Directional Solidification of Mg-Al Alloys and Microsegregation Study of Mg Alloys AZ31 and AM50: Part I. Methodology

Mirković, Djordje; Schmid–Fetzer, Rainer

doi:10.1007/s11661-009-9787-3

Cited by 27 publications

(13 citation statements)

References 32 publications

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“…It has been reported that the Al content of α-Mg cores in Mg-Al alloys depends on alloy composition and on the casting technique. [55][56][57] In the RC technique, an excess of solid fraction is generated during slurry preparation. These α-Mg particles have a solidus temperature corresponding to the liquidus temperature of the alloy, suggesting that they melt only by diffusion of Al into them.…”

Section: Discussionmentioning

confidence: 99%

Atmospheric Corrosion of Mg Alloy AZ91D Fabricated by a Semi-Solid Casting Technique: The Influence of Microstructure

Esmaily

Mortazavi

Svensson

et al. 2015

J. Electrochem. Soc.

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The atmospheric corrosion behavior of alloy AZ91D produced by a semi-solid metal (SSM) technique and by conventional high pressure die casting (HPDC) was investigated for up to 1176 hours in the laboratory. Alloy AZ91D in the SSM state was fabricated using a rheocasting (RC) technique in which the slurry was prepared by the RheoMetal process. Exposures were performed in 95% RH air at 22 and 4 • C. The RC alloy AZ91D exhibited significantly better corrosion resistance than the HPDC material at two temperatures studied. The effect of casting technology on corrosion is explained in terms of the microstructural differences between the materials. For example, the larger number density of cathodic β phase particles in the HPDC material initially causes relatively rapid corrosion compared to the RC material. During later stages of corrosion, the more network-like β phase particles in the RC alloy act as a corrosion barrier, further improving the relative corrosion resistance of the RC material. Conventional magnesium-aluminum (Mg-Al) alloys, i.e., AZ91D, AM50A and AM60B, offer an exceptional combination of ambient temperature strength and ductility, and good die-castability.1-4 Cast components made of Mg-Al alloys are usually cast by conventional high pressure die casting (HPDC). Despite its advantages over many other casting techniques for producing cast Mg-Al components, there are some inherent problems associated with HPDC. For example, there is a tendency for hot tearing during HPDC due to a relatively wide freezing range and a low solidus temperature. Also, a relatively high fraction of trapped air porosity may form during the turbulent die filling, especially in thick-walled components. Additionally, insufficient resistance to atmospheric and aqueous corrosion sometimes limits Mg-Al alloys applications in the fields of automobiles, aerospace, electronics, etc.5-8 During the past two decades, there have been extensive efforts to increase the corrosion resistance of Mg-Al alloys. Much of the effort has concentrated on the use of various coating systems such as chemical conversion coatings, anodizing, gas-phase deposition processes electro-or electro-less plating, and organic coating. [9][10][11][12][13][14][15] Lowering the impurity levels, alloying, rare earth additions, and heattreatment have also been explored to increase the corrosion resistance of these alloys. [16][17][18][19][20] Alternative casting processes are being developed to resolve the mentioned problems and meet the requirements of future applications of Mg-Al alloys. Semi-solid metal (SSM) processing is a promising manufacturing route capable of producing castings with a high level of complexity. 21,22 The main advantage of SSM processing, compared to the conventional casting processes, is the possibility to have a laminar flow of metal during mold filling.23 This is a consequence of the higher viscosity of the semi-solid material, and it reduces air entrapment compared to die-casting. This results in components with enhanced microstructural proper...

