Mg_2Si/AZ91D复合材料阻尼性能

以AZ91D镁合金为基体,采用搅熔铸造法将球磨后的粉煤灰漂珠颗粒加入到熔融态基体中,设置球磨漂珠质量分数(2%、6%和10%)和搅拌时间(3min和6min),成功制备了Mg2Si/AZ91D复合材料。采用金相分析、XRD分析和动态机械热分析等方法研究了铸态和固溶态Mg2Si/AZ91D复合材料的显微组织、成分及阻尼性能。研究表明:与AZ91D镁合金相比,加入球磨漂珠颗粒后制备的Mg2Si/AZ91D复合材料中生成了Mg2Si相,而且随着漂珠质量分数的增加,Mg2Si相呈现不规则形状,固溶后Mg2Si相呈现均匀块状。随着漂珠质量分数的增加,Mg2Si/AZ91D复合材料的阻尼性能越好,搅拌时间6min制备的复合材料阻尼性能高于搅拌时间3min制备的复合材料的阻尼性能,并且固溶态的阻尼性能优于铸态。在室温下,Mg2Si/AZ91D复合材料阻尼性能可用位错理论来解释。     

Compressive and ultrasonic properties of polyester/fly ash composites

The addition of hollow fillers having appropriate mechanical properties can decrease the density of the resulting composite, called syntactic foams, while concurrently improving its mechanical properties. In this study, hollow fly ash particles, called cenospheres, are used as fillers in polyester matrix material. Cenospheres are a waste by-product of coal combustion and, as such, are available at very low cost. In this study, the composites were synthesized by settling cenospheres in a glass tube filled with liquid polyester resin and subsequently curing the resin. This process resulted in a functionally graded structure containing a gradient in the cenosphere volume fraction along the sample height. Uniform radial sections were cut from each composite and were characterized to observe the relationship between cenosphere volume fraction and compressive properties of the composite. The composite was also tested using ultrasonic non-destructive evaluation method. Results show that the modulus of the composites increases with increasing cenosphere volume fraction. The modulus of composites containing more than 4.9 vol% cenosphere was found to be higher than the matrix resin. In general, the modulus of composites increased from 1.33 to 2.1 GPa for composites containing from 4.9–29.5 vol% cenospheres. The specific strength of the composite was found to be as high as 2.03 MPa/(kg/m³) compared to 0.96 MPa/(kg/m³) for the neat resin. Numerous defects present in fly ash particles caused a reduction in the strength of the composite. However, the reduction in the strength was found to be only up to 22%. Increase of over 110% in the specific modulus and only a slight decrease in the strength indicates the possibility of significant saving of weight in the structures using polyester/fly ash syntactic foams.     

粉煤灰漂珠粒径对粉煤灰漂珠/AZ91D镁合金复合材料阻尼性能的影响

通过搅拌铸造法向半固态AZ91D镁合金中添加粉煤灰漂珠（FAC）制备了FAC/AZ91D镁合金复合材料,研究了FAC粒径对该复合材料阻尼性能的影响。结果表明:FAC/AZ91D镁合金复合材料的阻尼性能明显优于基体材料,在FAC含量相同时,FAC的粒径越大,其阻尼性能越好。室温下FAC对提高FAC/AZ91D镁合金复合材料的阻尼性能起重要作用,FAC附近的基体产生了高密度的位错,形成了塑性区。室温下FAC粒径越大,在其附近产生的塑性区越大,阻尼性能越好。随温度的升高,FAC/AZ91D镁合金复合材料的阻尼性能迅速提高。位错、晶界以及FAC和基体之间的界面运动是提高阻尼性能的关键。      

Fabrication of SiC particles-reinforced magnesium matrix composite by ultrasonic vibration

Magnesium matrix composites reinforced with two volume fractions (1 and 3%) of SiC particles (1 μm) were successfully fabricated by ultrasonic vibration. Compared with as-cast AZ91 alloy, with the addition of the SiC particles grain size of matrix decreased, while most of the phase Mg₁₇Al₁₂ varied from coarse plates to lamellar precipitates in the SiCp/AZ91 composites. With increasing volume fraction of the SiC particles, grains of matrix in the SiCp/AZ91 composites were gradually refined. The SiC particles were located mainly at grain boundaries in both 1 vol% SiCp/AZ91 composite and 3 vol% SiCp/AZ91 composite. SiC particles inside the particle clusters may be still separated by magnesium. The study of the interface between the SiC particle and the alloy matrix suggested that SiC particles bonded well with the alloy matrix without interfacial reaction. The ultimate tensile strength, yield strength, and elongation to fracture of the SiCp/AZ91 composites were simultaneously improved compared with that of the as-cast AZ91 alloy.     

