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The friction stir weldability of a fine-grained high strength AZ31B magnesium alloy to A5083 Al alloy was evaluated at various welding conditions, by using a tool with shoulder diameter of 15 mm, pin diameter of 5 mm and pin length of 3.9 mm. A square butt dissimilar joint without any defect was obtained at the condition of welding speed 100 mm/min, tool rotating speed 500 rpm and offset 0 mm. Higher or lower welding speeds or rotating speeds led to either the formation of defect or lack of bonding in the joint. Defects occurred also in the case that the offset was not 0 mm, i.e. the insertion position of the probe was on either Mg side or Al side, when tool rotating speed was 500 rpm and welding speed was 100 mm/min. The maximum tensile strength of the dissimilar joints in the present study was about 115 MPa, lower than that of Al alloy base metal (about 308 MPa). Transmission electron microscopy showed that an intermetallic compound (IMC) layer, which consisted of Al 12 Mg 17 and Al 3 Mg 2 , formed at the bonding interface of the joints, and it was found that the formation and growth of the IMC were controlled by the react diffusion of Mg and Al atoms, instead of the eutectic reaction. The present study demonstrated that the tensile strength of the dissimilar joints was mainly affected by the thickness of IMC layer and the mechanical interlock between magnesium and aluminum alloys. The tensile strength decreased remarkably with the increase in the thickness of IMC layer, which made the mechanical interlock weaker.

Crystal structures of polymorphs of 2-(2'-hydroxyphenyl)benzimidazole (HPBI), Forms α and β, are analyzed by X-ray crystallography. The fluorescence excitation (FE) and fluorescence spectra of the polymorphs are separately observed at temperatures 77-298 K. It has been found that the electronic spectra of the two crystal forms are significantly different from each other. Photo-excitation of the enol forms in Forms α and β induces the excited-state intramolecular proton transfer (ESIPT) to produce the S(1) state of the keto forms. In the FE spectra of Forms α and β, the S(1) ← S(0) (ππ*) transition of the keto form is observed in the 360-420 nm region in addition to that of the enol form in the 250-420 nm region. In the FE spectrum of Form β a new band peaking at 305 nm is observed, which is assigned to the S(1) ← S(0) transition of a non-planar enol form based on the observation of dual fluorescence in the UV and visible regions and quantum chemical calculation on the transition energy against the twisted angle between the benzimidazole and hydroxyphenyl rings. The fluorescence quantum yield (φ(T)) for the keto form is remarkably dependent on polymorphs at room temperature; φ(T) = 0.53 for Form α is much larger than φ(T) ≤ 0.23 for Form β. At 77 K the φ(T) values for Forms α and β increase to 0.67 and ≤0.57, respectively. The changes in the φ(T) values are associated with the intramolecular charge transfer (ICT) state. The potential barrier height between the S(1)-keto and S(1)-ICT states is significantly lower for Form β than for Form α. At 77 K the S(1)-keto → S(1)-ICT process followed by S(1)-ICT → S(0)-keto internal conversion is significantly suppressed in Form β. We compare difference in the dynamics between Forms α and β in the electronic ground and excited states.

Infrared photodissociation spectra of [aniline-(H 2 O) n ] + (n = 1-8) are measured in the 2700-3800 cm-1 region. The spectra are interpreted with the aid of density functional theory calculations. The n = 1 ion has an N-H•••O hydrogen bond. The spectrum of the n = 2 ion demonstrates a large perturbation to both of the NH oscillators, indicating the 1-1 structure where each NH bond is bound to a water molecule. For the n = 3 ion, the calculated spectrum of the 2-1 branched structure coincides well with the observed one. For the n = 4 ion, there exist three strong bands at 2960, 3100, and 3430 cm-1 , and a very weak one at 3550 cm-1. The observed spectrum in the 3600-3800 cm-1 region is decomposed into four bands centered at 3640, 3698, 3710, and 3734 cm-1. The 2-2 branched isomer is responsible for all the features except the 3550 and 3710 cm-1 bands. These two bands are due to another isomer with a five-membered ring. An infrared band characteristic of the n = 5 ion appears at 3684 cm-1 , which is not seen in the spectra of the n = 1-4 ions. This band is indicative of a ring structure and assigned to the free OH stretching vibration of the three-coordinated (double-acceptor-single-donor