稀有金属材料与工程最新文献

Due to the excellent electrical conductivity and mechanical properties, Al/Pb-Ag alloy has a great potential to be used as an alternative anode for zinc electrowinning. In this work, the effects of Ag content and surface plating with β-PbO₂ on the anodic behavior and reaction kinetics were investigated by cyclic voltammetry (CV), anodic polarization curves, electrochemical impedance spectroscopy (EIS) and corrosion rate test. The phase composition and microscopic morphology of the anode oxide layers after electrolysis were observed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results indicate that high content of silver and electroplating β-PbO₂ layer can increase the oxygen evolution activity, electrocatalytic activity and corrosion resistance of the anodes. Al/Pb-0.75%Ag plating β-PbO₂ has the lowest oxygen evolution overpotential followed by Al/Pb-0.3%Ag plating β-PbO₂, Al/Pb-0.75%Ag and Al/Pb-0.3%Ag. Besides, high content of silver is more beneficial to improving corrosion resistance compared with electroplating β-PbO₂ on anode. In addition, the phase composition of four anodes layer are mainly composed of α-PbO₂, β-PbO₂, Pb and PbO.

The effect of cold deformation and aging on the microstructure and properties of Cu-3Ti-2Mg alloy was investigated. The microstructure and phase constituents were characterized by optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD), transmission electron microscope (TEM) and electron backscattering diffraction (EBSD), and the hardness and electrical conductivity were measured as well. The results show that the microstructure of as-cast Cu-3Ti-2Mg alloy consists of Cu₂Mg phase, plate-like Cu₄Ti phase and Cu matrix. The microstructural characterizations reveal that the βprime;-Cu₄Ti phase precipitates from the supersaturated Cu matrix during aging. However, excessive aging causes the phase transformation from metastable, coherent βprime;-Cu₄Ti to equilibrium, incoherent Cu₃Ti phases. In the range of experiments, the optimum process for Cu-3Ti-2Mg alloy is solutizing at 700 °C for 4 h, cold deformation of 60%, and aging at 450 °C for 2 h. The electrical conductivity and hardness HV of Cu-3Ti-2Mg alloy are 16.7 %IACS and 3280 MPa, respectively.

A new kind of grain refiner Al-5Nb-RE-B master alloy with uniform microstructure was prepared by melt reaction method. The effect of Al-5Nb-RE-B inoculation on grain refinement of A356 aluminum alloy was studied. The results show that the Al-5Nb-RE-B master alloy consists of α-Al phase, Al3RE, Nb2Al20RE, and NbB2 phases. When the prepared Al-5Nb-RE-B master alloy was added in an amount of 1.0 wt%, the grain size of the A356 alloy was reduced from 800 μm to 200 μm. Analysis of the A356 alloy solidified at a wide range of cooling rates indicate that 1.0 wt% Al-5Nb-RE-B inoculation exhibits the lowest sensitivity to cooling rate.

The effects of cold rolling reduction and annealing temperatures on the formation of cube texture and microstructural evolution have been investigated in Cu-44%Ni alloy. The results show that the recrystallized cube texture is strengthened by either increasing the rolling reduction or increasing the annealing temperature. And the strong cube texture can be observed for the severely cold-rolled (>90%) alloy after annealing at high temperature (>900 °C). Furthermore, high-angle grain boundaries (HAGBs) and annealing twin boundaries (Σ3 boundaries) decrease with the increase of rolling reduction. However, during isochronal annealing, the trend of Σ3 boundaries is consistent with that of HAGBs, which firstly increases during recrystallization process and then decreases with further increasing temperature. After annealing at 1100 °C for 1 h, the 99% cold-rolled Cu-44%Ni alloy obtains the fraction of the cube texture 99.8%, and the fractions of HAGBs and Σ3 boundaries are 2.5% and 1.3%, respectively.

Influence of the strain rate on microstructures, tensile properties and strain hardening behavior of the electron beam welded joint of TC18 titanium alloy under optimized welding parameters was investigated with three slices (top, middle and bottom). The results show that the welding leads to significant microstructural changes across the joint. The microstructure of fusion zone is composed of coarsened β phase and secondary α-phase. Compared with the base metal, the joint slices along the thickness exhibits a lower strength and plasticity but a further higher hardening capacity. The strength and ductility of the bottom slices are higher than those of the middle and top slices. The maximum yield strength and ultimate tensile strength of the welding slices reach 83% of those of the base metal at the strain rate of 1×10⁻² s⁻¹ . The hardening capacity of welding slices decreases with increasing of the strain rate. Tensile fracture occurs in the weld zone. The fracture process of the top slice is cleavage fracture. However, the middle and bottom slices are quasi-cleavage crack.

Interfacial reactions and growth kinetics between molten Mg-40Al and solid Mg-20Ce were investigated. Reaction temperatures were 475, 500 and 525 °C, with reaction time ranging from 5 to 30 min. The results show that Al₁₁Ce₃, Al₃Ce and Al₂Ce are formed via the reaction of Al and Ce in the diffusion reaction layers. The volume fraction of the intermetallic compounds in the diffusion reaction layers increases with temperature increasing. The growth kinetics of the diffusion reaction layers well conform to the parabolic law. The activation energy for the growth of the diffusion reaction layers is (42±3.7) kJ/mol. Liquid-solid diffusion experiment helps to better understand the formation of compounds in the smelting process. Kinetics data are provided for the formation of the compound during the smelting process.