Zhenlun Song

Effects of viscosity on cellular structure of foamed aluminum in foaming process

The effects of melt viscosity on the foaming process and the structures of foamed aluminum have been examined. Methods for measuring the melt viscosity, pore structure, and foaming process are introduced. To increase the stability of the foaming melt and get the sample with a uniform pore distribution, a proper viscosity is needed. Further, the structure of foamed aluminum can be controlled by adjusting the Ca addition and other process parameters.

Evolution of foamed aluminum structure in foaming process

This paper presents a method for determining the relations between the height of foaming aluminum melt and the foaming time in the foaming process. Based on image analysis, the effects of the foaming time on the pore size distributions in the foamed aluminum samples are studied. Dynamic models are used to explain the evolution of the structure of the melt foam in the foaming process.

Fabrication of closed cellular nickel alloy containing polymer by sintering method

Abstract A cellular solid of a Ni–P alloy containing polymer for passive damping was fabricated by sintering methods using a spark plasma sintering (SPS) system. The mechanical and damping properties of this material were measured. The obtained results showed that this cellular structural solid of Ni–P alloy containing polymer has a high capacity for damping.

Low frequency damping properties of Cu-Al-Be alloy during the phase transformation

Abstract The damping properties of Cu–Al–Be alloys are investigated by measurement of internal friction (IF). The IF and its dependence of the measuring frequency and amplitude during temperature variation and under isothermal condition are investigated by means of an inverted torsion pendulum. The IF peak associated with the martensitic transformation and the change of the sub-structure in the low temperature phase are obtained in a Cu–Al–Be alloy. Based on the dependence of measuring frequency and temperature rate, the mechanism of IF peaks are discussed.

Nanolayered manganese oxides: insights from inorganic electrochemistry

Nanolayered Mn oxides are among the important Mn-based catalysts for water oxidation. Mn(II), (III) and (IV) ions are present in the structure, and, thus, the electrochemistry of the solid is very complicated. Herein, the cyclic voltammetry of nanolayered Mn oxides in the presence of LiClO4 at pH = 6.3, under different conditions, was studied using scanning electron microscopy, transmission electron microscopy, electrochemical impedance spectroscopy, X-ray diffraction and visible spectroelectrochemistry. The scan rates, calcination temperatures and the range of the cyclic voltammetry have very important effects on the electrochemistry of nanolayered Mn oxides. The effect of the use of D2O instead of H2O on the electrochemistry of nanolayered Mn oxides was also considered. Such nanolayered Mn oxides were reported as water-oxidizing catalysts in the presence of cerium(IV) ammonium nitrate. As a next step, we studied the cyclic voltammetry of nanolayered Mn oxides under acidic conditions and in the presence of cerium(IV) ammonium nitrate.

Influence of magnetic fields on cobalt electrodeposition

Abstract Magnetic fields parallel to electrodes were introduced during plating process to prepare cobalt films from baths without additives. Effects of magnetic intensities on the nucleation process, electrochemical mechanism and surface morphology were investigated. It was found that limiting current and deposition mass increased gradually with the rise in magnetic intensities. Magnetohydrodynamic phenomenon (magnetic fields can induce currents in a moving conductive fluid, which in turn creates forces on the fluid and also changes the magnetic field itself) caused by Lorentz forces could agitate to decrease thickness of diffusion layers, which contribute to the increase in deposition rate. Reduction of cobalt on copper substrates without magnetic fields showed instantaneous nucleation process. However, cobalt reduction with 1 T magnetic intensity deviated from instantaneous nucleation process as a result of micromagnetohydrodynamic (micro-MHD) flows. Films of smaller grain size and compact surface could be obtained under 1 T magnetic intensity as a result of MHD effects.

Evolution and effects of surface degradation layer of Sm2Co17 magnets at high temperatures

The long-term application of SmCo-based magnets at high temperatures has been restricted by the irreversible loss of magnetic properties. In this work, degradation behavior of Sm2Co17 magnets was studied at 500 °C in air and vacuum by being focused on the surface degradation layer. The structure and the composition of the degradation layer were studied experimentally, and the magnetization was calculated to certify the deduction of the irreversible loss. The soft magnetic phases in the degradation layer can result in the decline of the magnetization and the irreversible loss of magnetic properties. Furthermore, the controversial formation reason of the degradation layer was also studied. It was found that the diffusion of the oxygen, but not the sublimation of Sm, could be the dominant formation reason of the degradation layers.

Fabrication of Ni-P alloy closed cellular solid containing polymer by the pulse current hot pressing technique

Phenol resin sphere particles covered with nickel-phosphorus alloy were used for fabricating a metallic cellular solid with a fine structure by using the pulse current hot pressing (PCHP), which is also called spark-plasma-sintering (SPS) technique. During the sintering process, strong electric current pulses were applied on the particles in a die. The particles in the die were sintered in a shorter time and at lower temperature than that of normal sintering methods. The polymer materials inside the cells seem to remain partly after the sintering process. The mechanical properties of the cellular materials containing phenol resins were measured. The influence of the PCHP process on the mechanical properties of the specimens was examined.

Development of metallic closed cellular materials containing organic materials

Abstract A metallic closed cellular material containing organic materials for damping systems has been developed. Powder particles of polystyrene coated with a nickel–phosphorus alloy layer using electroless plating were pressed into green pellets and sintered at high temperatures in a vacuum. A metallic closed cellular material containing organic materials was then fabricated. The density of this material is lower than that of other structural metals. Compressive tests and ultrasonic measurements were carried out to measure the mechanical and ultrasonic properties of this material, respectively. The results showed that this material had different stress–strain curves among the specimens that had different cell wall thicknesses, each stress–strain curve had a long plateau region, the sintering temperatures of the specimens affect the compressive strength of each specimen, and energy absorbing capacity is very high. The internal friction of this material measured by the half width method is very high. These results indicate that this metallic closed cellular material can be utilized as an energy absorbing material and passive damping material.

Phase-transformation-induced hardening in Zn–22Al alloys

A phase-transformation-induced hardening effect is reported in Zn–22Al (Al: 22 wt.%) alloys. The Zn–22Al specimens were held at 300 °C for 10 h and then quenched in water. A hardening effect took place in subsequent artificial aging at 100–200 °C, which was accompanied by a phase decomposition of a soft α 2 phase and a grain coarsening. The phase-transformation-induced hardening affects the hardness more than the grain-coarsening-induced softening, which leads to the age-hardening phenomenon.