Effect of differential speed rolling on microstructure and mechanical properties of an AZ91 magnesium alloy

Severe deformation by differential speed rolling (DSR) with a high-speed ratio could be successfully imposed on the AZ91 plate to produce thin sheets with submicron grain size and good planar isotropy. The sheets exhibited a good combination of high strength and high ductility, showing yield stresses of 327 MPa and tensile elongations of 9–11%. Comparison with other severe deformation processes indicates that DSR process is advantageous over ECAP process in obtaining higher strength and over ARB process in obtaining higher ductility. Moreover, the current DSR is a continuous process as well as a convenient method of imposing severe deformation on thin Mg sheets.     

Fabrication of ultrafine-grained AA1060 sheets via accumulative roll bonding with subsequent cryorolling

Ultrafine-grained (UFG) AA1060 sheets were fabricated via five-cycle accumulative roll bonding (ARB) and subsequent three-pass cold rolling (298 K), or cryorolling (83 K and 173 K). Microstructures of the aluminum samples were examined via transmission electron microscopy, and their mechanical properties were measured via tensile and microhardness testing. Results indicate that ultrafine grains in ARB-processed sheets were further refined by subsequent rolling, and the grain size became finer with reducing rolling temperature. The mean grain size of 666 nm in the sheets subjected to ARB was refined to 346 or 266 nm, respectively, via subsequent cold rolling or cryorolling (83 K). Subsequent cryorolling resulted in ultrafine-grained sheets of higher strength and ductility than those of the sheets subjected to cold rolling.     

Evaluation of mechanical properties and structure of multilayered Al/Ni composites produced by accumulative roll bonding (ARB) process

Multilayered Al/Ni composites were produced by accumulative roll bonding (ARB) process using Al 1060 and commercial Ni foils. In this process it was observed that nickel layers necked and fractured as accumulative roll bonding passes increased. After six ARB passes, a multilayered Al/Ni composite with homogeneously distributed fragmented nickel layers in aluminum matrix was produced. Structure and mechanical properties of these multilayer composites were evaluated at different passes of ARB process. During ARB, it was observed that as the strain increased with the number of passes, the strength, microhardness and elongation of produced composites increased as well. In addition, enhancement of the strength was shown to be higher than the tensile strength of Al/Al and Al/Cu multilayered composites produced by ARB process in the previous works by the same authors.     

Production of High-Strength Al/Al2O3/WC Composite by Accumulative Roll Bonding

In this study, Al/Al₂O₃/WC composites were fabricated via the accumulative roll bonding (ARB) process. Furthermore, the microstructure evolution, mechanical properties, and deformation texture of the composite samples were reported. The results illustrated that when the number of cycles was increased, the distribution of particles in the aluminum matrix improved, and the particles became finer. The microstructure of the fabricated composites after eight cycles of the ARB process showed an excellent distribution of reinforcement particles in the aluminum matrix. Elongated ultrafine grains were formed in the ARB-processed specimens of the Al/Al₂O₃/WC composite. It was observed that as the strain increased with the number of cycles, the tensile strength, microhardness, and elongation of produced composites increased as well. The results indicated that after ARB process, the overall texture intensity increases and a different-strong texture develops. The main textural component is the Rotated Cube component.     

Fabrication of MMC Strip by CRB Process

In this study, Al/Al₂O₃ composite strips were produced by the cold roll bonding (CRB) process. Microhardness, tensile strength, and elongation of composite strips were investigated as a result of changes in thickness reduction, quantity of alumina particles, and the production method used. It was found that higher values of reduction and quantities of alumina improved microhardness and tensile strength but decreased elongation. Furthermore, as-received strips exhibited the highest values for microhardness and tensile strength but the lowest for elongation. In contrast, post-rolling annealed strips recorded the lowest values for microhardness and tensile strength but the highest for elongation. Finally, it was found that pre-rolling annealing was the best method for producing this composite via the CRB process.     

Passive Behavior of Ultra-Fine-Grained 1050 Aluminum Alloy Produced by Accumulative Roll Bonding in a Borate Buffer Solution

In this study, the effect of the ARB process on the passive behavior of ultra-fine-grained 1050 aluminum alloy in a borate buffer solution(p H 6.0) has been investigated. The result of the microhardness tests revealed that the microhardness values increase with an increasing number of ARB cycles. The potentiodynamic polarization plots revealed that the higher number of cycles for the specimens proceeds with the ARB process rather than annealing yield to lower corrosion and passive current densities and more noble corrosion potential values. Moreover, electrochemical impedance spectroscopy measurements showed that increasing the number of ARB cycles offers better conditions for forming the passive films.     

