Although face-centered cubic (FCC) Al-Cu-Li alloys have received considerable attention due to their excellent light-weight and high-strength performance, its undesired strength-ductility balance still hinders the industrial application. The present work proposed a synergistic approach which combines cryo-pre-straining with subsequent precipitations for improving the mechanical properties of Al-Cu-Li alloys. Thermo-mechanical processing of Al-Cu-Li alloy sheets were carried out by pre-rolling at different temperatures (83 K, 298 K and 673 K) with large applied strains (the rolling reduction, 60% and 80%) and subsequence ageing. Cryo-pre-straining with a higher rolling reduction of 80% introduced refined grains and high-density dislocations leveraging the uniform-distribution dislocations and increased dislocation-accumulation capability at cryogenic temperature. Apart from 1/2<1 1 0> matrix dislocations, a large number of 1/6<1 1 2> partial dislocations were unexpectedly induced in the alloy deformed under 83 K compared with that under 298 K through molecular dynamics simulation. In addition, T-1, delta ' and theta' phases with different width, length and density occurred in the alloy after a period of ageing at 433 K. The coordinated dissociation of a perfect 1/2<1 1 0> matrix dislocation provides the displacement necessary for the formation of a new T-1 plate or plate ledge. The diffusional glide of growth ledges composed of pre-formed 1/6<1 1 2> partial dislocations on {111} matrix planes and the migration of the growth ledges through the ledge-kink lead to the growth of T-1 plate. Compared with the pre-AR (asymmetric rolling) and pre-AHR (asymmetric hot rolling), the hardening response of the alloy processed via pre-ACR (asymmetric cryorolling) was further improved and the peak ageing time was shorter due to the higher density of dislocations and dominant strengthening phases of T-1 plates. T-1 phases with the average size of 24.4 nm and the planar density of 21539.1 nm/mu m(2), originating from the high density of 1/2<1 1 0> perfect dislocations and 1/6<1 1 2> partial dislocations, further increased the ultimate tensile strength of the alloy processed by ACR-80% + 433 K/20 from 513 MPa to 530 MPa with not significantly reduced fracture ductility. These findings unveil the dynamic evolution of dislocations, precipitations and their intersection, providing theoretical guidelines for microstructure design and deformation process optimization of Al-Cu-Li alloys by simple thermo-mechanical processing.

CuNiSn alloys often generate cracks during traditional deformation. In this study, we report the development of the crack-free Cu9Ni6Sn strips by using twin-roll casting with subsequent asymmetric cryorolling. Although cracks appear in asymmetric hot-rolled and asymmetric room-temperature-rolled strips, no cracks were observed in asymmetric cryorolled (173 K and 83 K) strips. Electron back-scattered diffraction images indicate that deformation is relatively uniform for asymmetric cryorolled strips, with obvious shear bands appearing in asymmetric room-temperature-rolled and asymmetric hot-rolled strips. Energy dispersive spectroscopy images show that the segregation of Sn element appears near cracks in asymmetric hot-rolled and asymmetric room-temperature-rolled strips. The Sn element is uniformly distributed in asymmetric cryorolled strips. Uniform deformation, reduced Sn element segregation, and enhanced ductility at cryogenic temperature all contribute to the crack-free nature of the Cu9Ni6Sn strips prepared by asymmetric cryorolling.

The anisotropy of mechanical properties limits the applications of Al–Cu–Li alloys. In this study, microstructure evolution and mechanical properties of an Al–Cu–Li alloy via room-temperature rolling (RTR), room-temperature cross rolling (RCR), cryorolling (CR) and cross cryorolling (CCR) were investigated. The processing of Al–Cu–Li alloy by CCR gave the highest ultimate tensile strength of 471 MPa and an elongation of 8.4% along rolling direction (RD). The elongation of the CCR alloy along the diagonal direction (DD) was higher than those processed by CR, RCR, and RTR. The in-plane anisotropy (IPA) factor of the ultimate tensile strength (3.26%) of the CCR alloy indicated its relatively low anisotropy of the strength. Kernel average mapping (KAM) showed that the deformation was relatively uniform for the CCR alloy. A prominent local low KAM zone appeared in the alloy processed by RCR and RTR. The alloy in the CCR condition exhibits the highest strain hardening rate, progressively decreasing in a sequence of CR, RCR, and RTR. The refined grains and the texture, including mainly copper texture, little Cube texture, little Goss texture and little S texture, are the main reasons for the excellent mechanical properties and balanced strength-ductility of the CCR alloys.

