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.     

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%。     

CNTs/Mg-9Al复合材料微观组织、力学及导热性能EI北大核心

研究了CNTs的加入对Mg-9Al镁基复合材料时效行为的影响,探讨了时效处理过程中微观组织、力学性能及导热性能的演变规律。结果表明:添加的CNTs增大了基体合金中铝元素的固溶度,并在时效过程中限制晶界的迁移,在二者共同作用下,促进基体中连续β-Mg_(17)Al_(12)相的析出,且随着CNTs含量的增加,连续析出的比例增大;与基体呈共格关系的杆状连续析出相能够有效地阻碍位错运动,提高复合材料的力学性能,其中峰时效态0.4CNTs/Mg-9Al复合材料的屈服强度、抗拉强度、热扩散系数和热导率分别为275 MPa,369 MPa,34.5 mm^(2)/s和68.4 W/(m·K),相较于时效前Mg-9Al合金分别提升了17%,23%,43%和45%。     

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.     

Influence of Mg Addition on Graphite Particle Distribution in the Al Alloy Matrix Composites

Al alloy matrix composites reinforced with copper-coated graphite particle have been prepared by melt stirring process in this work. The effect of the addition of Mg on distribution of the graphite particles has been investigated. Scanning electron microscopy (SEM) was used to observe the micro-morphology of Al alloy matrix composites reinforced with graphite particles. Meanwhile, the content of graphite was analyzed in the different position of casting by dissolution method and the mechanical properties of the composites were detected. The results show that the content of graphite increase with increasing Mg content; the graphite particles distribute uniformly in the particle reinforced metal matrix composites (PMMC) with 0.6 wt pct Mg; however, the agglomeration of the graphite particles is observed obviously in the matrix when Mg content is more than 1.0 wt pct. In addition, the proper Mg addition amount is beneficial to enhance the mechanical properties of the graphite particles reinforced Al alloy matrix composites and the abrasion resistance of the materials due to a reduce friction coefficient.     

Improved processing of carbon nanotube/magnesium alloy composites

Carbon nanotubes (CNTs) are promising reinforcements for light weight and high strength composites due to their exceptional properties. However, until now, the main obstacle is to obtain a homogenous dispersion of the CNTs in the desired material matrix. Quite a few methods have been studied to help improving the dispersion of CNTs in a polymer matrix. But not much research has been conducted on how to disperse CNTs in metal matrices. In this study, a two-step process was applied. In the first stage, a block copolymer was used as a dispersion agent to pre-disperse multiwall carbon nanotubes (MWNTs) on Mg alloy chips. Then the chips with the well dispersed MWNTs on their surface were melted and at the same time vigorously stirred. The molten MWNT Mg alloy composites were poured into a cylindrical mould to solidify quickly. For the pre-dispersion step, the microstructures of the Mg alloy chips were studied under SEM. MWNTs were quite successfully dispersed on the surfaces of the Mg alloy chips. The mechanical properties of the MWNT/Mg composites were measured by compression testing. The compression at failure, the compressive yield strength and ultimate compressive strength have all been improved significantly up to 36% by only adding 0.1 wt% MWNTs to the Mg alloy. In order to predict the potential yield strengths of the MWNT reinforced Mg alloy composites, the contributions by load transfer, Orowan strengthening and thermal mismatch were added up.     

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.     

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.     

Microstructure,mechanical properties and corrosion behaviour of Al–Si–Mg alloy matrix/zircon and alumina hybrid composite

In the present study, the effect of reinforcement on microstructure, mechanical properties and corrosion behaviour of aluminium–silicon–magnesium (Al–Si–Mg) alloy matrix hybrid composites reinforced with varying amounts of zircon and alumina has been investigated. Hardness and room temperature compressive tests were performed on Al–Si–Mg alloy as well as composites. Hardness and compressive strength was found to be higher for composites containing 3.75?% ZrSiO₄?+?11.25?% Al₂O₃. Similarly, Al–Si–Mg alloy and its composites were studied for corrosion behaviour in 1 N HCl corrosive media. The weight loss of all the composites was found to decrease with time due to the formation of passive oxide layer on the sample surface. The results obtained indicate that composites exhibit superior mechanical properties and corrosion resistance compared to unreinforced alloy.     

