Morphology Of Si Research Articles

Efficient microstructure refinement of Al–Si–Mg alloy manipulated by nanocrystals formed by in-situ crystallization in melt

Al–Si–Mg alloys manipulated by in-situ synthesized nanoparticles have been prepared by casting method in this work. The addition of different contents of refiners promoted the obvious grain refinement of the Al–Si–Mg alloys. It was found that 0.10 wt% refiners addition caused a significant and efficient refinement on α-Al (from 1675 µm to 199 µm) and Mg2Si in the inoculated Al–Si–Mg alloys. The morphology of the eutectic Si in the inoculated Al–Si–Mg alloys transformed from needle-like structure to a fibrous one, and the mean size sharply decreased (from 26.56 µm to 11.89 µm) and increased a little with the increase of FeBSi amorphous refiners content. Tensile property tests showed that both strength and ductility of the alloys were improved by the addition of FeBSi amorphous refiners. The yield strength, tensile strength, fracture strain and elongation of the alloy inoculated with 0.10 wt% FeBSi amorphous refiners for 20 min were 226 MPa, 343 MPa, 18.4% and 16.7%, compared to those of the uninoculated alloy (170 MPa, 289 MPa, 13.7% and 12.2%), respectively. It was found that the Fe2B and Fe3Si nano-sized particles which were crystallized from FeBSi amorphous refiner contributed to the grain refinement of α-Al, resulting in higher strength. Moreover, grain refinement shortened the atomic diffusion distance and refines Mg2Si. The grain refinement and spheroidization of eutectic Si enhance uniform deformation during tension, and reduce the possibility of crack initiation and expansion, thus improving the plasticity.

Microstructure and mechanical properties of an aluminum alloy reinforced by Al–Ni–Co–Mn quasi-crystalline

The Al72Ni13Co10Mn5 quasi-crystalline was prepared by conventional casting method. The microstructures and the phase composition of Al72Ni12Co16 quasi-crystalline, Al70Ni11Co12Mn7 and Al2Ni phases were characterized by XRD, SEM and DSC. The (Al72Ni13Co10Mn5)p/ZL101A aluminium based composite was fabricated by using the Al72Ni13Co10Mn5 quasicrystals particles as the reinforcing phase and ZL101A as the matrix with electromagnetic stirring. The results showed that the Al72Ni13Co10Mn5 is a QC(quasi-crystalline) phase and the hardness of Al72Ni13Co10Mn5 is higher than d-Al72Ni12Co16; the as-cast (Al72Ni13Co10Mn5)p/ZL101A composites are composed of α-Al, eutectic Si, θ, γ and φ phase. With the increase of reinforcing particle fraction, the changed order for the morphology of coralline Si as follows: coral distribution → partially converted into strips → strip or thick sheet. The changes of mechanical properties were studied by tensile test and the resulting crystalline phase γ and φ phases contribute to the improvement of the mechanical properties of the composite. After adding 4%wt% quasicrystalline particles, the tensile strength increased by 20.3%. However, when additional increased to 7 wt% will cause agglomeration and clusters of the θ phase, which leads to the decrease of the mechanical properties.

Solidification Behavior and Microstructure of Al-7Si Alloys with Individual and Combined Additions of Sr and Yb

The effects of individual and combined additions of Sr and Yb on the solidification behavior and microstructure of Al-7Si alloys were investigated using thermal analysis, optical microscopy, and scanning electron microscopy. The results showed that the nucleation temperature, minimum temperature, and growth temperature of eutectic solidification were lower than those of the unmodified alloys, and eutectic recalescence at 2°C in the Yb- and (Sr + Yb)-modified alloys was observed. The decrease in the nucleation temperature and an increase in recalescence obviously refined the eutectic Si morphology of the Sr-, Yb-, and (Sr + Yb)-modified alloys from a coarse plate-like structure to a fine fibrous structure. Moreover, the three-dimensional microstructure of eutectic Si in the (Sr + Yb)-modified alloy showed the finer fibrous structure, which was mainly attributed to formation of the Al2Si2Yb phase. The formation enthalpy of Al2Si2Yb was lower than that of Al-(Si)-Sr in the (Sr + Yb)-modified alloy, thus suppressing the formation of the Al2Si2Sr intermetallic compound. The more effective Sr together with Yb further improved the modification effect of eutectic silicon.

