An Investigation of Interface Bonding of Bimetallic Foils by Combined Accumulative Roll Bonding and Asymmetric Rolling Techniques

The bond strength in bimetallic materials is an important material characteristic. In this study, 0.1-mm thick bimetallic foils (AA1050/AA6061) were produced using one pass of accumulative roll bonding followed by three passes of asymmetric rolling (AR). The AR passes were carried out at roll speed ratios of 1.0, 1.1, 1.2, 1.3, and 1.4 separately. Finite element simulation was used to model the deformation of the bimetallic foils for the various experimental conditions. Particular attention was focused on the bonding of the interface between AA1050 and AA6061 layers in the simulation. The optimization of the roll speed ratio was obtained for improvement of the bond strength of the interface of AA1050/AA6061 bimetallic foils during AR process. In the simulation, the mean equivalent strain at the interface zone between the AA1050 and AA6061 layers was seen to reach a peak value at a roll speed ratio of about 1.2 to 1.3, which also corresponded to a high quality bond at the interface as observed experimentally.     

Mechanical properties and bond strength of bimetallic AA1050/AA5083 laminates fabricated by warm-accumulative roll bonding

Accumulative roll bonding (ARB) is one of the most promising methods for the industrial production of bimetal sheet materials. In this study, ARB process has been used to combine aluminium alloys 1050 and 5083 sheets to produce a bimetal AA1050/AA5083 composite laminate. Materials with 2, 4, 8, 16 and 32 layers were roll bonded as alternate layers at 300°C for 5?min before each cycle. In this study, the microstructure and mechanical properties of composite laminates have been studied versus number of layers by tensile and peel testing. Moreover, the fracture surfaces of samples after the tensile test have been studied during various number of composite layers by scanning electron microscopy (SEM). Results showed that the tensile strength and tensile toughness improved by the number of layers. Also, the peeling strength among the layers and elongation decreased in the samples with less than 8 layers and improved by increasing the number of composite layers considerably. Also, SEM results revealed that the depth of dimples in the fracture surface decreased by increasing the number of layers.     

Effect of Operation Parameters on Diffusion Bonded AA5083, AA6082 and AA7075 Aluminum Alloys

Rolled plates of 5 mm thick AA5083, AA6082 and AA7075 aluminum alloys Joints were fabricated by diffusion bonding at different temperatures. The microstructure evolution of AA5083, AA6082 and AA7075 aluminium alloys were characterized by transmission electron microscopy. Metallurgical investigations and mechanical tests were also performed to correlate the microstructural investigations with the mechanical properties of the produced diffusion bonded joints. It was observed that the bonding and shear strength increased with the increase in bonding temperature due to the diffusion of micro-constituents in the interface. Higher temperature enhanced the uniform distribution of secondary phase particles, which further improved the reduction in pores/defects in the bonded joints.     

Properties and Mechanism of Al/St Bimetal Tube Bonding Produced by Cold Spin-Bonding (CSB) Process

Spin-bonding is a novel tube cladding method for fabrication of bilayer tubes based on flow-forming process. The bimetal Al/St tubular components have extensive application in different industries. In this paper, an Al/St bimetal tube was successfully produced at different thickness reductions from 35 to 65% and mechanical and metallurgical aspects of the joint were investigated. Peeling tests were done to investigate the strength of the bond. The results showed that an increase in the thickness reduction led to a significant increase in the bond strength. Besides, the bonding mechanism between Al as inner tube to St as an outer one resulting from spin-bonding process was investigated. The results showed that an excellent bonding of Al and St tubes could be achieved from this process. The results showed that the bonding process consisted of three stages. First, removal of surface layers resulting in contact between the virgin metals of two bond surfaces and then an unstable bond was formed that stabilized as deformation proceeded. Finally the bond strengthening occurred. The SEM micrographs of the peeled surfaces showed that removing surface films in aluminum and steel in the first stage was based on different mechanisms. Also, SEM back-scatter images of bond interface showed that no intermetallic phases were formed.     

Microstructure and Mechanical Properties of AA5005/AA6061 Laminated Composite Processed by Accumulative Roll Bonding

The AA5005/AA6061 laminated composite has been fabricated by the accumulative roll bonding (ARB) using commercial AA5005 and AA6061. In the ARB process, one piece of AA5005 sheet and one piece of AA6061 sheet were stacked together and rolled with a 50 pct reduction without any lubrication. The materials were heated at 473 K (200 °C) for 10 minutes before each rolling process and were deformed up to four cycles to accumulate an equivalent strain of 3.2 and form an AA5005/AA6061 laminated composite. Mechanical properties and microstructure of the laminated composites were tested. The hardness and tensile strength increased, and the grain size reduced with the number of ARB cycles. Ultrafine grains elongated along the rolling direction were developed during the ARB process. The thicknesses of the grains of both the AA5005 and AA6061 layers were less than 200 nm after the fourth cycle. The uniform elongation decreased drastically after the first cycle ARB and stayed almost unchanged after further ARB process. The hardness of the AA5005 layer was slightly lower than that of the AA6061 layer. The microstructures from optical microscope and transmission microscope showed that in the AA6061 layer large precipitates in the micron scale and small particles less than 100 nm were present, whereas in the AA5005 layer there were large scale precipitates, but no small-sized particles.     

