Xiufang Bian

Microstructures and grain refinement performance of rapidly solidified Al–Ti–C master alloys

Abstract In the present work, the microstructures and grain refining performance of melt-spun Al–3.5Ti–0.15C, Al–5Ti–0.3C and Al–10Ti–1C (in wt.%) alloys have been investigated, using X-ray diffraction (XRD), scanning electron microscopy (SEM), and grain refining tests. All three types of ingot-like alloys contain coarse slablike TiAl 3 and fine TiC particles. The microstructures of melt-spun Al–3.5Ti–0.15C and Al–5Ti–0.3C alloys are composed of spherical or near-spherical dispersed TiC particles and α-Al supersaturated solid solution, while melt-spun Al–10Ti–1C alloy consists of small blocky TiAl 3 , spherical or near-spherical TiC particles and α-Al solid solution. Furthermore, most of the TiAl 3 and TiC particles are distributed in the edge zone of the chill surface of the rapidly solidified alloy ribbons. Rapid solidification process (RSP) does not improve the grain refinement performance of Al–Ti–C master alloys. The reasons for the formation of microstructures and the grain refining performance of melt-spun Al–Ti–C master alloys have also been discussed.

Variation of activation energy in Al-Ni-based alloy melts

Viscosities of Al85Ni15 alloy melt and the Al–Ni-based melts with the addition of Ce, Cu, and Mn have been measured by an oscillating vessel viscometer. Liquidus temperatures of those alloys have been determined using differential scanning calorimetry (DSC). A high temperature area (HTA) and a low temperature area (LTA) can be used to describe the viscosity behavior. LTA is in the range of 100°C above liquidus. The activation energy of LTA is much higher than that of HTA. Variation of activation energy with temperature of Al–Ni-based melts was found for the first time. The relationship between the glass formability and viscosity of the alloy melts has been discussed.

Growth of dendrites in a rapidly solidified Al-23 Sr alloy

Abstract The microstructure of the melt-spun Al-23xa0wt% Sr alloy has been investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The phases present in the melt-spun Al-23 Sr alloy are identified to be α-Al and Al 4 Sr, identical to those in the ingot-cast alloy. Rapid solidification has a marked effect on the morphology of the primary Al 4 Sr phase and the preferred orientations of its dendrites in the Al-23 Sr alloy. The primary Al 4 Sr phase in the melt-spun Al-23 Sr alloy is dendritic, quite different from the coarse slab-like Al 4 Sr in the ingot-cast alloy. Some primary Al 4 Sr dendrites develop into secondary branches in directions 45° to the dendrite trunks but others continue to branch in the directions perpendicular to the trunks. Moreover, tertiary and higher-order branches are also observed in the melt-spun Al-23 Sr alloy. The preferred crystallographic orientations of the Al 4 Sr dendrites with 45° and 90° branches are determined to be the 〈1xa00xa00〉 and 〈1xa01xa00〉 directions, respectively. Rapid solidification enhances the formation of the Al 4 Sr dendrites with 45° branches in the 〈1xa00xa00〉 direction.

Microstructures and modification performance of melt-spun Al-10 Sr alloy

The microstructures of Al-10 Sr alloy quenched at various wheel speeds have been investigated using X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The experimental results show that the microstructures of melt-spun Al-10 Sr alloy are quite different from those of ingot-like alloy consisting of coarse plate-like Al4Sr embedded in the eutectic matrix. For lower wheel speeds of 500 and 1000 rpm, the microstructure is composed of nanoscale particle-like Al4Sr embedded in α-Al solid solution. With wheel speeds exceeding 1500 rpm, the formation of primary Al4Sr phase is completely suppressed and the eutectic microstructure consisting of alternate dark and bright zones is obtained. Eutectic Al4Sr in dark zones is stripe-like and irregular blocky, while regular stripe-like in bright zones, about 10–20 nm in width. Furthermore, modification tests indicate that the modification performance of melt-spun Al-10 Sr alloy is much better than that of ingot-like alloy, reducing the amount of Sr addition and greatly shortening the incubation time. The reasons for the formation of microstructures and the improvement of modification performance of melt-spun Al-10 Sr master alloy have also been discussed.

Microstructural characterization of a rapidly solidified Al-Sr-Ti alloy

The microstructure of the melt-spun Al-7Sr-3Ti alloy has been characterized using X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. The results show the microstructure of the melt-spun Al-7Sr-3Ti alloy is composed of the equilibrium {alpha}-Al, Al{sub 4}Sr, Al{sub 3}Ti and metastable Al{sub 23}Ti{sub 9}, different from that of the ingot-like alloy comprising {alpha}-Al, Al{sub 4}Sr and Al{sub 3}Ti. Moreover, the amount of Al{sub 3}Ti is much less than that of Al{sub 4}Sr and metastable Al{sub 23}Ti{sub 9} in the melt-spun alloy. The melting temperature of primary phases and enthalpies of fusion for the melt-spun Al-7Sr-3Ti alloy are lower than those for the ingot-like alloy. The formation mechanism of the microstructure of the melt-spun alloy has also been discussed.