Effects of ARB and ageing processes on mechanical properties and microstructure of 6061 aluminum alloy

Accumulative roll bonding (ARB) has been used as a severe plastic deformation process for the production of high-strength materials. Ageing treatment has been found to enhance the strength of alloys by precipitation of a second phase. In the present work, ARB followed by the ageing process was used for the fabrication of the high-strength 6061 aluminum alloy. Samples of the alloy thus made were subjected under annealed and ARBed conditions to ageing treatment at different temperatures for different times and their mechanical properties were evaluated. It was found that the microhardness and tensile strength of the specimens increased with the number of ARB cycles but their elongation values decreased. After the ageing treatment, the mechanical properties of the ARBed specimens improved in terms of both strength and ductility. Based on TEM observations, it may be concluded that the improved mechanical properties after the duplex ARB-ageing process can be attributed to the precipitation of very fine particles with a slight decrease in dislocation density and limited structure coarsening. SEM observation of fracture surfaces of aged specimens indicated that the fracture was predominantly caused by microvoid coalescence at constituent particles.     

Pre-aging time dependence of microstructure and mechanical properties in nanostructured Al-2wt%Cu alloy

This work is focused on the effect of pre-aging time on the properties of Al-2wt%Cu alloy processed by accumulative roll bonding (ARB) process. Following aged at 190 °C for 10 or 30 min, the samples were deformed up to a strain of 4.8 by the ARB process. The microstructure evolution was investigated by transmission electron microscope and electron backscattering diffraction analyzes. The results showed that the Al₂Cu precipitates were formed with different sizes due to the different pre-aging times and the finer precipitates were more effective on the formation of high angle grain boundaries during the ARB process. The grain size of Aged-10 min and Aged-30 min specimens decreased to 400 nm and 420 nm, respectively, after 6 cycles of the ARB process. Also, the final texture after 6 cycles of the ARB process, shown in the {111} pole figure, were different depending on the starting microstructures. The mechanical properties of specimens were investigated by the Vickers microhardness measurements and the tensile tests. The results showed that the mechanical properties are affected by the starting microstructure. The mechanical properties of Aged-10 min specimen were different compared to Aged-30 min specimen due to the different size of the pre-existing precipitates. Although by continuing process, the precipitates were probably dissolved due to the heavy deformation.     

多道次温轧对AZ31镁合金组织和性能的影响

以AZ31镁合金为实验材料,通过多道次温轧工艺,研究低温时效处理对温轧板材组织和性能的影响。结果表明:经5道次温轧后合金组织得到明显细化,从初始态38μm细化至2.2μm;在随后120~160℃时效过程中,晶粒并未发生显著长大。经低温时效处理后,合金在基本保持温轧态拉伸强度的同时,其塑性得到明显提升。由晶界强化和位错强化模型定量描述发现,经5道次温轧后合金显微硬度增量为30HV。然而随着时效温度的升高,位错强化贡献显著降低,而晶界强化由于晶粒长大不明显而几乎无显著变化。合金经160℃时效2 h后,两种主要强化机制对显微硬度的贡献为16HV。     

Electron back scattered diffraction (EBSD) characterization of warm rolled and accumulative roll bonding (ARB) processed ferrite

An interstitial free (IF) steel was severely deformed using accumulative roll bonding (ARB) process and warm rolling. The maximum equivalent strains for ARB and warm rolling were 4.8 and 4.0, respectively. The microstructure and micro-texture were studied using optical microscopy and scanning electron microscopy equipped with electron back scattered diffraction (EBSD). The grain size and misorientation obtained by both methods are in the same range. The microstructure in the ARB samples after 6 cycles is homogeneous, although a grain size gradient is observed at the layers close to the surface. The through thickness texture gradient in the ARB samples is different from the warm rolled samples. While a shear texture (〈1 1 0〉//rolling plane normal direction (ND)) at the surface and rolling texture at the center region is developed in the ARB samples, the overall texture is weak. The warm rolled samples display a sharp rolling texture through the thickness with increasing the sharpness toward the center. These differences are attributed to the fact that the central region of ARB strip is comprised of material that was once at the surface. The ARB process can suppress the formation of shear bands which are conventional at warm rolled IF steels. EBSD study on the sample with 6th cycle of ARB following the annealing at 750 °C verified a texture gradient through the thickness of the sheet. The shear orientations at the surface and at the quarter thickness layers can be identified even after annealing. The overall weak texture and existence of shear orientations make ARB processed samples unfavorable for sheet metal forming in compare with warm rolled samples.     

