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A theoretical model was built to describe the microstructure evolution during the solidification of a liquid–solid phase separation alloy under the effect of electric current pulses (ECPs). Solidification experiments were performed with Pb–0.15 wt pct Al alloy and the microstructure evolution was simulated. The simulation results are consistent with the experimental ones. They show that the Joule heating effect of ECPs can enhance the melt convection; the electromagnetic force induced by ECPs leads to a migration of minority phase particles (MPPs) from the surface to the center; the electromagnetic energy induced by ECPs can effectively promote the nucleation of MPPs, resulting in the refinement of MPPs. The peak current density j max of ECPs and the temperature drop of the melt in the nucleation region during one pulse cycle Δ T F , Nuc = F - 1 · ∂ T / ∂ t Nuc dominate the refinement extent of MPPs. When the peak current density is lower than a critical value, the size of MPPs is almost unchanged. While when the peak current density is higher, the size of MPPs decrease rapidly. For a fixed value of j max , there is an optimal value of Δ T F , Nuc to achieve the best refinement extent of MPPs. [ABSTRACT FROM AUTHOR]

Thus, the Marangoni migration of droplets together with the diffusional transfer of solute Gd described above causes the formation of the Gd-poor region (region II + III) next to the Gd-rich phase shell. 1E. It is this diffusional transfer of solute Gd which caused the formation of the Gd-rich phase shell on the ball surface. Enhancing the cooling rate causes a diminishment in the thickness of the Gd-rich phase shell and width of the Gd-poor region, and promotes the formation of a well-dispersed microstructure. [Extracted from the article]

Solidification experiments were carried out for Al–6Si alloys with different La addition levels. The results demonstrate that the average sizes of the α-Al grains and the eutectic Si have a tendency of first decreasing and then almost keeping constant with the La addition. About (0.04–0.06) wt% La addition is enough to achieve a satisfactory grain refinement and modification. An analytical model based on the Wilson equation, the Miedema model and the thermodynamics was proposed to investigate the mechanisms of the α-Al grain refinement and the eutectic Si modification in the hypoeutectic Al–6Si alloys with the trace La addition. The La effect on the grain refinement of α-Al and the modification of the eutectic Si are mainly attributed to the increase in the efficiency of the heterogeneous nucleation substrates to nucleate α-Al and the amount of La atoms in the eutectic Si. The grain refinement and the modification results achieve the maximum when the La concentration is near its maximum solid solubility in the primary α-Al phase. [ABSTRACT FROM AUTHOR]

Abstract: A model was developed to describe the microstructure evolution in a hyper-monotectic alloy directionally solidified in a static magnetic field. Solidification experiments were carried out with Al–Pb alloys and the microstructure formation in the sample was calculated. The numerical results agree with the experimental ones well. They indicate that the magnetic field affects the microstructure formation mainly through the damping of the convections. It causes a more uniform distribution of the nucleation rate and the volume fraction of the minority phase droplets along the sample radial direction. It also causes a decrease in the maximum size of the minority phase droplets in front of the solidification interface. All these are favorable for the obtaining of a hyper-monotectic alloy with well dispersed microstructure. [Copyright &y& Elsevier]

Abstract: A model is presented to describe the microstructure evolution during a liquid–liquid decomposition when cooling an alloy rapidly in the miscibility gap. The model was first verified by comparing with the experiments and then applied to investigate the microstructure formation in a rapid solidified Cu–Co alloy. The results indicate that the size of the minority phase particles is dominated by the nucleation behavior of the minority phase droplets (MPDs) during the liquid–liquid decomposition. Both the Brownian coagulations of the MPDs and the diffusional interaction between the MPDs affect the nucleation of the MPDs. The later has a relatively stronger effect. [Copyright &y& Elsevier]