The mechanical properties and microstructure of Al-Cu-Li alloy sheets subjected to cryorolling (−100 °C, −190 °C) or hot rolling (400 °C) and subsequent aging at 160 °C for different times were investigated. The dynamic precipitation and dislocation characterizations were examined via transmission electron microscopy and X-ray diffraction. The grain morphologies and the fracture-surface morphologies were studied via optical microscopy and scanning electron microscopy. Samples subjected to cryorolling followed by aging exhibited relatively high dislocation densities and a large number of precipitates compared with hot-rolled samples. The samples cryorolled at −190 °C and then aged for 15 h presented the highest ultimate tensile strength (586 MPa), while the alloy processed via hot rolling followed by 10 h aging exhibited the highest uniform elongation rate (11.5%). The size of precipitates increased with the aging time, which has significant effects on the interaction mechanism between dislocations and precipitates. Bowing is the main interaction method between the deformation-induced dislocations and coarsened precipitates during tensile tests, leading to the decline of the mechanical properties of the alloy during overaging. These interesting findings can provide significant insights into the development of materials possessing both excellent strength and high ductility.

Laminated metal composites are composed of alternating layers of metals or alloys, bonding together at their interface, which have gained extensive attention because of their advantages such as improved fracture toughness, impact behavior, corrosion, wear and damping capacity. Roll bonding is the most widely used method to process many metallic composites. In this study, we fabricated some kinds of Al/Ti/Al sandwich-like laminated composites by cryogenic roll bonding. We find that cryogenic roll bonding techniques can improve the mechanical properties of laminated composites. Finally, we will discuss the mechanism of improvement in bonding strength and mechanical properties.

Cu/Al clad sheets with a 304 stainless steel foil (SUS304) interlayer are successfully fabricated by the powder-in-tube method. The influence of SUS304 thickness on the interfacial structure, elemental diffusion, and peeling strength of the clad sheets is studied. Experimental results indicate that the initial Cu/Al interface is partially transformed into a Cu/SUS304/Al interface after introducing the SUS304 interlayer. The proportion of SUS304 fragments at the bonding interface is shown to increase with thickness of the SUS304 interlayer. Differences in deformability between SUS304 interlayer and Cu/Al matrix promote the occurrence of shear deformation at the bonding interface via the cladding process, enhancing atomic diffusion at the Cu/SUS304/Al interface. Peeling tests reveal that interfacial cracks in clad sheets with an SUS304 interlayer propagate along the Cu/SUS304 and Cu/Al interfaces. Under combined effects of interfacial transfer and large shear strain, the interfacial strength of clad sheets is apparently improved. Clad sheets with the thickest SUS304 interlayer (30 μm) exhibit highest peeling strength (30.9 N/mm), demonstrating 73.6% improvement over clad sheets without an interlayer. These findings provide novel insights into the innovative design of clad sheets possessing extraordinary interfacial strength.

The mechanical properties and microstructure evolution of an Al-Cu-Li alloy sheet processed via hot rolling (HR) (at 400 °C and 500 °C) or cryorolling (CR) (at −100 °C and −190 °C) and subsequence aging at 160 °C for 10 h were investigated. Before aging, the highest ultimate tensile strength of 502 MPa was achieved when the sheets were cryorolled at −190 °C, while the better ultimate tensile strength of 476 MPa and the best elongation rate of 11.1% was achieved simultaneously when the sheets were cryorolled at −100 °C. The refined grains and numerous uniform deformation-induced dislocations microstructures were responsible for the improved strength and enhanced ductility of the cryorolled sheets compared to that of the alloy processed by hot rolling with a low dislocation density zone (LDDZ) and high dislocation density zone (HDDZ). After aging at 160 °C for 10 h, the ultimate tensile strength further improved resulted from the greater precipitation strengthening, and the increased precipitates provided greater resistance to dislocations movement resulting in the increased ductility although the dislocation density decreased. The uniform dislocation microstructures in the cryorolled sheets provide numerous nucleation sites for the precipitates, leading to higher strength after aging.

Herein, sandwich‐like Cu/Al/Cu composites are fabricated by hot rolling (300 °C), cold rolling (25 °C), cryorolling (−100 and −190 °C), respectively. Tensile tests are conducted and the fracture surfaces of both the Al and Cu sides are examined using scanning electron microscopy (SEM) for fractography and SEM‐based energy‐dispersive analysis. The microstructure of the composites is evaluated by optical microscopy and SEM. Results reveal that the highest ultimate tensile strength and the best ductility of the composites have been achieved using cryorolling of the rolling temperature −100 °C. Finally, discussion on grain size, bonding quality, and the thickness of the intermetallic layer between Cu and Al layers on the mechanical properties of the sandwich‐like Cu/Al/Cu composites is focused.

