Morphology Of Primary Si Research Articles

Effect of pulsed magneto oscillation and phosphorus on microstructure and tensile properties of as-cast Al-25% Si alloy

Abstract The effect of pulsed magneto oscillation (PMO) on the microstructure and tensile properties of Al-25% Si alloys with and without phosphorus addition was investigated. When PMO was applied to the melt during solidification, the results show that the PMO treatment is an effective method for refining the primary Si of Al-25% Si alloy with and without phosphorus addition. The morphology of primary Si was considerably refined via coarse dendritic and polygon shape to fine and regular block under the PMO treatment, and the average size of primary Si was refined to 30.8 μm and 45.3 μm under the optimal processing conditions for the alloy with and without phosphorus addition, respectively. The tensile strength and elongation of the alloys first increased and then decreased with rise of current. Analysis shows that application of PMO decreases Gibbs free energy and critical nucleus radius of the Al-25% Si alloy during solidification. The nucleation rate first increased and then decreased with increasing PMO intensity. The variation tendency of average number of primary Si per unit area is consistent with the theory analysis.

Research on Distribution and Morphology of Primary Si Under the Effect of Direct Current

Research on Distribution and Morphology of Primary Si Under the Effect of Direct Current

Effect of Strontium Modification on the Morphology of Primary Si in Hypereutectic Al-Si Alloys

In the present study, hypereutectic Al-Si alloys were modified by strontium and the effect of the strontium content and holding time on the morphology of primary Si was investigated. Primary Si is modified to imperfect octahedron with primary dendrites or secondary dendrites when the amount of Sr exceeds 0.04wt.%. With extending the holding time, there is no significant difference with the morphology of primary Si. However, the size of primary Si decreases remarkably when the holding time prolongs to 120min. Further analysis reveals that the Sr content has a considerable impact on the morphology of primary Si due to growth mechanism influence, while the modifying time mainly influences the size of primary Si.

The evolution on the microstructure and thermal expansion behavior of Al–50Si alloy with different P contents

In the previous work, the Al–50Si alloy with fine primary Si is prepared by a low-cost technology. In addition, the morphology of primary Si and the metamorphic mechanism as well as the thermal expansibility of alloy are also investigated in this work. The mean size of primary Si can obtain the min value of 33.82 µm when the content of modifier is 3%. The thermal expansibility of alloy decreases with the increasing of modifier. The influence of microstructure, solid solubility as well as porosity on the thermal expansibility are also studied in this research. Moreover, several theoretical models such as ROM model, Turner model, Kerner model and Schapery model are also used to predict the coefficient of thermal expansion (CTE) of alloy.

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 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.

Effects of rare-earth element addition and heat treatment on the microstructures and mechanical properties of Al-25 % Si alloy

AbstractThe effects of pouring temperature, the content of a rare earth (RE) metal modifier, and T6 heat treatment on the microstructure and mechanical properties of Al-25 % Si alloy were investigated. The results show that for the unmodified alloy, the morphology of primary Si was transformed from coarse polygons and platelets to fine polyhedral, and the average size decreased with increasing pouring temperature. The primary Si exhibited a small blocky morphology with an average size of 47 μm at an optimal content of 1.2 % RE. The tensile strength and elongation were enhanced by the addition of RE followed by the T6 heat treatment, and the maximum tensile strength and elongation (208.3 MPa and 1.01 %) were obtained for the sample modified with 1.2 % RE followed by the T6 heat treatment.

Refinement of primary Si in the bulk solidified Al-20 wt.%Si alloy assisting by high static magnetic field and phosphorus addition

Effects of high static magnetic field (HSMF) on microstructures and solidification process of Al-20 wt.%Si alloys with and without phosphorus addition (P addition) have been investigated. The size of primary Si (SPS) is refined continuously as the increase of magnetic flux density (B), and the minimum SPS value is about 15.4 μm when B is 29 T without P addition. However, the SPS decreases firstly and then increases as the increasing B combined with P addition, the average SPS value reaches to the minimum about 21.1 μm when B is 1 T. A unified refinement mechanism has been suggested based on the theory of thermodynamic nucleation and kinetic growth under the HSMF. And the influence of P addition on the morphology of primary Si has also been discussed.