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Section: Discussionmentioning

confidence: 99%

Atmospheric Corrosion of Mg Alloy AZ91D Fabricated by a Semi-Solid Casting Technique: The Influence of Microstructure

Esmaily

Mortazavi

Svensson

et al. 2015

J. Electrochem. Soc.

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“…Segregation in Mg-based alloys has been studied via directional solidification. [24][25][26][27][28] The resulting microstructure depends strongly on the withdrawal rate used during directional solidification, since this controls the cooling rate of the alloy. [25] Many of these directional solidification studies have been undertaken as part of a larger study of the thermodynamic equilibrium in Mg alloy systems.…”

Section: Introductionmentioning

confidence: 99%

Partitioning of Solute to the Primary α-Mg Phase in Creep-Resistant Mg-Al-Ca–Based Cast Alloys

TerBush

Saddock

Jones

et al. 2010

Metall Mater Trans A

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The partitioning of elements during solidification of ternary and quaternary Mg-Al-Ca alloys has been measured by an electron microprobe segregation mapping technique. Differences in the degree of partitioning of Al and Ca to the a-Mg phase in as-solidified MRI230D, AX44, AXJ530, and MRI153M alloys was observed. MRI230D has a higher level of Al and Ca in the primary a-Mg phase, while only a higher level of Al is observed in MRI153M, compared with AX44 and AXJ530. While the increased levels of Al in the MRI alloys may be due in part to higher bulk Al concentrations, the higher level of Ca in the primary phase of MRI230D is attributable to the presence of Sn in this alloy. The differences in the partitioning of Al and Ca to the primary a-Mg phase during solidification influence both solid solution and precipitation strengthening, which can explain observed differences in creep behavior.

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“…[1] The main purpose of the present Part II is a comprehensive comparison of the Mg alloys AZ31 and AM50 with respect to their solidification behavior during directional solidification (DS), including a systematic variation of cooling rate. The microstructure and microsegregation developed during DS are in the focus of this comparison.…”

Section: Introduction and Proceduresmentioning

confidence: 99%

“…[1] This improved experimental procedure comprises sample tube material selection and protective coating, filling of tubes and DS procedure, and finally microstructure and microsegregation characterization. The dedicated processing of the quantitative EPMA data, as well the calculation of the Scheil-total solute profiles, is specified in Part I.…”

Section: Introduction and Proceduresmentioning

confidence: 99%

“…The dedicated processing of the quantitative EPMA data, as well the calculation of the Scheil-total solute profiles, is specified in Part I. Details on the starting material and compositions of the alloy AZ31 are also given in Part I [1] of this work. The ingot chemical composition of the alloy AM50 is shown in Table I, where the Fe, Cu, and Ni contents are not shown, being less then 50 lg/g.…”

Section: Introduction and Proceduresmentioning

confidence: 99%

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Directional Solidification of Mg-Al Alloys and Microsegregation Study of Mg Alloys AZ31 and AM50: Part II. Comparison between AZ31 and AM50

Mirković

Schmid–Fetzer

2009

Metall Mater Trans A

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Directional solidification (DS) of magnesium alloys AZ31 and AM50 was carried out to investigate microstructures and microsegregation under controlled solidification conditions. The methodology used is based on a customized DS technique elaborated on in Part I of this work. Dendritic microstructures observed in longitudinal sections of the quenched mushy zone, X-ray maps of fully directionally solidified cross sections, and quantitative solute profiles reveal the impact of cooling rate and alloy type. The solute-solvent correlation discloses the opposite segregation behavior of manganese compared to both aluminum and zinc and provides an impartial basis for the advanced weighted-interval ranking sort (WIRS) sorting scheme of electron probe microanalysis (EPMA) data. Precipitates Al 8 Mn 5 and c-Mg 17 Al 12 , predicted by thermodynamic calculations, are identified in the microstructure. The effect of back-diffusion during solidification, most pronounced for the component zinc, was clearly observed for both alloys in comparison with dedicated Scheil-total calculations.

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Directional Solidification of Mg-Al Alloys and Microsegregation Study of Mg Alloys AZ31 and AM50: Part I. Methodology

Cited by 27 publications

References 32 publications

Atmospheric Corrosion of Mg Alloy AZ91D Fabricated by a Semi-Solid Casting Technique: The Influence of Microstructure

Atmospheric Corrosion of Mg Alloy AZ91D Fabricated by a Semi-Solid Casting Technique: The Influence of Microstructure

Partitioning of Solute to the Primary α-Mg Phase in Creep-Resistant Mg-Al-Ca–Based Cast Alloys

Directional Solidification of Mg-Al Alloys and Microsegregation Study of Mg Alloys AZ31 and AM50: Part II. Comparison between AZ31 and AM50

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