Post Deformation at Room and Cryogenic Temperature Cooling Media on Severely Deformed 1050-Aluminum

The annealed 1050-aluminum sheets were initially subjected to the severe plastic deformation through two passes of constrained groove pressing (CGP) process. The obtained specimens were post-deformed by friction stir processing at room and cryogenic temperature cooling media. The microstructure evolutions during mentioned processes in terms of grain structure, misorientation distribution, and grain orientation spread (GOS) were characterized using electron backscattered diffraction. The annealed sample contained a large number of “recrystallized” grains and relatively large fraction (78%) of high-angle grain boundaries (HAGBs). When CGP process was applied on the annealed specimen, the elongated grains with interior substructure were developed, which was responsible for the formation of 80% low-angle grain boundaries. The GOS map of the severely deformed specimen manifested the formation of 43% “distorted” and 51% “substructured” grains. The post deformation of severely deformed aluminum at room temperature led to the increase in the fraction of HAGBs from 20 to 60%. Also, it gave rise to the formation of “recrystallized” grains with the average size of 13 μm, which were coarser than the grains predicted by Zener–Hollomon parameter. This was attributed to the occurrence of appreciable grain growth during post deformation. In the case of post deformation at cryogenic temperature cooling medium, the grain size was decreased, which was in well agreement with the predicted grain size. The cumulative distribution of misorientation was the same for both processing routes. Mechanical properties characterizations in terms of nano-indentation and tensile tests revealed that the post deformation process led to the reduction in hardness, yield stress, and ultimate tensile strength of the severely deformed aluminum.     

Effects of Neodymium and Calcium on the Thermal Stability of AZ71 Magnesium Alloys

The effects of an addition of 0–2 wt% Nd on thermal stability of 0–3 wt% Ca-containing modified AZ71 magnesium alloys was investigated. The ignition temperature was found to increase from that of AZ71, 574, to 825 °C with the addition of 0.5 wt% Ca and 1 wt% Nd. The ignition temperature was further increased to 1114 °C when 3 wt% Ca was added. The Ca- and Nd-added AZ71 was isothermally maintained at a temperature of 500 °C in air for 12 h. The MgO–CaO–Nd₂O₃ formed on the surface to improve the thermal stability of the AZ71–xCa–yNd alloys. While both the tensile strength and ductility decreased with the Ca concentration in the alloy, an addition of 1 wt% Nd was found able to alleviate the degradation effects of Ca on the tensile strength and ductility at 170 °C. Both solid solution formation and precipitation strengthening contributed to the increase in toughness. AZ71 containing 0.5–2 wt% Ca and 1 wt% Nd provides the optimum combination of ignition resistance and mechanical properties.     

First Principle and Experimental Study for Site Preferences of Formability Improved Alloying Elements in Mg Crystal

Some alloying elements (Al, Er, Gd, Li, Mn, Sn, Y, Zn) were proved recently by calculations or experiments to improve the formability of Mg alloys, but ignoring their site preference in Mg crystals during the calculated process. A crystallographic model was built via first principle calculations to predict the site preferences of these elements. Regularities between doping elements and site preferences were summarized. Meanwhile, in the basis of the crystallographic model, a series of formulas were deduced combining the diffraction law. It predicted that a crystal plane with abnormal XRD peak intensity of the Mg-based solid solutions, compared to that of the pure Mg, prefers to possess solute atoms. Thus, three single-phase solid solution alloys were then prepared through an original In-situ Solution Treatment, and their XRD patterns were compared. Finally, the experiment further described the site preferences of these solute atoms in Mg crystal, verifying the calculation results.     

Matrix Transformation in Boron Containing High-Temperature Co–Re–Cr Alloys

An addition of boron largely increases the ductility in polycrystalline high-temperature Co–Re alloys. Therefore, the effect of boron on the alloy structural characteristics is of high importance for the stability of the matrix at operational temperatures. Volume fractions of ε (hexagonal close-packed—hcp), γ (face-centered cubic—fcc) and σ (Cr₂Re₃ type) phases were measured at ambient and high temperatures (up to 1500 °C) for a boron-containing Co–17Re–23Cr alloy using neutron diffraction. The matrix phase undergoes an allotropic transformation from ε to γ structure at high temperatures, similar to pure cobalt and to the previously investigated, more complex Co–17Re–23Cr–1.2Ta–2.6C alloy. It was determined in this study that the transformation temperature depends on the boron content (0–1000 wt. ppm). Nevertheless, the transformation temperature did not change monotonically with the increase in the boron content but reached a minimum at approximately 200 ppm of boron. A probable reason is the interplay between the amount of boron in the matrix and the amount of σ phase, which binds hcp-stabilizing elements (Cr and Re). Moreover, borides were identified in alloys with high boron content.     

