Analyzing the methods and merits of recycling fiber metal laminates

It is technically possible to recycle fiber metal laminates (FMLs) by retrieving the aluminum fraction from FML scrap; this reprocessing becomes economically feasible at a throughput of 50 tonnes or more per year. Until then, FML scrap can be dealt with in conventional ways.     

Strength of fiber reinforced metal laminates with a circular hole

The effect of notching on fiber-reinforced metal laminates (FML) is studied 3-2 lay up carbon fiber aluminum laminates specimens containing a circular hole were employed in notch tests. The notch effect for a composite laminate was investigated and compared with carbon/epoxy composites and aluminum sheets. The degradation of notch strength for carbon fiber aluminum laminates was smaller than for carbon/epoxy composites. The point and average stress criteria were used in the notch strength analysis. A finite width correction factor was also used. The strength degradation models involve a single parameter that is a function of the hole size and the characteristic length. These models were compared with experimental data and good agreement was found.     

Al-Si系铝合金电弧增材再制造成形机理及性能评价

针对6082铝合金的磨损、腐蚀、掉块等损伤,采用CMT (Cold metal transfer)电弧增材再制造技术和自主研发的Al-Si-Cr-Er丝材在其表面制备了单层多道、多层单道及多层多道成形层。综合运用金相显微镜、扫描电子显微镜、万能力学实验机、电化学工作站等分析成形层微观组织并评价其力学及电化学等综合性能。结果表明：成形层平滑光亮,焊道和焊道之间搭接平整紧密,无气孔、热裂纹、咬边、焊瘤等缺陷,Cr及稀土元素Er的加入,有效抑制了晶粒长大,促进了成形组织细化。相较于通用ER4043丝材,Al-Si-Cr-Er成形层的平均抗拉强度达228.7 MPa,最高延伸率达13.5%,微孔聚集形韧窝断裂是其主要失效机制;自腐蚀电位提高了约0.2 V,自腐蚀电流密度降低了一个数量级,成形组织的细化和杂质元素含量的降低是其耐腐蚀性能提升的主要原因。     

Homogeneity of Mechanical Properties of Underwater Friction Stir Welded 2219-T6 Aluminum Alloy

Underwater friction stir welding (FSW) has been demonstrated to be available for the improvement in tensile strength of normal FSW joints. In order to illuminate the intrinsic reason for strength improvement through underwater FSW, a 2219 aluminum alloy was underwater friction stir welded and the homogeneity of mechanical properties of the joint was investigated by dividing the joint into three layers. The results indicate that the tensile strength of the three layers of the joint is all improved by underwater FSW, furthermore, the middle and lower layers have larger extent of strength improvement than the upper layer, leading to an increase in the homogeneity of mechanical properties of the joint. The minimum hardness value of each layer, especially the middle and lower layers, is improved under the integral water cooling effect, which is the intrinsic reason for the strength improvement of underwater joint.     

Estimation of impact-induced damage in CFRR laminates through ultrasonic imaging

Ultrasonic C-scans are used frequently to detect defects in composite components caused during fabrication and damage resulting from service conditions. Evaluation and characterization of defects and damage require experience and good understanding of the composites. Under low-velocity impact loading delamination is observed to be a major failure mode. In this paper, the results of extensive experimental work on damage of carbon fiber reinforced plastic (CFRP) laminates due to low-velocity impact are presented. The study was carried out on 10 different layups over four different thickness. Both drop-weight and projectile impacts simulating practical conditions like tool-drop and runway debris, respectively, were carried out at energy levels varying from 3 to 30 J. The ensuing delamination damage was determined by ultrasonic: C-scans using the pulse-echo immersion method for both projected and layer-wise distribution. While projected delamination was obtained by placing a gate over the backwall echo, layerwise distribution was obtained by successive time delay from the frontwall to the backwall echo covering each interface. Delamination areas were quantified accurately by processing the raw image data using a digital image processing technique. Based on the data obtained an empirical relation was established between the delamination area and the impact energy.     

