[en] In this research, the plane stress fracture toughness of ultra-fine grained aluminum specimens produced through accumulative roll bonding (ARB) process was investigated for the first time. The specimens were produced successfully by the ARB process up to 7 cycles with the amount of 50% thickness reduction in each cycle at room temperature without using lubricant. The fracture toughness was evaluated for the annealed and different ARB cycles using ASTM E561 standard and compact tension specimens. Additionally, mechanical properties, tensile fracture surfaces and crystallite size of ultra-fine grained aluminum ARBed specimens were evaluated by uniaxial tensile tests, microhardness measurements, scanning electron microscopy and X-ray diffraction. By increasing the number of the ARB cycles, fracture toughness was increased and the maximum value of this parameter was achieved in the last cycle, which was approximately 25.4 MPam^1/2 that it increased by 155% higher than the annealed specimen. Results of X-ray diffraction demonstrated that by increasing the number of the ARB cycles, crystallite size decreased so that it reached 175 nm for the 7th cycle ARBed specimen from 1341 nm for annealed samples. Furthermore, by increasing the number of the ARB cycles up to the 7th cycle, tensile strength and microhardness of ultra-fine grained aluminum increased to 232 MPa and 51VHN, respectively. At first, the value of elongation decreased and then increased. The SEM results showed that ductile fracture mode with large dimples occurring in the annealed specimen, changed to shear ductile fracture with elongated sophomoric shear and fine dimples after the ARB process.

[en] Negative ion formation following electron capture by mixed O₂/N₂ clusters was studied in a supersonic beam experiment. Inelastic electron scattering via the 2.3-eV negative ion state of N₂ greatly affects the formation of O₂^- and (O₂)₂^-. 21 refs., 4 figs., 1 tab

[en] In this article, the effect of the manufacturing process on the microstructure and mechanical properties of AA1050/Mg-AZ31B bilayer composite sheets has been studied experimentally. In multilayer composite sheets, the interface bond strength plays a significant role in the mechanical properties of the composite. The most important factor affecting the bond strength is the manufacturing process of these sheets. So, two processes of explosive welding and roll bonding have been used to manufacture the bilayer composite sheets. The results show that the atomic diffusion in the interface is 6.5 microns in the explosive welding and 6.7 microns in the roll bonding. No intermetallic compounds have been observed in the interface of the studied bonding methods. The wavy and straight interface morphologies have been observed for explosive welding and roll bonding, respectively. Also, recrystallization has been observed in the microstructure of both methods. In the magnesium microstructure of rolled sample, twinning and deformation bands have been seen, while adiabatic shear bands have been formed in the explosive-welded sample. The ultimate tensile strength, elongation, and work of fracture (WOF) of explosive-welded sheets have been increased by 145%, 31%, and 407% relative to the rolled sheets, respectively. Besides, considering the separation of layers in the tensile test of rolled sheets compared to explosive welded ones, it can be stated that the structural failure in explosive welding occurs simultaneously for all layers. However, for roll bonding, the layer failure is independent of the entire structure failure. In this case, first, necking and fracture of the magnesium layer occur, and then, after the separation of the interface, the fracture of the aluminum layer happens.

[en] The spectral line parameters of carbon dioxide have been measured in the laser band I (00011 ← 10001) centred at 10.4 μm. The spectra were recorded at room temperature using the spectroscopic instrumentation at the far-infrared beamline, Canadian Light Source, Saskatoon, Sask. The spectral line intensities, air- and self- broadened Lorentz half widths, and pressure induced shift coefficients were retrieved for 48 spectral lines using a multispectrum fit technique (Benner et al. J. Quant. Spectrosc. Radiat. Transfer, 53, 705 (1995)). Line parameters were retrieved using the Voigt and speed-dependent Voigt models. The deviations between our results and other results reported in the literature and in the HITRAN08 (Rothman et al. J. Quant. Spectrosc. Radiat. Transfer, 110, 533 (2009)) database were examined and discussed. The effect of errors in fitting channel spectra parameters was examined and found to be mitigated by the inclusion of channels in the multispectral fit. (author)

