Fabrication of magnesium based composites reinforced with carbon nanotubes having superior mechanical properties

Magnesium (Mg) composite reinforced with carbon nanotubes (CNTs) having superior mechanical properties was fabricated using both pure Mg and AZ61 Mg alloy matrix in this study. The composites were produced via powder metallurgy route containing wet process using isopropyl alcohol (IPA) based zwitterionic surfactant solution with unbundled CNTs. The produced composites were evaluated with tensile test and Vickers hardness test and analyzed by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) equipped with energy dispersive spectroscopy (EDS) and electron back scattered diffraction (EBSD). As a result, only with AZ61 Mg alloy matrix, tensile strength of the composite was improved. In situ formed Al₂MgC₂ compounds at the interface between Mg matrix and CNTs effectively reinforced the interfacial bonding and enabled tensile loading transfer from the Mg matrix to nanotubes. Furthermore, it was clarified that the microstructures and grain orientations of the composite matrix were not significantly influenced by CNT addition.     

激光选区熔化纳米SiC/AlSi7Mg复合材料微观组织及力学性能EI北大核心CSCD

采用机械混合法制备纳米SiC/AlSi7Mg混合粉末,利用激光选区熔化技术(selective laser melting,SLM)成形纳米SiC颗粒增强AlSi7Mg复合材料,观察和分析试样的相对密度、物相和微观组织,并测试材料的硬度和拉伸性能。结果表明:SLM成形纳米SiC/AlSi7Mg复合材料试样的相对密度随着扫描速度和扫描间距的增大均呈现先增加后减少的趋势,相对密度最高可达99.75%;试样微观组织与SLM成形铝合金相似,Si相呈网状结构均匀嵌入α-Al基体中,且在Al基体中存在与Si分布相似的纳米SiC团聚物及Mg_(2)Si相;与AlSi7Mg相比,复合材料微观组织由柱状晶转化为等轴晶,且晶粒明显细化(平均晶粒尺寸为1.36μm);由于SiC的加入,产生细晶强化和固溶强化,试样的硬度和强度均明显提高,硬度最高达到137.3HV,抗拉强度达到448.3 MPa,屈服强度达到334.7 MPa,但伸长率下降至3.9%,断裂模式主要为脆性断裂。     

A Novel Melt Processing for Mg Matrix Composites Reinforced by Multiwalled Carbon Nanotubes

Carbon nanotubes(CNTs) reinforced Mg matrix composites were fabricated by a novel melt processing.The novel processing consisted of two courses:CNTs pre-dispersion and ultrasonic melt processing.Mechanical ball-milling was employed to pre-disperse CNTs on Zinc(Zn) flakes.Serious CNT entanglements were well dispersed to single CNT or tiny clusters on Zn flakes.The ultrasonic melt processing further dispersed CNTs in the Mg melt,especially tiny CNT clusters.Thus,a uniform dispersion of CNTs was achieved in the as-cast composites.Hot extrusion further improved the distribution of CNTs.CNTs increased both the strength and elongation of the matrix alloy.Notably,the elongation of the matrix alloy was enhanced by 40%.Grain refinement and the pulling-out of CNTs resulted in the evident improvement of ductility for the composites.     

Effect of solidification on microstructures and mechanical properties of carbon nanotubes reinforced magnesium matrix composite

A novel approach was successfully developed to fabricate bulk carbon nanotubes (CNTs) reinforced Mg matrix composites. The distribution of CNTs in the composites depends on the solidification rate. When the solidification rate was low, CNTs were pushed ahead of the solidification front and will cluster along grain boundaries. When the solidification rate was high, CNTs were captured by the solidification front, so the CNTs remained inside the grain. Moreover, good interfacial bonding was achieved in the composite under high solidification rate. Meanwhile, compared with the matrix alloy, the ultimate tensile strength (UTS) and yield strength (YS) of the composite were significantly improved. The mechanical properties of the composite under higher solidification rate are better than composite under low solidification rate and the alloy. Moreover, most CNTs on the fracture surfaces were directly pulled out from the matrix. The Kelly–Tyson formula agreed well with the experimental tensile value in the composite under higher solidification rate, and the load-transfer efficiency is almost equal to 1.     

