SiC Particle-Reinforced Aluminum Matrix Composites Coatings by Cold Spraying

A dense Al/SiCp composite coating with high volume fraction(60%)of nano SiCp reinforcement was fabricated by cold spraying of ball-milled Al-60SiCp composite powder.The morphologies evolution of the Al-60SiCp composite powder during ball milling and the microstructure and microhardness of the cold-sprayed Al-60SiCp composite coating were investigated.The results show that Al particles undergone fracture deformation and nano SiC particles are uniformly distributed in soft Al matrix after ball milling.A dense Al-60SiCp composite coating can be fabricated by cold spraying of ball milled composite powder.Nano SiC particles in the cold-sprayed Al-60SiCp composites coating exhibit a reasonably uniform distribution.The Hv0.5 microhardness of the Al-60SiCp composite coating is reached up to(5.30±0.53)GPa due to the enhancement of SiC particles,compared to(0.34±0.03)GPa for the pure Al bulk.     

Semisolid forging electronic packaging shell with silicon carbon-reinforced copper composites

To fabricate electronic packaging shell of copper-matrix composite with characteristics of high thermal conductivity and low thermal expansion coefficient, semisolid forming technology, and powder metallurgy was combined. Conventional mechanical mixing of Cu and SiC could have insufficient wettability, and a new method of semisolid processing was introduced for billets preparation. The SiC/Cu composites were first prepared by PM, and then, semisolid reheating was performed for the successive semisolid forging. Composite billets with SiC 35% volume fraction were compacted and sintered pressurelessly, microstructure analysis showed that the composites prepared by PM had high density, and the combination between SiC particles and Cu-alloy was good. Semisolid reheating was the crucial factor in determining the microstructure and thixotropic property of the billet. An optimised reheating strategy was proposed: temperature 1,025 °C and holding time 5 min.     

EFFECT OF SILICON CARBIDE VOLUME FRACTION UPON INTERFACE REACTION IN SiC_p/Al COMPOSITES

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不同体积分数SiCp/Al复合材料单颗磨粒划切仿真与试验研究

SiCp/Al复合材料由性能差异巨大的碳化硅颗粒与铝合金基体组成,切削过程复杂,影响加工质量因素多,材料仿真建模困难。本文提出了虑及颗粒随机分布特性、形状、粒径、体积分数等因素的SiCp/Al复合材料参数化建模方法,研究了不同体积分数SiCp/Al复合材料的去除过程、切削力、表面形貌及损伤等,并进行了试验验证。仿真分析与试验结果表明,参数化建模效果较好。SiCp/Al复合材料具有表面损伤严重、切削力大、基体涂覆掩盖表面缺陷、实际切削深度小等特点,不能单纯以表面粗糙度评价SiCp/Al复合材料的加工质量。粒径大、体积分数高的SiCp/Al切削力、比磨削能更低,表面质量更差,实际切削深度更小,铝合金涂覆现象更严重且覆盖层易脱落。SiC粒径对表面损伤、切削力、比磨削能有重要影响。本文可为SiCp/Al复合材料表面去除特点研究与工程应用提供一定的借鉴。     

Hot Deformation Behavior of 6061 and 7108 Al-SiCp Composites

Hot deformation behavior of Al 6061- and Al 7108-SiC particulated composites (Al-PMMCs), prepared by stir casting with SiC particulates (SiCp) size of 8 and 15 μm and volume fraction from 0 to 20% is studied by uniaxial compression test carried out at temperature range from room temperature to 500 °C. The flow stress, work hardening behavior, and Young’s modulus are determined. Dynamic recrystallization is also studied. Work hardening and Young’s modulus are directly correlated with composite constituents, whereas the flow stress is greatly influenced by the porosity and SiCp agglomeration. The role of the SiCp in increasing the flow stress decreases by increasing the deformation temperature. The dynamic recrystallization process is stimulated by refining the SiCp and increasing their fraction in soft Al matrix. On the other hand, the PMMCs with Al6061 matrix has more potential for strain hardening than that with Al 7108 matrix. The strain hardening rate is influenced by the matrix type more than the SiCp volume fraction and size.     