Mechanical characterization of integral aluminum-FRP-structures produced by high pressure die-casting

Due to the growing demand for light-weight solutions in a wide range of industrial sectors, the selection and combination of different materials is becoming more and more important. As a result, there is an increasing need for suitable joining technologies. In a new joining process, flexible glass fiber textiles are integrated into aluminum by high pressure die casting in the first production step. These structures are used for the electrochemical insulation between aluminum and carbon fiber textiles, which are connected in the subsequent production step by textile technology. The finished compound is formed in a final resin impregnation process. Challenges faced by Fraunhofer IFAM lie in the positioning, pre-tensioning, and infiltration of the glass fiber textiles in the high pressure die-casting process. The advantage of this joining technology, in addition to the electrochemical insulation between aluminum and carbon fibers, is in a slim and light-weight connection. Therefore, no thickening of the individual joining partners is necessary, and the force flow lines are not deflected. Within mechanical investigations of those hybrid structures it was determined, that the infiltration content of aluminum has only a small influence on the achievable tensile strength. Rather, casting parameters such as the holding pressure have an influence. The subsequent resin infusion process enables an additional infiltration by the resin system of fiber bundles that have been only slightly infiltrated with aluminum. As a result, additional adhesion can be achieved and the infiltration gaps can be closed. Furthermore, an influence on the achievable tensile strength was observed regarding the use of the fiber material. Further increases in tensile strengths were also observed by adapting the textile parameters (e.g. reduction of the fiber undulations). A variety of failure behaviors could be observed in dependence on textile and process parameters. Tensile strength of the hybrid structures was compared to reference samples made of glass fiber reinforced epoxy resin, to determine the loss of strength caused by the joining technology. Further investigations were carried out, including a fracture surface analysis using a scanning electron microscope. Thus it was possible to determine mechanisms of adhesion between encapsulated glass fibers and the surrounding aluminum matrix.     

Mg/Al脉冲加压扩散连接接头显微组织及力学性能

采用脉冲加压扩散连接工艺,实现了AZ31镁合金与5083铝合金的连接.借助扫描电镜、EDS、X射线衍射仪和显微硬度计等手段对接头的显微组织及力学性能进行了研究.结果表明,接头有镁合金基体、冶金反应层、扩散层和铝合金基体组成.焊缝中形成了Mg₂Al₃,AlMg和Al_0.56Mg_0.44金属间化合物.接头最高硬度值达3300 MPa.随着保温扩散时间的延长,接头的抗拉强度出现了先升高后降低的现象,最高接头强度达46 MPa,在断口中发现了部分韧窝,断口属于韧性和准解理混合断口.在镁合金和铝合金两侧,硬度变化区域出现不对称现象.     

挤压熔体浸渗法制备金属涂覆碳纤维增强铝基复合材料的润湿性和力学性能改善

为了改善碳纤维与铝基体之间界面的润湿性和结合性能,采用挤压熔体浸渗法制备镍和铜涂覆碳纤维增强铝基复合材料,对两种不同涂层碳纤维增强铝基复合材料的界面润湿性、显微组织和力学性能进行比较和研究.显微组织结构分析表明,与无涂层碳纤维增强铝基复合材料相比,在相同的浸渗工艺条件下,在碳纤维表面涂覆两种金属均可以显著改善碳纤维与铝...     

Interfacial characterization of resistance spot welded joint of steel and aluminum alloy

The dissimilar material resistance spot welding of galvanized high strength steel and aluminum alloy had been conducted. The welded joint exhibited a thin reaction layer composed of Fe2Al5 and Fe4Al13 phases at steel/aluminum interface. The welded joint presented a tensile shear load of 3.3 kN with an aluminum alloy nugget diameter of 5.7 ram. The interfucial failure mode was observed for the tensile shear specimen and fracture occurred at reaction layer and aluminum alloy fusion zone beside the interface. The reaction layer with compounds was the main reason for reduction of the welded joint mechanical property.     

铝/钢异种金属电弧辅助激光对接熔钎焊方法

采用小功率TIG焊电弧辅助激光热源进行5A06铝合金和热镀锌钢ST04Z对接熔钎焊工艺试验,获得表面成形连续、美观的焊缝.采用SEM,EDS,XRD,拉伸试验机、显微硬度计对熔钎焊接头的微观组织和力学性能进行了研究.结果表明,与单纯激光相比,电弧辅助激光热源改变了焊接过程的温度场分布,从而促进液态铝向钢侧的铺展,所得对接接头最大抗拉强度可达到163 MPa,约为5A06铝合金母材抗拉强度的74%,是激光焊接头强度的1.3倍.接头过渡层形成的金属间化合物以脆硬的Fe₂Al₅,Fe₄Al₁₃为主.拉伸断裂起始于脆性的金属间化合物层,终止于韧窝断裂.     

