Mechanical properties and interfacial characteristics of 6061 Al alloy plates fabricated by hot-roll bonding

This work aims to investigate the mechanical properties and interfacial characteristics of 6061 Al alloy plates fabricated by hotroll bonding(HRB)based on friction stir welding.The results showed that ultimate tensile strength and total elongation of the hot-rolled and aged joints increased with the packaging vacuum,and the tensile specimens fractured at the matrix after exceeding 1 Pa.Non-equilibrium grain boundaries were formed at the hot-rolled interface,and a large amount of Mg_(2)Si particles were linearly precipitated along the interfacial grain boundaries(IGBs).During subsequent heat treatment,Mg_(2)Si particles dissolved back into the matrix,and Al_(2)O_(3) film remaining at the interface eventually evolved into MgO.In addition,the local IGBs underwent staged elimination during HRB,which facilitated the interface healing due to the fusion of grains at the interface.This process was achieved by the dissociation,emission,and annihilation of dislocations on the IGBs.

Excellent thermal stability and high energy storage performances of BNT-based ceramics via phase-structure engineering

Herein,a novel strategy for regulating the phase structure was used to significantly enhance the recoverable energy storage density(Wrec)and the thermal stability via designing the(1-x)[(Bi_(0.5)Na_(0.5))_(0.7)Sr_(0.3)TiO_(3)]-xBiScO_(3)((1-x)BNST-xBS)relaxor ferroelectric ceramics.The incorporation of BS into BNST ceramics markedly increases the local micro-structure disorder,causing a high polarization and inhibiting polarization hysteresis for 0.95BNST-0.05BS ceramics,leading to a large Wrec of 5.41 J/cm^(3)with an ideal efficiency(h)of 78.5%.Meanwhile,transmission electron microscope(TEM)results further proved that the nano-domain structure and the tetragonal(P4bm)phase superlattice structure of 0.95BNST-0.05BS ceramics possess an excellent thermal stability(20-200℃).An outstanding Wrec value of 3.18×(1.00±0.03)J/cm^(3)and an h value of 74.500±0.025 are achieved under a temperature range from 20℃to 200℃.This work provides a promising method for phase-structure design that can make it possible to apply temperature-insensitive ceramic dielectrics with a high energy storage density in harsh environments.

Structure and magnetostriction of high Pr/Ce-content(Tb_(0.2)Pr_(0.8))_(1-x)Ce_(x)Fe_(1.93) Laves compounds

The light rare earth Pr/Ce-contained(Tb_(0.2)Pr_(0.8))_(1–x)Ce_(x)Fe_(1.93)(0≤x≤1.0)intermetallics were arc melted and magnetoelastic properties were investigated.The compounds of x≥0.40 are found to stabilize at ambient pressure in a single Laves phase with MgCu2-type C15 structure,which is attributed to the strong Ce 4f bonding.The mixed-valence behavior,with a support of the deviation from the linear Vegard’s law for both lattice parameter a and saturation magnetization M_(S),is observed at room temperature.The easy magnetization direction(EMD)was determined by the analysis of XRD on both magnetically aligned samples and the(440)splitting,that is,EMD lies toward<111>axis for x≤0.50 rotating to<110>for x=0.60,accompanied with the structural distortion from rhombohedral to orthorhombic.The substitution of Ce for Tb/Pr is conductive to the reduction of magnetocrystalline anisotropy,giving rise to an improvement of the low-field magnetostriction.The excellent magnetoelastic properties can be tailored by the Ce introduction,e.g.,the spontaneous magnetostriction coefficient λ_(111) as large as 1150×10^(−6) for x=0.40,and the low-field induced magnetostriction achieving a high value of λ_(a)=180×10^(−6) at 80 kA/m for x=0.60.The excellent magnetoelastic properties and the combination in high Pr-content with low cost,suggest promising prospects in applications.

Microstructure,magnetic domain and dynamic loss of surface-textured Fe-based nanocrystalline alloy

Heterogeneous coarse surface crystallites induced in the industrial Fe-rich nanocrystalline alloy is an obstacle for high-frequency and high-power commercial applications.Herein,the phase,crystal orientation,nanostructure and magnetic domain evolution of the surface-crystallized Fe-rich alloy were systematically investigated.Microstructure and inverse pole figures analysis confirms that the DOordered dendriticcrystallites bear<001>-oriented fiber texture before and after annealing at the free surface,while ultrafine nanocrystals are randomly oriented in the interior and wheel surface after annealing.As compared to zero magnetic-field-annealing,the transverse magnetic-field-annealing induces weakly oriented fiber texture and relatively uniform dendritic-crystallites at the surface,and uniform anisotropy in the interior and surface,which promotes smooth wall motion at the surface and magnetization rotation in the interior.This synergetic effect reduces the excess loss and leads reduction in dynamic loss at 1.0 T and10 kHz by 36%.

Parameter identification of interconnected power system frequency after trip-out of high voltage transmission line

Accurate modeling and parameters of high voltage （HV） grid are critical for stability research of system frequency. In this paper, simulation modeling of the system frequency was conducted of an interconnected power system with HV transmission lines in China. Based on recorded tripping data of the HV transmission lines, system parameters were identified by using genetic algorithm （GA）. The favorable agreement between simulation results and recorded data verifies the validity of gird models and the accuracy of system parameters. The results of this paper can provide reference for the stability research of HV power grid.

Polypyrrole random-coil induced permittivity from negative to positive in all-organic composite films

Percolating composites with negative permittivity can be promising candidates for metamaterials.Herein,novel all-organic composite films containing of random coil polypyrrole(PPy)and poly(-vinylidene fluoride)(PVDF)are fabricated via a solution casting method.The random coil PPy is prepared by oxidative template assembly approach for the first time.The experimental result indicates that the negative permittivity is easily adjusted through controlling the random coil PPy contents.Especially,the random coil PPy contents exceeded 7 wt% the negative permittivity appear attributed to the formation of 3D interconnected PPy network.This facile approach not only opens a new way to preparing negative permittivity of all-organic composite films,but also points out a route to facilitate the practical applications of metamaterials.