粉煤灰微珠-TiO_2复合颗粒制备与性能表征

以粉煤灰微珠为基体,利用TiOSO_4水解法,制备TiO_2包覆微珠复合颗拉。通过扫描电镜、X射线衍射、比表面积、超声振荡和光电子能谱等检测手段,对复合微珠的表面形貌、包覆层相组成、比表面积、包覆层与基体结合强度与结合方式进行了研究和探讨。检测与分析表明:得到的复合微珠表面包覆层为均匀非连续包覆,包覆层主要为金红石相,包覆后微珠比表面积比未包覆前提高了超过600倍,且包覆层颗粒与基体结合强度较高,二者间存在化学键的联结。     

Synthesis of fly ash particle reinforced A356 Al composites and their characterization

A356 Al–fly ash particle composites were fabricated using stir-cast technique and hot extrusion. Composites containing 6 and 12 vol.% fly ash particles were processed. Narrow size range (53–106 μm) and wide size range (0.5–400 μm) fly ash particles were used. Hardness, tensile strength, compressive strength and damping characteristics of the unreinforced alloy and composites have been measured. Bulk hardness, matrix microhardness, 0.2% proof stress of A356 Al–fly ash composites are higher compared to that of the unreinforced alloy. Additions of fly ash lead to increase in hardness, elastic modulus and 0.2% proof stress. Composites reinforced with narrow size range fly ash particle exhibit superior mechanical properties compared to composites with wide size range particles. A356 Al–fly ash MMCs were found to exhibit improved damping capacity when compared to unreinforced alloy at ambient temperature.     

Synthesis and properties of light weight magnesium–cenosphere composite

Significantly light weight magnesium composite foams are synthesised by addition of fly ash cenosphere particles (waste from coal-fired power plants) in biocompatible pure magnesium using solidification-based disintegrated melt deposition technique. The density of the composite foams synthesised in this study approaches that of plastics- and polymer-based composites. Microstructure development of Mg/cenosphere composite foams was favourable as they exhibited better dimensional stability (reduced coefficient of thermal expansion) and remarkable improvements in tensile strengths, compressive strengths, compressive total strain and microhardness. The present study highlights the processing, microstructure and mechanical properties of Mg/cenosphere composite foams which hold great potential as light weight metal-based green materials for diverse weight critical applications spanning from engineering to biomedical sector.     

Investigation on mechanical properties and tribological behaviour of stir cast LM13 aluminium alloy based particulate hybrid composites

LM13 aluminium alloy with boron carbide (0 wt.%–7.5 wt.%) and fly ash (2.5 wt.%) reinforced particulate hybrid composites were fabricated using liquid metallurgy route. Microstructure and mechanical properties viz., hardness, ultimate tensile strength and ductility were investigated. Wear behaviour of composites was tested by varying sliding distance and load. Fracture surface and worn surface of composites were examined using field emission scanning electron microscope. Microstructure of hybrid composites revealed uniform dispersion of particles in LM13 aluminium alloy. Hardness and tensile strength of composites increased with increasing wt.% of boron carbide and fly ash particles. Wear test results showed that addition of particles significantly decreased the weight loss and coefficient of friction. Also cumulative weight loss decreased up to 47.2 % for 10 wt.% of hybrid composites as compared to LM13 aluminium alloy. Fracture surface of composites showed dimples with particle cracking on the surface. Worn surface of LM13 aluminium alloy showed continuous grooves due to ploughing with delamination. However, worn surface of composites showed fine grooves due to the presence of hard reinforcements on the surface. Boron carbide and fly ash reinforced LM13 aluminium hybrid composites exhibited superior mechanical properties with excellent wear resistance as compared to LM13 aluminium alloy.     