碳纳米管对激光选区熔化成形Al基复合材料的影响

基于激光选区熔化（SLM）方式,通过改变扫描速度,制备不同碳纳米管（CNTs,质量分数分别为0、0.5wt%、1.0wt%、1.5wt%、2.0wt%）含量的CNTs/Al复合材料试件,探究不同CNTs含量与激光扫描速度对试件性能的影响。结果表明,CNTs含量小于1.0wt%时,分散效果较好,大部分CNTs以单根状态黏附于Al粉表面;含量大于1.0wt%时,CNTs团聚尺寸增大、数量增多。相同SLM成形工艺下,低CNTs含量的CNTs/Al复合材料试件内部孔隙较少,致密度较高;高CNTs含量的CNTs/Al复合材料试件内部孔隙逐渐增多,致密度降低。激光扫描速度为1 300 mm/s工艺下,随着CNTs质量分数的增加,CNTs/Al复合材料试件硬度呈先上升后下降趋势,在CNTs含量为1.0wt%显微硬度达到最高。CNTs/Al复合材料试件平均晶粒尺寸相对于铝合金试件更加细化,在CNTs含量大于1.0wt%时,尽管晶粒依然细化,但试件致密度降低造成显微硬度下降明显。     

Interface tailoring to enhance mechanical properties of carbon nanotube reinforced magnesium composites

This study highlights the use of a metallic coating of nanoscale thickness on carbon nanotube to enhance the interfacial characteristics in carbon nanotube reinforced magnesium (Mg) composites. Comparisons between two reinforcements were targeted: (a) pristine carbon nanotubes (CNTs) and (b) nickel-coated carbon nanotubes (Ni–CNTs). It is demonstrated that clustering adversely affects the bonding of pristine CNTs with Mg particles. However, the presence of nickel coating on the CNT results in the formation of Mg₂Ni intermetallics at the interface which improved the adhesion between Mg/Ni–CNT particulates. The presence of grain size refinement and improved dispersion of the Ni–CNT reinforcements in the Mg matrix were also observed. These result in simultaneous enhancements of the micro-hardness, ultimate tensile strength and 0.2% yield strength by 41%, 39% and 64% respectively for the Mg/Ni–CNT composites in comparison with that of the monolithic Mg.     

A Multiscale Understanding of the Thermodynamic and Kinetic Mechanisms of Laser Additive Manufacturing

Selective laser melting (SLM) additive manufacturing (AM) technology has become an important option for the precise manufacturing of complex-shaped metallic parts with high performance. The SLM AM process involves complicated physicochemical phenomena, thermodynamic behavior, and phase transformation as a high-energy laser beam melts loose powder particles. This paper provides multiscale modeling and coordinated control for the SLM of metallic materials including an aluminum (Al)-based alloy (AlSi10Mg), a nickel (Ni)-based super-alloy (Inconel 718), and ceramic particle-reinforced Al-based and Ni-based composites. The migration and distribution mechanisms of aluminium nitride (AlN) particles in SLM-processed Al-based nanocomposites and the in situ formation of a gradient interface between the reinforcement and the matrix in SLM-processed tungsten carbide (WC)/Inconel 718 composites were studied in the microscale. The laser absorption and melting/densification behaviors of AlSi10Mg and Inconel 718 alloy powder were disclosed in the mesoscale. Finally, the stress development during line-by-line localized laser scanning and the parameter-dependent control methods for the deformation of SLM-processed composites were proposed in the macroscale. Multiscale numerical simulation and experimental verification methods are beneficial in monitoring the complicated powder-laser interaction, heat and mass transfer behavior, and microstructural and mechanical properties development during the SLM AM process.     

纳米WC增强选区激光熔化AlSi10Mg显微组织与力学性能EI北大核心CSCD

为了进一步增强选区激光熔化(SLM)成型AlSi10Mg合金的性能,采用物理混合方法混合纳米WC与AlSi10Mg得到WC质量分数为0.1%的WC/AlSi10Mg复合材料,利用选区激光熔化成型机制备试样块。通过对比同种工艺制备的AlSi10Mg试样,探究纳米WC对其微观组织形成、演变规律及其组织对力学性能的影响。结果显示,WC/AlSi10Mg粉末球形度好,粒度分布集中在20~60μm。WC/AlSi10Mg试样致密度达到99%以上,硬度约为158.89HV,相比AlSi10Mg试样增加了14.58%。WC/AlSi10Mg试样组织生长均匀、致密,有明显的熔池线。晶粒内部为α-Al基体,边界为夹杂着WC的共晶Si相。WC/AlSi10Mg试样屈服强度达到337.75 MPa,抗拉强度高达514.00 MPa,伸长率为3.78%,相比同种工艺AlSi10Mg试样分别增加了4.73%,6.25%和35.97%。因此,SLM成型WC/AlSi10Mg纳米复合材料零件相比AlSi10Mg零件具有更好的应用前景。     