Influence of annealing treatment on Si morphology and strength of rapid solidified Al-12 wt% Si powders

An experimental study is reported on heat treating rapid solidified Al-12 wt% Si alloy with 355–425 μm powder size. Fast heat treatments at 813 K revealed morphological shifts of eutectic Si from the as-atomized condition to those after annealing. The Si network of the as-atomized samples showed a fine dispersed coral fibrous architecture. This feature via rapid cooling brings the prospect of quickly disintegrating and spheroidizing Si in a few minutes without chemical modification. By adopting different exposure times, it was possible to investigate fragmentation and coarsening of the eutectic Si. The integrity of the Si network is very sensitive to the Si spheroidization treatment transforming into a network of round Si particles. It is also seen that the material softens in the earlier stages of heat treatment, especially after 2 min of heat treatment. The breakdown in Si rods in a rapidly solidified alloy is shown to take place with a mixed mechanism of interface or internal rod diffusion and diffusion of supersaturated Si through the α primary phase to the Si rods in the eutectic. The quantitative analysis of the microstructures coupled with an analytical strengthening model resulted in good agreement between experimental and calculated data.

Microstructure Solidification Maps for Al-10 Wt Pct Si Alloys

Hypo-eutectic Al-Si alloys are widely used in both the automotive and aerospace industries; however, they still have limited usage as structural materials, due to the inherent morphology of the Si phase that forms within the eutectic structure. This non-ideal Si morphology can be modified, via alloy additions and/or rapid solidification (RS), but the underlying mechanism(s) behind this is poorly understood. This work focused on understanding the influence of RS on the eutectic structure, for hypo-eutectic Al-10 wt pct Si alloys produced by Impulse Atomization and Differential Scanning Calorimetry. This study found that the eutectic Si forms into four distinct morphologies: (1) flaky, (2) fibrous, (3) globular + fibrous and (4) globular, depending on the solidification conditions. As a result, two solidification maps of the Si morphology are proposed, one based on local eutectic solidification conditions and another based on a solidification continuous cooling diagram (SCCT). Both maps help identify the required conditions for certain Si morphologies to form. Hardness measurements were also carried out and it was found that the Si morphology would influence the alloy hardness, with the highest value being achieved when the eutectic Si was globular. This result indicates that the Si morphology is an important factor that can alter the mechanical properties of hypo-eutectic Al-Si alloys.

Effects of Forming Processes on Microstructures and Mechanical Properties of A356 Aluminum Alloy Prepared by Self-inoculation Method

Semisolid slurry of A356 aluminum alloy was prepared by Self-Inoculation Method (SIM), and the microstructures and solidification behavior of rheo-forming process in different forming processes were researched. The results indicate that semisolid slurry of A356 aluminum alloy can be prepared by Self-Inoculation Method at 600oC. Primary α-Al particles with fine and spherical morphology are uniformly distributed when the isothermal holding time of slurry is 3 min. The different forming processes for semisolid rheo-forming can be regarded as the effect of cooling rate on rheo-forming. The primary particle sizes and shape factors are gradually increasing with the increase of cooling rate. The sizes of secondary particles are gradually increasing with the decrease of cooling rate, and the amount of secondary particles in the same areas are gradually decreasing with the decrease of cooling rate. The morphologies of eutectic Si are gradually coarsening from fibrous to needle-like in different forming processes, while the sizes and the lamellar spacing of the eutectic Si are gradually increasing with the decrease of cooling rate. The mechanical properties of the semisolid forming components are gradually increasing with the increase of cooling rate and forming pressure.

Segregation and Morphological Evolution of Si Phase during Electromagnetic Directional Solidification of Hypereutectic Al-Si Alloys.

Understanding the Si segregation behavior in hypereutectic Al-Si alloys is important for controlling the micro- and macrostructures of ingots. The macrosegregation mechanism and morphological evolution of the primary Si phase were investigated during electromagnetic directional solidification (EMDS). Both numerical simulations and experimental results strongly suggested that the severe macrosegregation of the primary Si phase was caused by fluid flow and temperature distribution. Microscopic analysis showed that the morphological evolution of the Si crystal occurred as follows: planar → cellular → columnar → dendritic stages during EMDS. Based on constitutional supercooling theory, a predominance area diagram of Si morphology was established, indicating that the morphology could be precisely controlled by adjusting the values of temperature gradient (G), crystal growth rate (R), and solute concentration (C0). The results provide novel insight into controlling the morphologies of primary Si phases in hypereutectic Al-Si alloys and, simultaneously, strengthen our understanding of the macrosegregation mechanism in metallic alloys.

