Effect of Thermal Cycling Treatment on Microstructure and Mechanical Properties of AlNp/2024Al Composite

The AlNp/2024 composite with a high volume fraction (50%) was fabricated by squeeze casting. Its mechanical properties were investigated by tensile tests at ambient temperature and the microstructure was observed by a transmission electron microscope (TEM). It was indicated that after six thermal cooling cycles treatment the AIN/2024Al composite exhibited higher elastic limit (σ0.01), tensile strength (UTS) and elastic modulus (E). TEM observation showed that there was higher dislocation density both in the matrix and the particle. δ′ phase is the mainly precipitate.     

低频电磁场对n-SiCp/2024复合材料组织与性能的影响

分别采用低频电磁铸造(LFEC)与传统半连续铸造(DC)制备n-SiC_p/2024复合材料铸锭,并对铸锭进行挤压以及T6热处理。通过金相组织观察(OM)、TEM、室温力学性能测试等手段,分别研究了低频电磁铸造与传统半连续铸造工艺对n-SiC_p/2024复合材料的微观组织、力学性能的影响情况。实验结果表明:DC制备的n-SiC_p/2024复合材料铸锭表面局部存在偏析瘤,大多数n-SiC_p团聚在晶界处,只有少数聚集在晶粒内部;LFEC制备的n-SiC_p/2024复合材料铸锭组织晶界清晰,n-SiC_p团聚现象基本消失,组织均匀,晶粒细化效果明显。LFEC制备工艺可以有效细化n-SiC_p/2024复合材料铸锭的晶粒尺寸,其电磁搅拌作用对消除n-SiC_p颗粒的团聚现象有显著作用;与DC工艺相比,LFEC可同时提高复合材料的强度与延伸率。     

SiC_p/2024Al复合材料尺寸稳定化处理工艺研究

采用挤压铸造技术制备了体积分数为40%的SiCp/2024Al复合材料,采用TEM对不同尺寸稳定化处理条件下复合材料的微观组织进行了观察,并探讨了尺寸稳定化热处理工艺对复合材料拉伸性能的影响.TEM观察表明:由于SiC颗粒与2024Al基体的热膨胀系数不同,热错配的作用使冷热循环处理后基体中的位错密度增加,为S′相的形成提供了有利的形核部位,促进了S′相的析出,这两种因素都有利于提高复合材料的强度.室温拉伸测试结果表明:零次冷热循环热处理后的SiCp/2024Al复合材料拉伸强度比较好,两次冷热循环处理后复合材料的强度有所下降,但随着循环次数的增加,复合材料的强度逐渐增加;不同的冷热循环次数对于拉伸断裂方式和断口形貌无显著影响.     

多重结构Ti-B4C/Al2024复合材料的组织和力学性能

为了研究多重结构对铝基复合材料力学性能的影响,将气雾化态Al2024合金粉末与球磨不同时间的Ti-10%(质量分数,下同)B_4C复合粉末混合,采用热压烧结和热挤压的方法制备多重结构Ti-B_4C/Al2024复合材料。通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和拉伸试验机对不同材料的显微组织与力学性能进行观察和测试,并对多重结构复合材料的强韧化行为进行讨论。结果表明:Ti-B_4C/Al2024复合材料多重结构包括基体Al2024、核壳结构Ti/Al₁₈Ti_2Mg_3组织和B_4C颗粒。向Al2024中加入5%预先球磨6h后的Ti-B_4C粉末时,其屈服强度从107MPa提高到122MPa,并且表现出与热挤压Al2024合金几乎相同的伸长率。当球磨时间延长至12h时,试样5TB-12h的伸长率可达到16.4%。然而,复合材料的伸长率随着Ti-B_4C添加量的增加而降低。     

粉末热压成形工艺对WCp/2024Al复合材料力学性能的影响

采用真空热压方法制备了WC颗粒增强2024铝基复合材料(WCp/2024Al),并利用XRD,SEM,拉伸性能测试等检测手段研究了复合材料的热压温度和WC颗粒尺寸对WCp/2024Al复合材料力学性能的影响.结果表明,热压温度是控制复合材料发生界面反应的关键因素之一,并且界面反应所生成的反应产物导致复合材料的强度和塑性...     

Preparation and characterization of carbon nanotubes/aluminum matrix composites

2024Al matrix composite reinforced with 1 wt.% carbon nanotubes (CNTs) was fabricated by cold isostatic pressing, followed hot extrusion techniques. The microstructure characteristics and the distribution of carbon nanotubes in the aluminum matrix were investigated. The mechanical properties of the composite were measured at room temperature. Experimental results showed that CNTs were distributed homogeneously in the composite, and the interfaces of Al–CNTs bonded well. The grain size of the matrix was as fine as 200 nm, and with a small amount of CNTs additions, the elastic modulus and the tensile strength were enhanced markedly over those of the 2024Al matrix fabricated under the same process. The reasons for the increments could be due to the extraordinary mechanical properties of CNTs, the bridging and pulling out role of CNTs in the Al matrix composite.     