Ultrafine‐grained (UFG) commercial purity titanium (CP Ti) has a significant potential for use in medical implants and aerospace structural parts. Herein, UFG CP Ti sheets are processed by cryorolling and room‐temperature rolling (RTR), respectively, followed by annealing for 1 h at temperatures from 250 to 350 °C. The grain size is reduced from ≈75 μm to ≈85 and ≈220 nm after cryorolling and RTR, respectively. The results show that the curves of tensile stress versus engineering failure strain for samples subjected to cryorolling and subsequent annealing are above those for samples subjected to RTR and subsequent annealing. In addition, the curves of ultimate tensile stress × fracture elongation versus grain size after cryorolling and annealing are above those for RTR and annealing. It is demonstrated that a combination of cryorolling and annealing leads to improved toughness compared with the processing by RTR and annealing.

Sandwich-like Al/Ti/Al-laminated composites have many advantages such as low density and high specific strength with value in mechanical manufacturing and aerospace engineering.Here,Al/Ti/Al-laminated composites were fabricated by hot roll bonding and subsequent processes: cryorolling (-190 ℃ and-100 ℃),cold rolling (25 ℃),and hot rolling (300 ℃).Their bonding strength and mechanical properties were then studied by an Autograph AGS-X universal electronic testing machine.The results show that cryorolling can improve the interface bonding strength and tensile strength of Al/Ti/Al-laminated composites.For the Al/Ti/Al-laminated composites subjected to cryorolling at-100 ℃,they have the highest strength near 260 MPa-this is 48 MPa and 41 MPa higher than the laminated composites subjected to cold and hot rolling,respectively.These results also show the strongest peeling strength.Finally,the mechanisms of the enhancement of bonding strength and mechanical properties of Al/Ti/Al-laminated composites subjected to cryorolling were mainly discussed.

An Al-3.6Cu-1Li alloy was subjected to room temperature rolling and cryorolling to investigate their effects on microstructure evolution and mechanical properties. The microstructure and aging characteristics of the room temperature-rolled and the cryorolled alloys with 70% and 90% of thickness reductions were studied by microstructure analysis and mechanical tests. The samples subjected to cryorolling with 90% of thickness reduction have high strength and good toughness. This is mainly due to the inhibition of dynamic recovery and the accumulation of high-density dislocations in cryorolled samples. In addition, the artificial aging reveals that the temperature at which peak hardness is attained is inversely proportional to the deformation amount and directly proportional to the rolling temperature. Moreover, bright field images of cryorolled samples after aging indicate the existence of T1 (Al2CuLi) precipitates. This suggests that the high stored strain energy enhances the aging kinetics of the alloy, which further promotes the nucleation of T1 phases.

Cu9Ni6Sn alloys were prepared by conventional casting (CC) and twin-roll casting (TRC). The CC-processed specimens possessed dendritic structures, and Sn was distributed mainly in the inter-dendritic region and formed dendritic segregation. The TRC-processed specimens were composed of equiaxed grains and a heterogeneous structure. The distribution of Sn showed gradient characteristics, with more Sn in the surface layer and less Sn in the center. The TRC-processed specimens had more inhomogeneous mechanical properties than the CC-processed specimens.

Laser remelting (LR) is a typical laser manufacturing technique. In this study, LR was used to fabricate gradient-structured CuNiBe alloy bars. A series of LR experiments with different parameters (such as the output power of the laser transmitter, scanning speed, and cooling condition) and subsequent aging treatments were designed. The remelted zone depth (RZD), the hardness with depth on the plane perpendicular to the LR track, the microstructure, and the precipitation characteristics of different zones of the remelted samples were analyzed. The results showed that the RZD increased with a higher output power of the laser transmitter and lower scanning speed. The hardness of the CuNiBe was significantly improved by the LR and subsequent aging treatment. A remelted zone (RZ) and heat affected zone (HAZ) were found in the remelted surface layer, and equiaxed substructures and columnar substructures were present in the RZ. Well-dispersed NiBe precipitates on the substructure boundaries in the transitional area between the RZ and HAZ were the main cause of strengthening of the sample that underwent LR without water-cooling. The strengthening effect was significantly enhanced by the refined grains for the sample that underwent LR with water-cooling.