Dry friction and wear performance of SiC 3D continuous ceramic frame reinforced 7075A1 alloy

The dry friction and wear behavior of 7075 Al alloy reinforced with SiC 3D continuous ceramic network against Cr12 steel was studied with oscillating dry friction and wear tester under the testing conditions of 70 °C, 30 min, and the load range of 40–100 N. The experimental result shows that the characteristic of abrasive wear and oxidation wear mechanisms are present for 3D continuous SiC/7075 Al composite. 3D continuous network ceramic as the reinforcement can avoid composite from the third body wear that usually occurs in traditional particle reinforced composite. Under low load, the composite with low volume fraction of ceramic reinforcement exhibits better wear resistance due to the homogeneous reinforcement distribution with small pore size; on the contrary, under high load, the composite with high reinforcement volume fraction exhibits better wear resistance because of the coarse frame size. Hard SiC frame leads to the wear of Cr12 steel mainly. The frame with high volume fraction corresponds to the high Fe content.     

SiCp/A357复合材料流动性数值模拟与实验研究

搅拌铸造方法易于成型大尺寸复杂的复合材料零件,但是碳化硅颗粒加入使得复合材料的流动行为变得更加复杂,开展复合材料流动性研究至关重要。本文建立了SiCp/A357复合材料的流动模型,采用数值模拟及实验研究相结合的方法,研究了浇注温度及碳化硅体积分数对SiCp/A357复合材料流动性及流动充型过程碳化硅分布的影响。结果表明,随着浇注温度的提高SiCp/A357复合材料的流动性升高,这一趋势在半固态区间更为明显;但是随着浇注温度的提高,试样前端的碳化硅体积分数较末端减少加剧,复合材料中碳化硅的整体分布均匀性降低;随着碳化硅体积分数的增加SiCp/A357复合材料的流动性降低,且随着碳化硅体积分数的增加,试样前端碳化硅的体积分数减少程度减弱,整体的均匀性提高。上述的模拟结果与实验结果具有较好的一致性。     

不同烧结方法及二次热压对SiCp／Al复合材料组织的影响

采用普通空气加热炉烧结和铝液浸渗保护烧结两种方法制备了不同体积分数的粉末冶金SiCp/Al复合材料,并在400℃对其进行二次热压变形。研究了不同烧结方法及二次热压对SiCp/Al复合材料组织的影响。结果表明,二次热压变形能改善SiCp/Al复合材料的组织,使基体晶粒细,致密度提高,SiC颗粒分布均匀;铝液浸渗保护烧结法可直接制备组织均匀、性能较好的复合材料。     

Effects of Mg content on microstructure and mechanical properties of SiCp/Al-Mg composites fabricated by semi-solid stirring technique

10%(volume fraction) SiCp/Al-Mg composites with different Mg contents were successfully fabricated by semi-solid mechanical stirring technique under optimum processing conditions.Effects of Mg content on microstructure and mechanical properties were studied by scanning electron microscopy(SEM),X-ray diffractometry(XRD) and transmission electron microscopy(TEM).The results indicate that SiC particles disperse homogeneously in Al-Mg matrix and interfacial reaction between Al matrix and SiC particles is effectively controlled.Distribution of SiCp reinforcement and interfacial bonding are improved by adding Mg.Additionally,the mechanical properties of composites are remarkably improved with the Mg content increasing.     

Microstructure Evolution of Semi-Solid 7075 Aluminum Alloy During Reheating Process

Microstructural evolution of semi-solid 7075 Al alloy manufactured by strain-induced melt activation (SIMA) process was investigated. The effects of different processing parameters, such as isothermal temperature and holding time on the semi-solid microstructures (the liquid volume fraction, average grain size, and degree of spheroidization of the solid particles) during partial remelting have been investigated on 7075 Al alloy that was extruded by an extrusion ratio of 20 before remelting. Experiments of remelting were carried out in the range of 560-610 °C for 10, 20, and 30 min holding time and then the specimens were quenched in cold water. Microstructure of quenched samples were observed under optical microscope and then analyzed via image analysis. The results showed that high semi-solid isothermal temperature would increase the liquid volume fraction and accelerate the spherical processing of the solid particles. Furthermore at long holding time, the globular grains coarsened slightly and the average grains size are increased. The experimental results showed that the optimum process parameters, should be chosen at isothermal temperature of 580 °C with the holding time, <30 min.     

