Wang Zhong-ren

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.

A comparison of the mesomechanism of dynamic deformation between copper and aluminum

Abstract In this paper, a comparison of the mesomechanism of dynamic deformation between Cu alloy and Al alloy is made. It is shown that, during dynamic deformation, two effects occur, one being a hardening effect by the increasing of dislocations, the other being a softening effect by the nucleation, growth and coalescence of microvoids. Fracture is due to the coalescence of a large amount of voids. It is shown also that the nucleation of microvoids is due to fault energy and second-phase particles. The nucleations of Al alloy rely on the second-phase particles and the nucleations of Cu alloy rely on the second slipping of dislocation by lower fault energy.