Papers by Author: Zhen Hua Chen

Abstract: Using tetrabutyltitanate as titanium source, amorphous TiO2 powder was firstly prepared by a sol–miniemulsion–gel method. Prepared powder was refluxed in basic solution and then calcined at different temperatures to synthesize titania nanofibers. The prepared samples were characterized by XRD, TG–DSC, FT–IR and TEM. The results show that when the heat–treatment temperature increases, crystallization of the titania nanofibers occurs with two Ti–OH bonds dehydrate, meanwhile morphology of the fibers is gradually obvious and ratio of length to diameter decreases. When the temperature was raised above 550 °C, titania nanofibers were sintered.

Abstract: Nano-particles of metal oxides Mn3O4, Cu2O, Fe3O4, the mixture of Zn(OH)2 and ZnO have been successfully prepared via a novel solid-liquid mechanochemical reaction technology. The metal powders are ground in water solutions using planetary ball mill. The solid-liquid reactions can occur on the surface of the powders and the reacted layer can be continuously peeled off during milling. The mean sizes of the as-prepared particles are approximately 20~100nm.The formation of nano-particles is attributed to the reactions between particles and solution as well as the repeated and quick peeling of the formed oxides on the surface of metal particles. Furthermore, the reaction rate and phase types of the products can be controlled by adjusting the pH value of the solution.

Abstract: In order to improve the formability of AZ31 magnesium alloy sheet at room temperature, a new process, so-called equal channel angular rolling (ECAR) and followed by annealing treatment was applied to process the sheet. The optical microstructure of the as-received sheet was similar with that of the ECARed one after annealing treatment, the Erichsen value and limiting drawing ratio of the ECARed sheet was about 6.26mm and 1.6, respectively, which was much larger than that of 4.18mm and 1.2 for the as-received sheet. These can be attributed to the low yield ratio and high strain hardening exponent due to the modified texture induced by the shear deformation during ECAR process, which is favor of the activations of basal slipping and twinning at ambient temperature, especially deforming at the rolling direction.

Abstract: In the present investigation, several novel techniques including sequential motion compaction, ceramic rolling and frame-confined rolling have been developed to improve the formability of spray deposited porous aluminum alloy preforms. The experimental results show that these techniques can greatly improve the workability of the spray deposited performs. Especially, sequential motion compaction can be used to densify the preforms of large dimensions which are difficult to further processing by the traditional techniques to fully dense.

Abstract: The evolution of SiC particle distribution in spray codeposition SiCp/7075Al composite during extrusion was investigated. A unique metallurgical pattern designated as ring- and band-pattern in the cross section of the extruded products occurred which comprises areas with higher and lower concentrations of SiC particles. The factors that contributed to the evolution of SiC particles distribution feather during plastic deformation were analyzed. The difference of flowability between the matrix and SiC particles was supposed to be the main factor accounting for the forming of the ring- and band-pattern. In addition, concentration difference of SiC particles between different deposition layers will also contribute to the forming of the ring- and band-pattern. A simple model was proposed to describe the evolution of SiC particle distribution during extrusion.

Abstract: A novel spray deposition technology with characteristic of the movable crucible, has been developed to prepare aluminum alloy and aluminum alloy matrix composite rings with large dimensions. The influences of process parameters on the microstructure and properties of the as-deposited rings were systematically investigated and the process parameters were optimized. Up to now, 7075Al/SiCp and A356/SiCp composite rings with the outer diameter of 1200mm, the inner diameter of 600mm and the thickness of 250mm, and LF6 aluminum alloy ring with the outer diameter of 3500mm, the inner diameter of 3100mm and the thickness of 250mm have been produced respectively. All the as-deposited performs were featured with the grain size about 3~5µm and a homogeneous distribution of ceramic particles the cooling rate up to 104K/s. Moreover, no cracking occurred in the performs because of the lower inner stress. The experimental results indicated that this novel technology was a promising and viable mean for the preparation of metal rings.