Processing and Characterization of In Situ (TiC–TiB2)p/AZ91D Magnesium Matrix Composites

In this paper, a practical and cost‐effective processing route, in situ reactive infiltration technique, was utilized to fabricate magnesium matrix composites reinforced with a network of TiC–TiB₂ particulates. These ceramic reinforcement phases were synthesized in situ from Ti and B₄C powders without any addition of a third metal powder such as Al. The molten Mg alloy infiltrates the preform of (Ti_p + B₄C_p) by capillary forces. The microstructure of the composites was investigated using scanning electron microscope (SEM)/energy dispersive X‐ray spectroscopy (EDS). The compression behavior of the composites processed at different conditions was investigated. Also, the flexural strength behavior was assessed through the four‐point‐bending test at room temperature. Microstructural characterization of the (TiB₂–TiC)/AZ91D composite processed at 900 °C for 1.5 h shows a relatively uniform distribution of TiB₂ and TiC particulates in the matrix material resulting in the highest compressive strength and Young's modulus. Compared with those of the unreinforced AZ91D Mg alloy, the elastic modulus, flexural and compressive strengths of the composite are greatly improved. In contrast, the ductility is lower than that of the unreinforced AZ91D Mg alloy. However, this lower ductility was improved by the addition of MgH₂ powder in the preform. Secondary scanning electron microscopy was used to investigate the fracture surfaces after the flexural strength test. The composites show signs of mixed fracture; cleavage regions and some dimpling. In addition, microcracks observed in the matrix show that the failure might have initiated in the matrix rather than from the reinforcing particulates.     

Structural,thermal, mechanical and dynamic mechanical properties of cenosphere filled polypropylene composites

Polypropylene (PP)/cenosphere based composites were fabricated and characterized for their structural/morphological and mechanical properties such as tensile, flexural, impact and dynamic mechanical properties such as storage and loss moduli as a function of temperature. The morphological attributes were characterized by scanning electron microscopy (SEM) and wide-angle X-ray diffraction (WAXD) while the thermal characterizations were done by conducting differential scanning calorimetry (DSC) and thermo-gravimetric analysis (TGA). The morphological investigations have revealed a uniformly distributed/dispersed state of the cenosphere in the bulk PP matrix of the composites. The WAXD/DSC studies have revealed a decrease in crystallinity of the composites with increase in cenosphere content. Dynamic mechanical analysis (DMA) revealed an enhancement in the energy dissipation ability of the composite with 10 wt.% of cenosphere and an increase in the storage modulus up to ∼30% in the composites relative to the soft PP-phase. The tensile modulus increased up to ∼43% accompanied by a nominal decrease in tensile strength while the strain at break remained largely unaffected. The impact strength of the composites marginally reduced compared to PP indicating a low-cost material-concept with maximized stiffness–toughness combination. The theoretical modeling of the tensile data revealed appreciable extent of phase-adhesion despite the cenospheres lack any surface modification indicating better extent of mechanical interlocking and surface-compatibility between polymer and filler. Fractured surface morphology indicated that the failure mode of the composites undergoes a switch-over from matrix-controlled shear deformation to filler-controlled quasi-brittle modes above a cenosphere loading of 10 wt.% in the composites.     

Performance and application study of silane coupling agent (KH550) modified wood fiber-fly ash cenosphere/epoxy resin composites

In this paper, the epoxy resin composite filled with wood fiber and fly ash cenosphere was prepared. In order to improve the bonding properties between wooden fiber/fly ash cenosphere and epoxy resin, the grafting treatment of wooden fiber and fly ash cenosphere surfaces was carried out here using KH550 type silane coupling agent. The effects of different process parameters on the surface modification effect of wooden fiber and fly ash cenosphere were investigated, the mechanical properties and energy absorption characteristics of the materials before and after the filler modification were tested, and the microscopic interfacial structures of the matrix with wooden fiber and fly ash cenosphere were investigated by scanning electron microscopy. Meanwhile, based on LS-DYNA simulation software, the energy-absorbing performance of energy-absorbing boxes prepared from AA6061 aluminum alloy and modified wooden fiber-fly ash cenosphere/epoxy resin composites were compared in low-velocity collisions.     

