Spheroidization of Eutectic Silicon in Direct-Electrolytic Al-Si Alloy

Wang, Ruyao; Lu, Weihua

doi:10.1007/s11661-012-1603-9

Cited by 14 publications

(11 citation statements)

References 12 publications

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“…This results in the segregation of Si particles along the α-Al grain boundaries. Also, coral-like eutectic Si fibers are fragmented and disintegrated at the shape discontinuities/instabilities such as joint of the Si branches and/or necks of the Si crystals [3,[25][26][27]. Upon the fragmentation of the Si branches, Si spheroidization is driven through surface self-diffusion (the element changes the location by diffusing on the surface) [28] or Al-Si interdiffusion at Si/Al interface (the silicon atoms move through the aluminum at the Si/Al interface).…”

Section: Microstructure Characterizationmentioning

confidence: 99%

Microstructural and small-scale characterization of additive manufactured AlSi10Mg alloy

Alghamdi

Haghshenas

2019

SN Appl. Sci.

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Additive manufacturing of aluminum alloys is considered a promising layer-wise manufacturing method which can produce lightweight critical automotive/aerospace/military components with enhanced physical and mechanical properties. This paper aims at assessing the correlation between microstructure and small-scale characteristics of an additive manufactured AlSi10Mg alloy in the as-printed and heat treated conditions. Depth-sensing nanoindentation testing, as a non-destructive, robust, and convenient testing approach, along with microstructural assessments, using optical microscopy and scanning electron microscopy, were employed to compare the nano-hardness of the printed (selective laser melting method) and the heat treated (age-hardening) materials. Considering the distance from the build plate, a gradation in the cooling rate, and therefore the microstructure, is expected which directly affect the nano-hardness gradient along the deposition direction. Results show a transition in the microstructure from cellular grains, with corallike silicon fiber colonies, to fragmented/spheroidized eutectic silicon particles upon the heat treatment. Unlike conventionally manufactured AlSi10Mg alloys, upon aging heat treatment in the additive manufactured AlSi10Mg alloy, the nano-hardness is decreased which is mainly contributed to stress relief, elimination of solid solution strengthening, and silicon spheroidization phenomena. These are considered in detail in the current paper.

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Section: Microstructure Characterizationmentioning

confidence: 99%

Microstructural and small-scale characterization of additive manufactured AlSi10Mg alloy

Alghamdi

Haghshenas

2019

SN Appl. Sci.

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“…On the contrary, as Si content is raised from 11.5wt% to 15.6wt% in hypereutectic alloy the Si grain number suddenly drops down; its volume and spacing greatly increase. It is obvious that Si content greatly affects the spheroidization of Si crystal, in which Si diffusion is a controlling factor rather than kinetics of Si growth [34,35]. Zhu and Lui indicated that the rate of diffusion of Si atoms from high to area of low energy is proportional to Si concentration, curvature of surface of Si grains and lattice deformation energy of Si phase, and inversely to the spacing of Si grains [35,49].…”

Section: Fig 12 Plot Of Distribution Of Width(a) Length(b) and Aspmentioning

confidence: 99%

“…Moreover, electrolytic hypereutectic Al-Si alloys with Si concentration up to 17wt% made from DEASA ingot provided a primary-free completely eutectic structure, even in a modified manner [33]. The most important event is that the eutectic Si precipitation in DEASA becomes small nodules after heating at a lower temperature of 505°C-515°C in a shorter time of 4-8 hrs [34] than in a Na-modified eutectic Al-Si alloy [35]. It would be expected that such a hypereutectic Al-Si alloy is capable of a spheroidizing Si phase at a lower temperature of near 510°C for a shorter heating time.…”

Section: Introductionmentioning

confidence: 99%

Hypereutectic Al-Si Alloy with Completely Nodular Eutectic Silicon: Microstructure and Process