[en] In this contribution we compare the electron scattering processes observed in pure O₂ clusters and mixed clusters like O₂/Ne, O₂/Ar and O₂/N₂. The overlap and positions of the potential curves of O₂ states show the different possible electron attachment processes and also explain the formation of O₂ in clusters. (author)

[en] In this study, for the first time, the effect of applied strains and volume percentage of components of layered composite on the mechanical properties and fracture toughness of Al/Mg were investigated experimentally. The multilayered Al/Mg were produced by the accumulative roll bonding (ARB) process. For the investigation, three Al/Mg composites with different volume percentages (25%, 50%, and 66.6%Al) at different applied strains (0.8–3.2) were produced. The experimental evaluation included microscopic examination by optical microscope imaging, uniaxial tensile test, and plane strain fracture toughness. As the applied strain for all three composites increased, plastic instability in the magnesium reinforcement intensified, but due to the low thickness of the Al layers compared to the Mg layer, uniform structure of Mg distribution in Al for all three composite was not achieved. Also, by adding Al layers to the primary composite, a lower shear strain was applied to the magnesium reinforcement, and instability intensity in the reinforcement layer decreased. For this reason, as Al layers increased, plastic instability diminished. By raising the exerted strain, the values of tensile strength increased, and by adding Al layers, the elongation increased. The maximum amount of tensile strength and elongation for each composite was achieved in the same ARB pass (last pass) and the highest values of UTS and elongation were reached to 384.1 MPa and 1.95% for Al25%Mg, respectively. However, the highest amount of fracture toughness for each composite was obtained in the different exerted strains and the maximum value of 41.4 MPa·m^1/2 was achieved for Al33.3% in the third pass. The present phenomena indicated that many factors such as higher Mg volume with higher energy absorption, plastic instability, thickness ratio, plastic instability, and value of applied strain affected the fracture toughness. In summary, the relationship between fracture toughness with applied strain and also with volume percent of Al was not always straightforward. It depends on other factors, such as how the reinforcement was distributed, the thickness of the layers, the workability, and the addition of aluminum. Also, the applied strain has a more significant effect on increasing fracture toughness in multilayered composite if they cause a uniform distribution of reinforcement particles in the field or continuity in the reinforcement layer. (paper)

[en] In this article, for the first time, the forming limit diagram (FLD) and mechanical properties of aluminum foil samples processed by the accumulative roll bonding (ARB) process have been studied experimentally. For this purpose, thin aluminum foils with a thickness of 200 microns have been produced using ARB in five passes at ambient temperature. By rising the number of ARB passes, the ultimate tensile strength (UTS) enhanced drastically, and at the end pass of ARB, it reached 393 MPa, about 5.9 times larger than the initial sample. Also, during the ARB process, the applied strain increased, and the thickness of the layers decreased, and the bonding quality between layers improved. SEM images of tensile fracture surface after five cycles showed the mechanism of fracture retained ductile. However, due to the unevenly applied strain, the dimples were drawn in different directions, and their depth and number were reduced relative to the raw material. The area under the FLDs, a criterion of formability, declined sharply after the first pass and then increased at a low rate until the final pass. The trend of similar changes of formability in the tensile (elongation) and Nakazima tests (FLDs) was reported. Responsibility for all mechanical properties and ductility changes is related to the ARB process’s nature and the two dominant mechanisms of strain hardening and grain refinement. (paper)

[en] In this article, the mechanical properties, microstructure, forming limit diagram (FLD) and anisotropy of dual phase Mg-7Li–1Zn alloy have been evaluated by a uniaxial tensile test at three directions, scanning electron microscopy (SEM), optical microscopy (OM) and hemispherical punch test at ambient temperature. The optical microscopy images showed that the microstructure of as-cast LZ71 alloy possesses a dual phase microstructure such as β-Li matrix with body-centered cubic (BCC) structure and a partitioned α-Mg phase with hexagonal closest packed (HCP) structure in lath shape. After rolling process, the α-Mg phase has been elongated and arranged in the rolling direction and anisotropy at different directions increased, but after full annealing, microstructure arranged more uniform and changed from elongated to the uniform structure which this is the factor that reflects the reduction of anisotropy. FLD shows the limiting surface strains that sheet metal can endure before the start of localized necking and fracture at different deformation modes in tension-tension and tension-compression loading paths. The FLD of Mg–7Li–1Zn showed that this material has desirable formability due to the BCC structure with high slip system in the ambient temperature. Also, the results of the tensile test matched with the obtained FLD. Results of SEM revealed many dimples and some flat and cleavage planes. They showed the combination of ductile and brittle fracture, but the ductile fracture is the dominant fracture mechanisms for Mg–7Li–1Zn. In summary, in the dual phase, Mg–Li alloys via controlling the weight percent of lithium and other alloying elements can be achieved the desired mechanical properties and used for various applications. (paper)

