Effect of Silicon on the Thixoformability of Al-Si-Cu Alloys

Benati, Davi Munhoz; Zoqui, Eugênio José

doi:10.1007/s11665-014-1103-8

Cited by 7 publications

(4 citation statements)

References 23 publications

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“…Based on Liu et al 's theory [7], recent studies have been focused on the evaluation the thixoformability through processing temperature and modifying alloy elements [8][9][10].…”

Section: Introductionmentioning

confidence: 99%

What is the Process Window for Semi-solid Processing?

Zhang

Dong

Atkinson

2015

Metall Mater Trans A

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Abstract.In semi-solid processing, the liquid fraction versus temperature is commonly used to define the process window.Conventionally it is assumed a freezing range is required for semi-solid processing but recently both high-purity aluminium and binary Al-Si eutectic alloy have been rheo-processed. Here, the kinetics during melting and solidification of pure metal are analyzed and a comparison between the liquid fraction versus temperature and the liquid fraction versus time presented. It is found that liquid fraction versus time is a significant criterion for semi-solid processing.Keywords: Process window; Aluminium; DSC; Semi-solid processing Process window is defined as a collection of process parameters that allow materials to be manufactured and to operate under desired specifications [1]. In semi-solid processing, the process window is related to a stage between the solidus and the liquidus of a metallic alloy. Semi-solid processing from a solid state starting point (thixoforming) is normally carried out with between 30% and 50% liquid as it leads to an optimum slurry viscosity and a good die filling property [2,3,4]. Kazakov [5] examined the processability from a thermodynamic prediction and Differential Scanning Calorimetry (DSC) view point focusing on the slope of the liquid fraction versus temperature. He defined several critical parameters including that the slope ( / ) of the liquid fraction versus temperature curve and noted that at 50% fraction liquid this should be relatively low. Atkinson et al. [6] identified that it is the slope of the liquid fraction versus temperature curve in the region of 30-50% liquid which is the key parameter. More recently, Liu et al. [7] using the MTDATA thermodynamic package and DSC predicted the liquid fraction sensitivity ( / ) =0.4 at 40% fraction liquid (mid-way through the process range of 30-50% liquid) and argued that it should not change too rapidly with temperature in the process window.As pure metals and the eutectic alloys do not have a freezing (or melting) range, it has been conventionally expected that it is not possible for them to be semi-solid processed because ( / ) is ∞. Based on Liu et al. 's theory [7], recent studies have been focused on the evaluation the thixoformability through processing temperature and modifying alloy elements [8][9][10].Surprisingly Curle et al. [11,12] recently demonstrated that both high-purity aluminium and binary Al-Si eutectic alloy can be rheocast. Rheocasting involves cooling from the liquid state into the semi-solid range and forming at about 60% liquid or higher. This is a different approach from thixoforming but the principles that will be drawn out in this paper are applicable in both cases. Curle et al. [11,12] identify that the processing in the semi-solid state is achievable because of the solidification kinetics during the thermo-arrest i.e. solidification is not instantaneous. It seems, therefore, that time can be a critical factor during processing and not just temperature. In addition, this will be rele...

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“…Based on Liu et al 's theory [7], recent studies have been focused on the evaluation the thixoformability through processing temperature and modifying alloy elements [8][9][10].…”

Section: Introductionmentioning

confidence: 99%

What is the Process Window for Semi-solid Processing?

Zhang

Dong

Atkinson

2015

Metall Mater Trans A

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“…The apparent viscosity (l) and average shear rate (_ c) were obtained according to Eqs. [5] and [6], respectively.…”

Section: Hot Compression Testsmentioning

confidence: 99%

“…[5] Among these techniques, chemical grain refinement by the addition of elements such as Ti and B is advantageous compared with the traditional routes as it does not require any specific equipment to obtain an equiaxial microstructure, resulting in a simple and cheap technique for obtaining a good-quality semi-solid material. [6] One of the issues related to the grain refinement technique in aluminum alloys is the poisoning effect of Si, where Si levels > 3 pct decrease the effect of the refining elements. [7] Several studies have been conducted trying to overcome this effect.…”

Section: Introductionmentioning

confidence: 99%

The Influence of Strontium on Microstructural and Rheological Behavior of the Semi-solid A380 Aluminum Alloy

Ferreira

Lourençato

Roca

et al. 2020

Metall Mater Trans A

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This article aims to correct the lack of information regarding the combined effect of grain refinement and strontium modification on the microstructure and rheological behavior of semi-solid slurries. The A380 aluminum alloy was studied in the semi-solid state in three different conditions: as received, grain refined and grain refined/modified with Sr. To determine the semi-solid temperature, a DSC analysis and Thermo-calcÒ simulations were used. SEM, optical and polarized light microscopy analyses were performed to analyze the microstructural changes caused by the refiner and modifier agents as well as to evaluate the morphological evolution of the alloys in the semi-solid state. The rheological behavior was studied with a hot compression test between parallel plates. The main results show that the addition of Sr, besides its influence on the Si and Fe-b particles, also leads to a better globularization of a-Al phase particles in the semi-solid state. Furthermore, the rheological analysis of stress vs strain and apparent viscosity vs average shear rate also point to a better behavior of the alloy in the semi-solid state after Sr modification, thus indicating that Sr addition could improve the performance of the A380 alloy as a semi-solid feedstock.

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“…Figura 4 -Microestruturas obtidas pelas diversas rotas de processamento: (a, b) liga Al7Si2.6Cu (similar à liga A356) processada via refi no de grãos reaquecida à temperatura semissólida de 580 °C (BENATI et al, 2014), (c, d) liga A356 processada via agitação mecânica, (e, f) liga A356 processada via agitação eletromagnética, (g, h) liga A356 processada via ECAP reaquecidas à temperatura semissólida de 580 °C (CAMPOS et al, 2013) e (i, j) liga A355 processada via refi no de grãos por ultrassom reaquecida à temperatura semissólida de 595 °C (DE PAULA et al, 2018).…”

Section: Matéria-prima Processada Matéria-prima Reaquecidaunclassified