Abnormal Ductility Increase of Commercial Purity Al During Accumulative Roll Bonding

In this paper, sheets of commercial purity Al were fabricated by the accumulative roll-bonding (ARB) method up to six cycles. To increase the shear deformation, no lubricant was used during the ARB processing and the samples were carried out for ARB processing without any preheat treatment. One interesting finding is that the ductility and strength both increased during the first several cycles of ARB processing. It is proposed that the initial rolling texture might play an important part in the subsequent ARB processing since the original Al sheets for ARB processing have not been subjected to any annealing. The microstructures of the specimens after each ARB cycle were investigated by transmission electron microscopy and correlated with the mechanical properties.     

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.     

叠轧无氧纯铜制备超细晶材料的EBSD分析

主要对不同条件下叠轧并退火处理的无氧铜试样进行扫描背散射电子衍射(EBSD)分析。EBSD反极图表明，试样内晶粒分布比较均匀，晶体学择优取向不是特别明显，但在局部仍存在微小的取向；EBSD晶粒图分析表明低道次叠轧后材料局部出现细小晶粒和小区域小角度晶界；晶粒度图表明低道次叠轧后大晶粒和小晶粒并存。结果表明利用叠轧法制备超细晶材料可以达到一定的细化目的。     

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.     

块体超细/纳米结构金属材料的累积叠轧制备技术

综述了一种制备大块状超细/纳米结构金属材料很有效的剧烈塑性变形工艺——累积叠轧(Accumulative Roll Bonding,ARB).重点阐述了ARB的工艺原理及变形过程中的界面结合机理、ARB材料的晶粒细化机理、组织特征、织构演变及强韧化机制等,分析了ARB工业应用中存在的主要问题及应对措施,并展望了该技术在制备超细晶材料领域的应用前景.     

Evaluation of Mechanical Properties and Structure of Al-1100 Composite Reinforced with ZrO<Subscript>2</Subscript> Nanoparticles via Accumulative Roll-Bonding

In this study, aluminum metal matrix composites reinforced with ZrO₂ nano-particles in volume fraction of 0.5, 0.75 and 1 % were manufactured through accumulative roll bonding (ARB) process. The results of composite microstructure indicated excellent ZrO₂ particle distribution in the Al matrix after 10 cycles of ARB process. The X-ray diffraction results also showed that nanostructured Al/ZrO₂ nano-particles composite with the average crystallite size of 48.6 nm was successfully achieved after 10 cycles of ARB process. The tensile tests were conducted on the ARBed strips. The tensile strength increased 2.15 times more than the initial value. The elongation dropped abruptly at the first cycle, and then increased slightly. The SEM images observations from the fracture surface showed that after 10 cycles of ARB process the fracture was almost shear fracture mode with fine and stretched pores.     

累积叠轧焊制备超细晶IF钢微观组织与力学性能

采用累积叠轧焊方法制备了超细晶IF钢，对其微观组织和力学性能进行了分析。实验结果表明，累积叠轧后IF钢的平均晶粒尺寸为700nm；抗拉强度为621．3MPa，达到冷轧IF钢抗拉强度的2．02倍，屈强比σ0.2/σb为0．81。在累积叠轧过程中产生的氧化物夹杂导致超细晶IF钢的脆化。     

The positive effect of pretreatment with serotonin and gangliosides on the development of early mouse embryos after cryopreservation

Blood pressure (BP) during siesta declines to levels similar to those of night time sleep. The objective of the study was to assess the effect of siesta on 24-h ambulatory BP (ABP) data. Two different approaches were employed for the definition of day and night periods: (1) actual patient reported day and night intervals (ACT) with siesta period analysed as a third time period; and (2) arbitrary day and night time intervals (ARB) with the presence of siesta being ignored. A total of 203 24-h ABP recordings were analysed, with a siesta during ABP monitoring reported in 154 of them. Mean siesta BP was very close to ACT night time BP. Among recordings with a siesta, ACT daytime BP was higher and night time BP lower than the corresponding ARB BPs (P < 0.001). The magnitude of night time BP drop was greater with ACT intervals, resulting in a lower percentage of non-dippers (P < 0.001). Among 49 recordings without a siesta, differences between ACT and ARB BPs were less pronounced for daytime but not for night time. Differences in the magnitude of nocturnal BP drop between ACT and ARB periods, although statistically significant, did not affect the prevalence of non-dippers. In conclusion, analysis of 24-h BP profiles by using ARB instead of ACT day and night intervals results in underestimation of the nocturnal BP drop and overestimation of the proportion of non-dippers. This bias is more pronounced in patients who take a siesta during ABP monitoring.     

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.     

Nanostructured NiTi Shape Memory Alloy Via Ni/Ti Nanolamination

Ultrafine grained NiTi shape memory alloy was consolidated from Ni/Ti laminates via accumulative roll bonding (ARB) followed by hot isostatic pressing (HIP). Due to the extensive plastic deformation arising from ARB and the attainment of ultra-thin layers of both Ti and Ni laminates, the subsequent HIP processing time was significantly reduced. Differential scanning calorimetry (DSC) analysis confirms that the shape memory effect was obtained in the consolidated NiTi alloy.     