碳纳米管与铝合金基体材料的混合工艺研究

为改善碳纳米管在铝合金基体中的分散性和发挥其增强作用,分别采用湿混、球磨以及湿混后球磨的方式将碳纳米管与铝合金粉末进行混合,再经真空烧结制备出碳纳米管增强铝合金复合材料.不同混合工艺的对比试验结果表明:碳纳米管于液相环境下被均匀分散并吸附于铝合金颗粒表面,但在烧结过程中易再次发生团聚;而较长时间的机械球磨会对碳纳米管结构造成一定程度的破坏.相比下,液相分散与机械球磨结合的方式提高了碳纳米管的分散程度和缩短了球磨时间,碳纳米管增强铝合金材料(3%CNTs/5083Al)的抗拉强度达620 MPa.     

高能球磨法制备高性能均一分散CNTs/Al5083复合材料

采用卧式高能球磨法制备0%~2%CNTs/Al5083(质量分数)复合材料,研究球磨时间和CNTs含量对复合材料性能的影响。采用扫描电镜(SEM)和透射电镜(TEM)对复合材料的形貌进行表征,测试复合材料的抗拉强度及硬度。结果表明:当球磨时间为1.5h时,CNTs可均匀分散在Al5083基体中;CNTs质量分数为1.5%时,CNTs/Al5083界面结合力最好,复合材料的抗拉强度和硬度分别为188.8MPa和136HV,比未加CNTs的Al5083合金基体分别提高了32.2%和36%。     

压铸(Al63Cu25Fe12)p/AZ91复合材料的组织、性能和热处理特征

在CO2/SF6气氛保护下,采用压铸的方法将-200目的Al63Cu25Fe12准晶粉末注入到熔融的AZ91镁合金中,于720℃和一定的压力下保压30min,制备了新型的(Al63Cu25Fe12)p/AZ91镁基复合材料.结果表明,在复合过程中,准晶相分解出的自由Cu向基体扩散并与基体中的Al发生反应,生成的金属间化合物分布在准晶颗粒周围,同时Mg向颗粒中浸渗填充到颗粒的孔隙中;复合材料具有不同于基体镁合金的固溶时效特征,需要更长的时间才能达到时效峰值;复合材料经过热挤压和热处理后的力学性能显著提高,抗拉强度从AZ91铸态材料的189.54MPa提高到359.38MPa,但塑性有所降低.     

Effect of matrix strength on the mechanical properties of Al–Zn–Mg/SiCP composites

The mechanical properties of Al–Zn–Mg alloy reinforced with SiC_P composites prepared by solidification route were studied by altering the matrix strength with different heat treatments. With respect to the control alloy, the composites have shown similar ageing behaviour in terms of microhardness data at 135°C. It was shown that although composites exhibited enhanced modulus values, the strengthening was found to be dependent on the damage that is occurring during straining. Thus the initial matrix strength plays an important role in determining the strengthening. Consequently, compression data had shown a different trend compared to tension.     

球磨工艺对原位合成碳纳米管增强铝基复合材料微观组织和力学性能的影响

将原位化学气相沉积法合成的碳纳米管(CNTs)与铝的复合粉末进行球磨混合,进而粉末冶金制备CNTs/Al复合材料,研究球磨工艺对复合材料的微观组织和力学性能的影响。结果表明:球磨过程中不添加过程控制剂所得到的复合材料力学性能优异;随着球磨时间的增加,CNTs逐步分散嵌入铝基体内部,复合材料的组织也变得更加致密均匀。CNTs/Al复合材料的硬度和抗拉强度均随球磨时间的延长持续增加,但是伸长率先增后减。经90min球磨的CNTs/Al复合材料展现了强韧兼备的特点,其硬度和抗拉强度较原始纯铝提高了1.4倍和1.7倍,并且具有17.9%的高伸长率。     

亚微米Al2O3P/Al-Mg-Si复合材料时效行为

为了研究亚微米级Al₂O₃颗粒对基体合金时效过程的影响规律,在 6061 铝合金基础上调整Mg、Si含量,采用压力浸渗法,制备了Al₂O₃体积分数为30%的亚微米级Al₂O_3P/Al-2.26Mg-0.63Si复合材料。通过硬度试验、SEM和TEM等手段,研究了复合材料及其基体合金的时效行为。结果表明,Al-2. 26Mg-0.63Si 合金的时效过程比较明显,随时效温度的提高峰时效时间提前,190℃时出现时效软化现象。亚微米Al₂O₃颗粒的加入强烈抑制复合材料的时效过程,时效曲线未出现明显时效峰。分析认为,由于大部分Mg 元素被消耗在界面形成MgAl₂O_4,且基体中位错稀少,不利于溶质原子扩散,因此复合材料中沉淀相在过时效阶段仍停留在GP区状态,没有充分长大,时效析出受到抑制。     

