Reciprocating wear behavior of 7075Al/SiC in comparison with 6061Al/Al2O3 composites

In the present study, the reciprocating wear behavior of 7075Al/SiC composites and 6061Al/Al₂O₃ composites that are prepared through liquid metallurgy route is analyzed to find out the effects of weight percentage of reinforcement and load at the fixed number of strokes on a reciprocating wear testing machine. The Metal Matrix Composite (MMC) pins are prepared with different weight percentages (10, 15 and 20%) of SiC and Al₂O₃ particles with size of 36 μm. Hardness of these composites increases with increase in wt.% of reinforcement. However, the impact strength decreases with increase in reinforcement content. The experimental result shows that the volume loss of MMC specimens is less than that of the matrix alloy. However, the volume loss is greater in 6061Al/Al₂O₃ composites when compared to 7075Al/SiC composites. The temperature rise near the contact surface of the MMC specimens increases with increase in wt.% of reinforcement and applied load. The coefficient of friction decreases with increase in load in both cases.     

纳米SiC颗粒增强ADC12铝基复合材料的制备及性能

采用机械搅拌和超声分散相结合的方法制备出了纳米SiC颗粒增强ADC12铝合金基复合材料,并对制备出的复合材料进行微观结构分析和力学性能测试.结果表明,与基体合金相比,当纳米SiC颗粒的含量为2.0%时,所制得的复合材料的抗拉强度、弹性模量、断面收缩率及硬度分别提高23%、43%、160%和7.4%.用扫描电镜对试样拉伸断口的形貌和SiC颗粒的分散情况进行观察,发现纳米SiC颗粒在基体内呈均匀的弥散分布,没有发现大的团聚.同时,纳米SiC颗粒的均匀分布起到了阻碍或者阻止裂纹产生和扩展的作用.     

SiCP增强泡沫铝基复合材料的制备工艺研究

将SiC颗粒增强铝基复合材料的制备技术与泡沫铝熔体发泡技术相结合,探索了制备SiC颗粒增强泡沫铝基复合材料的工艺方法。讨论了SiC颗粒与铝基体之间存在的润湿性,界面反应以及SiC颗粒在熔体中沉降等问题,通过选择合适的合金成分,对SiC颗粒进行预处理,采用特定的搅拌和发泡等一系列工艺方案成功地予以解决。在熔体发泡过程中,通过严格控制发泡温度、搅拌速度和搅拌时间等工艺参数,制得了孔隙率基本可调,SiC颗粒和孔洞分布均匀的泡沫铝样品。     

Tribological Analysis of Copper-Coated Graphite Particle-Reinforced A359 Al/5 wt.% SiC Composites

Copper-coated graphite particles can be mass-produced by the cementation process using simple equipment. Graphite particulates that were coated with electroless copper and 5 wt.% SiC particulates were introduced into an aluminum alloy by compocasting to make A359 Al/5 wt.% SiC(p) composite that contained 2, 4, 6, and 8 wt.% graphite particulate composite. The effects of SiC particles, quantity of graphite particles, normal loading, sliding speed and wear debris on the coefficient of friction, and the wear rate were investigated. The results thus obtained indicate that the wear properties were improved by adding small amounts of SiC and graphite particles into the A359 Al alloy. The coefficient of friction of the A359 Al/5 wt.% SiC(p) composite that contained 6.0 wt.% graphite particulates was reduced to 0.246 and the amount of graphite film that was released on the worn surface increased with the graphite particulate content. The coefficient of friction and the wear rate were insensitive to the variation in the sliding speed and normal loading.     

Effect of tool rotating rate on foaming properties of porous aluminum fabricated by using friction stir processing

A1050 porous aluminum is fabricated by the FSP route and the effect of the tool rotating rate on the porosity and morphology of the pores is investigated. To fabricate high-porosity porous aluminum with a uniform pore size distribution, a certain amount of stirring action is necessary; however, excessive stirring action is ineffective. A sufficiently uniform mixture is realized by traversing the FSP tool two times at a tool rotating rate exceeding 2200 rpm. The results indicate the minimum necessary amount of stirring action and will provide a guideline for improving productivity. Also, to improve the morphology of pores, optimizing the amount of Al₂O₃ is effective. Closed-cell porous aluminum with a porosity of about 80% was successfully fabricated by 2-pass FSP at 2200 rpm with the addition of 7 mass% Al₂O₃, a holding temperature of 998 K and a holding time of 10 min.     