A novel modifier on eutectic Si and mechanical properties of Al-Si alloy

In this study, a novel Al-Si alloy eutectic Si modifier was proposed and prepared. The microstructure, metamorphism mechanism and mechanical properties of the eutectic Si of the alloy after adding Mg-15La master alloy were investigated. The results show that high-density nano-cluster particles appear within the eutectic Si after Mg-15La master alloy addition. After adding the master alloy, the eutectic Si morphology changes from strip to fiber or granular. The average length of eutectic Si changed from 6.04 µm to 1.04 µm. The mechanical properties after casting and heat treatment have been significantly improved.

Modification of Al-Si Alloys by Ce or Ce with Sr

Al-Si alloys were modified by addition of cerium (Ce) or Ce plus strontium (Sr) to study the effect on the eutectic silicon (Si) morphology. The modified alloys were characterized using scanning electron microscopy (SEM), x-ray diffraction (XRD) analysis, and thermal analysis to understand the effect of Ce and Sr on their microstructure. The results showed that addition of 1% Ce resulted in only partial modification of the Si phase, whereas addition of Ce with 0.04% Sr resulted in complete modification of the alloy. Addition of 1% Ce decreased the eutectic arrest temperature by about 10°C, compared with a 5°C drop with Sr addition only. SEM energy-dispersive spectroscopy (EDS) and XRD results revealed formation of Al2Si2Ce intermetallic in the Ce-modified Al-Si alloys. Differential scanning calorimetry (DSC) showed that the intermetallic formed just before the eutectic phase.

Microstructure and mechanical properties of as-cast and T6 treated Sc modified A356-5TiB2in-situ composite

The present article presents the effect of Sc addition on the secondary dendritic arm spacing, eutectic Si modification, intermetallic phase modification, aging behavior and subsequently the mechanical behavior in A356-5TiB2in-situ composite. The A356-5TiB2in-situ composite showed a 40% reduction in SDAS compared with A356 alloy, whereas addition of 0.4 wt% Sc and 5 wt% TiB2 in A356 alloy resulted in a 65% reduction in SDAS. The eutectic Si in A356-5TiB2 composite had a plate like morphology similar to A356 alloy but showed a reduction in length, whereas the addition of Sc resulted in a fibrous and particulate morphology of eutectic Si. The needle like β-Al5FeSi phase in A356-5TiB2 composite changed to Al5Fe(Si,Sc) phase having smaller size and irregular morphology with the addition of Sc. The intermetallic phase formation and phase modification was confirmed and characterized using X-ray diffraction, Transmission electron microscopy - Energy dispersive spectroscopy and Scanning electron microscopy. Addition of Sc to A356-5TiB2in-situ composite resulted in improved mechanical properties. Further, T6 heat treatment revealed a significant improvement in mechanical properties for A356-5TiB2in-situ composite with and without Sc addition.

Surface modification of fly ash by mechano-chemical treatment

Fly ash (FA), as an industry by-product, has attracted much attention as a suitable supplier of silicon (Si) and aluminum (Al) in preparation of geopolymer for the sustainable environment and material science applications. Here, the effect of mechano-chemical (MC) treatment for surface modification of FA powder was systemically investigated by analyzing the size, surface morphology, crystal structure and dissolubility of Si and Al ions in alkali solutions. The dissolution dynamic as a function of MC treatment time is discussed in details and concluded with a recombination model of “grinding effect” and “activation effect”, which can be well correlated with the change of surface morphology and crystal structure, respectively.

Unsteady-State Horizontal Solidification of an Al–Si–Cu–Fe Alloy: Relationship Between Thermal Parameters and Microstructure with Mechanical Properties/Fracture Feature

Aluminum casting alloys have properties which are of great industrial interest, such as low density, good corrosion resistance, high thermal and electrical conductivities, good combination of mechanical properties, good workability in machining processes and mechanical forming. Currently, these alloys are produced in various systems and dozens of compositions. In this investigation, a mutual interaction of thermal parameters, scale of the dendritic microstructure, intermetallic compounds (IMCs), microhardness and tensile properties/fracture characteristics of a casting Al–7wt%Si–3wt%Cu–0.3wt%Fe alloy was analyzed. Solidification experiments were developed using a furnace that promoted horizontal growth under transient heat flow conditions. Then, growth rate (VL), cooling rate (CR), and local solidification time (tSL) were determined from measured temperature profiles. Secondary dendritic spacings (λ2), Si particles, Fe-rich and Al2Cu intermetallic phases were characterized by optical and SEM microscopy, as well as the area mapping and point-wise EDS microanalysis. Hence, the interrelations involving Vickers microhardness (HV), yield strength (σYS), ultimate tensile strength (σUTS) and elongation (E%) with microstructural features were evaluated by mathematical equations. IMCs as well as morphologies of Si were also analyzed in the fracture regions. In addition, the experimental growth law of λ2 = f(tSL) proposed in this study was compared with a predictive theoretical model reported in the literature for multicomponent alloys. It was observed that areas that tend to grow faster (lowest λ2 values) were associated with the highest σUTS and E% values, while HV and σYS properties were not affected by the thermal and microstructural parameters (CR and λ2). In addition, less extensive cleavage planes accompanied by small dimples in were observed in fractured samples with lower λ2 values.