Effect of deformation temperature and degree on tensile properties of the extruded 2024Al/Al18B4O33w composite with extrusion – forging multistage hot deformation

The effect of extrusion – forging multistage hot deformation on tensile properties of the 2024Al/Al₁₈B₄O₃₃w composites is investigated. The extruded 2024Al/Al₁₈B₄O₃₃w composites are used as blanks. The tensile properties of the extruded 2024Al/Al₁₈B₄O₃₃w composite followed by secondary deformation are studied. The effects of holding temperature and deformation degree on tensile properties of the extruded composite are discussed. The results show that due to the reduction in stress concentration and dislocations, ultimate tensile strength of the extruded 2024Al/Al₁₈B₄O₃₃w composite held at 400 °C for 1 h is lower than that of the extruded composite without holding. Increasing holding temperature from 300 °C to 450 °C, ultimate tensile strength of the extruded 2024Al/Al₁₈B₄O₃₃w composite increases firstly and then decreases. The extruded 2024Al/Al₁₈B₄O₃₃w composite held at 400 °C for 1 h followed by secondary forging with the larger length to width ratio of 4 : 1 has the ultimate tensile strength of 456.1 MPa, higher than that of the extruded 2024Al/Al₁₈B₄O₃₃w composite without secondary forging.     

碳化硅颗粒增强LY12铝合金复合材料超塑性研究

本文研究了粉末冶金法制造的SiCp/LY₁₂复合材料的超塑性。测定了热挤压态SiCp/LY₁₂复合材料的拉伸、压缩m值,分析了工艺参数对超塑性的影响,确定了超塑性成形工艺参数,并初步分析了SiCp/LY₁₂复合材料的显微结构和超塑拉伸试样断口形貌和断裂机制。      

Microstructure and Mechanical Properties of in-situ TiCp/2024 Composite

The microstructure of TiCp/2024 composite and the structure of interface between TiCp and Al are studied using SEM and TEM. The results show that the in-situ synthesized TiC particle has face-centered cubic structure (fcc). Meanwhile, particles are characterized as tiny and nearly globular. The orientation between TiC particles and Al matrix can be described as ((2) over bar(2) over bar0)(Al)//(02 (2) over bar)(Tic) and [(1) over bar 12](Al)//[011](TiC). Results of the mechanical property tests reveal that the ultimate strength (sigma (b)) and the yield strength (sigma (s)) of the composite are improved by 30% and 47% respectively, compared with the properties of 2024 matrix. In addition, the elongation (delta) value can still reach 4.3%. Thus TiCp/2024 composite has high comprehensive performance.     

Deformation behavior of aluminum alloy matrix composites reinforced with few-layer graphene

Microstructure and mechanical properties of aluminum alloy 2024 (Al2024)/few-layer graphene (FLG) composites produced by ball milling and hot rolling have been investigated. The presence of dispersed FLGs with high specific surface area significantly increases the strength of the composites. The composite containing 0.7 vol.% FLGs exhibits tensile strength of 700 MPa, two times higher than that of monolithic Al2024, and around 4% elongation to failure. During plastic deformation, restricted dislocation activities and the accumulated dislocation at between FLGs may contribute to strengthening of Al2024/FLG composites.     

利用静电纺丝技术制备纳米黏土/聚乳酸复合纳米纤维与其表征

利用静电纺丝技术制备了纳米黏土/聚乳酸(PLA)复合纳米纤维,并将该复合纳米纤维收集成无纺布薄膜,采用SEM和TEM观察了复合纳米纤维的微观形貌和结构,分别利用XRD和TGA测试了复合纳米纤维的结晶行为及热学行为,并分析了复合纳米纤维薄膜的拉伸力学性能随纳米黏土含量的变化关系。结果表明:当PLA含量为10wt%、纳米黏土含量为1wt%、CHCl3与DMF体积比为3∶1溶剂条件下,所制备的纳米黏土/PLA复合纳米纤维的细度和均匀性均得到改善;XRD测试结果表明,纳米黏土成功附着在PLA中。TGA和力学测试结果表明,纳米黏土/PLA复合纳米纤维的热稳定性和力学性能相对于纯PLA纤维有较大幅度提高,当纳米黏土含量为1wt%时,其初始分解温度提高了60℃,拉伸强度、断裂伸长率和弹性模量分别提高了111.3%、74.9%和20.0%。     