Properties and microstructure of Al-11Si/SiCp composite coatings fabricated by thermal spray

Thermal spraying has been used to coat 6082-T6 aluminium alloy with aluminium matrix composites. Mixtures of Al-11Si powder and 20 vol.% SiC and 40 vol.% SiC particles in the powder feeder were used as spraying material. In some conditions, SiC particles were coated with a sol-gel silica coating, which acts as an active barrier enhancing the wettability of the reinforcement by molten aluminium reducing the porosity of the composite coatings and inhibiting the formation of aluminium carbide. Coatings with a reinforcement volume fraction up to 17 vol.% (for 20 vol.% SiC in feeder) and 27 vol.% (for 40 vol.% SiC in feeder) were obtained with porosities below 1.0%. In all cases, the incorporation of sol-gel silica coatings on SiC particles reduced the porosity and increased the reinforcement volume fraction and the hardness of the coatings. The role played by the different spraying parameters has been also studied.     

Investigation on mechanical properties of aluminium 7075-boron carbide-coconut shell fly ash reinforced hybrid metal matrix composites

The present research work reports the fabrication and evaluation of the mechanical properties of hybrid aluminium matrix composites(HAMC). Aluminium 7075(Al7075) alloy was reinforced with particles of boron carbide(B_4 C) and coconut shell fly ash(CSFA). Al7075 matrix composites were fabricated by stir casting method. The samples of Al7075 HAMC were fabricated with different weight percentages of(0, 3, 6, 9 and 12 wt.%) B_4 C and 3 wt.% of CSFA. The mechanical properties discussed in this work are hardness, tensile strength, and impact strength. Hardness of the composites increased 33% by reinforcements of 12 wt.% B_4 C and 3 wt.% CSFA in aluminium 7075 alloy. The tensile strength of the composites increased 66% by the addition of 9 wt.% B_4 C and 3 wt.% CSFA in aluminium 7075 alloy. Further addition of reinforcements decreased the tensile strength of the composites. Elongation of the composites decreased while increasing B_4 C and CSFA reinforcements in the matrix. The impact energy of the composites increased up to 2.3 J with 9 wt.% B_4 C and 3 wt.% CSFA addition in aluminium alloy. Further addition of reinforcement decreased the impact strength of the composites. The optical micrographs disclosed the homogeneous distribution of reinforcement particles(B_4 C and CSFA) in Al7075 matrix. The homogeneously distributed B_4 C and CSFA particles added as reinforcement in the Al7075 alloy contributed to the improvement of hardness, tensile strength, and impact strength of the composites.     

Codeposition of micro- and nano-sized SiC particles in the nickel matrix composite coatings obtained by electroplating

Micro- and nano-sized SiC particles were codeposited with nickel by electrolytic plating from a nickel sulfamate bath and the effects of plating parameters such as pH of the plating bath, SiC content in the plating bath, and stirring speed on the deposition behaviors of Ni-SiC composite coating layers were studied. The result revealed that the micro-sized SiC particles are more negative than the nano-sized SiC particles in the Zeta potential. The codeposition of SiC can be increased by increasing the SiC content in the plating bath and the pH of the plating bath within the present experimental range. In case of micro-sized SiC particles, increasing stirring speed always lowered the codeposition of SiC. In case of nano-sized SiC particles, the codeposition of SiC showed a maximum at the stirring speed of 100 rpm. The nano-sized SiC particles are more difficult to codeposit than the micro-sized SiC particles and showed rougher plated surface compared with the micro-sized SiC particles, which may be attributable to the agglomeration of nano-sized SiC particles in the plating bath.     

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.     

7075铝基复合材料多级固溶和时效处理工艺

研究了多级固溶和时效处理工艺对制备的Al3Ti/7075铝基复合材料显微组织和力学性能的影响。结果表明,经XRD衍射图谱分析,该铝基复合材料存在的第二相颗粒为MgZn2。复合材料经440℃/3h+480℃/2h处理后,其显微硬度值为110.2HV,硬度比单级固溶提高了10%。在同一固溶温度下,随着固溶时间的延长,第二相颗粒回溶较多,但是会发生晶粒长大现象。基体合金和复合材料在同一温度(120℃)下时效时,复合材料时效速度要比基体合金时效速度快,复合材料的时效峰值硬度为147.73HV。     

Microstructure and Mechanical Properties of Spray Deposition Al/SiCp Composite After Hot Extrusion

