Wang Erde

Hydrogen absorption and desorption characteristics of mechanically milled Mg35wt.%FeTi1.2 powders

Abstract Mg35wt.%FeTi1.2 hydrogen storage materials were made by mechanical milling of mixed elemental magnesium and FeTi1.2 alloy powders. The hydrogen absorption and desorption characteristics of powders milled for various times were evaluated. The results show that the PCT characteristics, hysteresis, plateau pressure, storage capacity, and hydriding and dehydriding rates change substantially with increasing milling time. Mechanical milling produces fine powder with nanometer-sized grains and large microstrain, which results in an increase in the hydriding and dehydriding rates.

Fabrication and mechanical properties of SiCw/ZK51A magnesium matrix composite by two-step squeeze casting

A modified squeeze casting process, two-step squeeze casting, was proposed for fabrication of metal matrix composites (MMCs), and SiCw/ZK51A magnesium matrix composite was fabricated by this new technique. The mechanical properties of the composite were investigated by means of tension test, and the microstructure and fracture surface were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. It was revealed that the two-step squeeze casting is an effective route for fabrication of magnesium matrix composites. The SiCw/ZK51A composite fabricated by this new technique possesses very high modulus and mechanical strength as compared with the unreinforced matrix alloy, with the increment in modulus and 0.2% offset yield strength of the composite being linearly proportional to the whisker volume fraction. The optimal casting temperature for the fabrication of the SiCw/ZK51A composite was found to be about 760°C. Furthermore, no evidence of any interfacial reaction was found in the SiCw/ZK51A composite, attesting that SiC whiskers are very stable reinforcements for magnesium matrix composites.

Hydrogen storage properties of the Mg–Ni–CrCl3 nanocomposite

The effects of the addition of the transition metal chloride CrCl3 on the hydriding and dehydriding behavior of Mg–3 wt.% Ni hydrogen storage material were investigated. The characteristics of the ball-milled nanocomposite Mg–3 wt.% Ni–1CrCl3 such as hydriding capacity in the ball-milling process and the kinetics of hydriding/dehydriding were examined. The hydrogen absorption capacity of the composite is greatly increased in the ball-milling process under hydrogen pressure (0.5 MPa). The absorption rate of the composite is fast and the hydrogen storage capacity is more than that of the sample without CrCl3.

Thermal stability and mechanical properties of mechanically alloyed Al-10Ti alloy

The mechanical properties of Al-10Ti alloy prepared by mechanical alloying and subsequent hot hydrostatic extrusion were evaluated at room and elevated temperatures. Transmission electron microscopy was used to characterize the microstructural changes of this alloy on heat treatment at 500 °C for various times. The results show that the mechanically alloyed Al-10Ti has high strength and high thermal stability at elevated temperature. The strength and stability of this alloy are attributed to its fine grain size and to the high volume fraction of small Al3Ti intermetallic compounds dispersed in the aluminium matrix. After 50 h annealing at 500 °C, no serious coarsening of either the Al3Ti dispersoids or the grains was observed.

Hot hydrostatic extrusion and microstructures of mechanically alloyed Al4.9Fe4.9Ni alloy

Abstract Mechanical alloying has been used to synthesize Al4.9Fe4.9Ni powders from mixed elemental aluminum, iron and nickel powders, the mechanically-alloyed powders being consolidated by hot hydrostatic extrusion. The mechanical properties of the extruded rod were measured, and microstructures of the consolidated materials were investigated by X-ray diffraction and TEM analysis. The results show that the tensile strength increases and the elongation decreases with the increasing of the milling time, which results from the reduction of the grain size and the increasing of the volume fraction of particles in the aluminum matrix as the milling time increased. Alloys of extruded 14 h-milled powders show good strength at both room and elevated temperature. The extrusion temperature, extrusion ratio and lubricant have great effects on the properties. A mixture of graphite and glass powders as lubricant can prevent the oxidization of a cold compacted billet when the billet is clad with this lubricant before heating, the consolidated materials showing no obvious oxidation.

Structural change of rapidly solidified 2024 aluminium alloy powders in mechanical milling and subsequent consolidation process

Abstract Rapidly solidified 2024 aluminium powders were mechanically milled, and then consolidated by vacuum hot-pressing and hot hydrostatic-extrusion. The grain-growth and phase-separation behaviors during the consolidation process were studied by X-ray diffraction and TEM observation. The results show that mechanical milling (MM) produces a supersaturated solid solution with a fine microstructure of nanometer-sized grains. In the consolidation process, the grain size increased, and Al 2 Cu and Al 2 (Cu, Mg, Si, Fe, Mn) intermetallic-phases precipitated. A deformation-enhanced grain growth behavior was observed. Vacuum hot-pressing results in more obvious grain growth than simple annealing does, and hot hydrostatic-extrusion results in more serious grain-size coarsening than hot pressing does.

Effects of ball-milling intensity on the amorphization rate of mixed Ni50Ti50 powders

Abstract Mixed elemental Ni50Ti50 powders were milled in an attritor ball mill, the structural changes of the milled powders being monitored by X-ray diffractometer (XRD) and scanning electron microscope (SEM). The effects of the rotational velocity and the ratio of the total ball volume to the tank volume on the layer thickness of the laminated structure and the crystallite size of the nickel crystals as a function of milling time under different ball milling conditions were determined, and the relationships of the layer thickness, the crystallite size and the amorphization time with the power inputted were measured. The results show that the greater the power inputted, the less the layer thickness and crystallite size are, and the less amorphization time is needed to obtain a fully amorphous phase.

Optimization analysis on gap size of molding for Pb-GF composite wire

Under the condition of equal flow, the maximum and minimum theoretical values of gap size were studied and an estimation equation was established for the clad extrusion of the brittle core cladded by plastic metal materials. The results show that the gap size is a key parameter for the continuous clad extrusion and the molding speed. Its maximum value (Hmax) is 0.24 mm and the minimum one (Hmin) is 0.12 mm. At a gap size of 0.18 mm, the maximum of metal extrusion per unit of time and the optimal coating speed can be obtained.