Effect of Strontium Modification on Hydrogen Content and Porosity Shape of Al-Si Alloys

Bian, Xiu Fang; Zhang, Zhong Hua; Liu, Xiang Fa

doi:10.4028/www.scientific.net/msf.331-337.361

Cited by 24 publications

(14 citation statements)

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“…Bian and co-workers 105 also studied the effect of strontium modification on the hydrogen content and pore shape in Al-Si alloys, and found that Sr addition markedly increases the hydrogen content in the Al-Si melts and accelerates the gassing rate of the melt. They concluded that Sr-containing oxide films (SrO.A^Os) are less protective than pure alumina (AI2O3), and are responsible for the more rapid gas pick-up in modified alloys.…”

Section: Role Of Sr Modificationmentioning

confidence: 99%

Paramètres métallurgiques contrôlant l évolution microstructurale dans les alliages de fonderie Al-Si-Mg et Al-Si-Cu

Liu¹

2004

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With their characteristics of low specific gravity, low melting point, excellent castability and good corrosion resistance, aluminum-silicon (Al-Si) alloys are extensively employed in automotive applications. Castings produced from these alloys range from transmission cases and intake manifolds to more critical components such as engine blocks, cylinder heads and wheels.Two of the most popular commercial alloys used in such applications are the A356 and 319 type alloys, belonging to the Al-Si-Mg and Al-Si-Cu alloy systems. The casting quality and properties are determined by the quality of their microstructure, controlled by various parameters such as the dendrite arm spacing (DAS -as determined by the solidification rate), the degree of eutectic Si modification and grain refinement, and the amount of microporosity, intermetallics and inclusions observed in the microstructure. Among these, solidification rate is the most important, as it directly or indirectly affects almost all the other microstmctural parameters.Modification of the eutectic silicon morphology from its acicular, flake-like form to a fibrous form is usually carried out through the addition of strontium (Sr) to improve the alloy ductility. Intermetallics commonly present in these alloys are the P-AlsFeSi and a-Al 5 (Fe,Mn) 3 Si2 iron intermetallics, sludge, Mg2Si and, in the case of 319 alloys, the copper intermetallic, CuAl 2 . Due to its brittle, platelet-like nature, the P-AlsFeSi iron intermetallic can be quite deleterious to the alloy properties, as can the presence of porosity, particularly in terms of surface quality and soundness.The aim of the present work has been to investigate the metallurgical parameters controlling the microstmctural evolution of Al-Si-Mg and Al-Si-Cu alloys, through a study of the microstmctural characteristics of directionally solidified A356 and 319 type alloys as a function of iron content, Sr addition (~250 ppm), and cooling rate. The iron levels selected varied from 0.12 to 0.8 wt pet, and cover the range of Fe levels found in commercial casting alloys. The use of an end-chill mold provided different cooling rates along the height of the same casting, with DAS values that varied from ~23 to 85 |^m, corresponding to levels of 5, 10, 30, 50 and 100 mm above the chill end.The effects of these variables on the precipitation of the P-Al 5 FeSi phase, the characteristics of the a-Al dendrite stmcture, eutectic silicon modification, and porosity formation were examined in detail. Various techniques were used for microstmctural characterization and phase identification, including optical and scanning electron microscopy, electron probe microanalysis coupled with energy dispersive X-ray (EDX) and wavelength dispersive spectroscopy (WDS) facilities, and thermal analysis. An image analyzer was used in conjunction with the optical microscope for quantification purposes.

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Section: Role Of Sr Modificationmentioning

confidence: 99%

Paramètres métallurgiques contrôlant l évolution microstructurale dans les alliages de fonderie Al-Si-Mg et Al-Si-Cu

Liu¹

2004

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“…[19][20][21][22] However, although there are several contradictory results, [13,14,23,24] contradictory results are perhaps to be expected. This is because the melt would be expected to increase its hydrogen content only because of an increased rate of oxidation in the presence of environmental water vapor, as is to be expected, and as may only occur if the surface of the melt is disturbed so as to expose fresh surface for oxidation.…”

Section: Introductionmentioning

confidence: 96%

Precipitation of Sr-rich intermetallic particles and their influence on pore formation in Sr-modified A356 alloy

Miresmaeili¹,

Campbell

Shabestari

et al. 2005

Metall Mater Trans A

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The nature of enhanced pore formation in Sr-modified A356 Al alloy melts has been investigated, leading to the observation of the precipitation of Sr-rich compounds on the wetted side of oxide films. Scanning electron microscopy of casting surfaces showed that the surface oxide film might be a good possible nucleation site of Sr-rich compounds. The observation of internal pores using secondary electron microscopy and X-ray microanalysis mapping showed precipitation of Sr-rich compounds on the wetted side of the oxide films in most pores. The possibility of Sr-rich intermetallics being nucleated on oxide films was assessed by determining their planar disregistry factor; good matching planes were found between Al 2 Si 2 Sr intermetallics and ␥-Al 2 O 3 and spinel oxide films. The crystallographic alignment revealed in scanning electron microscope (SEM) images also corroborates an epitaxial relationship. Mechanisms by which Sr in Al-Si alloys may contribute to the formation of porosity are discussed.

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“…It was also reported that Sr may enhance the hydrogen solubility in the melts. 69 It is interesting to note that, in general, the pore length in alloy Y6S is higher than it is in Y1S when the temperature is below 500°C. When the temperature reaches 520°C, however, the reverse is observed.…”

Section: Porosity Characteristicsmentioning

confidence: 99%

“…Bian et al 69 used the HYSCAN II apparatus to measure the hydrogen content in unmodified and modified hypoeutectic Al-10wt%Si alloy melts. The results showed that Sr-addition markedly increased the hydrogen content and accelerated the gassing rate of the Al-Si melts.…”

mentioning

confidence: 99%

Phénomène de fusion locale des phases du cuivre dans les alliages Al-Si-Cu-Mg /

Yumei¹

2007

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Effect of Strontium Modification on Hydrogen Content and Porosity Shape of Al-Si Alloys

Cited by 24 publications

References 0 publications

Paramètres métallurgiques contrôlant l évolution microstructurale dans les alliages de fonderie Al-Si-Mg et Al-Si-Cu

Paramètres métallurgiques contrôlant l évolution microstructurale dans les alliages de fonderie Al-Si-Mg et Al-Si-Cu

Precipitation of Sr-rich intermetallic particles and their influence on pore formation in Sr-modified A356 alloy

Phénomène de fusion locale des phases du cuivre dans les alliages Al-Si-Cu-Mg /

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