Microstructure, Composition, and Depth Analysis of Surface Films Formed on Molten AZ91D Alloy under Protection of SF6 Mixtures

Xiong, Shengwu; Liu, Xiaolong

doi:10.1007/s11661-006-9035-z

Cited by 24 publications

(17 citation statements)

References 3 publications

(8 reference statements)

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“…Protective atmospheres [34][35][36][37][38][39][40][41][42][43] are used to prevent oxidation or burning of molten Mg and consequently to reduce the formation of inclusions in the melt. Some cover gases, including [34][35][36][38][39][40][41][42][43]. All these compounds can enter the melt and lead to the formation of inclusions.…”

Section: Reactions With Protective Gasesmentioning

confidence: 99%

“…Protective atmospheres [34][35][36][37][38][39][40][41][42][43] are used to prevent oxidation or burning of molten Mg and consequently to reduce the formation of inclusions in the melt. There are two types of protective gas atmospheres [61]: non-reactive gases and oxide film modifiers.…”

Section: Protective Atmospheresmentioning

confidence: 99%

“…The other method of melt protection involves the use of a gas which modifies the magnesium oxide film forming naturally on the surface of the melt, thereby suppressing vaporization. Since the 1970s, the Mg industry has largely used SF 6 to protect Mg melts [30,34,35,42,[61][62][63][64][65][66].…”

Section: Protective Atmospheresmentioning

confidence: 99%

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Inclusion removal and grain refinement of magnesium alloy castings

Elsayed¹

2021

Preprint

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Magnesium alloys show promise to be materials for lightweighting of automotive and aerospace vehicles improving fuel efficiencies and vehicle performance. A majority of magnesium alloy components are produced using casting where susceptibility to forming inclusions and coarse grain sizes could result. Development of effective inclusion removal techniques and better understanding of grain refinement of magnesium alloys could help in improving their mechanical properties to advance them to more structurally demanding applications. This research aimed to develop an environmentally friendly alternative to the grain refinement and inclusion removal capabilities of carbon based hexachloroethane as it releases dioxins, chlorine gas and corrodes foundry equipment. A secondary aim was to pioneer in-situ neutron diffraction to examine the solidification of magnesium alloys. The research involved preparing tensile samples of AZ91E magnesium alloy using permanent mould casting. Inclusion removal was conducted by using filtration and argon gas bubbling. Castings grain refined using hexachloroethane (0.25, 0.50 and 0.75 wt.%) were compared against ex-situ aluminum-silicon carbide and in-situ aluminum-carbon based grain refiners combined with filtration and argon gas bubbling. Further, in-situ neutron diffraction was utilized for phase analysis and fraction solid determination of magnesium-zinc and magnesium-aluminum alloys. There was a significant improvement in yield strength, ultimate tensile strength and elongation with filtration plus argon bubbling, carbon inoculation or both filtration plus argon bubbling and carbon inoculation. The results indicated that the mechanism of the observed ~20% reduction in grain sizes with carbon inoculation (hexachloroethane, ex-situ aluminum-silicon carbide and in-situ aluminum-carbon) was explained through duplex nucleation of Mn-Al and Al-Mg-C-O (likely Al2MgC2) phases. Finally, in-situ neutron diffraction was used to follow the formation of Mg17Al12 eutectic phase in a magnesium-9 wt.% aluminum alloy. For the magnesium-zinc alloys, in-situ neutron diffraction enabled characterization of the effects of zirconium to the fraction solid growth of (1010), (0002) and (1011) α-Mg planes. The societal and environmental impact of this research is significant. There is a clear demonstration of alternatives to the universally used hexachloroethane grain refiner promoting harmful emissions. Improved mechanical properties resulting from new grain refinement and iv inclusion filtration are a major advancement in promoting weight reduction, improved castability and decreased environmental impact for automotive and aerospace industries.