Direct-Chill Co-Casting of AA3003/AA4045 Aluminum Ingots via Fusion™ Technology

Laboratory-scale experiments were conducted to cast AA3003/AA4045 clad ingots via Fusion? Technology, a novel process developed by Novelis Inc. for the production of aluminum clad materials such as brazing sheet. Experimental results were used to validate a steady-state thermofluids model of the Fusion? Technology co-casting process. The numerical model was able to accurately predict the temperature field within the AA3003/AA4045 clad ingot as well as the shape of the AA3003 liquid sump. The model was also used to quantify the temperature, fraction solid, and velocity fields in a clad ingot cast with an asymmetrical molten metal-feeding system. Feeding of core and clad molten metals at opposite corners of the mold was found to reduce the risks of hot spots and liquid metal breakthrough from the core sump to the clad side of the Fusion? Technology mold. The use of a diffuser for the AA3003 core molten metal and of a vertical feeding tube for the AA4045 clad produced different flow patterns and liquid sump shapes on either side of the mold. The quality of the metallurgical bond at the core/clad interface appeared good near the clad inlet and at the ingot centerline, but poor near the edges of the ingot. SEM–EDS analysis of the chemical composition across the interface showed that a 1 to 20-μm-deep penetration of silicon from the AA4045 clad into the AA3003 core had occurred at visually acceptable interfaces, whereas silicon diffusion across poor interfaces was very limited. A study of the model-predicted fraction solid history at different points along the interface indicated that reheating of the AA3003 core is not required to form a visually acceptable metallurgical bond. However, a sufficient amount of interaction time between the solid AA3003 core shell and the silicon-rich AA4045 clad liquid is required to chemically dissolve the surface of the core and form a good metallurgical bond. An approximate dissolution depth of 750 to 1000 μm was observed along the visually good interface. Partial dissolution of the Mn-rich AA3003 core led to the formation of Al(Mn,Fe)Si intermetallic particles in the AA4045 clad and an increased manganese concentration near the core/clad interface.     

Microstructural characterization of dissimilar friction stir welds between AA2219 and AA5083

Fusion welding of dissimilar aluminum alloys is very challenging. In the present work, Al-Cu alloy AA2219-T87 was friction stir welded to Al-Mg alloy AA5083-H321. Weld microstructures, hardness, and tensile properties were evaluated in as-welded condition. Microstructural studies revealed that the nugget region was primarily composed of alloy 2219, which was placed on the advancing side. No significant mixing of the two base materials in the nugget region was observed. Hardness studies revealed that the lowest hardness in the weldment occurred in the heat-affected zone on alloy 5083 side, where tensile failure were observed to take place. Tensile tests indicated a joint efficiency of around 90%, which is substantially higher than what can be achieved with conventional fusion welding. Overall, the results show that satisfactory butt welds can be produced between AA2219-T87 and Al-Mg alloy AA5083-H321 sheets using friction stir welding.     

Dissimilar friction stir welds in AA5083-AA6082. Part I: Process parameter effects on thermal history and weld properties

The aim of this study was to explore the so-called processing window, within which good-quality welds can be produced, for the friction stir welding of AA5083 to AA6082. To that end a systematic set of nine instrumented welds were made using rotation speeds of 280, 560, and 840 rpm and traverse speeds of 100, 200, and 300 mm/min with AA5083 on the advancing side and another nine with the materials reversed. For comparison a smaller series of AA5083-AA5083 and AA6082-AA6082 welds were also made. Thermocouple measurements, tool torque, extent of material mixing, and macrostructural observations all indicate that the temperature under the tool is more strongly dependent on the rotation than the traverse speed. It was found that in the current case, the power (energy/s) and heat input (energy/mm) do not correlate simply with the weld temperature. As a result, such metrics may not be suitable for characterizing the conditions under which welds are produced.     