Investigations of composite based on a spray deposition Al-Zn-Mg-Cu alloy reinforced with SiC particles with the volume fraction of 15% and various extrusion ratios of 11-39 are presented. Bars with a diameter of 8-15 mm were obtained as the end product. Based on the microstructural examinations of the composite, we can find that SiC particles adhered mainly to the surface of the alloy droplets during deposition, leading to more SiC particles at the surface of the droplets and less in the inner. Thus, the distribution of SiC particles in the billet was characteristic of the layered feature. This layered feature of SiC particles was not completely removed by the following hot extrusion. The SiC particles were distributed like the streamline in the longitudinal direction. A higher extrusion ratio resulted in an more uniform distribution of SiC particles. Ambient tensile tests made it possible to demonstrate that the mechanical properties improve with the increasing of extrusion ratio. The ultimate tensile strength and elongation achieve 475 MPa and 16.5% at an extrusion ratio of 39.     

激光熔注制备Al-Cr/7075Al梯度复合涂层的性能

采用激光熔注技术在7075铝合金表面制备了Al-Cr/7075Al梯度复合涂层。采用扫描电镜(SEM)、能谱仪(EDS)和X-射线衍射(XRD)和显微硬度计等研究了复合涂层的微观结构、物相及显微硬度。结果表明:Al-Cr/7075Al梯度复合涂层与基板结合良好,无裂纹、孔隙等明显缺陷;复合涂层的表面硬度为324.2 HV0.2,是7075铝合金基体的2.28倍,涂层的硬度分布沿熔池深度方向逐渐递减,呈梯度分布;复合涂层中的增强体是由Al0.983Cr0.017、Al86Cr14、AlCr2、和Cr等混合组成,受熔池温度、熔液黏度等影响,增强体含量沿熔池深度方向逐渐减少,也呈梯度分布;Al、Cr之间的反应机理为液-固反应、固-固反应2种;复合涂层的强化机制主要是增强体承载、界面传载和位错强化。     

Easy and Large Scale Synthesis Silver Nanodendrites: Highly Effective Filler for Isotropic Conductive Adhesives

Dendritic silver (Ag) nanoparticles have been successfully prepared by an easy and large scale liquid-phase reduction method. Transmission electron microscope (TEM), scanning electron microscope (SEM), and x-ray diffraction (XRD) have shown that the Ag particles prepared by this method are pure and with uniform dendritic morphology. The bulk resistivity and bonding strength of isotropic conductive adhesives (ICAs) filled with Ag nanodendrite and micrometer-sized Ag have been measured. The results show that the dendritic morphology of Ag nanoparticles has a strong effect for improving the reinforcement of the composite electrical performance. ICA filled with small amounts of Ag nanodendrites exhibits lower bulk resistivity and higher bonding strength than ICA filled with micrometer-sized Ag. When ICA is filled with 50 wt.% micrometer-sized Ag and 10 wt.% Ag nanodendrites, the bulk resistivity is 1.3 × 10⁻⁴ Ω cm, and the bonding strength reaches 18.9 MPa.     

45钢在超细SiC颗粒作用下的正向冲蚀行为*

选用超细SiC颗粒作为磨料,研究了韧性材料45钢在正向冲击条件下的冲蚀行为并与7075-T6铝合金对比。使用高强度磁铁捕获了45钢冲蚀磨屑,利用扫描电子显微镜(SEM)对冲蚀磨损后试样表面以及磨屑形貌进行观测;采用质量分析法,分析45钢在不同冲蚀条件下的失重情况与材料去除率;利用X射线应力测定仪,分析45钢在不同冲蚀条件下的表层及深度方向的残余压应力分布情况。结果表明,正向冲击条件下,韧性材料表面主要发生塑性变形,偏向堆积脊部还存在片层剥落的材料去除形式,超细磨料产生的材料去除率相对较小,材料去除率随磨料量的增加呈先增加后减小的趋势;表层应力随磨料量呈先增加后降低的趋势,微磨料冲蚀残余压应力的影响深度约为10μm。     

Aluminum-silicon carbide coatings by plasma spraying

An aluminum base composite (Al-SiC) powder has been developed for producing plasma sprayed coatings on Al and other metallic substrates. The composite powders were prepared by mechanical alloying of 6061 Al alloy with SiC particles. The concentration of SiC was varied between 20 and 75 vol%, and the size of the reinforcement was varied from 8 to 37 μm in the Al-50 vol% SiC composites. The 44 to 140 μm composite powders were sprayed using an axial feed plasma torch. Adhesion strength of the coatings to their substrates were found to decrease with increasing SiC content and with decreasing SiC particle sizes. The increase in the SiC content and decrease in particle size improved the erosive wear resistance of the coatings. The abrasive wear resistance was found to improve with the increase in SiC particle size and with the SiC content in the composite coatings.     

