Papers by Author: Hong Ge Yan

Abstract: AZ91 alloy powder was prepared by two-roller quenching equipment. The powders were consolidated and extruded into bar. The microstructures of the powders and bars were observed by optical microscope (OM), XRD, HRTEM and SEM. The results suggested that the grain size of the powder were equiaxed with the sizes of about 1~5μm. The as-extruded alloy bars retain equiaxed grains with a large number of precipitated phases, β-Al12Mg17 and AlMg2Zn. The alloy exhibited excellent mechanical properties, the ultimate and yield tensile strength were 383.2MPa and 275.1MPa respectively. The shape of the precipitated phase was approximately globular with the size of about 50~200nm.

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: Al-Cu-Co and Al-Cu-Ni ternary alloy nanopowders were prepared via a self-developed solid-liquid reaction milling technique. The milling balls were made of the metals with highest melting point for each alloy systems. And the binary alloy melts of other two elements were used as raw materials. Formation regularities of Phases in the milling process were investigated and solid-liquid reaction mechanism of ternary alloy systems was discussed.

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.