Quantitative evaluation of initial galvanic corrosion behavior of CNTs reinforced Mg–Al alloy

The macroscopic corrosion phenomenon of the CNTs reinforced Mg composites remarkably occurred in the moist environment, due to a large potential of the galvanic cells formed between α-Mg matrix and CNTs. Therefore, it is necessary to reduce the potential difference at their interfaces in order to obstruct the galvanic corrosion phenomenon. In this study, AZ61B alloy composites reinforced with CNTs (CNT/AZ61B) were fabricated by powder metallurgy method, and their potential differences between CNTs and the α-Mg matrix were reduced by concentration of Al atoms around CNTs via heat treatment. The potential distribution around CNTs was measured by using scanning Kelvin probe force microscopy (SKPFM). Heat treatment of CNT/AZ61B composites at 823 K for 10 h caused the obvious concentration of Al atoms around CNTs, and resulted in the remarkable decrease of the potential difference at the interface between the α-Mg matrix and CNTs. Additionally, the salt water immersion test results indicated that the corrosion rate of CNTs/AZ61B composite materials after heat treatment was obviously reduced to less than about 30% of the non-treated composite material. Thus, the changes of α-Mg matrix potential by concentrating Al atoms around CNTs was effective to improve initial galvanic corrosion resistance of CNTs reinforced Mg composites.     

Dual strengthening mechanisms induced by carbon nanotubes in roll bonded aluminum composites

The dual role of carbon nanotubes (CNTs) in strengthening roll bonded aluminum composites has been elucidated in this study. An increase in the elastic modulus by 59% has been observed at 2 vol.% CNT addition in aluminum, whereas tensile strength increases by 250% with 9.5 vol.% CNT addition. CNTs play a dual role in the strengthening mechanism in Al–CNT composite foil, which can be correlated to the degree of dispersion of CNTs in the matrix. Better CNT dispersion leads to improvement of elastic properties. In contrast, CNT clusters in the aluminum matrix impede dislocation motion, causing strain hardening and thus improvement in the tensile strength. Dislocation density of the composites has been computed as a function of CNT content to show the effect on strain hardening of the metal matrix–CNT composite.     

无压浸渗制备SiC/Al电子封装材料的结构与性能

将粒度为F280的SiC颗粒振实后直接无压浸渗液态AlSi12Mg8铝合金,制备出高SiC含量的铝基复合材料,并对其结构和性能进行了研究。结果表明:采用该方法制备的SiC/A1复合材料内部组织结构均匀致密,无明显气孔等缺陷,界面产物主要为Mg₂Si,MgO,MgAl₂O₄;平均密度为2.93 g·cm^-3,抗弯强度在320 MPa以上,热膨胀系数为6.14×10^-6～9.24×10^-6 K^-1,导热系数为173 W·m^-1·K^-1,均满足电子封装材料要求。     

Effects of wear load on mechanical and morphological properties of A356 matrix carbon nano tube composites

In this study, CNT-A356 composites were prepared by reinforcing an aluminum alloy A356 matrix material with carbon nanotubes (CNT) in 4 different ratio (0.5, 1, 1.5 and 2) and the hardness, abrasion and microstructure properties of these composites were investigated. The powder metallurgy method was used in the production of composite samples. A356 powder and CNTs’ were mixed by ball milling for 1?hour and cold pressed in the powder compression mold. The mold was then taken into a functional oven and hot pressing was performed. The compacted powder bodies were sintered at 550° C for 1?hour in a 10^?6 millibars vacuum environment. Hardness measurements, wear tests and microstructure analyzes of the produced samples were carried out. As a result of experimental studies; it has been observed that the CNTs’ are placed in bulk and between the matrix grains and a more hollow structure is formed by increasing the CNT ratio. Moreover, while the CNT ratio exceeded 1%, the hardness values decreased and weight loss increased. The highest hardness value was obtained in the composites containing 1% CNT.     