漂珠/AZ91D镁合金复合材料的高温压缩变形行为

采用搅拌铸造法制备了漂珠(FAC)/AZ91D镁合金复合材料。研究了该复合材料的高温压缩变形行为,分析了压缩变形温度和应变率对FAC/AZ91D镁合金复合材料压缩变形行为的影响规律,并计算了其热变形激活能。结果表明:FAC/AZ91D镁合金复合材料的高温压缩真应力-真应变曲线分为4个阶段:弹性变形、加工硬化、峰值应力和稳态流变阶段。相同应变率下,FAC/AZ91D镁合金复合材料的峰值应力和稳态流变应力随压缩变形温度的升高而降低;相同压缩变形温度下,流变应力随应变率增大而升高。在相同应变率或相同压缩变形温度下,FAC/AZ91D镁合金复合材料的热变形激活能随压缩应变率或压缩变形温度的升高而增大,其热压缩行为可以用双曲正弦函数形式的Arrhenius关系来描述。压缩变形温度与应变率对FAC/AZ91D镁合金复合材料的高温压缩组织均有重要影响。提高压缩变形温度或增大应变率,均可加速动态再结晶的进程。     

空心微珠表面化学镀Ni-Co-P合金镀层研究

用化学镀的方法将空心微珠改性,使它具有电、磁等性能,是拓宽空心微珠应用领域的一种新方法.以AgNO3代替常见的贵金属盐PdCl2为活化剂,在空心微珠表面化学镀Ni-Co-P合金镀层,用X射线衍射仪、能谱仪和扫描电镜对其进行了分析表征.结果表明,以AgNO3活化剂代替常用的PdCl2活化剂,可在空心微珠表面得到Ni-Co-P合金镀层,同时分析了以AgNO3代替常用的PdCl2活化剂制备Ni-Co-P合金镀层的形成机理.本方法能改善Ni-Co-P合金镀层的性能,成本低,具有良好的应用前景.     

Microstructure and some mechanical properties of fly ash particulate reinforced AA6061 aluminum alloy composites prepared by compocasting

Fly ash has gathered widespread attention as a potential reinforcement for aluminum matrix composites (AMCs) to enhance the properties and reduce the cost of production. Aluminum alloy AA6061 reinforced with various amounts (0, 4, 8 and 12 wt.%) of fly ash particles were prepared by compocasting method. Fly ash particles were incorporated into the semi solid aluminum melt. X-ray diffraction patterns of the prepared AMCs revealed the presence of fly ash particles without the formation of any other intermetallic compounds. The microstructures of the AMCs were analyzed using scanning electron microscopy. The AMCs were characterized with the homogeneous dispersion of fly ash particles having clear interface and good bonding to the aluminum matrix. The incorporation of fly ash particles improved the microhardness and ultimate tensile strength (UTS) of the AMCs.     

Microstructure and strengthening mechanism of bimodal size particle reinforced magnesium matrix composite

One kind of (submicron + micron) bimodal size SiCp/AZ91 composite was fabricated by the stir casting technology. After hot deformation process, the influence of bimodal size particles on microstructures and mechanical properties of AZ91 matrix was investigated by comparing with monolithic A91 alloy, submicron SiCp/AZ91 and micron SiCp/AZ91 composites. The results show that micron particles can stimulate dynamic recrystallized nucleation, while submicron particles may pin grain boundaries during the hot deformation process, which results in a significant grain refinement of AZ91 matrix. Compared to submicron particles, micron particles are more conducive to grain refinement through stimulating the dynamic recrystallized nucleation. Besides, the yield strength of bimodal size SiCp/AZ91 composite is higher than that of single-size particle reinforced composites. Among the strengthening mechanisms of bimodal size particle reinforced composite, it is found that grain refinement and dislocation strengthening mechanism play a larger role on improving the yield strength.     