Effects of Solution Treatment Temperatures on Microstructure and Mechanical Properties of TIG–MIG Hybrid Arc Additive Manufactured 5356 Aluminum Alloy

A novel additive manufacturing method with TIG–MIG hybrid heat source was applied for fabricating 5356 aluminum alloy component. In this paper the microstructure evolution, mechanical properties and fracture morphologies of both as-deposited and heat-treated component were investigated, and how these were affected by different heat-treated temperature. The as-deposited microstructure showed dominant equiaxed grains with second phase, and the size of them is coarse in the bottom region, medium in the middle region and fine in the top region owing to different thermal cycling conditions. Compared with as-deposited microstructure, the size of grain becomes large and second phases gradually dissolve in the matrix as heat-treated temperature increase. Different microstructures determine the mechanical properties of component. Results show that average ultimate tensile strength enhances from 226 to 270 MPa and average microhardness increases from 64.2 to 75.3 HV0.1 but ductility decreases from 33 to 6.5% with heat-treated temperature increasing. For all components, the tensile properties are almost the same in the vertical direction (Z) and horizontal direction (Y) due to equiaxed grains, which exhibits isotropy, and the mechanisms of these are analyzed in detailed. In general, the results demonstrate that hybrid arc heat source has the potential to fabricate aluminum alloy component.     

Reducing resistance and curing temperature of silver pastes containing nanowires

Low temperature silver pastes can be widely applied on thin-film switch, flexible printing line and touch screen. In this article, we investigated printability and conductivity of silver pastes with silver wires of different diameters and content, and the conductivity of the silver pastes cured at different temperatures filled with different types silver powders and silver wires. The sheet resistance of silver pastes cured at 100 °C with Ag1 powders and Ag2 powders filled with 10 wt% silver wires of 100 nm diameters is 21.93?±?1.63 and 23.16?±?1.44 Ω/□, which is lower than the same samples cured at 135 °C without silver wire fillers. Tap density of Ag1 and Ag2 powders mixed with silver nanowires is higher than that of Ag3 powders mixed with nanowires, due to a higher filling ratio of Ag1 and Ag2 powders with silver nanowires. SEM results show silver pastes filled with Ag1 and Ag2 powders formed network when silver nanowires were added.     

Oscillation Transition Routes of Buoyant-Thermocapillary Convection in Annular Liquid Layers

There are various oscillation transition routes of buoyant-thermocapillary convection in an annular liquid layer. Three types of transition routes including quasi-periodic bifurcation, period-doubling bifurcation and tangent bifurcation have been observed. In our ground experiments, the depth of liquid layer is in a range of 1.6–2.4 mm. The silicone oil with Prandtl number of 28.6 is selected as the liquid medium. The temperature oscillation is detected by a single-point temperature measuring system and the surface oscillation is measured by a laser displacement-sensor with high resolution. The step-heating mode is adopted in the experiments. Transition routes of temperature oscillation and surface oscillation are studied systematically, and the relationship between them is discussed, too.     

A performance evaluation of a fault-tolerant path recommendation protocol for smart transportation system

Recommending traveling vehicles to take a certain path towards their targeted destinations have received great interest recently. At the downtown area several paths can lead to the same located destination, this is due to the grid-layout architecture of modern downtowns. Drivers always wish to reach their destinations as fast as possible and without traveling drastically long distance or without consuming extra fuel. The best path towards any destination is determined based on the relative location of the vehicle from its destination and based on other vehicles traffic distribution on the road network. Although numerous studies have investigated this issue over the road network, the communication failures and their effects on the obtained path have been neglected in those previous studies. In this paper, we investigate these potential faults and their effects on the correctness of the selected paths. We then proposed a new protocol to tackle these potential failures while selecting the best path towards each destination over the road network, fault tolerant path recommendation protocol (FT-PR). From the experimental results, we can see that the FT-PR protocol has a higher success ratio than previous path recommendation protocols, such as ICOD. This is demonstrated by obtaining paths with shorter traveling time and shorter traveling distance. The FT-PR protocol also eliminates extra loops over the road network in each selected path.     

Internal structure visualization of flow and flame by process tomography and PLIF data fusion

To address the increasing demands on pollution control and energy saving, the study of low-emission and high-efficiency burners has been emphasized worldwide. Swirl-induced environmental burners (EV-burners), have notable features aligned with these requirements. In this study, an EV burner is investigated by both an ECT system and an OH-PLIF system. The aim is to detect the structure of a flame and obtain more information about the combustion process in an EV burner. 3D ECT sensitivity maps are generated for the measurement and OH-PLIF images are acquired in the same combustion zone as for the ECT measurements. The experimental images of a flame by ECT are in good agreement with the OH radical distribution pictures captured by OH-PLIF, which provide a mutual verification of the visualization method.