Mechanical characterization of copper coated carbon nanotubes reinforced aluminum matrix composites

In this investigation, carbon nanotube (CNT) reinforced aluminum composites were prepared by the molecular-level mixing process using copper coated CNTs. The mixing of CNTs was accomplished by ultrasonic mixing and ball milling. Electroless Cu-coated CNTs were used to enhance the interfacial bonding between CNTs and aluminum. Scanning electron microscope analysis revealed the homogenous dispersion of Cu-coated CNTs in the composite samples compared with the uncoated CNTs. The samples were pressureless sintered under vacuum followed by hot rolling to promote the uniform microstructure and dispersion of CNTs. In 1.0 wt.% uncoated and Cu-coated CNT/Al composites, compared to pure Al, the microhardness increased by 44% and 103%, respectively. As compared to the pure Al, for 1.0 wt.% uncoated CNT/Al composite, increase in yield strength and ultimate tensile strength was estimated about 58% and 62%, respectively. However, in case of 1.0 wt.% Cu-coated CNT/Al composite, yield strength and ultimate tensile strength were increased significantly about 121% and 107%, respectively.     

Properties of ultrafine-grained Mg-based composites modified by addition of silver and hydroxyapatite

In this study, hydroxyapatite and silver were added to Mg–1Zn–1Mn–0.3Zr alloy to fabricate ultrafine-grained metal matrix composites. Grain sizes of approximately 85?nm were recorded by atomic force microscopy for the Mg–1Zn–1Mn–0.3Zr–5 wt-% HA–1 wt-% Ag composite. The contact angles in water and simulated body fluid on the ultrafine-grained Mg–1Zn–1Mn–0.3Zr-based composites were determined. Following a hydrofluoric acid treatment, the surface wettability changed from hydrophilicity to hydrophobicity. The electrochemical test showed that the corrosion resistance of the fluoride-treated specimens was higher, when compared with the untreated samples. The Mg–1Zn–1Mn–0.3Zr–5 wt-% HA and Mg–1Zn–1Mn–0.3Zr–5?wt-% of HA–1 wt-% Ag composites modified with MgF₂ have a higher degree of biocompatibility, which makes them potential candidates for medical applications     

碳纳米管增强镁基复合材料导热性能研究

镁及其合金是目前最轻的金属结构材料,合金化虽然提升了镁合金的力学性能,但导致其导热性能严重下降,限制了镁合金的应用。碳纳米管(CNTs)因具有优异的力学、热学等性能,是最理想的增强体之一,可以用于改善镁合金的力学性能和热学性能。采用粉末冶金法分别以纯Mg、Mg-9Al合金、Mg-6Zn合金为基体制备了不同CNTs含量的镁基复合材料,利用光学显微镜、扫描电子显微镜、透射电子显微镜对复合材料微观组织、基体与增强体界面及析出相进行表征,并对复合材料的拉伸性能和热学性能进行测试。研究结果表明,当CNTs质量分数不超过1.0%时,可提高纯镁基复合材料的导热性能,力学性能仅有稍微降低;将CNTs添加到Mg-9Al合金中,可以促进纳米尺度β-Mg 17 Al 12相在CNTs周围析出,降低了Al在Mg基体中的固溶度,使CNTs/Mg-9Al复合材料的导热性能有所提高。此外,在CNTs/Mg-6Zn复合材料界面处存在C原子和Mg原子的相互嵌入区,这种嵌入型界面不仅有利于复合材料力学性能的提高,也使CNTs起到加速电子移动的“桥”的作用,有利于该复合材料热导率的提高。当CNTs质量分数为0.6%时,CNTs/Mg-6Zn复合材料具有较为优异的热学性能和力学性能,其热导率为127.0 W/(m·K),抗拉强度为303.0 MPa,屈服强度为204.0 MPa,伸长率为5.0%。     

Effect of Cu/Zn on microstructure and mechanical properties of extruded Mg–Sn alloys

In this paper, the effect of Cu and Zn addition on mechanical properties of indirectly extruded Mg–2Sn alloy was investigated. Mg–2Sn–0.5Cu alloy exhibits a moderate yield strength (YS) of 225?MPa and an ultimate strength of 260?MPa, which are much higher than those of the binary Mg–2Sn alloy, and the elongation (EL) evolves as ～15.5%. Mechanical properties of the Mg–2Sn–0.5Cu alloy are deteriorated with more 3 wt-% Zn addition, and YS and EL are reduced as 160?MPa and ～10%. The detailed mechanism is discussed according to the work-hardening rate and strengthening effect related to the grain sizes, second phases and macro-textures. Grain refinement and proper texture are believed to play a critical role in both strength and ductility optimisation.     