短切碳纤维/AZ91D镁合金复合材料高温变形动态再结晶行为

在变形温度为340~400℃、应变速率为0.001~0.1 s^-1、最大真应变为0.7的条件下,采用等温压缩实验研究了短切碳纤维（CF_s）/AZ91D复合材料和AZ91D镁合金的动态再结晶行为。结果表明：CF_s/AZ91D复合材料和AZ91D镁合金在高温压缩过程中均发生了显著的动态再结晶;CF_s极大地促进了AZ91D基体的动态再结晶过程,减小了动态再结晶临界应变并细化了再结晶晶粒组织;AZ91D镁合金动态再结晶体积分数随应变量增加表现为典型的"S"型变化曲线,而CF_s/AZ91D复合材料则呈现出快速增长-缓慢增长-趋于平稳的非线性变化规律。根据实验结果分别建立了CF_s/AZ91D复合材料和AZ91D镁合金的动态再结晶临界应变模型和动力学模型,在此基础上分析了二者高温变形动态再结晶行为的差异。     

Machining characteristics,wear and corrosion behavior of AZ91 magnesium alloy - fly ash composites produced by friction stir processing

In the present work, fine grained AZ91 magnesium alloy – fly ash composite has been successfully fabricated by friction stir processing. Microhardness measurements show marginally higher hardness with uniform distribution compared with the base material. No significant difference in the mean cutting force was observed during drilling of the base metal and the composite. However, lower cutting forces were recorded in the sub-surface region of the composites. Interestingly, decreased corrosion resistance was noticed for the composite compared with the base material. Lower mass loss has been observed for the composite during reciprocating wear experiments. The results strongly suggest that the surface composite of AZ91 magnesium alloy – fly ash exhibits better mechanical and wear properties. However, decreased corrosion resistance is a significant observation that warns the applicability of these composites in corroding environment.     

Fabrication,microstructures, and tensile properties of magnesium alloy AZ91/SiCp composites produced by powder metallurgy

Abstract

The tensile properties and microstructural evolution of hot extruded AZ91 magnesium alloy with and without reinforcement of SiC particles have been investigated in terms of extrusion parameters, such as extrusion ratio and extrusion temperature. Also, the effect of SiC particles on the grain size of the matrix in the composites was evaluated using the Hall-Petch equation. The AZ91 magnesium alloy powders prepared by wet attrition milling from magnesium machined chips were hot pressed with and without SiC particles, hot extruded, and then solution treated. Microstructural observation revealed that both the composites and the magnesium alloy have fine equiaxed grains due to the dynamic recrystallisation during hot extrusion. The tensile strength of both materials increased with increasing extrusion ratio, and the strengths of the composites were higher than that of the magnesium alloy without reinforcement. It was found that the tensile strength of both the materials decreased after solution treatment, and the decrease in tensile strength of the composites was considerably smaller than that of the magnesium alloy. From analyses of the microstructures and the mechanical properties, combined with examination of the H all–Petch relationship, the refinement of the matrix was primarily responsible for the improvement in the yield strength of the composites. The grain growth of the matrix was inhibited by the introduction of the SiC particles.     

漂珠聚氨酯复合泡沫力学特性及本构模型研究

以粉煤灰漂珠为主要组分的复合泡沫具有较高的比强度和比吸能,在轻质抗冲击结构设计和缓冲防护领域极具应用潜力。然而,漂珠尺寸和增强相等因素对材料力学性能和行为的影响机制尚不清楚,且当前研究尚未构建该类复合泡沫的力学模型,不利于开展结构设计中材料选型和数值仿真等工作。为此,该研究针对漂珠尺寸和蜂窝铝增强相对复合泡沫的力学性能和变形行为的影响规律进行系列准静态压缩实验研究,在此基础上采用Avalle理论构建该复合泡沫的力学模型。结果表明:①当相对密度小于0.29时,漂珠尺寸对复合泡沫的力学性能几乎没有影响;当相对密度大于0.29时,漂珠尺寸对复合泡沫力学性能的影响随密度的增大而增大;②对于含增强相的复合泡沫,含小尺寸漂珠的复合泡沫力学性能有明显提高,铝蜂窝的额外增强效果对包含小尺寸漂珠的复合泡沫更为明显,该增强机制主要是将材料的初始失效模式由剪切转变为轴向压溃;③使用Avalle理论构建的本构模型,其应力平台阶段和能量耗散特性的拟合与实验结果一致,可较为准确地预测该材料的基本力学性能。该研究可为粉煤灰的综合利用及其复合泡沫在轻质抗冲击结构设计中的应用提供理论参考和基本预测模型。