Papers by Author: Zhi Hui Li

Abstract: In this study, the microstructure and properties of an Al-7.5Zn-1.7Mg-1.4Cu-0.12Zr alloy in T74 condition have been investigated using TEM, tensile properties testing, conductivity measurement, fracture toughness testing, fatigue testing, corrosion testing and soaking quench method etc. The results indicate that When T74 tempers are performed, the alloy can obtain a good comprehensive performance with GPII zones, η' phases and η phases as the major precipitates in the matrix and coarser and discontinuous precipitates on the grain boundaries. The alloy also exhibits a good combination of tensile strength, fracture toughness, fatigue and corrosion properties. And the alloy has a good quench performance, after soaking quenched in water, the strength of the forging with 210mm thickness is stable and varies less than 10% along the depth direction.

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 present work, the microstructure and properties of an Al-7.5Zn-1.5Mg-1.4Cu-0.12Zr alloy forging in T7452 condition has been investigated by means of OM, TEM and EBSD analysis and varied properties test. The results indicate that there are obvious differences in grain morphology, precipitation characteristics and recrystallization degree along the thickness direction of the forging. The strength of the alloy forging is stable and varies less than 10% along the thickness direction. The alloy forging in the T7452 condition shows high strength, high toughness and good corrosion resistance, with the UTS, TYS, elongation and electrical conductivity values being 500~530 MPa, 460~500 MPa, 7.0~15.0% and 23.9~24.2 MS/m, respectively, and the fracture toughness in L-T, T-L and S-L direction being 33.5~39.5, 25.5~27.0, 23.0~24.5 MPa.m^1/2, respectively, and the EXCO rating being EA.

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: Microstructural characterization of Al-Cu-Mg-Ag alloy ageing at low and elevated temperature were investigated by differential scanning calorimeter (DSC) and transmission electron microscopy (TEM). The results show that the precipitation sequence is significantly influenced by the ageing temperature. With prolonging of ageing at 65°C, G.P. zones on the plane of {100}α separates out with no precipitation of Ω phase. After 10h ageing at 160°C,the phase of Ω separates out and dominant the microstructure, while a small quantity of θ′separates out as well.

Abstract: Oxygen diffusion in MgO stabilized zirconia has been studied by molecular dynamics simulation method with MOLDY software. The results illustrate that oxygen diffusion in MgO stabilized zirconia can be decided by temperature and amount of MgO. Both increase of amount of MgO and temperature in the system may promote the oxygen diffusion. Further increase in temperature is helpful to the oxide ions diffusion. There is always a maximum value of oxygen diffusion coefficient, which is represented by the slope of MSD curves, corresponding to a certain amount of MgO. In MgO stabilized zirconia, the most suitable doped amount of MgO exists in a range , which is decided by the working temperature of MgO stabilized zirconia.