High Strength and Thermal Stability of Multilayered Cu/Al Composites Fabricated Through Accumulative Roll Bonding and Cryorolling

Multilayered Cu/Al composites with high strength and thermal stability were successfully fabricated by combining accumulative roll bonding (ARB) and cryorolling. The microstructure, tensile properties, and thermal stability of the multilayered Cu/Al composites subjected to cold rolling and cryorolling were analysed. Subsequent cryorolling can be used to modify interfacial flatness and local necking, induce the formation of high-density stacking faults in the Cu matrix, and enhance interfacial bonding strength, which improves the mechanical properties of ARB composites. The initial lamellar structure is gradually transformed into serious mixing with an increase in annealing temperature, accompanied by the formation of excessive Cu–Al intermetallic compounds (IMCs). Cryorolled samples exhibited higher thermal stability than cold-rolled samples. At low annealing temperature, high-density stacking faults induced by cryorolling facilitated the transition from low-angle grain boundaries to high-angle grain boundaries, which led to the formation of ultra-fine grains. For the samples annealed at high temperatures, cryorolling led to the effective inhibition of Cu–Al IMC formation and growth due to the genetic effect of less heat input.

Graphical Abstract

     

Microtexture Development of Niobium in a Multilayered Ti/Al/Nb Composite Produced by Accumulative Roll Bonding

Multilayered Ti/Al/Nb composites were produced by the accumulative roll bonding (ARB) process utilizing pure Ti, Al, and Nb element sheets. Up to four cycles of ARB were applied to the composites. The microstructure and texture evolution on the Nb phase were studied by X-ray diffraction (XRD), transmission electron microscopy, scanning electron microscopy, and electron backscattered diffraction. Nb and Ti layers necked and fractured as the number of ARB passes increased. After four ARB cycles, a nearly homogeneous distribution of Nb and Ti layers in Al matrix was achieved. As-received Nb sheet exhibited a fully lamellar structure and had a strong cold-rolling texture. After subjecting to ARB, slight grain refining was observed and the high-angle boundary fraction was increased. The intensity of the α-fiber was weakened, while that of the γ-fiber was strengthened during ARB. The texture evolution was attributed to partial recrystallization during the ARB process as a result of adiabatic heating.     

ARB工艺对1060工业纯铝组织和性能的影响

采用ARB技术中两种轧制工艺, 研究变形后1060工业纯铝的显微组织和力学性能变化. 结果显示, 在两种ARB轧制工艺中, 单向轧制工艺的晶粒细化效果明显好于换向轧制. ARB7道次后, 采用单向轧制工艺试样的显微组织由拉长的细小纤维状晶粒组成, 平均晶粒尺寸是470 nm;采用换向轧制工艺试样由等轴状晶粒组成, 平均晶粒尺寸是680 nm. 同时, 单向轧制后, 材料的抗拉强度和显微硬度提高程度大于换向轧制, 但延伸率却不如换向轧制. 分析了ARB过程材料的变形规律和细小晶粒的形成机制.     

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.     

Corrosion Behavior of Ultra Fine Grain Copper Produced by Accumulative Roll Bonding Process

In this study the effect of microstructure changes on the corrosion behavior of pure tough pitch copper in 3.5 % NaCl solution with pH = 5.5 at ambient temperature was studied. Accumulative roll bonding process as severe plastic deformation was applied up to 8 cycles to produce the ultrafine grain copper. For corrosion resistance investigations, the polarization and electrochemical impedance spectroscopy was used. Corrosion morphologies analyzed by FE-SEM microscopy after polarization and immersion tests. Results show the minimum corrosion resistance for cycle 2 and maximum corrosion resistance for cycle 8. Corrosion rate of copper decreased after it was rolled for forth time. The corrosion degradation in cycle 8 was uniform and it was intergranular for sample of cycle 2 and unrolled counterpart. The higher corrosion rate in cycle 2 was attributed to unstable microstructure and the uniform corrosion of cycle 8 was due to ultra fine grain formation.     

累积叠轧焊对退火态纯铝的显微组织和力学性能的研究

采用累积叠轧焊的方法对退火态的1060纯铝进行了累积叠轧实验,研究了累积叠轧次数对金属材料抗拉强度、延伸率、显微硬度、塑性的影响规律,通过透射电镜、拉伸及显微硬度实验分析了规律形成的原因。结果表明：经过多道次的轧制实验后,晶粒尺寸急剧细化,7道次后超细晶增多,晶粒最小细化到500nm。材料的抗拉强度和显微硬度也有显著提高。     

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。     

Texture Evolution of Nanostructured Aluminum/Copper Composite Produced by the Accumulative Roll Bonding and Folding Process

In this study, the accumulative roll bonding and folding (ARBF) process was used for manufacturing nanostructured aluminum/copper multilayered composites. Textural evolution during the ARBF process of composites was evaluated using X-ray diffraction. Microstructural observation of some samples was evaluated by scanning electron microscopy and transmission electron microscopy. The ARBF process induced formation of a strong preferred orientation along the β-fiber and also to the pronounced copper texture component. In the aluminum side, occurrence of dynamic recovery reduced the intensity of the β-fiber rolling texture due to change in dislocation structure and decrease in the degree of strain hardening. On the other hand, occurrence of discontinuous dynamic recrystallization at the third and fourth ARBF cycles led to decreasing the intensity of fibers and texture components in the copper side. The average grain sizes of the final sample for the copper and aluminum sides were ~50 and ~200 nm, respectively.     