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Section: Reactions With Protective Gasesmentioning

confidence: 99%

“…Protective atmospheres [34][35][36][37][38][39][40][41][42][43] are used to prevent oxidation or burning of molten Mg and consequently to reduce the formation of inclusions in the melt. There are two types of protective gas atmospheres [61]: non-reactive gases and oxide film modifiers.…”

Section: Protective Atmospheresmentioning

confidence: 99%

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Inclusion removal and grain refinement of magnesium alloy castings

Elsayed¹

2021

Preprint

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“…SF 6 is a typical cover gas and still popular in the main Mg-producing countries such as China, Brazil and India [8][9][10] [11]. The oxide film formed in a SF 6containing cover gas has been attracting researchers' attention [10,[12][13][14][15][16][17][18][19][20][21][22][23]. In 1970s, Fruehling [22] found that the surface film formed under SF 6 was MgO and then Couling [23] noticed that the SF 6 was also consumed by reacting with the melt to form MgF 2 and/ or adsorbing into MgO surface film.…”

Section: Introductionmentioning

confidence: 99%

Revealing the structure and evolution of entrained oxide film in Mg–Y alloy castings

Davies

Zhu

2021

J Mater Sci

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The structure and evolution of oxide film in Mg alloys have been a research objective for a long time but are still unclear up to now. In the present work, the structure of the entrained oxide film (which is also known as bifilm) in Mg–Y alloy castings protected by SF6/air cover gas was characterized. It was found that the entrained oxide film can be divided into two typical types: (1) single-layered F-rich films and (2) double-layered films with a F-rich inner layer and a F-poor outer layer. Based on the experimental phenomena and thermodynamic calculation, the evolution mechanism of the oxide film was also revealed. It was found that F element from the cover gas reacted with the melt firstly to form the initial F-rich single-layered film. Then, O and S were also involved in the reaction, transforming the initial film to be a (F, O, S)-rich single-layered film. Finally, when the F element was depleted, the newly formed layer on the existing oxide film is characteristically F-poor but (O, S)-enriched, leading to a double-layered oxide film. It was also found that the oxide film grew faster in SF6/air cover gas than in SF6/CO2 cover gas, resulting in a higher repeatability of mechanical properties of Mg–Y alloy castings.

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“…Since SF 6 has been identified as a GHG [5,7,8], the protective films formed on molten magnesium and its alloys under gas protection have been an active subject of research, with the aim of finding suitable industrial alternatives to SF 6 gas for melt protection [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. The use of SF 6 gas will be banned from the European Union from 2018 [22] (as cited in Reference [23]), in which case, replacement of SF 6 as a cover gas in the Mg industry would no longer be eligible as Clean Development Mechanism (CDM) project or Joint Implementation (JI) project, nor sell the reduced emission as 'carbon credits' [24].…”

Section: Introductionmentioning

confidence: 99%

Melt Protection of Mg-Al Based Alloys

Balart

Patel

Fan

2016

Metals

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This paper reports the current status of Mg melt protection in view to identify near-future challenges, but also opportunities, for Mg melt protection of Mg-Al based alloys. The goal is to design and manufacture sustainable Mg alloys for resource efficiency, recycling and minimising waste. Among alternative cover gas technologies for Mg melt protection other than SF 6 : commercially available technologies containing-HFC-134a, fluorinated ketone and dilute SO 2 -and developed technologies containing solid CO 2 , BF 3 and SO 2 F 2 , can potentially produce toxic and/or corrosive by-products. On the other hand, additions of alkaline earth metal oxides to Mg and its alloys have developed a strong comparative advantage in the field of Mg melt protection. The near-future challenges and opportunities for Mg-Al based alloys include optimising and using CO 2 gas as feedstock for both melt protection and grain refinement and TiO 2 additions for melt protection.

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Microstructure, Composition, and Depth Analysis of Surface Films Formed on Molten AZ91D Alloy under Protection of SF6 Mixtures

Cited by 24 publications

References 3 publications

Inclusion removal and grain refinement of magnesium alloy castings

Inclusion removal and grain refinement of magnesium alloy castings

Revealing the structure and evolution of entrained oxide film in Mg–Y alloy castings

Melt Protection of Mg-Al Based Alloys

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