Abstract: Cu–1.2wt.%Cr and Cu–3.2wt.%Cr alloys were prepared by spray forming. The as-deposited alloys were subsequently warm rolled at 300°C with a 40% reduction and then two types of thermo-mechanical treatments were adopted to enhance the mechanical properties of the Cu–Cr alloys. The microstructural features of the Cu–Cr alloys in different thermo-mechanical processing conditions were characterized using optical, scanning electron and transmission electron microscopy techniques. The results show that the spray-formed Cu–Cr alloys exhibit a better response to heat treatment compared to the conventional casting alloys. The chromium content has a great effect on the aging behaviors of the Cu–Cr alloys. Although a higher chromium content leads to a larger volume fraction of chromium precipitates generated during the solidification, it does not cause an increase in the mechanical properties. The chromium content should be lower than 1.2wt.%. [Copyright &y& Elsevier]

In order to describe the microstructure evolution of a supercooled droplet under the situation that the nucleation and the growth of the grains occur concurrently during spray forming, a model has been developed based on the population dynamics method. This model is solved numerically to investigate the solidification behaviors of the gas atomized Al–4.5 wt.% Cu droplets. The results show that the nucleation takes place under a critical supercooling for a given droplet. The grain sizes are significantly different during the period of nucleation and recalescence, but become uniform with the progress of the solidification. In addition, a smaller droplet has a higher cooling rate and a finer microstructure at the end of the solidification. [Copyright &y& Elsevier]

Liquid immiscible systems present a unique opportunity in designing composites with sphere-dispersed microstructure. The authors report here phase formation of a multicomponent Al82.87Pb2.5Ni4.88Y7.8Co1.95 alloy upon melt spinning. The alloy undergoes liquid-liquid phase transformation in the liquid immiscibility gap and subsequently solidifies into Pb-rich crystalline phase and Al-rich amorphous phase. The Pb-rich phase with sphere shape is dispersed in the Al-based metallic glass matrix. The average diameter of the Pb-rich spheres is ∼0.62 μm near the free side and ∼0.03 μm near the wheel side of the ribbon. [ABSTRACT FROM AUTHOR]

Studies the low cyclic fatigue behavior of spray-formed AlZn[sub 12]Mg[sub 2]Cu[sub 2] alloy. Microstructure and tensile property of the alloy; Fracture surfaces of the fatigued specimen using scanning electron microscope; Propagation of fatigue cracks.

All-inorganic phosphor-in-glass (PiG) converter withstanding high power laser excitation has garnered attention for laser-driven white lighting, while its poor heat dissipation and low fluorescence conversion efficiency has been serious challenges in high-brightness white lighting. Herein, a thermally robust PiG film converter with a sandwich phosphor structure and microstructure interface was designed for ultrahigh-brightness laser-driven white lighting. The yellow-emitting YAG PiG film was thermocompression bonded to microstructure sapphire (MS) and planar alumina (PA) to construct the MS-PiG-PA converter. The YAG PiG film possess higher luminescence intensity than YAG phosphor and was tightly attached to sapphire and alumina without microcracks. Benefiting from the double-sided heat dissipation design and microstructure interface light field strengthening effect, the MS-PiG-PA converter emits ultrahigh luminous flux white light (5197 lm) at power density of 30 W/mm2 and displays excellent CRI and CCT stability. The MS-PiG-PA converter has a lower working temperature, higher saturation threshold and luminous efficacy. [ABSTRACT FROM AUTHOR]

Al-5Ti-1B master alloys were prepared by reacting K 2 TiF 6 and KBF 4 salts with Al melt. During the reaction period between the fluoride salts and Al melt, the non-homogenous distribution of solutes B and Ti in the Al melt close to the salts/Al melt interface causes the formation of the unstable AlB 2 phase. The AlB 2 phase transforms to TiB 2 particles by the diffusion of solutes Ti and B in the Al melt during the afterward holding temperature period, which causes an increase both in the number density of TiB 2 particles and in the grain refining efficiency of the master alloys. After the transformation of AlB 2 phase to TiB 2 phase, TiB 2 particles coarsen by Ostwald ripening, which leads to a decrease both in the number density of TiB 2 particles and in the grain refining efficiency of the master alloys. [ABSTRACT FROM AUTHOR]