Electrochemical corrosion behaviour of Mg–Al alloys with thermal spray Al/SiCp composite coatings

The corrosion protection of Mg–Al alloys by flame thermal spraying of Al/SiC particles (SiCp) composite coatings was evaluated by electrochemical impedance spectroscopy in 3.5 wt.% NaCl solution. The volume fraction of SiCp varied between 5 and 30%. The as-sprayed Al/SiCp composite coatings revealed a high number of microchannels, largely in the vicinity of the SiCp, that facilitated the penetration of the electrolyte and the subsequent galvanic corrosion of the magnesium substrates. The application of a cold-pressing post-treatment reduced the degree of porosity of the coatings and improved the bonding at the coating/substrate and Al/SiC interfaces. This resulted in improved corrosion resistance of the coated specimens. The effectiveness of the coatings slightly decreased with the addition of 5–30 vol.% SiCp compared with the unreinforced thermal spray aluminium coatings.     

SiCp/Al复合材料的离心熔渗法制备及其性能

研究了反应离心熔渗法制备高体积比SiCp／Al复合材料的工艺过程及其抗弯强度。结果表明：通过适当的粒度配比，可在低温、低离心力下熔渗制备组织均匀的高体积比SiCp／Al复合材料，SiC颗粒体积分数可达到63％；复合材料的强度在很大程度上依赖于SiC颗粒尺寸及界面反应程度，合适的界面结合及细SiC颗粒的掺入有利于复合材料强度的提高；基体热处理改变了SiC颗粒所受应力状态，提高了复合材料的强度，其最高值可达519MPa。     

Fabrication and Characterization of Functionally Graded Al/SiCp Composites Produced by Remelting and Sedimentation Process

A new process termed here as remelting and sedimentation (RAS) was developed to produce functionally graded Al/SiC composites with a smooth concentration gradient of SiC particles along the height of samples, as opposed to a step change. For this purpose, first settling velocities of different-sized SiC particles in aluminum A356 melt were measured, and the results exhibited a reasonably good agreement with those predicted via the modified Stokes law. Then slices of particulate Al/SiC composites with different SiC contents of 5, 10, 15, and 20 vol.% were stacked in a cast iron mold and heated at 650 °C resulting in remelting and unification of the different composite parts. Considering the preliminary settling experiments, the composite slurry was held at this temperature for three different times to investigate the optimum holding time for obtaining a smooth gradient of SiC concentration along the height of the sample. After quenching, the samples were sectioned and subjected to metallographic studies and hardness measurements. The results confirmed that holding the melt for 60 s provides sufficient settling and redistribution of SiC particles and results in successful production of a functionally graded material.     

Effect of SiC volume fraction on the age-hardening behavior in SiC particulate-reinforced 6061 aluminum alloy composites

The age-hardening behavior in the SiC particulate-reinforced 6061 aluminum alloy composites (SiCp/6061 Al alloy composites) was investigated using hardness measurement, calorimetric technique and transmission electron microscopy. The aging time for the peak hardness in 10%SiCp/6061 Al and 20%SiCp/6061 Al alloy composites was shorter than that of the unreinforced 6061 Al alloy, and the age-hardening was most accelerated in the 20%SiCp/6061 Al alloy composite. It is induced from the high density of dislocations in SiCp/6061 Al alloy composites which act as heterogeneous nucleation sites of precipitates and as a high diffusivity path of alloy elements. The precipitation sequence and the aspect of precipitates in the 6061 Al alloy cannot be affected considerably by the presence of SiC particulate and the volume fraction of SiC particulate. The activation energies for the formation of the intermediate β' phase in the unreinforced 6061 Al alloy, 10%SiCp/6061 Al and 20%SiCp/6061 Al alloy composite were 142.6 kJ/mol, 127.3 kJ/mol, 106.1 kJ/mol, respectively.     

SiCp/Al合金复合材料时效强化的综合模型

以颗粒强化和时效强化理论为基础,结合铝合金时效动力学研究了SiCp／Al合金复合材料中增强体尺寸、体积分数以及时效制度对屈服强度的影响．分析不同时效制度下复合材料屈服强度与时效参数的关系,建立了一个SiCp／Al合金复合材料的时效强化综合模型,利用该模型可以预测复合材料屈服强度随增强体体积分数和尺寸以及时效时间的变化规律,将模型应用于SiC颗粒增强2XXX铝合金复合材料,结果显示模型预测值与实验数据吻合很好．     