The group-contribution (GC) methods suffer from a limitation concerning to the prediction of process-related indexes, e.g., thermal efficiency. Recently developed analytical models for thermal efficiency of organic Rankine cycles (ORCs) provide a possibility of overcoming the limitation of the GC methods because these models formulate thermal efficiency as functions of key thermal properties. Using these analytical relations together with GC methods, more than 60 organic fluids are screened for medium-low temperature ORCs. The results indicate that the GC methods can estimate thermal properties with acceptable accuracy (mean relative errors are 4.45%–11.50%); the precision, however, is low because the relative errors can vary from less than 0.1% to 45.0%. By contrast, the GC-based estimation of thermal efficiency has better accuracy and precision. The relative errors in thermal efficiency have an arithmetic mean of about 2.9% and fall within the range of 0–24.0%. These findings suggest that the analytical equations provide not only a direct way of estimating thermal efficiency but an accurate and precise approach to evaluating working fluids and guiding computer-aided molecular design of new fluids for ORCs using GC methods.

For most ultrafine-grained metals, the yield stress increases with finer grain size, but the thermal stability reduces. In this study, high purity (99.999%) copper sheets were fabricated using three different techniques: symmetric rolling, asymmetric rolling and asymmetric cryorolling. In each case, the sheets were annealed at a temperature ranging from 50 degrees C to 125 degrees C for 1 h. Their mechanical properties were tensile-tested using dog-bone samples, and their microstructure evolution was examined using electron backscatter diffraction and transmission electron microscopy. The results show that the asymmetric-cryorolled copper sheets have finer grains and higher tensile strength, and better thermal stability compared with the copper sheets subjected to symmetric rolling and asymmetric rolling and low-temperature annealing. The finer grains in copper sheets subjected to asymmetric cryorolling result from the additional shear strain and severe plastic deformation at low temperature. The improvement in the thermal stability may be due mainly to the vacancy clusters, small laminate thickness, low-angle grain boundary and high misorientation angle in asymmetric cryorolled samples. These results can provide significant insights into the development of ultrafine-grained metal sheets with both excellent mechanical properties and high thermal stability.

Cu/Al multilayers were produced by high-temperature accumulative roll bonding (ARB) methods up to three passes. To achieve a high bonding strength, prior to ARB processing, the Cu and Al sheets were heated to 350, 400, 450 and 500 °C, respectively. The mechanical properties were evaluated by tensile tests. The microstructure was examined by optical microscopy and scanning electron microscopy equipped with energy dispersive spectrometry. The ultimate tensile stress, the grain size and the thickness of diffusion layer of lamellar composites increase with rolling temperature. When the rolling temperature is 400 °C, the laminates show the highest ductility, but the yield stress is the lowest. As the rolling temperature further increases, both the yield stress and the ultimate tensile stress increase and the ductility decreases slightly. The mechanical properties of lamellar composites processed by low and high temperature ARB are determined by grain size and the thickness of diffusion layer, respectively.

The intercrystalline corrosion and exfoliation corrosion properties of 7A52 aluminum alloy were investigated at different aging temperatures and time using constant temperature immersion corrosion method,polarization curve measure,optical microscopy and transmission electron microscopy.The results show that intercrystalline corrosion and exfoliation corrosion sensibility of 7A52 aluminum alloy decrease gradually with the increase of aging temperature and time.Corrosion sensibility order from high to low at different aging temperature is as follows: nature aging,100 ℃ /24 h(under aging),120 ℃ /24 h(peak aging),150 ℃/ 24 h(over aging).Aging at 120 ℃,corrosion sensibility order from high to low is as follows: 120 ℃ /16 h(under aging),120 ℃ /24 h(peak aging),120 ℃/ 60 h(over aging).Corrosion sensibility of alloy is related to the characteristics of equilibrium phases(MgZn2) and precipitated free zone(PFZ) at grain boundaries.When grain-boundary equilibrium phases have reticulate or chain distribution,the corrosion sensibility of alloy is high.On the contrary,with the equilibrium phases discontinuous and PFZ widening,the corrosion sensibility of alloy decreases.

The microstructure and the chemical compositions in micro-zone of densified TiAl base alloy specimen manufactured from 1:1 Ti-Al mixture by reaction hot-pressing have been reviewed and analysed by using scanning electronic microscope.According to the distribution of Al element and composition range in various phases,it has been found that during the process of reaction between Ti and Al,four phases TiAl 3,TiAl,Ti3Al and α-Ti were firstly formed in original Ti particles. Then continuous reaction among these four solid phases was carried out.With the diffusion and homogenization of Al element,the TiAl3 and α-Ti phases which have been formed were eliminated.Finally,the microstructure was constituted by two phases TiAl and Ti3Al.