Modification of Hypereutectic Al–20 wt%Si Alloy Based on the Addition of Yttrium and Al–5Ti–1B Modifiers Mixing Melt

The effect of the addition of yttrium (Y) and Al–5Ti–1B modifiers mixing melt (3M) on the microstructure and mechanical properties of hypereutectic Al–20Si alloy was studied in the present work. The as-cast specimens were examined by scanning electron microscope equipped with energy spectrometer, electron probe microanalysis and X-ray diffraction. The results demonstrated that the morphology of primary Si could be refined from coarse irregular star-like/plate-like structures into fine blocks with the addition of 0.6 wt% Y and 1.0 wt% Al–5Ti–1B at 650 °C. The average grain size of primary Si was reduced from 82 to 29 µm, and the aspect ratio was decreased from 1.81 to 1.47. Similarly, the eutectic Si structure was modified from coarse needlelike/flake-like structures into fine coral fibrous structures and partial granular structures, with the mean roundness of eutectic Si decreased from 7.8 to 2.32. In addition, the coarse α-Al dendrites were significantly refined into the uniform equiaxed dendrites. With the refinement and homogenization of Si phases, the optimal modified alloy obtained the optimal ultimate tensile strength (UTS) and elongation (EL). The UTS was enhanced from 94 to 154 MPa, and the EL was increased from initial 1.12 to 1.79%. Furthermore, the refinement and modification mechanism of the addition of yttrium and Al–5Ti–1B modifiers mixing melt on Al–20Si alloy were also discussed.

Vertical twin-roll cast Al-50Si alloy with different Mg content

In the present work, the sheets of Al-50Si alloys with different Mg content (0, 5, and 10 wt% Mg) are fabricated by vertical twin-roll casting (VTRC) technology at different roll-casting speeds. The size and morphology of primary Si are studied systematically. The central congregation mechanism of primary Si and the central fracture mechanism as well as the relationship between thickness and roll-casting speed are illuminated in detail. The thickness of the sheet increases with decreasing of roll-casting speed. The central congregation phenomenon of primary Si and the layer phenomenon caused by crack will appear when the roll-casting speed is slow. The size of primary Si and the hardness of alloy are mainly influenced by roll-casting speed and Mg content. The min size of primary Si and the max value of hardness obtained at the speed of 30 m min−1 with 10% Mg content are 7.0 μm and 384, respectively.

Effect of heat treatments on fatigue property of selective laser melting AlSi10Mg

The fatigue property of selective laser melting AlSi10Mg samples with different heat treatments was investigated. The samples were tested in the state of as-built condition, stress relief treatment, solution treatment and solution + artificial aging treatment. It is found that the as-built sample displays the highest fatigue property, and the solution treatment samples exhibit the lowest fatigue property. Heat treatment reduces the fatigue property. The fatigue cracks originate from the surface or subsurface of all the samples, surface or subsurface pores have quite important effect on fatigue property. It is found that the fatigue property is closely related to the yield strength other than ultimate tensile strength or elongation. The change in fatigue property and static mechanical properties is mainly due to the microstructural transformation. Heat treatment changes the size and morphology of Si, which leads to a decrease in fatigue property.

Microstructure and mechanical properties of Al–Si–Mg–Cu–Ti alloy with trace amounts of scandium

ABSTRACTThe effect of Sc on the microstructure and mechanical properties of Al–Si–Mg–Cu–Ti alloy was investigated. Results obtained in this research indicate that, with increasing Sc content, the microstructure of the investigated alloys exhibits finer equiaxed dendrites with rounded edges and the morphology of the eutectic Si shows a complete transition from a coarse needle-like structure to a fine fibrous structure upon modification of eutectic Si. Subsequent T6 heat treatment had further induced the precipitation of nano-scaled secondary Al3(Sc, Ti) phase, as well as spheroidisation of eutectic Si. Combined with T6 heat treatment, the ultimate tensile strength, yield strength, percentage elongation and hardness were achieved in 0.20 wt-% Sc-modified alloy.