电弧熔丝增材制造钛/铝复合材料的组织与性能

通过基于冷金属转移的电弧熔丝增材制造技术制备了铝/钛复合材料. 观察到钛/铝结合界面存在元素扩散,形成一定厚度的中间反应层,表明界面结合良好. 同时,通过硬度测试得到界面附近的硬度介于钛侧与铝侧之间,这主要是由于元素扩散导致界面附近生成了硬脆金属间化合物. 考虑到不同的复合比会导致不同力学性能,通过拉伸试验,研究了复合比对带缺口的钛/铝复合材料拉伸力学性能的影响规律. 结果表明,在持续拉伸载荷作用下,钛/铝复合材料的两组成层之间相互影响. 随着复合比的增加,抗拉强度和屈服强度增加,断后伸长率由于受钛铝之间冶金反应的影响较大,当钛/铝试样具有较低复合比时,其断后伸长率甚至小于单一沉积铝,随后才随着复合比的增加而增大. 另外,运用ABAQUS补充了多组复合比下钛/铝复合材料的拉伸过程,得到了复合比与屈服强度和抗拉强度的关系式.     

Microstructure and mechanical properties of 3D fine-woven punctured C/C composites with PyC/SiC/TaC interphases

The 3D fine-woven punctured C/C-(P_yC/SiC/TaC) composites, composed of P_yC/SiC/TaC interphases and pyrocarbon (PyC) matrix, were synthesized by isothermal chemical vapor infiltration (ICVI) methods. The alternating layers and the structure of these composites were examined by polarized light microscopy (PLM), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). It is found that the P_yC matrix has rough laminar (RL) structure, the TaC layer has NaCl-type cubic structure, and the SiC layer has few wurtzite type 10H-SiC besides β-SiC structure. The effects of fiber coating and the bulk density on the tensile and flexural properties of composites along X or Y and Z direction were investigated. It is shown that fiber coated 3D woven punctured C/C composites have good tensile and flexural strength, and the maximum of flexural strength is 375 MPa in X or Y direction at density of 1.89 g/cm³, which is about three times higher than that of samples without TaC/SiC fiber coating. The flexural strength and bending strength increase with increasing the density of the composites. The analysis of fracture surfaces reveals that fibers and fiber bundles are pulled out in composites, indicating that the composite exhibits a non-linear failure behavior through propagation and deflection of the cracks.     

Effect of annealing temperature on joints of diffusion bonded Mg/Al alloys

To study the effect of annealing temperature on the joints between magnesium and aluminum alloys, and improve the properties of bonding layers, composite plates of magnesium alloy (AZ31B) and aluminum alloy (6061) were welded using the vacuum diffusion bonding method. The composite specimens were continuously annealed in an electrical furnace under the protection of argon gas. The microstructures were then observed using scanning electron microscopy. X-ray diffractometry was used to investigate the residual stresses in the specimens. The elemental distribution was analyzed with an electron probe micro analyzer. The tensile strength and hardness were also measured. Results show that the diffusion layers become wide as the heat treatment temperature increases, and the residual stress of the specimen is at a minimum and tensile strength is the largest when being annealed at 250 °C. Therefore, 250 °C is the most appropriate annealing temperature.     

纯铝中间层厚度对铝/钢点焊接头性能的影响

采用纯铝作为中间层对铝合金与低碳钢进行了电阻点焊,分析中间夹层厚度对界面反应层厚度和接头抗拉强度的影响。在钢/中间夹层界面观察到有界面反应层生成,其主要由靠近钢侧的Fe2Al5和靠近中间夹层铝侧的FeAl3两种金属间化合物组成。与不加中间夹层相比,利用纯铝作为中间夹层点焊的铝合金与低碳钢的接头具有较薄的界面反应层和较高的接合强度。随着中间夹层厚度的增加,界面反应层厚度逐渐减小,而接头抗拉强度则呈增大趋势。结果表明,采用纯铝作为中间夹层点焊铝合金与钢具有一定的有效性。     

硬质颗粒重复冲击TiN/Ti涂层损伤分析

航空发动机压气机叶片表面制备硬质涂层可显著提高其抗砂尘冲蚀性能,但砂粒高角度冲击对涂层损伤严重,易出现脆性裂纹。采用受控动能型重复冲击设备模拟硬质颗粒对涂层的高角度冲击,研究调制比、层数结构对TiN/Ti涂层冲击损伤的影响,并根据涂层损伤特征、冲击力学响应以及应力分布分析涂层的破坏机理。结果表明,TiN/Ti涂层出现剥落和圆周裂纹;硬质层内部、硬质层与结合层/过渡层界面存在高的应力梯度,而冲击坑点边缘硬质层上表层受到拉应力且由于材料堆起,在重复冲击下将导致涂层的疲劳剥落和圆周疲劳裂纹。调制比、层数显著影响涂层冲击响应过程,其中不同调制比的2层涂层,调制比为3:1的抗冲击性能较好;调制比为9:1的不同层数涂层,4层结构的抗冲击性能较好。     

