Developing a friction-stir welding window for joining the dissimilar aluminum alloys AA6351 and AA5083

Abstract: In this study a welding window was constructed for the relatively new welding process of friction-stir welding (FSW) to join the 6-mm-thick dissimilar aluminium alloys AA5083-H111 and AA6351-T6. The dissimilar joints were fabricated using different combinations of tool rotational speeds and welding speeds. The effect of the process parameters on the macrostructure of the joints was analysed and reported. Established along with the macrostructural analysis, a welding window was made. These windows will act as reference maps for selecting the appropriate FSW process parameters to produce defect-free welds of dissimilar aluminium alloys

Studies on thermal hysteresis of KNO3 by thermo-Raman spectroscopy

[[abstract]]In this work, the polymorphic phase transformations of KNO3were studied by thermo-Raman spectroscopy in a dynamical thermal process with a heating rate of 5°C min−1 from 30°C to 170°C and then cooling down to 30°C at the same rate. Three distinct phase transformations were detected. The characteristic spectrum for each phase was identified. The nature of each phase transformation was investigated in detail through the studies on spectral variation, intensity, intensity variation and shift in band position. In addition, the intensity variation of the ν1 mode at 1042 cm−1 clearly revealed thermal hysteresis involved in the phase transformation of KNO3. Furthermore, the thermal hysteresis of each phase was also obtained from the ν3 mode in the range from 1341 to 1354 cm−1

Lithium ion conductivity of Li_5+x Ba _x La _3-x Ta₂O₁₂ (x∈=∈0-2) with garnet-related structure in dependence of the barium content

The stoichiometry range and lithium ion conductivity of Li5+x Ba x La3-x Ta2O12 (x∈=∈0, 0.25, 0.50, 1.00, 1.25, 1.50, 1.75, 2.00) with garnet-like structure were studied. The powder X-ray diffraction data of Li5+x Ba x La3-x Ta2O12 indicated that single phase oxides with garnet-like structure exist over the compositional range 0≤x≤1.25; while for x∈=∈1.5, 1.75 and 2.00, the presence of second phase in addition to the major garnet like phase was observed. The cubic lattice parameter increases with increasing x and reaches a maximum at x∈=∈1.25 then decreases slightly with further increase in x in Li 5+x Ba x La3-x Ta2O12. The impedance plots of Li5+x Ba x La3-x Ta 2O12 samples obtained at 33 °C indicated a minimum grain-boundary resistance (R gb) contribution to the total resistance (R b∈+∈R gb) at x∈=∈1.0. The total (bulk∈+∈grain boundary) ionic conductivity increases with increasing lithium and barium content and reaches a maximum at x∈=∈1.25 and then decreases with further increase in x in Li5+x Ba x La 3-x Ta2O12. Scanning electron microscope investigations revealed that Li6.25Ba1.25La 1.75Ta2O12 is much more dense, and the grains are more regular in shape. Among the investigated compounds, Li 6.25Ba1.25La1.75Ta2O12 exhibits the highest total (bulk∈+∈grain boundary) and bulk ionic conductivity of 5.0∈×∈10-5 and 7. 4∈×∈10-5 S/cm at 33 °C, respectively.</p

Lattice parameter and sintering temperature dependence of bulk and grain-boundary conduction of garnet-like solid li-electrolytes

The dependence of the bulk and grain-boundary lithium-ion conduction on the lattice parameter by substitution of trivalent La by divalent Mg, Ca, Sr, Sr0.5 Ba0.5, or Ba and monovalent Li in garnet-like Li5 La3 Ta2 O12, and the effect of sintering temperature were investigated. The ionic bulk conductivity increases with increasing ionic radius of the divalent alkaline earth ion and corresponding increased lattice parameter. An exception is Mg, which is too small for replacing La and forms a second phase. The lattice parameter is also found to increase with increased sintering temperature, except for the mixed Sr0.5 Ba0.5 substituted sample. The Ca, Sr, Sr0.5 Ba0.5, and Ba compounds show mainly bulk resistances with minor boundary contribution at room temperature, which decreases with increasing size of the alkaline earth ion. In contrast, the multiphase Mg-substituted sample exhibits an appreciable grain-boundary contribution to the total resistance. Microstructural investigations indicate the dependence of the grain-boundary resistance on the grain size, sinterability, and formation of transient or steady-state phase boundary compositions, which are caused by different chemical diffusion coefficients of the components. This is related to the higher conductivities of Li6 Mg La2 Ta2 O12 and Li6 Ba La2 Ta2 O12 annealed at 900°C compared to samples annealed at 950°C.</p