Zheng Ziqiao

Influence of Nano-Al2O3 Particles on Nickel Electrocrystallization at Initial Stage

Abstract The influence of nano-Al 2 O 3 particles on nickel deposition on copper matrix from acid sulphate solution was studied under various potentials (vs. SCE) by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The results show that the beginning potential of Ni-Al 2 O 3 co-deposition is at −740 mV or so. The effect of nano-Al 2 O 3 particles on nickel deposition process may be different under various potentials. In the potentials range from −740 to −830 mV, Al 2 O 3 particles on cathode surface may be favorable for nickel deposition nucleation and promote electron crystallization nucleation because the induction period t m corresponding to the peak current of Ni-Al 2 O 3 co-deposition is apparently shortened, compared with that of pure Ni deposition. However, Al 2 O 3 particles adsorbed on cathode surface may obstruct electric discharge of partial ions and mass transmission process, resulting in the impedance increment of Ni-Al 2 O 3 co-deposition, especially in the potentials range from −250 to −650 mV. The favorable effect of Al 2 O 3 particles weaken in the range of high over potential, and the particles accumulated on electrode surface will decrease the reduction current of Ni-Al 2 O 3 deposition. At the potential −890 mV, the nucleation process of Ni-Al 2 O 3 co-deposition at initial stage follows the instantaneous model of Scharifker-Hill with three-dimensional fashion.

Effect of heat treatments on tensile properties and microstructure of 2195 alloy

Effect of various aging treatments on the tensile properties and microstructure of 2195 alloy has been investigated. The experimental results show that promising combination of strength and ductility is achievable under T8 temper. The lower aging temperature reduces T1 precipitation on the subgrain or grain boundaries and favors uniform dispersion of T1 phases in the matrix, resulting in better strength and ductility. Prior deformation before aging has improved tensile strength with a slight decrease in ductility. Pre-aging after prior deformation had little effect on the age-hardening behavior of 2195 alloy.

Curing mechanism of TDE-85/MeTHPA epoxy resin modified by polyurethane

Diglycidyl 4,5-epoxy tetrahydro phthalate/methyl tetrahydrophthalic anhydride (TDE-85/MeTHPA) epoxy resin modified by polyurethane (PU) was prepared with 1,4-butanediol (1,4-BDO), trimethylol propane (TMP) and polyurethane prepolymer synthesized by polypropylene glycol and toluene diisocynate. Chemical reaction and curing mechanism of this system were discussed by incorporating the results of infra spectrum analysis. The results indicate that the epoxy polymeric network I is obtained by the curing reaction between TDE-85 and MeTHPA, while the PU polymeric network II is obtained by the chain-extended and crosslinking reaction between 1,4-BDO, TMP and polyurethane prepolymer(PUP). The graft chemical bonds are formed between polymer networks I and II that therefore increase the degree of blend and compatibility between epoxy polymer and PU.

Effects of trace silver and magnesium on the microstructure and mechanical properties of Al−Cu−Li alloys

The effects of trace silver and magnesium additions on the microstructure and mechanical properties of the Al−Cu−Li alloys were investigated. The experimental results indicate, that the effect of combined additions of Ag and Mg is the most obvious, the next is that of individual addition of Mg, and that of individual addition of Ag is the least. The addition of Ag and Mg in Al−Cu−Li alloy accelerates the precipitation of T1 and results in increasing the ageing hardness and strength. Prior cold work significantly improves the tensile strength by enhancing T1 precipitation in all the alloys investigated.

Special epoxy silicone adhesive for inertial confinement fusion experiment

The effects of toughener and coupling agent on special epoxy silicone adhesive were discussed by researching the surface morphology characters, thermal properties and shear strength of the adhesive. The results indicate that silicone coupling agent (KH-550) can improve the shear strength of the epoxy silicone adhesive effectively. The mass fraction of the toughener in the epoxy silicone adhesive plays an important role in its properties. When the mass fraction of the toughener is less than 14%, the shear strength of the adhesive is low. When the mass fraction of the toughener is over 33%, thermal properties and shear strength of the adhesive decrease with the increasing of the toughener. The mass fraction of toughener of 25% results in good integral properties of the epoxy silicone adhesive. The morphologic analysis indicates that the micro-phase separation exists in the epoxy molecular chain and the silicone molecular chain of the epoxy silicone adhesive.

Ostwald Ripening Behavior of Al8CeCu4 Phase in Al-14Cu-7Ce Alloy

Abstract The Ostwald ripening behavior of Al 8 CeCu 4 phase in the Al-14Cu-7Ce alloy annealed at elevated temperatures was investigated using hardness testing, scanning electron microscopy, image analyses and physical modeling. Results indicate that the average radius of Al 8 CeCu 4 particles increases while the hardness of the alloy decreases with increasing of annealing temperature and time. The ripening process of Al 8 CeCu 4 phase is mainly controlled by the volume diffusion of Ce. The ripening kinetic of Al 8 CeCu 4 particles satisfies well the modified Lifshits-Slyozov-Wagner theory, taking into account the effect of the volume fraction of Al 8 CeCu 4 particles. The volume diffusion coefficient of Ce and the interfacial energy between the matrix and Al 8 CeCu 4 phase were also calculated based on the general rate equation.

Spheroidizing Behavior of the Lamellar Al8CeCu4 Phase in Al-14Cu-7Ce Alloy

The spheroidizing behavior of the lamellar Al8CeCu4 phase in the Al-14Cu-7Ce alloy annealed at elevated temperatures was investigated by microstructure observation, hardness testing and theoretical calculation. Results show that with increasing the annealing temperature, the spheroidizing process of the Al8CeCu4 phase is accelerated. The controlling element for the spheroidizing process is determined to be Ce by theoretical calculation using the general rate equation. Microstructure observation indicates that the spheroidizing process of the Al8CeCu4 phase includes two successive steps, i.e., the curved lamella breaking into long rods by Gibbs-Thompson effect and then the rods separating into spherical particles further by Rayleighs capillary induced perturbation mechanism.

Modeling for Predicting Flow Stress of Al-14Cu-7Ce Alloy at Elevated Temperature

Abstract Isothermal hot compression tests of annealed Al-14Cu-7Ce alloy were carried out on Gleeble-3500 system in the temperature range from 573 K to 823 K and the stain rate range from 0.001 s −1 to 1 s −1 . The resulted true stress-true strain data were employed to establish a constitutive equation for predicting high temperature flow stress. The results show that the flow stress follow well the rate equation ɛ ˙ = A D L G b / κ T [ sinh ( α L σ / G ) ] n . The effect of strain was taken into account by fitting of polynomials into the material parameters A , α L and n . The proposed constitutive equation can predict precisely high temperature flow stress of Al-14Cu-7Ce alloy. The control mechanism of hot deformation is dislocation climb.

Effect of preaging on precipitation of the S′ phase in 8090 and 2091 type Alz.sbnd;Li alloys

Abstract Effect of preaging at room temperature and at 150°C on the precipitation of the S′ phase in 8090 and 2091 type Alz.sbnd;Li alloys has been investigated. The results indicate that in the specimens naturally aged at room temperature prior to aging at 190°C, the S′ phase is preferentially nucleated and grows on dislocation loops. Preaging at 150°C also promoted S′ precipitation due to the increased driving force for precipitation. Higher Cu and Mg contents are favourable for S′ precipitation.