Solidification experiments were carried out for Al-Bi alloys with the addition of TiC. It is demonstrated that the average size of the Bi-rich minority phase particles (MPPs) shows a tendency of keeping constant, increasing, decreasing and then keeping constant again with the increase of the additive amount of TiC. The MPPs can be refined effectively with the addition of an appropriate amount of TiC. A model was developed to describe the kinetic behavior of the TiC particles in the melt and the microstructure evolution during the liquid-liquid (L-L) phase transformation of the Al-Bi alloys with the addition of TiC. The numerical results show that TiC particles may dissolve and coarsen during the heating period, and precipitate out during the cooling period of the melt. There may be two kinds of TiC particles: the one remained during holding temperature and the one precipitated during a cooling of the melt. Both of them can work as the inoculants for the nucleation of the minority phase droplets. What determines the refining efficiency is the resultant number density of the TiC particles in the melt cooled to the binodal line temperature. This research demonstrates that inoculation is an effective method for controlling the L-L phase transformation. The addition of the efficient inoculant may promote the formation of a monotectic alloy with a well dispersed microstructure. [ABSTRACT FROM AUTHOR]

Abstract Al-Bi-Sn alloy was solidified directionally in space. The sample shows a well-dispersed microstructure. A model was developed to describe the microstructure formation during solidification. Calculations demonstrate that the Stokes settlement of the Minority Phase Droplets (MPDs) and the convection of the melt are against the establishment of the steady state of solidification and macro-segregation occurs soon after the beginning of the solidification on ground. The diminished melt convection and the Stokes motions of the MPDs under microgravity conditions promote the establishment of the steady state of solidification and the formation of a well-dispersed microstructure. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Al-Ti-C master alloys were fabricated by using aluminum melt reaction method with graphite powders (GPs) or carbon nanotubes (CNTs) as carbon source. The microstructure formation during the reaction process was analyzed. The α-Al grain refinement abilities of the master alloys were checked. The results demonstrate that the TiC particles form mainly through the reaction between the solid C (GPs or CNTs) and the solute Ti. Using CNTs as the carbon source can significantly enhance the recovery rate of carbon and promote the formation of Al-Ti-C master alloy with a well dispersed microstructure and high α-Al grain refining ability. [ABSTRACT FROM AUTHOR]

The influence of rare earth on the microstructures as well as properties of Al and its alloys has attracted great attention recently. However, contradictory results always were reported, some previous studies found that rare earth promoted the increment of the tensile properties of Al alloy, some other researchers though rare earth had no significant effect on the tensile properties or decreased the tensile properties. In the present work, the effects of minor rare earth element La on the solidification, aging behaviors and the tensile properties of Al-Mg-Si alloys have investigated by thermal analysis, microstructural characterizations and properties tests. The results demonstrate that the ultimate tensile strength and yield strength of Al-Mg-Si alloy can be increased by adding minor rare earth La. The effect mechanism of La has also been explored, it indicates that minor La enhances the strength of the Al-Mg-Si alloy by decreasing grain size and promoting the precipitation of (Mg, Si) phase. This study provides a way for manufacturing Al-Mg-Si alloys with excellent mechanical properties. • Trace La addition can refine α-Al and promote the precipitation of Mg 2 Si and β ′ phase. • Trace La addition significantly improve the mechanical properties of Al-Mg-Si alloy. • The effect mechanisms of trace La addition on Al-Mg-Si alloy have been clarified. [ABSTRACT FROM AUTHOR]