Particle weakening in superplastic SiC/2124 Al composites at high temperature

High-strain-rate superplastic behavior of powder-metallurgy-processed 2124 Al matrix alloy and 10%, 20% and 30% SiC particulate reinforced 2124 Al composites were investigated over the temperature range from 370°C to 565°C, and the strain rate range from 10⁻⁴/s to 1/s. The true activation energy for the plastic flow after threshold stress compensation was close to that for lattice diffusion in aluminum for the 2124 Al alloy, while the activation energies for the 2124 composites were considerably higher than those for the unreinforced alloy, increasing with an increase in the volume fraction of SiC. The strength of the 2124 Al composites is lower than the strength of the 2124 Al alloy at high temperatures. The strength differential between the unreinforced and reinforced 2124 Al alloys is a function of temperature and is seen to decrease systematically with decrease in temperature and virtually vanishes at 460°C. Particle weakening is discussed in the light of load transfer effect, interphase diffusion, dissolution of second phase particles into matrix and the presence of liquid phase. It is proposed that interphase weakening, possibly with some liquid formation, is the principal factor contributing to the results obtained. Interphase and boundary sliding is believed to be the rate-controlling process in plastic flow of the SiC/2124 Al composites.     

T6热处理对SiCp/Al复合材料摩擦磨损性能的影响

采用粉末冶金法制备出不同SiC颗粒体积分数(30%、35%和40%)的SiCp/Al复合材料。采用MMU-5GA微机控制真空高温摩擦磨损试验机对比研究SiCp/Al复合材料在不同体积分数以及T6热处理前后情况下平均摩擦因数和磨损率的变化,通过扫描电镜分析了SiCp/Al复合材料表面磨损形貌,探讨了摩擦磨损机理。试验结果表明,SiC颗粒体积分数在30%~40%变化时,随其体积分数增加耐磨性下降。SiC颗粒体积分数在30%~35%范围内,SiC颗粒与基体结合较好,SiC颗粒作为硬质点起到抵抗磨损和限制基体合金塑性变形产生磨损的双重作用;但SiC含量过多时,颗粒与基体的结合不紧密,磨损时颗粒极易脱落,复合材料耐磨性降低;T6热处理后复合材料的平均摩擦因数和磨损率均降低,这是由于热处理后试样强度及硬度提高,从而提高了试样的耐磨性;常温下复合材料在磨损初期的磨损机理主要以磨粒磨损为主,而在磨损期则为磨粒磨损与剥落磨损共存。     

Fabrication of Al6061 composite with high SiC particle loading by semi-solid powder processing

Aluminum alloys reinforced with silicon carbide (SiC) particles have been studied extensively for their favorable properties in structural and thermal applications. However, there has been only limited research into investigating the loading limit of a reinforcement phase of a metal matrix composite. In this paper, semi-solid powder processing (SPP), a fabrication method that exploits the unique behavior of a solid–liquid mixture, was used to synthesize SiC particle-reinforced Al6061. A high volume loading (>45 vol.%) of SiC in Al6061 matrix was investigated by varying the SiC loading volume fraction, forming pressure, SiC particle size and Al6061 particle size. The compaction and synthesis mechanism of the composite by SPP was discussed based on reinforcement phase compaction behavior and processing parameters. Microstructure, hardness, fracture surface and X-ray diffraction results were also analyzed. Results showed that SPP can achieve over 50 vol.% loading of SiC in Al6061 matrix with near theoretical density.     

Fatigue properties of Al–Si casting alloy with cold sprayed Al/SiC coating

Abstract

The fatigue properties of Al–Si alloy cold sprayed Al and Al–SiC composite coatings have been studied. The specimens coated with composites reinforced with a large volume (25%) of fine SiC particles exhibited improved adhesion strength at the interface due to crater formation, and cyclic fatigue lives at room temperature more than three times those of uncoated specimens. In high temperature low cycle fatigue tests at 250°C, the pure Al coatings showed longer fatigue lives than the Al–SiC composite coatings, which is attributed to an increment in ductility at the surface retarding fatigue crack initiation.     

稀土Ce和变形参数对SiCp/Al复合材料热变形的影响

制备了SiC质量分数为5％、8％,Ce质量分数为0.05％的SiCp/Al复合材料.利用Gleeble-1500热模拟试验机,在不同变形温度、变形速率下进行压缩试验,研究了稀土Ce对SiCp/Al复合材料热变形行为的影响.结果表明,SiC质量分数为8％的SiCp/Al复合材料在低温高应变速率条件下发生了动态再结晶.同样条件下,高应变速率的复合材料动态再结晶晶粒比低应变速率下的细小.稀土元素Ce对SiCp/Al复合材料具有明显的强化作用,并且稀土元素Ce能抑制复合材料的动态再结晶.