Papers by Author: Gen Cang Yang

Abstract: The kinetic process of liquid-liquid phase separation in the undercooled Ni-20at%Pb hypermonotectic alloy melts was analyzed theoretically. The results showed that liquid-liquid separation could not be inhibited due to smaller nucleation barrier and bigger nucleation rate of Pb-rich droplets. In the course of liquid-liquid phase separation, the volume fraction of Pb-rich droplets was thought as a function of time or temperature. At a certain cooling rate, the volume fraction was mainly controlled by the undercooling of Ni-Pb hypermonotectic melts. Based on the above results, a homogeneous solidification criterion for the undercooled Ni-20at%Pb hypermonotectic alloy melts was developed. Such a criterion predicted that the homogeneous microstructure could be obtained at the undercooling 263K, and the experimental results accorded with the predicting ones on the whole.

Abstract: The influence of T6 heat treatment on the microstructures and aging precipitation in the grain-refined A356 alloys were investigated. Experimental results showed that, when T6 heat treatment was performed, the average values of mean diameter, aspect ratio, and roundness of silicon particles in the grain-refined specimens were decreased to 2.26~3.14 μm, 2.06~2.2, and 3.1~4.2, respectively. DSC curves revealed that three kinds of precipitates, i.e., β″, β′, and β, were observed in both unrefined and grain-refined A356 alloys. The exothermic peaks in the grain-refined A356 alloy shifted to high temperatures, suggesting the nucleation of β″ precipitates was decelerated. This could be ascribed to the minor solution of Ti or B elements during solid solution treatment.

Abstract: Fe-Co single-phase alloy melts with different Co contents were undercooled using fluxing method. The maximum undercooling DT = 457K (relative undercooling DT/Tm=0.259) was achieved in this work. At low undercooling (DT), single-phased microstructure was observed, but metastable bcc phase emerged in the as-solidified microstructure once DT exceeded a critical value, DTcrit. In the presence of classical nucleation theory, phase selection in the undercooled Fe-Co melt was investigated, and the theoretical calculation was coincided with the experimental result.

Abstract: Assuming phenomenological thermal flow balance and solute conservation, a numerical model was proposed for recalescence in bulk undercooled alloy. During the calculation, the evolution of residual melt temperature and concentration is solved as function of the transformed solid fraction. After quantitative thermodynamic calculations, a transition from non-equilibrium to equilibrium process can be described by the change of liquid/solid Gibbs energy difference. The proposed model has been applied to Cu-Ni solid solution and Fe-B hypereutectic alloy. The predicted post-recalescence temperature TR agrees well with the experimental results.

Abstract: An investigation on low frequency strain amplitude dependence damping characteristic of as-cast high damping Mg-based alloys continuously extending to microplastic strain was carried out. Two-stage damping behavior via strain amplitude was particularly reported. The first is the strain amplitude strongly dependent part due to breakaway loss and the second is the strain amplitude weakly dependent part due to microplastic deformation loss, which is also frequency dependent. The damping mechanism is discussed in detail.

Abstract: Experiments have been carried out to investigate the damping behaviors of commercially pure aluminum (L2) prepared by equal-channel angular pressing (ECAP). The damping characterization was conducted on a DMTA-V apparatus. The internal friction was measured at frequencies of 0.1, 0.3, 1.0, 4.0 and 8.0 Hz over the temperature range of 20~150°C. The measured damping capacity shows that ultra-fine grained structure pure Al (L2) prepared by ECAP has a damping capacity that is enhanced in comparison with coarse one, especially when the temperature is higher than 60°C. The dependence of the damping capacity at room temperature on the strain amplitude shows a nonlinear characteristic, and increases rapidly with the strain amplitude (
0) when
0 is comparatively low. While the strain amplitude is higher than certain value, the damping capacity will become saturated slowly. The high damping capacity of the pure Al prepared by ECAP was attributed to the high density of dislocations and ultra-fine grained structure.