Influence of Constituent Materials on the Impact Toughness and Fracture Mechanisms of Hot-Roll-Bonded Aluminum Multilayer Laminates

Two aluminum multilayer laminates have been processed by hot roll bonding following similar processing paths. The first one is constituted by alternated Al 2024 and Al 1050 layers (ALH19) and the second one by alternated Al 7075 and Al 1050 layers (ADH19). The influence of the constituent materials in the multilayer laminates both during the processing at high temperature and during the subsequent mechanical characterization has been analyzed. The mechanical behavior of the as-received materials at the processing conditions has been characterized by hot torsion. Multilayer laminates have been tested at room temperature under impact Charpy tests, three-point bend tests, and shear tests on the interfaces. The relative toughness increase compared to the constituent materials was much higher for the ADH19 laminate based on the high-strength Al 7075 alloy than for the ALH19 laminate. This is attributed to the different fracture mechanism.     

Microstructure and Mechanical Properties of Aluminum/Copper Composite Rod Fabricated by Axisymmetric Spiral Extrusion

In the present investigation, an axisymmetric spiral extrusion was used for fabrication of bimetallic Al/Cu composite rods. In this process, a cylindrical bimetallic sample was extruded through an extrusion die having engraved spiral grooves to produce near net shaped composite part. After preparation of composite rods, the bonding strength was evaluated by applying shear stress on Al/Cu interface using compression test. Also the bonding interface was examined by optical metallography and scanning electron microscopy. The results showed that the bond strength increased in Al/Cu composite rods after spiral extrusion and the bonded interface was free of intermetallic layer. The stress imposed on interface region during spiral extrusion broke the work hardened layer in the mating surfaces, and consequently, the cold weld was established between virgin Al and Cu in the contact area. The obtained results showed a feasibility of spiral extrusion processing for production of Al/Cu bimetallic composite rods.     

Failure mechanisms in superplastic AA5083 materials

The mechanisms of tensile failure in four 5083 aluminum sheet materials are evaluated under conditions of interest for superplastic and quick-plastic forming. Two mechanisms are shown to control failure of the AA5083 materials under uniaxial tension at elevated temperatures: cavitation and flow localization (i.e., necking). Conditions for which failure is controlled by cavitation correspond to those under which deformation is primarily by grain-boundary-sliding creep. Conditions for which failure is controlled by flow localization correspond to those under which deformation is primarily by solutedrag creep. A geometric parameter, Q, is used to determine whether final failure is controlled by cavitation or by flow localization. Differences in elongations to failure between the different AA5083 materials at high temperatures and slow strain rates are the result of differences in cavitation behaviors. The rate of cavitation growth with strain is nearly constant between the AA5083 materials for identical testing conditions, but materials with less tensile ductility evidence initial cavitation development at lower strain levels. The rate of cavitation growth with strain is shown to depend on the governing deformation mechanism; grain-boundary-sliding creep produces a faster cavitation growth rate than does solute-drag creep. A correlation is found between the early development of cavitation and the intermetallic particle-size population densities of the AA5083 materials. Fine filaments, oriented along the tensile axis, are observed on fracture surfaces and within surface cavities of specimens deformed primarily under grain-boundary-sliding creep. As deformation transitions to control by solute-drag creep, the density of these filaments dramatically decreases.     

Producing of AA5083/ZrO2 Nanocomposite by Friction Stir Processing (FSP)

In this study, friction stir processing (FSP) was used to produce AA5083/ZrO₂ nanocomposite layer. Optical microscopy and SEM were used to probe the microstructures formed in the composite layer. In addition, the mechanical properties of each sample are characterized using both tensile and hardness tests. Results showed that FSP is an effective process to fabricate AA5083/ZrO₂ nanocomposite layer with uniform distribution of ZrO₂ particles, good interfacial integrity, and significant grain refinement. On processing, in the proper combination of process parameters, the metal matrix composite layer was observed to have increased tensile and hardness properties.     

Flexural Strength of RC Beams with GFRP Laminates

The results of an experimental and numerical study of the flexural behavior of reinforced concrete beams strengthened with glass-fiber-reinforced-polymer (GFRP) laminates are presented in this paper. In the experimental program, ten strengthened beams and two unstrengthened beams are tested to failure under monotonic loading. A number of external GFRP laminate layers and bond length of GFRP laminates in shear span are taken as the test variables. Longitudinal GFRP strain development and interfacial shear stress distribution from the tests are examined. The experimental results generally showed that both flexural strength and stiffness of reinforced concrete beams could be increased by such a bonding technique. In the numerical study, an eight-node interface element is developed to simulate the interface behavior between the concrete and GFRP laminates. This element is implemented into the MARC software package for the finite-element analyses of GFRP laminate strengthened reinforced concrete beams. Reasonably good correlations between experimental and numerical results are achieved.     

