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For ultralight Mg–Li alloys, the improvement of strength is the most concerned issue. In this work, we successfully realize the incredible enhancement of strength in the Mg-8.5Li-7.5Zn-1.5Y alloy via a series of preparation processes, and the excellent tensile properties containing high yield strength of 312.4 MPa and good elongation of 14.2 % are obtained. Yield strength increment is as high as 213 MPa through deformation processing, which is rarely reported in Mg–Li alloys. Qualitative and quantitative studies reveal that the dislocation cutting of semi-coherent MgLi 2 Zn nano-precipitates is mainly responsible for such a high yield strength. The new finding for strengthening way is expected to contribute to the design of high-performance Mg–Li alloys. [ABSTRACT FROM AUTHOR]

In this paper, the microstructural characteristics and deformation behaviors of a CoCrFeNiMo 0.15 high-entropy alloy (HEA) with a low volume fraction of σ precipitates during rolling deformation at cryogenic temperature and room temperature were investigated. The stacking fault energy of the HEA was experimentally estimated via measuring the widths of the dissociated dislocations. Deformations at two temperature conditions were both characterized by dislocation activities and extensive nano-twinning, while the rate of these microstructural evolution was accelerated with the aid of the cryogenic temperature. Abundant microbands, nanotwins and stacking faults were detected during deformation under both temperature conditions. Moreover, the hexagonal close-packed structure can only be observed in the cryogenic rolled sample, which was produced via the glide of Shockley partials on every other {111} FCC plane. At the late deformation stage of cryogenic rolling, the nanotwins were markedly distorted or even fractured, and shear bands were also formed. The contributions of different strengthening mechanisms of cryogenic rolling were discussed. [ABSTRACT FROM AUTHOR]

Abstract In this work, microstructural evolution of a solutionized Al-Cu-Mg alloy during rolling at liquid-nitrogen temperature was studied and concomitant strengthening effect was elucidated. It was found that a prior solid-solution treatment as well as a lowering of deformation temperature to the cryogenic range essentially suppressed dislocation mobility. This promoted an abrupt increase of dislocation density but considerably retarded microstructural processes, particularly texture evolution and development of deformation-induced boundaries, thus suppressing grain refinement. Hence, the strengthening effect of the cryogenic rolling was mainly contributed by the work hardening mechanism. [ABSTRACT FROM AUTHOR]

Abstract Cu–Cr alloys have been widely used in industrial applications owing to their good combination of mechanical properties and electrical conductivity. However, the comprehensive performance of the alloy needs to be further improved to meet the harsh working environment. Hence, in this study, a new type of Cu–Cr alloy with Co and Si additions together with cryogenic rolling (CR) was designed and investigated. Microstructure analysis confirms that the Cr 15 Co 9 Si 6 and Co 2 Si phases are formed with Co and Si additions into the Cu–Cr alloy. For the more, partial Cr 15 Co 9 Si 6 phase decomposes during heat treatment process, and the Co 2 Si and Cr precipitates are precipitated from matrix during aging process. The improvement of tensile properties of the Cu–1Cr–1Co–0.6Si alloy is mainly attributed to the precipitation strengthening and grain boundary strengthening, and is also benefited from dislocation density strengthening, twin boundary strengthening, and solid solution strengthening. The electrical conductivity of the Cu–1Cr–1Co–0.6Si alloy decreases dramatically mainly due to the increase of impurity scattering caused by surplus Si atoms. CR deformation is helpful for more solute atoms precipitated from the supersaturated solid solution during aging process, and thus the electrical conductivity of the Cu–1Cr–1Co–0.6Si alloy increases with increasing deformation amount. After homogenizing treatment at 900 °C for 2 h, hot rolling by 60% at 900 °C, solution treating at 990 °C for 4 h, cold rolling by 90%, and aging at 440 °C for 1 h, the hardness, yield strength (YS), ultimate tensile strength (UTS), and electrical conductivity of the Cu–1Cr–1Co–0.6Si alloy are 214.6 HV, 663.7 MPa, 745.9 MPa and 41.6%IACS, respectively, which exhibit good mechanical properties with a proper electrical conductivity. These results provide a feasible route for developing high performance Cu–Cr alloys. [ABSTRACT FROM AUTHOR]

In the present study, commercial Cu-35Zn α-brass sheets were subjected to cryogenic rolling (CR) to obtain samples with different amounts of deformation in the thickness direction. A self-designed liquid nitrogen cooling system that can simultaneously cool the work rollers and samples was used to ensure an ultra-low temperature condition during the rolling process. The grains, deformation twins, and dislocation density of the samples were studied by optical microscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD). Uniaxial tensile tests and Vickers hardness measurements were conducted to measure the mechanical properties of the samples. The microstructures and mechanical properties of CR samples were apparently improved compared to the room temperature rolling (RTR) samples with increasing deformation amount. As a typical example, when the deformation amount is 90%, the CR sample possesses ultrafine microstructures and demonstrates extraordinary mechanical properties. The average tensile and yield strengths of a 90% deformation CR sample can be improved to 835.3 MPa and 711.5 MPa, while those of a 90% deformation RTR sample are 718.6 MPa and 481.2 MPa. The average elongation of the CR sample is 2.9%, which is acceptable compared with the RTR sample whose average elongation is 3.1%. The ultrafine microstructures containing ultrafine grains, high density dislocation, and nanometer scale deformation twins in the 90% deformation CR sample may be the main reason for its extraordinary mechanical properties. Therefore, samples with a good combination of strength and ductility were obtained in the present study. This may be a valuable exploration to fabricate Cu-35Zn alloy sheets with excellent microstructures and mechanical properties. [ABSTRACT FROM AUTHOR]