Formation of nano-sized grains in Cu and Cu−Fe−P alloys by accumulative roll bonding process

Mechanical properties and formation of nano-sized grains in Cu and Cu−Fe−P alloys by the accumulative roll bonding (ARB) process were investigated. Nano-sized grains were successfully obtained in OFC and PMC-90 alloys by the ARB process after the third cycle. Once the 200 nm grains formed, further reduction in the grain size was not observed up to 8 ARB process cycles. For both alloys, the tensile strength values increased drastically in the initial stage of the ARB process. The tensile strength values of both alloys tended to saturate after the third ARB process cycle. The tensile elongation value greatly decreased by 1 cycle of the ARB process due to the strain hardening. After the third cycle of the ARB process, each alloy showed a gradual increase in tensile elongation due to the dynamic recovery. For PMC-90 alloy, the strength value was higher than that of OFC due to addition of the alloying elements. With increased annealing temperature, the nanosized grains tended to grow in OFC at 150°C, and after annealing at 200°C, coarse grains formed. On the other hand, in PMC-90 alloy, there was no grain growth up to 250°C due to the alloying elements (Fe, P).     

The combined effect of aging and accumulative roll bonding on the evolution of the microstructure and mechanical characteristics of an Al–0.2 wt % Zr alloy

This work is devoted to the effect of processes initiated by the combined action of aging (A) and accumulative roll bonding (ARB) on the evolution of the microstructure and the mechanical characteristics of an Al–0.2 wt % Zr alloy. Upon solution treatment (ST), followed by aging at temperatures of 350 and 450°C, the specimens were subjected to deformation to a degree of deformation of 80% using ARB. The evolution of the microstructure was examined using atomic force microscopy and the mechanical characteristics of the specimens were determined using tensile tests and Vickers microhardness measurements. The results have shown that, upon ten ARB cycles, the grain size decreased to 0.3, 0.4, and 0.32 μm in the specimens subjected to ST followed by ARB (ST–ARB), ST followed by A at a temperature of 350°C and ARB (350°C–A–ARB), and ST followed by A at a temperature of 450°C and ARB (450°C–A–ARB), respectively. This study has also shown that the combined use of preliminary A and subsequent ARB holds promise in enhancing the mechanical characteristics of the alloy due to precipitates that appear in the course of annealing. Fracture surfaces of the rolled specimens subjected to the tensile tests were examined using scanning electron microscopy. The results of these examinations have shown that in the specimens subjected to ST followed by ARB brittle fracture has been observed at the stage of the final ARB cycles, while in the A–ARB specimens cleavage facets (sites of fracture over the cleavage plane) and river lines have appeared on the fracture surfaces.     

Effects of Annealing on the Fabrication of Al-TiAl3 Nanocomposites Before and After Accumulative Roll Bonding and Evaluation of Strengthening Mechanisms

The strengthening mechanisms of Al-TiAl₃ nanocomposite, fabricated using cold roll bonding, annealing, and accumulative roll bonding (ARB) on Al sheets sandwiching with pure Ti powder were investigated in the present study. With annealing at 590 ℃ for 2 h, TiAl₃ intermetallic compound was formed. After subsequent ARB process up to 5 cycles, final composite consists of ultrafine Al grains of less than 500 nm with TiAl₃ particles larger than 200 nm. The strength and hardness of the final composite are 2.5 and 3.5 times the initial values, with an ultimate tensile strength of 400 MPa, which is dominated by grain-boundary strengthening due to the ultrafine Al grains, and Orowan strengthening due to the small TiAl₃ particles. For comparison, an alternative fabrication route of cold roll bonding-ARB-annealing was also studied. This study showed that annealing before ARB is a critical factor in producing an ultrafine grain structure containing TiAl₃ particles.     

累积叠轧技术的研究现状与展望

对采用累积叠轧工艺制备超细晶组织的技术进行详细的综述,介绍了累积叠轧技术的原理、ARB材料的组织与力学性能特征,并对ARB变形过程中的剪切变形、晶粒细化机制和强化机制进行分析。采用ARB技术可以制备大尺寸的超细晶组织材料,其室温抗拉强度通常比粗晶材料的高2～4倍。ARB材料的强化源于晶粒细化、位错强化、在大变形轧制时形成的稳定基面织构、表面的氧化膜以及内生原有夹杂物在强烈塑性变形情况下的破碎与弥散分布。分析了ARB技术的优越性,对其在制备超细晶材料领域的应用进行了展望。     

严寒条件下X80钢管道全自动外焊焊缝组织与性能

在?30 ℃严寒环境下进行了X80管线钢MAG电弧多层多道焊接试验,研究了22 mm厚管线钢焊接接头的显微组织、拉伸性能、显微硬度以及低温冲击韧性. 结果表明,在严寒条件下采用高强韧焊丝获得的接头,其焊缝组织组成主要为针状铁素体和先共析铁素体,粗晶区存在大量板条状贝氏体铁素体;焊接接头硬度呈“M”形分布,粗晶区的大量板条状贝氏体铁素体是该区域显微硬度值最大的主要原因;焊接接头的平均抗拉强度为684 MPa,具有延性断裂的典型特征;接头韧性薄弱区集中于焊缝区域,其平均冲击吸收能量为83 J. 与常温焊接相比,由于严寒条件焊接提高了冷却速度,促进了针状铁素体和M/A岛状组织的析出,严寒条件下接头的抗拉强度和显微硬度增加,但焊缝区域低温断裂韧性显著下降;同时,严寒条件下施焊更易产生气孔缺陷.     