Be/HR-1不锈钢扩散连接界面附近的元素扩散

为了优化热静压扩散连接工艺参数,应用有限元法对Be/HR-1不锈钢扩散连接界面附近铁和铍元素的分布进行了计算机模拟,并通过俄歇电子能谱(AES)进行实验测定。结合计算机模拟结果和实验数据探讨了扩散连接界面附近铁和铍元素的分布、扩散宽度与温度、压力和时间的关系。结果表明:在1050℃/60 MPa/2 h和750℃/60 MPa/2 h热静压下,扩散连接界面附近Be,Fe元素分布的实测数据与计算机模拟结果基本吻合;在60 MPa/2 h热静压下,加热温度分别为1050和750℃时对扩散宽度影响的实测数据与计算机模拟结果基本吻合,1050℃时的扩散宽度是750℃时的2.5倍;在750℃/2 h热静压下,压力分别为30,40,50,60 MPa时对扩散宽度影响的实测数据与计算机模拟结果基本吻合,扩散宽度与压力成抛物线关系;在750℃/60 MPa热静压下,扩散宽度与扩散时间的模拟曲线也成抛物线关系。     

Effect of asymmetric rolling on the texture and mechanical properties of AA6111-aluminum sheet

Aluminum-alloy sheets are considered to be one of the high-potential substitutes for steel sheets, when considering the weight reduction of automobiles. However, aluminum-alloy sheets have inferior formability, mainly due to their lower plastic-strain ratios. The plastic-strain ratios of aluminum-alloy sheets can be increased with the formation of shear-deformation texture through the sheet thickness. Asymmetric rolling, in which the circumferential velocities of working rolls are different, is a favorable process for imposing shear-deformation texture through the sheet thickness. In this study, commercial AA6111-alloy sheets were used to compare the effects of conventional symmetric rolling and asymmetric rolling in controlling the shear textures and grain refinement, as well as the mechanical properties of the tensile and plastic-strain ratio.     

Deformation and failure of a superplastic AA5083 aluminum material with a cu addition

A modified AA5083 aluminum sheet material containing a Cu addition of 0.61 wt pct has been investigated under conditions relevant to commercial hot-forming technologies. This material was produced by continuous casting followed by industrial hot and cold rolling into sheet. Deformation and failure mechanisms at elevated temperatures were investigated through mechanical testing, thermal analysis, and microscopy. The effects of Cu addition are evaluated by comparisons with data from AA5083 sheet materials without Cu addition, produced both by continuous and direct-chill (DC) casting techniques. At low temperatures and fast strain rates, for which solute-drag (SD) creep governs deformation, the Cu addition slightly increases tensile ductility at 450 °C but does not otherwise alter deformation behaviors. At high temperatures and slow strain rates, for which grainboundary-sliding (GBS) creep governs deformation, the Cu addition decreases flow stress and, at 450 °C, improves tensile ductility. A strong temperature dependence for tensile ductility results from the Cu addition; tensile ductility at 500 °C is notably reduced from that at 450 °C. The Cu addition creates platelike particles at grain boundaries, which produce incipient melting and the observed mechanical behavior.     

Experimental and Simulation Studies on Fabricating GCr15/40Cr Bimetallic Compound Rollers Using Electroslag Surfacing with Liquid Metal Method

Electroslag surfacing with liquid metal （ESSLM） is an excellent method for producing high quality bimetallic compound rollers. The quality of each compound roller is primarily determined by the metallurgical quality of the combined interface. A GCrl5/40Cr compound roller is produced using an ESSLM non-consumable electrode electro- slag heating method. The temperature and electric fields produced by the ESSLM system are calculated. As the roller core moves downward in the mold, it passes through five sections., the preheating section, the rapid heating section, the temperature homogenizing section, the bimetal fusing section and the cooling section which listed from the top to bottom of the mold, respectively. The temperature distribution and the degree of the surface temperature fluctuation in the roller core are different for each section. Near the combined interface, four layers are found from the roller core to the cladding layer= the remelting layer, the fusion layer, the interface solidification layer and the chilling layer, re spectively. Among these, the fusion and interface solidification layers are the key transition zones that greatly influ- ence the combination quality. The surface temperature of the roller core prior to cladding is mainly determined by the drawing velocity, and the thickness of the transition layer increases as the drawing velocity decreases. A transition layer that is too thick or too thin will reduce the mechanical properties at the combined interface. Therefore, the drawing velocity should be limited to a moderate range to produce a satisfactory bimetallic Compound roller.     

金属材料累积叠轧焊界面的结合特性

 金属材料的界面结合特性是累积叠轧焊技术的关键,在多功能强力热轧机上利用ARB工艺分别对Q235钢和L2纯铝进行了累积叠轧焊自身界面结合特性的试验研究。重点研究了累积叠轧焊材料的界面结合特性,界面结合强度,界面断裂特性,材料组织状态对界面结合的影响。研究结果表明：材料的界面结合性能不仅与首次压下量、变形温度有关,而且,在再结晶温度以下,累积叠轧次数与首次临界变形量共同决定了材料的显微结构,从而决定了材料的界面结合特性,当累积次数超过2次时,材料的界面结合接近基体强度。