Modification of eutectic Si and the microstructure in an Al-7Si alloy with barium addition

The effect of Barium (Ba) addition (0, 0.05, 0.15, 0.5 wt. pct) on the microstructure and mechanical properties of an Al-7Si alloy was studied. Differential scanning calorimetry was employed to analyze the nucleation behavior of eutectic Si. Transmission electron microscopy was used to clarify growth mechanism of eutectic Si. The result indicates that the addition of 0.15 wt. pct Ba modifies the morphology of eutectic Si from coarse flake-like to fine fibrous, which dramatically improves the ultimate tensile strength and elongation. However, Ba addition (≥ 0.15 wt. pct) induces the formation of coarse blocky Ba containing phase (i.e. Al2Si2Ba phase) and porosity increment, and resultantly has a deleterious effect on the ductility. Thermal analysis reveals that Ba addition suppresses the nucleation of eutectic Si due to the formation of Ba3P2 phase. Significant multiply Si twins with high density was observed in the Ba containing alloy, which provides an experimentally support to the impurity-induced twinning growth mechanism.

Synchrotron radiation micro-beam analysis of the effect of strontium on primary silicon in Zn–27Al–3Si alloy

The influence of Sr on two- and three-dimensional morphology of primary Si in Zn–27Al–3Si alloy was investigated. Distribution and crystalline structure of Sr were analyzed by using synchrotron radiation micro-beam. The results show that Sr could modify polygonal primary Si to nearly standard spherical shape. Modified primary Si enriched with Sr, which partially evolves as Al2Si2Sr, while partially presents as independent atoms. Sr promotes high-density paralleled and intersected {111}Si twins during the growth of primary Si. These observations thus provide experiment evidence to support the modification mechanisms based on impurity-induced twinning and poisoning of twin plane reentrant edge.

Effect of yttrium addition on the microstructures and mechanical properties of hypereutectic Al-20Si alloy

The effects of Y additions (0.2, 0.4, 0.6, 0.8 and 1.0 wt%) on the microstructure and mechanical properties of hypereutectic Al-20Si alloy have been studied in the present work. The as-cast specimens were examined by scanning electron microscope (SEM) equipped with energy spectrometer (EDS), electron probe micro-analysis (EPMA) and X-ray diffraction (XRD). The results demonstrated that the morphology of primary Si could be refined from coarse irregular star-like and plate-like shape to fine block-like when the addition contents of Y increased to 0.8%. The average size of primary Si reduced by 62.9% from 89 µm to 33 µm and the aspect ratio decreased by 38.6% from 2.07 to 1.27. In addition, the eutectic Si structure was modified from coarse needle / flake to fine coral fibrous structure and partial particles. With the refinement and homogenization of Si phases, the optimal elongation (El) increased by 22.5% from 1.13% to 1.36% when the Y content was 0.6%. However, the ultimate tensile strength (UTS) enhanced by 47.9% from 94 MPa to 139 MPa when the addition content of Y was up to 0.8%. Moreover, the refinement and modification mechanism of Y on Al-20Si alloy was also discussed.

Fabrication of low reflective nanopore-type black Si layer using one-step Ni-assisted chemical etching for Si solar cell application

Nanotextured Si fabricated through metal-assisted chemical etching (MACE) technique exhibits a promising potential for producing antireflective layer for photovoltaic (PV) application. In this study, a novel single-step nickel (Ni) assisted etching technique was applied to produce an antireflective, nonporous Si (black Si) in an aqueous solution containing hydrofluoric acid (HF), hydrogen peroxide (H2O2) and NiSO4 at 40 °C. Field emission scanning electron microscope was used to characterize different morphologies of the textured Si. Optical reflection measurements of samples were carried out to compare the reflectivity of different morphologies. Results indicated that vertical as well as horizontal pores with nanosized diameters were bored in the Si wafer after 1 h treatment in the etching solution containing different molar ratios of H2O2 to HF. Increasing H2O2 concentration in electrochemical etching solution had a considerable influence on the morphology due to higher injection of positive charges from Ni atoms onto the Si surface. Optimized concentration of H2O2 led to formation of an antireflective layer with 2.1% reflectance of incident light.