Solidification microstructure formation of an Al–Ce–Sr alloy under conventional and rapid solidification conditions

Abstract In the present work, the microstructures of the Al–10Ce–5Sr alloy solidified under conventional and rapid solidification conditions have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) together with energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The microstructure of the Al–10Ce–5Sr alloy solidified under conventional conditions is composed of a primary intermetallic phase embedded in a matrix of α-Al dendrites with interdendritic eutectic. The primary intermetallic phase is Al 4 (Sr, Ce), with an occupation of about 25% Sr sites by Ce atoms. The eutectic may comprise distinct α-Al/Al 4 Sr and α-Al/α-Al 11 Ce 3 zones or comprise the single fully coupled α-Al/Al 4 Sr/α-Al 11 Ce 3 ternary eutectic. Furthermore, most of the Ce exists in the form of eutectic and most of the Sr exists in the primary intermetallic phase in the ingot-like Al–10Ce–5Sr alloy. In comparison, the microstructure of the melt-spun alloy is dominantly eutectic comprising distinct α-Al/Al 4 Sr and α-Al/α-Al 11 Ce 3 zones. Moreover, a certain orientation relationship exists in the α-Al/Al 4 Sr eutectic while no orientation relationship was found for the α-Al/α-Al 11 Ce 3 eutectic. Zones composed of cellular α-Al with intercellular α-Al 11 Ce 3 are also observed in the melt-spun alloy. The formation mechanisms of these microstructures are discussed.

Microstructural characterization of rapidly solidified Al 90 Ce 10 alloy

In the present work, the microstructure of the melt-spun Al 90 Ce 10 alloy has been characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM) together with energy-dispersive spectrometry. It has been found that the microstructure of the melt-spun Al 90 Ce 10 alloy is composed of the amorphous phase, f-Al, f-Al 11 Ce 3 , Al 3 Ce and unidentified phases, quite different from that of the ingot-like alloy consisting of coarse primary f-Al- f-Al 11 Ce 3 dendrites embedded in the f-Al- f-Al 11 Ce 3 eutectic matrix. Moreover, the amorphous phase is dominant in the melt-spun Al 90 Ce 10 alloy according to the XRD and TEM results. Al 3 Ce particles, less than 100 nm in size, are dispersed in the partial amorphous phase. Polygonal f-Al 11 Ce 3 crystals embedded in the f-Al matrix are also observed. The presence of the hexagonal, kite-like and petal-like intermetallic particles surrounded by the amorphous phase indicates that there exist micro-inhomogeneous structures in the Al 90 Ce 10 melt. These results demonstrate that the overheating of the melt has a significant effect on the amorphization of the Al 90 Ce 10 alloy.

Preferred orientations of primary Al4Sr dendrites in a rapidly solidified Al-Sr alloy

Abstract Preferred crystallographic orientations of primary Al4Sr dendrites in a rapidly solidified Al–23 Sr (wt.%) alloy have been investigated using transmission electron microscopy (TEM). The Al4Sr dendrites with 90° branches are dominant in the Al–23 Sr alloy melt-spun at 500 rpm and the dendrite orientation is the 〈110〉 direction. Wheel speed has a significant effect on the morphology and preferred orientation of the Al4Sr dendrites in the melt-spun Al–23 Sr alloy.

Structural Relaxation Phenomenon in Amorphous Al85Ni10Ce5 Alloy during Natural Aging

The structural relaxation phenomenon in amorphous Al85Ni10Ce5 alloy during natural aging has been investigated. It has been found that the crystallization temperature (Tp) increases with increasing relaxation time (τ) during the natural structural relaxation, indicative of a higher thermal stability of the alloy. After the structural relaxation, the crystallization temperature and thermal stability become invariable with increasing aging time. Based on X-ray diffraction measurements, it has been assumed that this effect is attributed to the structural unit corresponding to the prepeak, transforming from defective icosahedra to normal icosahedra composed of 13 atoms with Ni as the central atom. With the structural relaxation complete, the double icosahedra or the atomic clusters of icosahedra are formed, which leads to a higher short-range order.

Annealing-induced microstructural evolution in melt-spun Al-10% Sr alloy

In the present work, the annealing-induced microstructural evolution of melt-spun Al–10% Sr (in wt.%) alloy has been investigated, using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). A monotonically decreasing signal was observed on the DSC trace of the melt-spun Al–10% Sr alloy isothermally annealed at 600 °C, indicating that the microstructural evolution is a grain growth process rather than one of nucleation and growth. The nanoscale Al4Sr phase in as-quenched Al–10% Sr alloy grows with increasing annealing temperature and time. Furthermore, the Al4Sr particles are not randomly oriented and grow along a certain direction with respect to the Al matrix.