[en] In this study, for the first time, fracture behavior and rupture energy absorption of Mg-Li alloys are evaluated. At the first, dual-phase Mg LZ71 and LZ91 alloys were melted at the temperature of 770 °C under argon atmosphere. After this, high plastic deformation was applied during a warm rolling process to prepare thin sheet from the initial ingot, for the present investigation. Fracture behavior and rupture energy absorption were evaluated through plane stress fracture toughness tests, extracted R-curve and calculated the area below force-displacement curves. Plane stress fracture test and compact tension (CT) were performed according to ASTM E-561 and E-399. Also, microstructure, mechanical properties, and fractography are evaluated using x-ray Diffraction (XRD), Optical Microscopy (OM), microhardness measurement, uniaxial tensile test and Scanning Electron Microscopy (SEM). The optical images and XRD analysis demonstrated that Mg-Li alloys possess a dual-phase microstructure containing β-Mg-Li matrix with Body Centered Cubic (BCC) and partitioned α-Mg phase with Hexagonal Closest Packed (HCP) structures. According to the OM images, HCP phase of as-cast specimens has been observed in lath shape and after rolling process, the α–Mg phase was elongated and arranged in the rolling direction. The results showed that increasing of the lithium mass portion from 7% to 9%, not only did not increase mechanical properties, absorbed energy and fracture toughness, but also all of them decreased. Moreover, results of XRD analysis depict that adding more Li into the alloys chemical composition did not cause to the formation of any new phases. Hence, the ultimate tensile strength, microhardness, absorbed energy and fracture toughness of Mg LZ71 were achieved 1.07, 1.06, 1.91 and 1.51 times higher than LZ91 respectively. Due to the dependence of fracture toughness on two significant parameters, namely strength and ductility, adding lithium into the composition will increase the value of fracture toughness with compared to AZ alloys, because of the fact that a significant increase in ductility compensates the reduced strength. Furthermore, SEM photographs of tensile fracture surfaces of as-rolled LZ71 and LZ91 samples displayed dimples and microvoids which are characterized as a ductile rupture mode. Thus, Mg-Li alloys had ductile fracture, which were consistent with the results of the tensile test. (paper)

[en] In the present work, the effects of annealing temperature on fracture toughness and anisotropy properties of Mg-Li alloys have been studied for the first time, comprehensively. To do this, two different annealing temperatures, including 200 °C and 350 °C, have been exerted on the produced sheets of LZ71 and LZ91 alloys. Also, microstructure observations, microhardness measurements, and phase analysis of the samples have been accomplished using optical microscopy (OM), vickers microhardness test, and x-ray Diffraction (XRD) analysis, respectively. Moreover, uniaxial tensile tests were accomplished to study the mechanical and anisotropy properties of the produced plates. Furthermore, to evaluate the fracture properties and observe the fracture behavior of the samples, the first mode fracture test and fractography have been carried out. From the OM photographs and XRD results, present Mg-Li alloys contain dual-phase microstructures including a partitioned lattice Hexagonal Closest Packed (HCP) structures of α-Mg phase spread in a Body Centered Cubic (BCC) matrix of β-Mg-Li. Calculated anisotropy coefficients demonstrated that r-values of as-rolled and annealed specimens of LZ71 were more than that of LZ91 in all directions. The results of performed fracture tests showed that the fracture toughness values of all samples of LZ71 were considerably more than that of LZ91 while the trends of the changes in fracture toughness of the alloys were not the same. In addition, in the present study, Response Surface Method (RSM) has been applied to fit a model between variables and responses. (paper)