Effects of Primary Si and Applied Load on the Dry Sliding Wear Behaviors of Hypereutectic Al-20Si Alloy

The effects of the primary Si phase and applied load on the dry sliding wear behaviors of hypereutectic Al-20Si alloy were investigated. The results show that coarse polygonal and star-like primary Si was refined into fine blocky shape by increasing superheat treatment temperature. The friction coefficient and wear rate significantly decrease after decreasing the size and changing the morphology of primary Si. Moreover, the friction coefficient and wear rate increase with the increase of applied load. Therefore, the wear properties are greatly influenced by the parameters like morphology and size of primary Si as well as applied load.

Effect of T6 Heat Treatment on Dry Sliding Frictional Wear Characteristics of Al-20Si-5Cu Alloy

The effect of T6 heat treatment on dry sliding friction and wear characteristics of Al-20Si-5Cu under a fixed sliding speed of 200r/min and sliding time of 30mins was illustrated in this paper. The result reveals that T6 heat treatment can improve morphology of primary Si and Al2Cu particles, enhance the hardness of the matrix. Wear rate increased with increasing of applied load. T6 heat treated samples have high wear resistance which is related to the improvement of microstructure, particularly with their increased hardness of matrix. But friction coefficient varies with heat treatment processes and has no sensitivity to applied loads, which fluctuates in a small range, so the friction coefficient can be considered to be stable. The wear mechanisms of T6 heat treated samples are also changed with increasing of applied load, from oxidative wear to fatigue wear.

Coarsening Mechanism of Isothermal Heat Treatment for ADC14 Semi-Solid Alloy

The strain-induced melt activation (SIMA) process is one form of the thixoforming for aluminum alloy. However, the non-uniform stress distribution restricts its application. In order to avoid this problem, a chip recycling strain-induced melt activation (CR-SIMA) process has been developed to prepare semi-solid billet. Microstructures of semi-solid ADC14 aluminum alloy billets heated to different temperatures and held for various times were investigated. The typical semi-solid microstructure with globular solid particles distributed in the liquid matrix is obtained in the temperature range of 560 and 565oC. The spheroidizing mechanism of ADC14 alloy prepared by the CR-SIMA process was studied. It was found that the severe deformation not only influences the solidification of spherical α-Al particles, but also affects the morphology of primary Si. The primary Si phases become tiny particles and distribute around the α-Al particles.

Effect of Nd on Structure and Properties of Hypereutectic Al-Si Alloys

The influence of Nd on structure and properties of hypereutectic Al-Si alloys (Al-17.5%Si, Al-25%Si) was investigated in this paper. For Al-17.5%Si alloy, there is no obvious variation in morphology of primary Si before and after Nd modification, but the average size of primary Si is decreased from 34.73µm to 23.39µm after 0.3%Nd modification. Compared with initial sample, the tensile strength and yield strength of 0.3%Nd-modified sample are increased by 11.6% and 1.5%, and wear resistance of Al-17.5%Si alloy is enhanced to a factor of 2.1 after 0.3%Nd modification. However, for Al-25%Si alloy, the tensile strength and yield strength of 0.3%Nd-modified sample are respectively improved by 22.1% and 9.5% as compared to initial sample. Meanwhile, wear resistance of modified sample is improved to a factor of 3 relative to initial sample. The property improvement of two alloys can be attributed to the change in morphology and size of primary Si after Nd modification.

Kinetic Analyses of the Growth and Dissolution Phenomena of Primary Si and α-Al in Partially Molten Al-Si (-Cu-Mg) Alloy Particles Using In Situ Transmission Electron Microscopy

The growth and dissolution behavior of primary Si and α-Al in partially molten hypereutectic Al-Si–based alloy particles was investigated using in situ TEM to reveal the dynamic and instantaneous processes occurring during these phenomena. Direct evidence for the preferential growth of Si {113} facets compared with {111} facets resulting in prominent {111} facets bounding the Si crystals was obtained. The nucleation of primary Si was found to occur heterogeneously on the encapsulating alumina shell, whereas the α-Al phase nucleated homogeneously from the liquid Al-Si phase. The morphology of primary Si during growth was found to be highly faceted during growth but smoothly curved during dissolution, revealing fundamental mechanistic differences during these processes. We provide a ledge-based interpretation to explain the difference in growth and dissolution behavior. The α-Al phase displayed smoothly curved growth and dissolution morphologies, which are characteristic of an isotropic interfacial energy and a continuous growth mechanism.