铝合金与高强钢摩擦塞铆焊接头连接性能

为了解决铝合金与高强钢材料之间连接困难的问题,保证铝合金与高强钢之间的连接质量,采用摩擦塞铆焊工艺实现了6061-T6铝合金和DP1470高强钢的连接,并通过对接头宏观形貌和微观组织特征的观察、接头力学性能的测试以及接头失效形式的对比,研究了摩擦塞铆焊所获接头连接性能的变化规律. 结果表明,转速是影响焊接质量的重要因素. 在焊接试验过程中,转速控制范围为5000 ~ 8000 r/min,接头的抗拉强度随转速的增加先升高后降低,当转速达到7000 r/min时,接头所承受的剪切载荷最大,可以达到6.3 kN,此时得到的接头表面平整,无明显孔洞、裂纹等缺陷. 铝合金板材在接头处发生断裂失效时,接头所能承受载荷相对较大,焊接质量较高. 因此,铝合金和高强钢能够通过摩擦塞铆焊工艺实现高质量连接.     

Research on Properties of Carbon Fiber/Epoxy Resin Composite Material by Microwave Curing

Microwave irradiation was used to reduce the curing time of carbon fiber/epoxy resin composite material.The properties of carbon fiber/epoxy resin composite material under microwave curing were investigated by thermogravimetry(TG),dynamic mechanical analysis(DMA),impact strength test and scanning electron microscope(SEM).The results show that composite materials patch have high thermal stability after microwave curing.The initial degradation temperature is 330.9℃,the maximum thermal decomposition rate is at 368.1℃.When the layer of composite materials patchis 4 layers,the dynamic mechanical properties are the best after microwave curing.The initial storage modulus is 43.2 GPa,increased 28.3 GPa and 27.1 GPa than 3 layers and 5 layers,the glass transition temperature(Tg)is 67.48℃,increased about 12 ℃than 3 layers and 5 layers.Microwave curing can significantly improve the infiltration capacity of epoxy resin,enhance interfacial bonding,and increase the impact strength of composite patch.Under microwave curing,the impact strength of 3,4,5-layers composite material patches increases 35.9%,6.4% and 15.1%,respectively than heating curing.The SEM analysis of impact fracture surface shows that microwave curing can improve the interface of carbon fiber and epoxy resin.     

600MPa级高Al冷轧双相钢点焊接头断裂方式

通过拉伸剪切试验以及对拉剪断口的微观组织和扫描电镜分析,研究了高Al冷轧双相钢点焊接头的断裂方式,并分析了接头断裂方式对接头力学性能的影响规律.研究结果表明,高A1冷轧双相钢的点焊接头主要有3种断裂方式,即:母材撕裂的焊点拔出、沿熔核边界的焊点拔出及界面断裂.3种不同的断裂方式分别代表了3种不同的裂纹萌生和扩展方式.此...     

Effects of Plasma Nitriding on the Tensile Properties of Al-Mg-Si

Effects of plasma nitriding on the tensile behavior of Al-Mg-Si alloy were investigated in this study. The specimens were nitrided at 70?W input pulsed DC power at 1?mbar pressure of nitrogen for 4?h using glow discharge plasma. The formation of aluminum nitride layer on the specimen's surface was confirmed by the XRD analysis. Stress-strain curves of both un-nitrided and nitrided specimens were obtained using Universal Testing Machine. The comparison of these curves reveals that yield stress, ultimate tensile stress, percentage elongation, and stress relaxation rate decrease after plasma nitriding. The changes in the tensile properties after nitriding have been correlated with the changes in the microstructure of the specimens as observed using scanning electron microscope.     

铝合金表面电弧喷涂Ag基涂层及其低温钎焊行为

在波导器件中,铝合金壳体较差的润湿性制约了其与微带电路板之间大面积、可靠低温钎焊连接. 通过电弧喷涂技术在5A06铝合金表面制备了厚度约为80 μm的Ag-15%Ni(质量分数)单一涂层和Ni-5%Al/Ag-15%Ni(质量分数)复合涂层,以提升Sn-Pb钎料在其表面的润湿性. 对比研究了两种涂层的显微结构、涂层界面结合性能、低温钎焊行为及钎焊接头剪切失效机制. 结果表明,涂层与铝合金基板间形成了良好的界面结合,并且两种涂层均具有较好的低温焊接性. 其中,Ag-15%Ni单一涂层与铝合金基板的结合强度为40 MPa,喷涂后铝合金基板与T2紫铜形成的钎焊接头抗剪强度为26 MPa. 相较而言,Ni-5%Al /Ag-15%Ni复合涂层展现出更佳的涂层结合强度(42 MPa)和钎焊接头抗剪强度(31 MPa).