不同路径下316不锈钢电弧增材组织和性能

以316不锈钢为材料,探讨了平行往复、“十”字正交、插补堆积三种不同路径下TIG电弧增材试件微观组织及力学性能的差异. 结果表明,三组试件中部组织存在明显差异,平行往复试件树枝晶粗大发达,生长方向高度一致. “十”字正交试件树枝晶生长方向多,枝晶紊乱,层间过渡区域大. 插补堆积试件二次枝晶不发达,组织细密. 在显微硬度方面,三组试件的维氏硬度自底板至顶部呈现先减小后增大的趋势,平行往复试件显微硬度最大. 在拉伸性能方面,平行往复试件纵向抗拉强度最高,纵向受力时可采用该方式增材. 插补堆积试件横向抗拉强度最高,横向受力时可采用该方式增材. “十”字正交试件力学性能表现出各向同性,多向受力且对塑性要求较高时可采用该方式增材.     

Tensile behavior of commercially pure copper sheet fabricated by 2-and 3-layered accumulative roll bonding (ARB) process

The tensile properties of two- and three-layered accumulative roll-bonding (ARB) processed copper sheets containing deoxidized low-phosphorous copper (DLP) and PMC90 are investigated with varying numbers of ARB process cycles. The tensile strength of the DLP is determined by the applied equivalent strain, showing that the tensile strength values for both 2-L and 3-L ARBed DLP specimens follow a single trend line. Unlike the DLP, the 3-L ARBed PMC90 follows a trend line that is completely different compared to that of its 2-L counterpart above an equivalent strain value of 7.6, suggesting that the amount of applied equivalent strain alone does not control the tensile strength of PMC90. The mechanism determining the tensile behavior of 2-L and 3-L ARB processed commercially pure copper sheets is discussed.     

Al-6Mg-0.8Zn-0.5Mn-0.2Zr-0.2Er合金高强耐损伤工艺与微观组织研究

以Al-6Mg-0.8Zn-0.5Mn-0.2Zr-0.2Er合金为基础,对该材料的冷轧态,温轧态,完全退火态进行拉伸测试和疲劳裂纹扩展速率测试。运用电子背散射衍射(EBSD),透射电镜(TEM),扫描电镜(SEM)对合金的原始组织、疲劳断口、裂纹扩展路径进行观察,研究微观组织对材料拉伸性能及疲劳裂纹扩展速率的影响。结果表明:温轧态屈服强度高,裂纹扩展抗力大,实现了高强高耐损伤性能的匹配。这主要是由于温轧态轧制过程中发生动态回复,位错缠结规整化,具有较多的亚晶界,该种组织模式对材料的屈服强度和疲劳裂纹扩展抗力均有提高。     

累积叠轧焊对L2纯铝力学性能影响的研究

通过实验研究了轧制道次、温度与材料状态对L2纯铝力学性能的影响。结果表明：材料的抗拉强度、屈服强度和显微维氏硬度随轧制道次的增加而增加，第10道次分别为190．44MPa、152．27MPa和49．3HV（载荷100g）；室温叠轧材料的强度要高于热叠轧的，而延伸率却低于热叠轧的；半硬化态L2纯铝和完全退火态L2纯铝的强化能力是一致的，但半硬化态L2纯铝的强化幅度要低于完全退火态的。     

Al-6Mg-0.8Zn-0.5Mn-0.2Zr-0.2Er合金低温力学性能与微观组织研究

以Al-6Mg-0.8Zn-0.5Mn-0.2Zr-0.2Er合金为基础,对该材料的冷轧态,温轧态,完全退火态进行从室温降到77 K时的拉伸测试和冲击性能测试。运用背散射电子衍射(EBSD),透射电镜(TEM),扫描电镜(SEM)对合金的原始组织,拉伸断口,冲击断口进行观察,研究不同温度下微观组织对材料拉伸性能及冲击性能的影响。结果表明:随着测试温度的升高,样品的抗拉强度、屈服强度及冲击韧性均逐渐降低;温轧的H114态由于位错缠结规整,亚晶界比较多等原因保持了较高的强度和冲击韧性,实现了高强高韧性能的匹配。