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.     

Processing Parameter Influence on Texture and Microstructural Evolution in Cu-Nb Multilayer Composites Fabricated via Accumulative Roll Bonding

A combination of accumulative roll bonding and rolling is used to fabricate bulk sheets of multilayer Cu-Nb bimetallic composites. Alterations in the processing sequence are made in comparison with prior studies in order to expand the processing window available for bimetallic multilayer composites. Cu-Nb composites with layer thicknesses ranging from 45 μm to 10 nm with accompanying total strains of 3.8 to 12.21 are characterized via neutron diffraction, electron back scatter diffraction, and transmission electron microscopy. These characterization methods provide microstructural information such as layer morphology and grain morphology as well as orientation information such as texture and interface plane normal distribution. The evolution of these microstructural characteristics is collected as a function of increasing strain. These results can provide guidance, inputs, and validation for multiscale predictive models that are being developed on materials with interfacially-driven properties. Finally, synthesis pathways are presented that allow the fabrication of nanoscale multilayer composites with predominant interfacial structures. These fabricated materials are ideal for exploring the relative importance between inter-phase interfacial density and atomic interfacial structure in determining material properties.     

累积叠轧焊制备Al／AZ31多层复合材料及其强度

采用累积叠轧焊法制备了Al/AZ31多层复合材料,并通过扫描电镜、X射线能谱仪和显微硬度计对所制备的Al/AZ31多层复合材料进行了横截面形貌观察、能谱分析以及显微硬度测试.结果表明,经过三道次的累积叠轧焊之后可制备Al/AZ31多层复合材料.能谱分析表明,在Al层和AZ31层的界面处产生了扩散层.随着轧制道次的增加扩散层的厚度逐渐增加.显微硬度测试表明,随着轧制道次的增加,Al/AZ31多层复合材料的层组元的强度也随之增加,但Al层的强度较AZ31增加得快,并且形成的界面扩散层具有一定的硬度梯度.     

Accumulative Roll Bonding of Alloy 2205 Duplex Steel and the Accompanying Impacts on Microstructure,Texture, and Mechanical Properties

Metallurgical and Materials Transactions A - The mechanical and microstructural evolution of Alloy 2205 during severe plastic deformation is examined in this study. A combination of accumulative...     

Fabrication of High-Strength Al/SiC<Subscript><Emphasis Type="Italic">p</Emphasis></Subscript> Nanocomposite Sheets by Accumulative Roll Bonding

Accumulative roll bonding (ARB) was successfully used as a severe plastic deformation method to produce Al-SiC nanocomposite sheets. The effects of process pass and amount of SiC content on microstructure and mechanical properties of the composites are investigated. As expected, production of ultrafine grain structures by the ARB process as well as nanosize particulate reinforcements in the metal matrix composite (MMC) resulted in excellent mechanical properties. According to the results of the tensile tests, it is shown that the yield and tensile strengths of the composite sheet increased with the number of ARB cycles without saturation at the last cycles. Scanning electron microscopy (SEM) revealed that the particles had a random and uniform distribution in the matrix by the last ARB cycles, and strong mechanical bonding takes place at the interface of the particle matrix. Transmission electron microscopy (TEM) and the corresponding selected area diffraction (SAD) demonstrate ultrafine grains with large misorientation in the structure. It is also shown that by increasing the volume fraction of particles up to 3.5 vol pct, the yield and tensile strengths of the composite sheets increased more than 1.3 and 1.4 times the accumulative roll-bonded aluminum sheets, respectively.     

Effect of Particles Content on Microstructure,Mechanical Properties,and Electrochemical Behavior of Aluminum-Based Hybrid Composite Processed by Accumulative Roll Bonding Process

Metallurgical and Materials Transactions A - Effect of B4C/SiC particles content on the microstructure, deformation, and electrochemical behavior of aluminum-based hybrid composite processed by...     

Influence of the Processing Temperature on the Microstructure, Texture, and Hardness of the 7075 Aluminum Alloy Fabricated by Accumulative Roll Bonding

The 7075 alloy is an Al-Zn-Mg-Cu wrought age-hardenable aluminum alloy widely used in the aeronautical industry. The alloy was accumulative roll bonded at 300 °C (573 K), 350 °C (623 K), and 400 °C (673 K), and the microstructure, texture, and hardness were investigated. Cell/(sub)grain size in the nanostructured range, typical β-fiber rolling texture, and homogeneous hardness through thickness were determined in all cases. Misorientation was different at each processing temperature. At 400 °C, the presence of elements in solid solution and the partial dissolution of the hardening precipitates lead to a poorly misoriented microstructure with a high dislocation density and a homogeneous β-fiber texture of low intensity, typical of intermediate degrees of rolling. At 350 °C and 300 °C, highly misoriented microstructures with smaller dislocation density and intense heterogeneous β-fiber rolling texture are observed, especially at 350 °C, wherein the degree of dynamic recovery (DRV) is higher. Hardness of the accumulative roll bonded samples is smaller than that of the starting material due to particle coarsening, and it is affected by solid solution and/or by fine precipitates produced by reprecipitation of the elements in solid solution.