The microstructure/mechanical properties, annealing behavior, and post-annealed microstructure/property relationship of 5052 Al alloy processed by cryogenic rolling (CR) and room-temperature rolling (RTR) have been investigated. It was observed that the CR-processed 5052 Al alloy exhibits a refined crystallite size along with higher-density dislocations than that of the RTR-processed sample. As a result, the tensile strength of the CR-processed alloy increased significantly to 345 MPa because of the enhanced dislocation strengthening and grain-boundary strengthening. The effective suppression of dynamic recovery and accumulation of high-density dislocations caused by CR help accelerate recrystallization kinetics and refine the grain size, gaining higher yield strength for the post-annealed CR 5052 Al alloy compared to that of other commercial 5052-O Al alloys. [ABSTRACT FROM AUTHOR]

Abstract: The effect of cryogenic rolling on the natural aging behavior of a commercial AA7050 aluminum alloy was investigated. Solutionized 10mm-thick sheets were cryo-rolled to true strains of 0.5, 0.9, 1.1 and 1.4 followed by natural aging (T4 temper) at times ranging from 10 to 1000h. Light optical microscopy (LOM), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were used to follow the microstructural changes upon processing. Mechanical properties were assessed by Vickers hardness measurements and tensile tests. During natural aging the hardness values increased from 100 HV to approximately 145 HV after 100h. The strength of the undeformed specimen, naturally aged for 100h, was much higher than that in the as-quenched state. The yield strength (YS) increased from 130 to 375MPa (188% increase) and the increment of ultimate tensile strength (UTS) was almost 47% (321–470MPa). A superior combination of mechanical properties was achieved for the specimen cryo-rolled to a true strain of 0.5 followed by natural aging for 1000h (YS=611MPa and 15% total elongation). These results suggest that a combination of cryogenic rolling with natural aging is a useful method for achieving optimized mechanical properties for the AA7050 alloy. [Copyright &y& Elsevier]

Cryogenic deformation had been proved to promote the strength and toughness in several kinds of alloys. The microstructure responses and mechanical properties of cryogenic rolling 2195 Al–Cu–Li alloy after heat treatment were investigated systematically in this study. The annealed 2195 Al–Cu–Li alloy plates were subjected to cryogenic rolling to a reduction of 80% at −190 °C, followed by the solid solution at 540 °C for 2 h and aging treatment at 175 °C for different durations. Both the tensile strength and ductility of heat-treated specimen increased compared with the as-rolled sample, while the yield strength of the cryogenic rolling sample was higher anomaly. In addition, the tensile strength, yield strength, and elongation of the heat-treated samples increased firstly and then decreased with the increase of aging time. The number of T 1 phases was initially increased with the aging time extended to 12 h and decreased after the aging duration was increased to 16 h. While the number of θ' gradually decreases with aging time increased. Based on the precipitation kinetics, aging kinetics, and dislocation theory, a physically based model considering the variation of dislocation density and volume fraction of the T 1 phase and aging duration was established in this paper, which is in good agreement with the experimental data. Meanwhile, a strong connection between the dislocation density and fraction of the T 1 phase and aging duration is established. [ABSTRACT FROM AUTHOR]

Microstructure and mechanical properties of cryogenic-rolled LA141-xYb (x = 0, 0.1) alloys were investigated. With the addition of Yb, the grains of the alloy are refined, and some fine Al 3 Yb phases are formed. The submicron scale dynamic recrystallized grains can be observed in the cryogenic rolled specimen. The addition of Yb inhibits the dynamic recrystallization and refines the grains during cryogenic rolling. As a result, the work softening is greatly reduced, and the strength is significantly increased. The results show that, due to the addition of Yb, the ultimate tensile strength of as-cast and CR-processed alloys is increased by 14.5% and 40.1%, respectively, reaching 197 MPa and 241 MPa. It is mainly caused by the combined effects of refinement, dispersive fine Al 3 Yb particles, high density dislocation and stack faults (SFs). • The excellent mechanical properties of LA141 alloy were obtained by combination effects of Yb addition and cryogenic-rolling. • With the addition of Yb, the grains of the alloy are refined, and some fine Al 3 Yb phases are formed. • The mechanism of microstructure evolution of the CR-processed specimen was discussed. [ABSTRACT FROM AUTHOR]

The pure copper sheets were rolled with a small strain in one pass at cryogenic and room temperature, respectively. The total thickness was reduced by 55% through three rolling passes. The microstructural evolution and mechanical properties of Cu sheets were investigated by metallographic characterizations, tensile tests and fracture analysis. It is found that several nanoscale mechanical twins are generated in the cryogenically rolled Cu sample. The restricted atomic motion at ultralow temperature inhibits the dislocation slip and then induces the occurrence of grain kinking and mechanical twining. The yield strength and ultimate tensile strength of cryo-rolled Cu sample are enhanced by the remarkable accumulation of dislocations and mechanical twins. During annealing treatment, the recrystallization behavior is accelerated by the dramatic strain energy and microstructural defects in cryogenically rolled Cu samples. Compared with the recrystallization concentrated on the surface of room temperature rolled Cu sample, a few of recrystallized grains are formed in the central position of cryogenically rolled Cu sample at 180 °C annealing. The rapid progress of thermal recovery during annealing treatment improves the tensile ductility and strain-hardening capacity of cryo-rolled Cu sample. Several pores are formed on the tensile fracture due to the incompatible deformation between the inhomogeneous grains. The results demonstrate that combining the cryogenic rolling and 200 °C annealing is able to improve the mechanical properties of pure copper sheet. [ABSTRACT FROM AUTHOR]