Papers by Author: Feng Wang

Abstract: An innovative spray deposition technique has been applied to produce in situ TiB₂/Zn-30Al-1Cu composites. The microstructures of the spray-deposited composite were studied using optical microscopy, scanning electron microscopy, and X-ray diffraction. Both theoretical and experimental results have shown that the TiB₂ particulates are formed in the microstructure. It was found that the TiB₂ particles were distributed in Zn-30Al-1Cu matrix uniformly, and the TiB₂ particles are about 2 μm in size. Moreover, the presence of the TiB₂ particles was led to increasing of α’ phase with less 2 μm size in the composites which have a tendency to decompose to α+η structure.

Abstract: Anti-extrusion process for the cylinder of spray-formed ultra-high strength aluminum alloy is researched in this paper. The spray-formed 7xxx aluminum alloy is treated by a two-step homogenization treatment (440 °C / 12h + 472 °C / 24h) after hot isostatic pressing (HIP), and then hot compression tests are carried out for getting the stress-strain relationship under different forming conditions. Anti-extrusion process for the cylinder is improved including changing the shape of mould and billet, and numerical simulation is used for researching the anti-extrusion process. According to the distribution of strain-effective, it can be seen that the improved scheme of anti-extrusion process can get more deformation than the common scheme at the bottom. The result of anti-extrusion experiments shows that the microstructure is evenly distributed across the cylinder under the improved scheme.

Abstract: The microstructure and mechanical properties of the Al-2.24Cu-1.42Mg-0.9Fe-0.9Ni alloy were studied using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and tensile tests. The results indicate that the microstructures of the as cast alloy involve α-Al matrix, Al/Al₂CuMg eutectic structure, Al₇Cu₂Fe, Al₇Cu₄Ni and Al₉FeNi compounds. The tensile test results indicate that the alloy at elevated temperature (200°C) displays superior tensile strength due to the presence of the thermally stable Al₇Cu₂Fe, Al₇Cu₄Ni and Al₉FeNi compounds.

Abstract: The CuCr25 alloys were prepared by spray forming technology, and effect of process parameters on the deposit was studied. The microstructure of CuCr25 alloy prepared by spray forming was studied, and the size of chromium particles was 3-10μm. It is fond that spray-deposited CuCr25 alloys were hot forged and hot isostatically pressed to full densification,and the size of chromium particles was increased little after being hold at 1070°C for 60mins. Conclusions were drawn from the researching results that spray forming was an ideal method to prepare CuCr25 alloys with fine chromium precipitates and homogeneous dispersion. After hot forging and hot isostatic pressing, the size of chromium particles was increased to 10-15μm. the density of the CuCr25 alloy could be 99%.

Abstract: The microstructure evolution of automotive sheet 6016 aluminum alloy has been studied by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimeter (DSC) analysis. The as-cast microstructure was the typical dendritical structure, consisting of four phases: α-Al, β-AlFeSi, Mg2Si and Si. The electron diffraction analysis indicated that the β-AlFeSi phase was Al5FeSi. After 545°C for 20h homogenization treatment, Mg2Si and Si have been dissolved into matrix completely, and the remaining phase was β-Al5FeSi intermetallic compound. The transformation of β-AlFeSi→α-AlFeSi was not found during the homogenization process.

Abstract: In this study, Al-8.6Zn-2.6Mg-2.2Cu (wt,%) alloy was synthesized by the spray atomization and deposition technique. Electron beam welding (EBW) joint in the spray-deposited Al-8.6Zn-2.6Mg-2.2Cu alloy is composed of fusion zone, heat affected zone and base metal region. The microstructure of the fusion zone has been found to be very fine equiaxed grains, and the microstructure of the heat affected zone is mainly composed of α-Al and Al/MgZn2 eutectic microstructure. Extensive microhardness measurements were conducted in the weld regions of the nuggets exhibited a hardness loss in the fusion zone due to the loss of strengthening phases. Tensile properties test results indicated that tensile strength of these welds approached 82.3~85.3% of the base metal. The analysis of fracture surface has confirmed that the specimen fractured within the weld region during tensile test.

Abstract: In this study, the Al-Zn-Mg-Cu alloy was prepared by spray forming process. The ageing precipitation and strengthening behavior of the spray formed Al-Zn-Mg-Cu alloy were studied by microhardness tests, differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) .The results show that the main strengthening precipitates of the spray formed Al-Zn-Mg-Cu alloy are GPI (solute-rich clusters), GPII (vacancy-rich clusters) under peak aging condition. The effect of the microstructure on ageing hardness is controlled by the size and amount of the existing precipitates, and therefore depends critically on the ageing temperature and ageing time. Strength of this alloy is influenced significantly during natural ageing at room temperature, which is related to the dominant formation of GPI. During the initial stage of artificial ageing at 120°C, strong age-strengthening response is due to the formation of GP zones (both GPI and GPII ) .During later stages of artificial ageing , GPII precipitation is accelerated significantly but GPI is not affected clearly.

Abstract: In the present work, quench sensitivity of an Al-7.5Zn-1.7Mg-1.4Cu-0.12Zr alloy is investigated by temperature-time-property (TTP) curve and TEM analysis, comparing with traditional AA 7B04 and AA 7150. The results indicate that the nose temperature of TTP curve and the corresponding incubation period of the alloy, AA 7150 and AA 7B04 are about 290°C/4.5s, 320°C/2.6s and 335°C/0.1s, respectively, The nose temperature of the alloy is the lowest among three alloys and the critical time at the nose temperature is the longest for the alloy, which is obvious that the alloy has lower quench sensitivity. Further TEM analysis shows that, with the prolongation of keeping time at the nose temperature, quench-induced precipitation phenomenon becomes obvious.

Abstract: In this study, Zn-30Al-1Cu alloy was synthesized by the spray atomization and deposition technique. The microstructure and mechanical properties of the alloy were studied using optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and tensile tests. It can be seen that the microstructure of spray-deposited Zn-30Al-1Cu alloy is composed of the Zn/Al eutectoids and few compounds. The Zn/Al eutectoids were shown lamellar, particle and Chinese script morphologies. The compound phases in the microstructure of the spray-deposited alloy were examined. The property test results indicate that the spray-deposited Zn-30Al-1Cu alloy displays superior tensile strength.

Abstract: Abstract. The microstructure and mechanical properties of a metal inert gas welds in a medium strength Al-4Zn-1Mg alloy were characterized by optical microscope (OM), scanning electron microscope (SEM) and tensile tests. It is found that the joint of the alloy contained three distinctive regions, i.e. fusion zone, heat affected zone and base metal region. Extensive microhardness measurements were conducted in the weld regions of the nuggets exhibited a hardness loss in the fusion zone due to the loss of strengthening phases. Microstructural examination of the joints revealed typical eutectic structure was appeared in the heat-affected zone. Tensile properties of the joints were obtained by testing flat transverse tensile specimens, and the results indicated that tensile strength of these welds approached 83.3~84.2% of the base metal.