Changlin Yang

Effects of cooling rate on solution heat treatment of as-cast A356 alloy

The effect of cooling rate of the solidification process on the following solution heat treatment of A356 alloy was investigated, where the cooling rates of 96 K/s and 3 K/s were obtained by the step-like metal mold. Then the eutectic silicon morphology evolution and tensile properties of the alloy samples were observed and analyzed after solution heat treatment at 540 °C for different time. The results show that the high cooling rate of the solidification process can not only reduce the solid solution heat treatment time to rapidly modify the eutectic silicon morphology, but also improve the alloy tensile properties. Specially, it is found that the disintegration, the spheroidization and coarsening of eutectic silicon of A356 alloy are completed during solution heat treatment through two stages, i.e., at first, the disintegration and spheroidization of the eutectic silicon mainly takes place, then the eutectic silicon will coarsen.

Phase selection in highly undercooled Fe-B eutectic alloy melts

Abstract The high undercooling technique by molten glass slag purification and cyclical superheating in Ar atmosphere was applied to bulk Fe-B alloy melts. A hypercooling was achieved which suppressed the formation of stable phase and consequently promoted the nucleation of metastable phase. Fe-17%B and Fe-20%B alloys were investigated, respectively. TEM and X-ray powder diffraction analyses verify the formation of metastable phase in the highly undercooled Fe-B alloy melts. Besides, the critical nucleation work of Fe 2 B and Fe 3 B phases was calculated to predict phase selection in the undercooled melts. The results show that the metastable phase formation is a function of the undercooling achieved prior to nucleation. And the amount of undercooling is an important factor in determining microstructural development by controlling phase selection in the undercooled melts.

Liquid-phase Separation in Rapid Solidification of Undercooled Fe-Co-Cu Melts

The homogeneous liquid was separated into two phases, (Fe, Co)-rich L1 and Cu-rich L2, once the melt was undercooled below a liquid-phase separation temperature T sep . If the duration from T sep to T s1 (solidification temperature of L1 phase), termed the liquid-phase separation interval Δ t , exceeded a critical value, an eggtype structure was observed. By utilizing differential thermal analyses (DTA), the solidification process of the undercooled Fe-Co-Cu alloys was studied. Additionally, an immiscible boundary was obtained, which was a convex parabola with a symmetrical axis of x Cu =0.52. Depending on the relative amounts of L1 and L2, the minor phase was nucleated firstly to form liquid droplets and separated from the original liquids at the beginning of liquid-phase separation.

Application of an analytical phase transformation model

Abstract An analytical phase transformation model has been used to study the kinetics of crystallization of amorphous alloys subjected to either isothermal or isochronal anneals. The model has been applied to Mg 82.3 Cu 17.7 and Pd 40 Cu 30 P 20 Ni 10 , employing isothermal and isochronal differential scanning calorimetry. Applying different combinations of nucleation and growth mechanisms to the same experiments, the nucleation and growth modes dominating the crystallization and the values for the corresponding kinetic parameters, including the constant activation energies for nucleation and growth, have been determined. Further, the influence of isothermal pre-annealing on subsequent isochronal crystallization kinetics, involving a gradual change of nucleation mode up to site saturation with increase of pre-annealing, can be analyzed.

Nano-eutectic structure formation and soft magnetic properties of bulk ternary Fe-B-M (M = Si, Cu) alloys

The bulk Fe-B-M (M = Si, Cu) ternary eutectic alloys with nano-lamellar structure and excellent soft magnetic properties were successfully prepared by undercooling combined with Cu-mold casting. Different effects of Si and Cu elements on the structural refinement and soft magnetic properties were studied. The results show that the lamellar spacing can be decreased to less than 50 nm with addition of Si or Cu of 1 at. % into the Fe-B eutectic alloy. Based on the classical random anisotropy model, a quantitative correlation between the intrinsic coercivity (HC) and the lamellar spacing (λ) was also obtained.