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The precipitation behavior and development of grain structure have been investigated to reveal their association with the microhardness and corrosion resistance of probeless friction stir spot welded (P-FSSW) joint of an Al–Li alloy. Results identified the primary strengthening phase of T1 (Al2CuLi) to be completely dissolved in the stir zone (SZ), while equiaxed grains were formed. Grain refinement was directly associated with the combined effect of continuous dynamic recrystallization and geometrized effect of imposed strain. However, as localized grain boundary bulging indicated, limited discontinuous recrystallization also participated in the microstructure evolution. The hardness dropped noticeably in the heat affected zone (HAZ) due to the weakening of precipitation and dislocation strengthening, which resulted from partial dissolution or coarsening of T1 phase and recovery effect. Grain refinement and solution strengthening were responsible for the slight increase in hardness of the SZ. In addition, the SZ had minute increased pitting resistance due to the homogenization of intermetallic particles, precipitate dissolution and refined grains.

The effect of tool morphology on the joint forming during probeless friction stir spot welding (P-FSSW) of an Al–Li alloy was evaluated with the assistance of experiments and numerical simulation. Compared to the flat tool, the surface temperature not only increased rapidly at the inner side of the shoulder periphery, but also locally appeared high value at the groove features using the tools with annular and involute profiles. In addition, the primary texture that developed during welding was determined to be a simple shear texture component of A/ A ¯ , followed by B/ B ¯ and A1∗/A2∗, with the occurrence of continuous dynamic recrystallization. Based on the texture development, the circumferential material flow remained predominant due to the shear acting of the rotation shoulder. Meanwhile, the radial inward flow also existed to a certain extent, promoted by the involute feature, which was beneficial to improve the material circulation to obtain an enlarged welding area. Nevertheless, higher rotation speed for a long time should be avoided in P-FSSW as the surface material was prone to be excessively squeezed out to form flash due to the excavation effect.

Synergetic double-sided probeless friction stir spot welding is a novel process proposed in this study, which is used to solve the contradiction between the improvement of metallurgical bonding and deterioration of hook defect. The effect of the coordinated movement of the tools on the joint formation was evaluated based on the coupled Eulerian-Lagrangian technique. By flexibly adjusting the welding parameters on both sides, the mechanical interlock caused by hook defect could be effectively regulated while significantly improving the metallurgical bonding, due to the enhancement of thermo-mechanical cycle along the thickness direction. According to the microstructure analysis, the interfacial evolution was ascribed to the combined effects of plastic deformation, material flow, atom diffusion, and recrystallization, as well as local abrasion. In addition, the microhardness profile exhibited a uniform distribution. Based on the above characteristics, the technology is expected to obtain higher strength joints, which will promote its applications in the manufacture fields.

We controllably synthesized CH3NH3PbBr3 quantum dots with a tunable spectrum with the emission peaks covering the range from green (523.6 nm), to blue and eventually to deep violet (432.9 nm), which is wider than that of quantum dots obtained without changing the halide component. The mechanism of photoluminescence spectral blueshift of CH3NH3PbBr3 quantum dots was investigated. The CH3NH3PbBr3 quantum dots with 5–30 μL n-octylamine showed an ideal color-saturated green emission and a narrow full width at a half-maximum of 19–24 nm. The photoluminescence quantum yielded up to 90.2%. All these properties indicate that these quantum dots can provide the effective data support for application to white LEDs, and may potentially be used as single-component multicolor-emitting materials, which can be applied to lighting and display technology.

A further acquaintance to surface SOM contents, especially the spatial pattern, can provide theoretical foundation for developing precision agriculture and reducing farming costs. In spite of high accuracy spatial distribution map of surface SOM contents by means of the common sampling method at present (Grid sampling method and Zone sampling method), long natural cycle and high demand for manpower and material resources bring down the guiding significance, let alone easily restricted by geographical location.