Microstructure and mechanical properties of Mg-4.0Zn alloy reinforced by NiO-coated CNTs

Mg-4.0Zn alloy composite reinforced by NiO-coated CNTs(NiO@CNTs) was synthesized by combining ball-milling and a casting process. The yield strength(YS) and elongation to failure of the composite were dramatically increased by 44.9% and 38.6%, respectively, compared to its alloy counterpart. The significantly enhanced mechanical properties of the as-synthesized composite are mainly ascribed to an improved interfacial bond, grain refinement and good dispersion of CNTs in the matrix via. coating NiO on CNTs.It is shown that the NiO-nanolayer on the CNTs significantly enhances the interfacial bonding strength and effectively prevents the agglomeration of CNTs. NiO@CNTs are, therefore, expected to be a highly sustainable and dispersible reinforcement for magnesium matrix composites with superior performance.     

Investigations on mechanical and tribological properties of Al-Si10-Mg alloy/sugarcane bagasse ash particulate composites

Aluminum metal matrix composites are a new generation of metal matrix composites that have the potential of sustaining the emerging demand for advanced engineering applications. These demands were satisfied due to massive mechanical and tribological properties of the aluminum hybrid composite material. In this work, abundantly available agricultural waste product (i.e., sugarcane bagasse ash) was used as a reinforcement material in AlSi10Mg alloy to enhance the alloy material properties for their better accomplishment in industrial applications. Initially, the chemical composition of the sugarcane bagasse ash particles was analyzed using Energy Dispersive X-ray Spectroscopy test, which revealed the presence of rich Silica content in the ash particles. Sugarcane bagasse ash particles of three different weight percentages (i.e., 6, 9, and 12%) are reinforced with aluminum alloy (AlSi10Mg) using stir casting process. The wear mechanisms and fractured morphology of the tensile tested specimen were analyzed with the aid of scanning electron microscopy. The result shows that the tensile, hardness, and impact strength were increased with increase in the weight percentage of sugarcane bagasse ash particles but ductility decreased when increasing the weight percentage. Further, dry sliding wear behavior of the fabricated composites was tested using Pin-on-Disc for three different loads (10 N, 20 N, 30 N). The wear rate and coefficient of friction for the hybrid matrix composites were found to be decreased while increasing the weight percentage of ash content, but they increase while increasing the applied load.     

Mg–3Zn–0.5Zr/HA nanocomposites fabricated by high shear solidification and equal channel angular extrusion

Magnesium alloy matrix and hydroxyapatite (HA) nanoparticle reinforced composites for biomedical applications were fabricated by combined high shear solidification and equal channel angular extrusion (ECAE). The high shear treatment was performed immediately prior to casting at 680°C using a rotor–stator mechanism. The as-cast composite ingots were processed by ECAE at 300°C to various strains. The high shear treatment effectively reduced HA particle agglomeration and produced a fine grain structure for all HA contents. ECAE processing resulted in further grain refinement and an improved HA particle distribution, with the formation of a desirable HA dispersion. The composites with 3–5 wt-% HA displayed an optimum combination of strength and ductility, with a yield strength of 150–210?MPa and compressive reductions of 9～13% before fracture.     

Properties of polypropylene composites containing aluminum/multi-walled carbon nanotubes

Polypropylene/aluminum–multi-walled carbon nanotube (PP/Al–CNT) composites were prepared by a twin-screw extruder. The morphology indicates that the CNTs are well embedded or implanted within Al-flakes rather than attached on the surface. During preparation of composites, the CNTs came apart from Al–CNT so that free CNTs as well as Al–CNT were observed in PP/Al–CNT composite. The crystallization temperatures of PP/CNT and PP/Al–CNT composites were increased from 111 °C for PP to 127 °C for the composites. The decomposition temperature increased by 55 °C for PP/CNT composite and 75 °C for PP/Al–CNT composite. The PP/Al–CNT composite showed higher thermal conductivity than PP/CNT and PP/Al-flake composites with increasing filler content. PP/Al–CNT composites showed the viscosity values between PP/CNT and PP/Al-flake composites. PP/Al–CNT composite showed higher tensile modulus and lower tensile strength with increasing filler content compared to PP/CNT and PP/Al-flake composites.