The effect of sintering temperature on some properties of Cu-SiC composite

Copper matrix composites reinforced with 1 wt.%, 2 wt.%, 3 wt.% and 5 wt.% SiC particles were fabricated by powder metallurgy method. Cu and Cu-SiC powder mixtures were compacted with a compressive force of 280 MPa and sintered in an open atmospheric furnace at 900-950 °C for 2 h. Within the furnace compacted samples were embedding into the graphite powder. The presence of Cu and SiC components in composites was verified by XRD analysis. Optical and SEM studies showed that Cu-SiC composites have a uniform microstructure in which silicon carbide particles are distributed uniformly in the copper matrix. The results of the study on mechanical and electrical conductivity properties of Cu-SiC composites indicated that with increasing SiC content (wt.%), hardness increased, but relative density and electrical conductivity decreased. The highest electrical conductivity of 98.8% IACS and relative density of 98.2% were obtained for the Cu-1 wt.%SiC composite sintered at 900 °C and this temperature was defined as the optimum sintering temperature.     

Microstructural Characterization of TLPD bonded 6061-SiCp Composite

Microstructural development during transient liquid phase diffusion (TLPD) bonding of extruded aluminum-based metal matrix composite (6061-15 wt.% SiCp) using 50-μm-thick copper interlayer was investigated by optical microscopy, scanning electron microscopy (SEM) together with SEM-based energy dispersive x-ray spectroscopy (EDS). Microstructural changes in the joint region were examined for a bonding temperature of 560 °C with five different holding time (20 min, 1 h, 2 h, 3 h, and 6 h) under two different applied pressure (0.1 and 0.2 MPa). Kinetics of the bonding process was significantly accelerated in presence of reinforcement (SiC). This acceleration is attributed to the increased solute diffusivity through defects as well as decreased incubation time required for nucleation (SiC particles acting as nucleating agent).     

Microstructure and mechanical properties of 7075 Al alloy based composites with Al2O3 nanoparticles

A new method was used to fabricate 7075 Al alloy based composites with Al₂O₃ nanoparticles to improve the distribution of particles. In this study, nano-sized particles were fed into the molten alloy through the flow of argon gas, then the Al₂O₃/7075 composites were prepared by solid-liquid mixed casting. The results indicated that the composite samples showed fine microstructure and achieved a homogeneous distribution of particles. Also, it was found that relative to the as-cast 7075 alloy, the Al₂O₃/7075 composites exhibited higher mechanical properties, which is due to the effect of uniform distributed Al₂O₃ nanoparticles reinforcement.     

The Microstructure and Mechanical Properties of SiC Reinforced Magnesium Based Composites by Rheocasting Process

In the present study, rheocasting process was adopted to synthesise AZ91D composites reinforced with silicon carbide (SiC) particulates. Particle-matrix interfacial reaction, distribution of particles, hardness and mechanical properties of as cast and T4 heat-treated alloy-composites were reported. The rheocast composite materials reveal uniform distribution of SiC particulates. The composite materials show an increase in hardness and elastic modulus compared to unreinforced rheocast alloy. Τhe ultimate tensile strength and ductility of composite materials were lower than those of the unreinforced alloy. 15 μm particles-composite shows significantly higher elastic modulus than the 150 μm SiC particles-composite.     

Fabrication and Wear Behavior of Nanostructured Plasma-Sprayed 6061Al-SiCp Composite Coating

6061Al powder with 15 wt.% SiC particulate (SiC_p) reinforcement was mechanically alloyed (MA) in a high-energy attrition mill. The MA powder was then plasma sprayed onto weathering steel (Cor-Ten A242) substrate using an atmospheric plasma spray process. Results of particle size analysis and scanning electron microscopy show that the addition of SiC particles as the reinforcement influences on the matrix grain size and morphology. XRD studies revealed embedment of SiC_p in the MA-processed composite powder, and nanocrystals in the MA powder and the coating. Microstructural studies showed a uniform distribution of reinforced SiC particles in the coating. The porosity level in the coating was as low as 2% while the coating hardness was increased to 232VHN. The adhesion strength of the coatings was high and this was attributed to higher degree of diffusion at the interface. The wear rate in the coatings was evaluated using a pin-on-disk type tribometer and found to decrease by 50% compared to the 6061Al matrix coating. The wear mechanism in the coating was delamination and oxidative type.