Abstract: The solidification process of the immiscible alloys exhibit a unique opportunity in designing the composites with the spherical crystalline particles dispersed in the amorphous metal matrix. The typical Al–Pb immiscible alloy and the additional elements Ni, Y and Co were selected, and the Al82.87Pb2.5Ni4.88Y7.8Co1.95 multicomponent immiscible alloy has been designed. The ribbon samples of the multicomponent alloy were prepared by using the melt spinning technique. The ribbons were characterized by the scanning electron microscopy (SEM). The phase constitution and transformation were studied by the X-ray diffraction (XRD) and the differential scanning calorimeter (DSC). It was revealed in the as-quenched ribbons the Al-based metallic glass matrix is embedded by the spherical crystalline Pb-rich particles. The microstructure evolution, the glass formation and the thermal stability of the as-prepared composite have been discussed in detail. A method has been developed based on the mechanism of the liquid–liquid phase transformation in the miscibility gap of the multicomponent immiscible alloy to produce the spherical crystalline particles in the amorphous matrix. [Copyright &y& Elsevier]

The effects of rare earth element on the microstructures, tensile properties and electrical properties of aluminum alloys have brought about widespread interesting in the last few decades. However, contradictory results are usually reported, and there is little research concerning the effect law of trace lanthanum (the addition is below 0.1 wt%) on the as-cast microstructures, electrical conductivity and the tensile properties of 8176 aluminum alloy which is one of the most widely used aluminum conductor alloy. In this work, solidification experiments were performed with 8176 aluminum alloy and the effects of lanthanum addition was investigated. The results demonstrated that the lanthanum addition can promote the refinement of the alpha Al grains, the modification of Al 13 Fe 4 intermetallic phase. The elongation and electrical conductivity simultaneously enhance with lanthanum addition when the additive amount is less than 0.08%, while the elongation decreases when the additive amount reaches to 0.1% due to the formation of intermetallic phase. The enhancement of the elongation is mainly ascribed to the modification of Al 13 Fe 4 intermetallic phase, the enhancement of the electrical conductivity is attributed to the reduction of solid solubility of Si and Fe elements in Al matrix. These results indicate that the addition of micro-alloying element lanthanum is a prospective method for simultaneously elevating the electrical conductivity and tensile properties of the 8176 aluminum alloy. • The elongation and electrical conductivity can be simultaneously improved by trace La addition. • Trace La can work as a surfactant and thus refine the α-Al grains. • Trace La modifies Al 13 Fe 4 phase by absorbing in the growth edges. • The improvement of elongation induced by trace La is ascribed to the modification of Al 13 Fe 4 phase. • The improvement of electrical conductivity is ascribed to the reduction of Si and Fe solute content. [ABSTRACT FROM AUTHOR]

Wheel belt continuous casting and hot extrusion experiments were performed with the Al-0.5wt.%Fe alloys. The effects of minor lanthanum (La) on the microstructures as well as the electrical conductivity and tensile properties have been investigated. The microstructure analyses indicated that minor addition of rare earth element La (500 ppm) not only can achieve the α-Al grain refinement, but also can modify the Al 13 Fe 4 intermetallic phase. The test results of tensile and electrical properties indicated that minor La addition can concurrently enhance the yield strength, ultimate tensile strength, elongation as well as the electrical conductivity of Al-Fe alloys. The improvements of strength, ductility and electrical conductivity are mainly ascribed to the α-Al grain refinement, the modification of Al 13 Fe 4 intermetallic phase and the reduction of the solubility of Fe and Si elements in α-Al, respectively. The minor La addition is a promising approach for altering the microstructures and simultaneously enhancing the tensile properties and electrical conductivity of Al-Fe alloys. This study lays foundation for manufacturing Al-Fe alloys with good tensile and electrical properties. Unlabelled Image • Minor La addition can refine α-Al grains, modify minority phase and reduce the solubility of Fe and Si. • The addition of minor La can achieve simultaneous improvements of the tensile properties and electrical conductivity of Al-Fe alloy. • The effect mechanisms of minor La element on the microstructures and properties of Al alloys have been clarified. [ABSTRACT FROM AUTHOR]