40vol%SiC_P/2024Al复合材料的动态压缩性能

利用分离式霍普金森压杆(SHPB)研究了40%体积分数的SiCP/2024Al复合材料和基体材料2024Al在不同应变率下的动态压缩性能。在高应变率动态压缩时该复合材料与2024Al均表现出应变率不敏感,复合材料屈服应力高于2024Al;与2024Al的应变硬化性能不同,复合材料表现出应变软化性能。利用扫描电镜(SEM)观察动态压缩后复合材料试件的微观组织,发现试件内部出现一些孔洞、微裂纹以及一些增强颗粒的破碎等损伤现象,并且在较高应变率下基体呈现出明显的热软化甚至发生局部熔化,由此判断,在高应变率下SiCP/2024Al复合材料宏观应变软化的机制为内部损伤及基体热软化。将SiCP/2024Al复合材料与2024Al经400℃下烧蚀3 h后自由冷却至室温,利用SHPB再次进行测试,与烧蚀前的测试结果相比,2024Al的性能明显下降,而复合材料的性能变化较小,表现出比基体材料更好的抗高温稳定性能。     

搅拌铸造SiCp/2024复合材料热挤压-轧制变形组织及性能

利用搅拌铸造-热挤压-轧制工艺制备SiCp/2024复合材料薄板。通过金相观察(OM)、扫描电镜(SEM)及力学测试等手段研究了该复合材料在铸态、热挤压态及轧制态下的显微组织及力学性能,分析了材料在塑性变形过程中显微组织及力学性能的演变。结果表明,该复合材料铸坯主要由80～100μm的等轴晶组成,粗大的晶界第二相呈非连续状分布,SiC颗粒较均匀地分布于合金基体中;热挤压变形后,晶粒沿挤压方向被拉长,SiC颗粒及破碎的第二相呈流线分布特征;轧制变形后,基体合金组织进一步细化,晶粒尺寸为30～40μm,SiC颗粒破碎明显,颗粒分布趋于均匀,轧制变形对挤压过程中形成的SiC颗粒层带状不均匀组织有显著的改善作用。数学概率统计指出,塑性变形有利于提高颗粒分布的均匀性。力学测试表明,塑性变形后,复合材料的抗拉强度、屈服强度和延伸率显著提高。SiCp/2024铝基复合材料主要的断裂方式为:合金基体的延性断裂、SiC颗粒断裂及SiC/Al界面脱粘。     

Tensile properties and thermal stability of ZnO-coated aluminum borate whiskers reinforced 2024Al composite

ZnO-coated aluminum borate whiskers reinforced 2024Al composite was fabricated by squeeze casting. Interfacial microstructures and tensile properties of the composite in as-cast and after thermal exposure were investigated. Fracture mechanisms of the composite in as-cast and after thermal exposure were also investigated. The results show that ZnO coating of the whiskers reacts with molten 2024Al and MgAl₂O₄ forms at the interface during squeeze casting. On the one hand, the interfacial reaction between ZnO and 2024Al can improve the wettability of the whiskers by molten 2024Al, increasing the tensile properties of as-cast composite. On the other hand, during thermal exposure, MgAl₂O₄ at the interface can effectively hinder serious interfacial reactions between the whiskers and magnesium in the matrix of 2024Al, improving the thermal stability of the composite at high temperatures.     

The Effect of Composite Patches on the Failure of Adhesively-Bonded Joints Under Bending Moment

In this study, it was aimed to compare mechanical behavior of double-strap joints with aluminum (AA2024-T3) or 16-ply laminate of carbon/epoxy composite (T300/934) patches of different orientation angles at their overlap area subjected to bending moment. For this purpose, AA2024-T3 aluminum was used as adherend, while the adhesive was a two-part paste (DP 460). Six different types of joint samples were subjected to bending moment. The effect of patch material on failure load and stress distribution was examined experimentally and numerically. In the numerical analysis, the composite patches were assumed to behave linearly elastic, while adherend and adhesive layers were assumed to be nonlinear. It was found that the data obtained from 3-D finite element analysis were coherent with experimental results. Meanwhile, experiments showed that fiber orientation angles of the patches markedly affected the failure load of joints, failure mode and stress distributions appeared in adhesive and composite.     