准晶增强镁、铝基复合材料的研究进展

综述了利用准晶作为镁、铝合金增强相的研究进展。Mg3Zn6Y准晶的界面能低,与α-Mg基体之间形成稳定的界面结合,在高温变形过程中,准晶本身不发生粗化且可以抑制基体组织演化,因此,Mg3Zn6Y准晶增强变形Mg基复合材料具有中等强度和较高的室温、高温塑性。由于到目前为止发现的Al系稳定准晶都不与Al相共生,准晶增强Al基复合材料主要采用快速凝固的方法和外加的方法制备,如粉末冶金法、机械合金化法和液态搅拌法等。综述了采用以上方法制得的准晶增强Al基复合材料的组织特征及其力学性能。     

Al含量对漂珠/镁合金可溶复合材料组织与性能的影响

采用搅拌铸造法制备了不同Al含量下的漂珠（FAC）/镁合金可溶复合材料。采用金相显微镜、SEM及XRD观察分析了FAC/镁合金可溶复合材料的微观组织、溶解表面形貌及溶解产物的物相组成,采用力学性能试验机研究了复合材料的压缩性能,采用电化学工作站对复合材料进行电化学性能测试,在常温及水浴锅内进行复合材料在不同温度下的KCl溶液中的溶解试验。结果表明：该FAC/镁合金可溶复合材料主要由α-Mg基体相、β-Mg₁₇Al₁₂相、Mg₂Si相和MgO相组成。随着Al含量的增加,FAC/镁合金可溶复合材料的溶解速率先变快后减慢,在80℃的3wt% KCl溶液中,含15wt% Al的FAC/镁合金复合材料溶解速率最快,为56 mg/（h·cm²）。Al-FAC/镁合金可溶复合材料的抗压强度随Al含量的增加先提高后下降,四种合金的抗压强度均大于300 MPa,最高强度达到372 MPa。     

碳纳米管和石墨烯纳米片复合增强AZ91镁基复合材料组织与力学性能

目的 解决纳米碳材料在镁基体中分散难的瓶颈问题,制备出力学性能优异的镁合金复合材料。方法 采用超声工艺将质量分数为3.0%的碳纳米管插入到质量分数为0.5%的石墨烯纳米片的片层之间,添加到AZ91镁合金基体中,借助粉末冶金技术+热挤压工艺制备了0.5%GNS+3.0%CNTs复合增强的镁基复合材料。采用光学显微镜和透射电子显微镜观察和分析了复合材料的显微组织和界面结合。测试了复合材料的力学性能,并利用扫描电子显微镜观察了复合材料的拉伸断口形貌。结果 复合材料的屈服强度、伸长率和显微硬度分别为（274±5.0）MPa,（8.4±0.2）%,HV（90.5±1.8）,与基体合金相比,分别提高了63.1%,20.0%,20.1%。结论 GNS+CNTs的加入有效细化了基体合金的晶粒组织,且与镁基体形成了较好的界面结合,促使细晶强化、应力转移强化等各种强化机制的共同作用,使复合材料力学性能显著提高。     

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.     

碳纳米管增强开孔铝基复合泡沫的疲劳性能

采用原位化学气相沉积、短时球磨和填加造孔剂法相结合的工艺制备了碳纳米管(CNTs)/Al复合泡沫,研究了其在压缩-压缩循环载荷下的力学性能及失效机制。结果表明,CNTs/Al复合泡沫的应变-循环次数曲线经历线弹性、应变硬化及应变快速增长三个阶段。不同于泡沫铝的逐层坍塌变形失效模式,CNTs/Al复合泡沫疲劳失效的主要原因是大量剪切变形带的形成,试样出现快速的塑性变形。此外,CNTs含量为2.5wt%、孔隙率为60%的复合泡沫试样的疲劳强度相比于泡沫铝提高了92%。CNTs的均匀分布及增强相与基体材料之间良好的界面结合性保证了疲劳载荷能够以剪切力的形式从基体传递到CNTs上,使其充分发挥自身高强度、高韧性的特点,进而提高了疲劳性能。