Wang¹

2016

IJMSA

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The achievement of hypereutectic Al-Si alloys with completely nodular eutectic Si has been studied. The procedure contained two steps: firstly, achieving hypereutectic direct electrolytic Al-Si alloys (HDEASA) with completely eutectic structure and secondly, spheroidizing eutectic Si upon soaking. HDEASAs with Si level in the range from 13.2 wt% to 17.6 wt% were made from direct electrolytic eutectic Al-Si alloy ingot and Al-50 wt% Si hardener. As cast microstructure of HDEASA was composed of primary-free quasi-eutectic cells. In comparison with commercial alloys, the lower heating temperature of 505°C-515°C for 4-8 hrs was required to fully spheroidize Si crystal, either fine fibrous or even flaky in casting. Most of the spheres ranged in size from 1.0µm to 4.0µm. Many measurements were focused on the variety of Si phase size in eutectic cells against the distance from the center of the cells. The origin of granulation of primary-free quasi-eutectic Si crystal is associated with its thermodynamic structural instability, accompanied by crystallographic defects, related to the electrolytic process.

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“…Similar to the combined processing with solidification rate and Sr additions, it can be expected that other techniques that promote finer, less elongated, and more spherical Si particles will enhance the conductivity of the alloy. This can include spheroidization processes during high temperature heat treatments [164][165][166], as well as fragmentation methods such as ultrasonic vibration [167]. Further research into such techniques is therefore warranted.…”

Section: 4-4 Discussionmentioning

confidence: 99%

Mechanisms of Improving the Thermal and Electrical Conductivity of Aluminum Alloy Cylinder Heads

Vandersluis¹

2023

Preprint

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<p>One of the major causes of premature failure in automotive cylinder heads is the accumulation of thermal stresses, due to their large internal temperature gradients in-service. To ensure mechanical integrity, engine operating temperatures are typically restricted. However, this response reduces fuel efficiency, which increases costs and carbon emissions. A more sustainable solution can involve enhancing alloy conductivity, which improves temperature uniformity in the heads. In aluminum alloys, solidification rate, silicon modification, and precipitation heat treatment have each been reported to influence conductivity. Yet, the mechanisms and interactions regarding these parameters were unclear in the literature. Accordingly, the objective of this dissertation was to provide an in-depth, systematic investigation of the individual and combined effects of these processes on the microstructure and conductivity of automotive 319 aluminum alloy.</p> <p>After performing a baseline characterization of commercial cylinder heads, permanent-mould castings were produced with a range of solidification rates and strontium contents. These castings were analyzed to establish the dominant microstructural factors affecting electron mobility in the as-cast condition. Then, samples were subjected to multiple combinations of solution, natural aging, artificial aging, and direct aging heat treatments, to elucidate the roles of the dissolution, spheroidization and precipitation transformations. Furthermore, this work was complimented by several innovative, state-of-the-art experiments, which were the first to analyze the kinetics of solidification, chemical modification, thermal expansion, dissolution, and precipitation in 319. As a result, this dissertation contributed numerous, novel and meaningful insights regarding heat transfer in aluminum alloys. This included elucidation of the independent, major impacts of porosity, silicon morphology, and the size, distribution and coherency of the aluminum-copper precipitates, despite insensitivity to the dendritic size. The appropriate combination of solidification rate, strontium content, and heat treatment was demonstrated to promote superior conductivity to what was possible through their individual variation. Given low-porosity castings, this research revealed the potential for approximately 40% improvements in thermal and electrical conductivity, compared to the strontium-free, as-cast condition. Overall, the extensive conductivity data generated in this research supports strategic and practical materials processing procedures, demonstrates opportunities for balancing high conductivity with mechanical integrity, and ensures enhanced component performance and environmental sustainability.</p>

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Spheroidization of Eutectic Silicon in Direct-Electrolytic Al-Si Alloy

Cited by 14 publications

References 12 publications

Microstructural and small-scale characterization of additive manufactured AlSi10Mg alloy

Microstructural and small-scale characterization of additive manufactured AlSi10Mg alloy

Hypereutectic Al-Si Alloy with Completely Nodular Eutectic Silicon: Microstructure and Process

Mechanisms of Improving the Thermal and Electrical Conductivity of Aluminum Alloy Cylinder Heads

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