Deformation textures of AA8011 aluminum alloy sheets severely deformed by accumulative roll bonding

A fully annealed AA8011 aluminum alloy sheet containing a number of large particles (∼5 μm) was severely deformed up to an equivalent strain of 12 by an accumulative roll-bonding (ARB) process. The texture evolution during the ARB process was clarified, along with the microstructure. The ARB-processed aluminum alloy sheets had a different texture distribution through the sheet thickness, due to the high friction between the roll and the material during the ARB process. The shear textures composed of {001} 〈110〉 and {111} 〈110〉 orientations developed at the sheet surface, while the rolling textures, including Cu {112} 〈111〉 and Dillamore {4,4,11} 〈11,11,8〉 orientations, developed at the sheet center. The textural change from a shear texture to a rolling texture at the sheet center during the ARB process contributed to an increase in the fraction of high-angle boundaries. Also, a large number of second-phase particles in the AA8011 alloy sheets weakened the texture. Up to the medium strain range (below ɛ=6.4), relatively weak textures developed, due to the inhomogeneous deformation around the second-phase particles; after the strain of 6.4, strong rolling-texture components, such as the Dillamore and Cu orientations, developed. This remarkable textural change can be explained by the reprecipitation of fine particles in grain interiors.     

Microstructural Evolution and Mechanical Property of AA5050 Alloy Deformed by Accumulative Roll Bonding

In this study, ultrafine-grained AA5050 sheets were fabricated by the accumulative roll bonding (ARB) process. Transmission electron microscope observations showed that at the early stage of ARB, the grain size was reduced in the normal direction and became elongated along the rolling direction. The elongated grains were cut out by dense dislocations, which then tangled and condensed, resulting in the formation of dislocation cells. As the deformation proceeded, the dislocation cells evolved to sub-grain boundaries and then grain boundaries. The ultrafine-grained microstructure was obtained via four ARB cycles. The tensile tests at 473 K and 523 K (200 °C and 250 °C) showed large elongations for strain rates of 1 × 10³ s^?1 and 1 × 10⁴ s^?1.     

Analysis of Strain Rate Sensitivity of Ultrafine-Grained AA1050 by Stress Relaxation Test

Commercially pure aluminum sheets, AA 1050, are processed by accumulative roll bonding (ARB) up to eight cycles to achieve ultrafine-grained (UFG) aluminum as primary material for mechanical testing. Optical microscopy and electron backscattering diffraction analysis are used for microstructural analysis of the processed sheets. Strain rate sensitivity (m-value) of the specimens is measured over a wide range of strain rates by stress relaxation test under plane strain compression. It is shown that the flow stress activation volume is reduced by decrease of the grain size. This reduction which follows a linear relation for UFG specimens, is thought to enhance the required effective (or thermal) component of flow stress. This results in increase of the m-value with the number of ARB cycles. Strain rate sensitivity is also obtained as a monotonic function of strain rate. The results show that this parameter increases monotonically by decrease of the strain rate, in particular for specimens processed by more ARB cycles. This increase is mainly linked to enhanced grain boundary sliding as a competing mechanism of deformation acting besides the common dislocation glide at low strain rate deformation of UFGed aluminum. Recovery of the internal (athermal) component of flow stress during the relaxation of these specimens seems also to cause further increase of the m-value by decrease of the strain rate.     

泡沫铝及其三明治结构累积叠轧制备

通过累积叠轧法制备泡沫铝.采用称重法研究泡沫铝孔隙结构,利用光学显微镜观察泡沫铝孔隙形貌.发现以TiH₂为发泡介质,当发泡温度660~680℃和发泡时间6~10 min时,利用累积叠轧法制备泡沫铝的孔隙结构特性最好.发泡温度和发泡时间的最佳值与发泡剂用量有关,TiH₂质量分数为1.5%,在670℃发泡8 min,泡沫铝的孔隙率可达到42%,孔径为0.43 mm.以制备的泡沫铝为夹芯,通过轧制复合制备了TC4钛合金/泡沫铝芯和1Cr18Ni9Ti不锈钢/泡沫铝芯三明治板.利用光学显微镜和能谱仪研究了三明治板的界面.面板与芯板间的化合反应形成了界面的反应层,界面实现了冶金结合.      

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.     

浅析层状复合板轧制新工艺

本文在对国内外层状金属复合板生产研究文献查阅分析的基础上,着重介绍了钎焊热轧法、燃烧合成轧制法、包套轧制法、PPR方法、ARB方法、PIT方法等复合新工艺基本工作原理,以及目前国内外应用各种新工艺所生产研究的新材料复合板,同时分析了复合板生产存在的问题,展望了复合板生产工艺的发展方向。     

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。     

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

     

Effect of ARB Cycle Number and Second Phase Content on Mechanical properties and Microstructure of Pb–Ag Composite

A solid state method has been found for manufacturing of lead–silver composites for use as anodes in electrowinning production. Mechanical properties and microstructure of composite were characterized via peeling, tensile and microhardness tests, and scanning electron microscopy, transmission electron microscopy and fractography. Based on the peeling test results, maximum bond strength was achieved in the presence of 0.125 wt% of Ag (1.8 N/mm). Best mechanical properties were achieved in the Pb–0.5 wt% Ag composite after 10 ARB cycles by the enhanced tensile strength rising up to 50%, yield strength up to 170%, shear strength up to 63% and hardness up to 2.6 times higher, and the strain decreasing to 68% lower. These advanced properties led to higher stiffness and considerable enhancements in dimensional stability of the anodes and they improved creep characteristics. The advanced properties of the processed Pb–Ag composite anodes could be introduced as certification for slower anode failure, upkeep, surcharge and capital expenditure of industries with essential lead anode requirement.