SiCw＋B4Cp／MB15镁基复合材料力学性能与微观结构

对真空反压浸渍方法制备的挤压态ＳｉＣＷ＋Ｂ４ＣＰ／ＭＢ１５镁基复合材料及基体合金进行了一系列的力学性能测试，并用ＳＥＭ观察增强剂分布与断口形貌，用ＴＥＭ和ＥＤＳ方法对复合材料的界面结构进行分析。研究结果表明，上述复合材料同基体相比有更高的强度、弹性模量和比强度、比弹性模量。深浸蚀ＳＥＭ相分析表明均匀排布的晶须、颗粒起到很好的增强效果。复合材料的断口有晶须露头与韧窝存在，该复合材料具有一定的韧性；并在ＳｉＣ／ＭＢ１５界面上发现Ｚｎ析出相。     

Defect features and mechanical properties of friction stir lap welded dissimilar AA2024–AA7075 aluminum alloy sheets

5 mm-Thick dissimilar AA2024-T3 and AA7075-T6 aluminum alloy sheets were friction stir lap welded in two joint combinations, i.e., (top) 2024/7075 (bottom) and 7075/2024. The influences of process conditions (welding speed and joint combination) on defects (hook and voids) features and mechanical properties of joints were investigated in detail. It was found that the hook deflects largely upwards into the stir zone (SZ) at lower welding speeds (50, 150 mm/min) in both combinations. The process conditions significantly affect the hook geometry which in return affects the lap shear strength. In all 2024/7075 joints, voids appear and the joints fracture from the tip of hook on AS along the SZ/TMAZ (thermomechanically affected zone) interface in lap shear test (tensile fracture mode). In 7075/2024 joints, the hook on RS horizontally extends a large distance into the bottom stir zone at higher welding speeds (225, 300 mm/min). The joints fracture in three modes: shear fracture along the lap interfaces, tensile fracture and the mix fracture of both. In both joint combinations, the lap shear strength generally increases with the increase of welding speed. 7075/2024 Joints show higher failure load than 2024/7075 joints at lower welding speeds while the opposite result appears at higher welding speeds.     

Effects of laminate carbon/epoxy composite patches on the strength of double-strap adhesive joints: Experimental and numerical analysis

In this study, mechanical properties of double-strap joints with aluminum or composite patches of different orientation angles at their overlap area were investigated under tensile loading. For this purpose, AA2024-T3 aluminum was used as adherend, while patches were either AA2024-T3 aluminum or 16-ply laminate of carbon/epoxy composite with five different orientation angles ([0]₁₆, [90]₁₆, [0/90]₈, [45/−45]₈, [0/45/−45/90]₄). A two-part paste adhesive (DP 460) was used to bond adherend and patches. Six different types of joint samples were subjected to tensile loading. The effect of patch material on failure load and stress distribution was examined experimentally and numerically. As a result, it was concluded that the data obtained from 3-D finite element analysis were coherent with experimental results and additional to that fiber orientation angles of the patches markedly affected the failure load of joints, failure mode and stress distributions appeared in adhesive and composite.     

微悬浮法CaCO3表面接枝PMMA及其在PVC中的应用

在水介质中,超声作用下用油酸对纳米碳酸钙进行表面修饰,再以微悬浮原位聚合法用PMM A进行接枝包覆,成功制备了PMM A/C aCO3复合粒子。借助透射电镜(TEM)、红外光谱(FT-IR)、热失重(TG)等分析手段对复合粒子的形态结构进行了表征。实验结果表明,油酸可通过羧酸盐的形式吸附于碳酸钙粒子表面,一定量PMM A通过油酸分子的不饱和双键接枝于碳酸钙粒子表面。将所得PMM A/C aCO3复合粒子与PVC共混制得PVC/PMM A/C aCO3复合材料。复合材料的TEM照片表明,C aCO3粒子非常均匀地分散在PVC基体中,两相界面模糊。随着PMM A/C aCO3纳米复合粒子用量的增加,复合材料的强度和韧性同时提高。当复合粒子用量高于12%时,复合材料的冲击强度可提高3倍,而拉伸强度下降很少。     

热机械循环对B/Al复合材料拉伸性能及显微结构的影响

热机械循环是复合材料所面临的苛刻空间环境因素.对B/Al复合材料进行温度变化范围为-125～125℃,外加拉伸载荷为30MPa的热机械循环试验,通过室温拉伸试验测量了B/Al复合材料的拉伸性能,利用SEM及TEM分析了复合材料的拉伸断口形貌及显微结构,研究了热机械循环对B/Al复合材料拉伸性能及显微结构的影响.研究表明,热机械循环造成了B纤维与Al基体之间界面的弱化,产生了可测的弹性模量的降低;同时,引起基体塑性应变,造成基体内位错密度增加.在热机械循环初期,B/Al复合材料的抗拉强度是增加的,但随即随热机械循环周次的增加而下降.