Observations on the control of grain size in magnesium casting alloys

Holm, V. C. F.; Krynitsky, A. I.

doi:10.6028/jres.039.014

Cited by 2 publications

(5 citation statements)

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“…This treatment consists of just a simple heat cycle in which molten metal is held at an elevated temperature, quickly cooled to the casting temperature and then poured. Many researchers [2][3][4][5][6][7][8] discussed theories of why the treatment effectively produced fine grains, but they could not establish a mechanism. To date, there have been many hypotheses of this grain-refining mechanism.…”

Section: Introductionmentioning

confidence: 99%

Observation of Manganese-Bearing Particles in Molten AZ91 Magnesium Alloy by Rapid Solidification

et al. 2003

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Magnesium alloy AZ91 contains 0.1 to 0.3 mass% manganese as an alloying element. Such manganese always reacts with aluminum and produces various compounds. Actually, numerous Mn-bearing particles are visible in polished surfaces under an optical microscope. Some Mnbearing particles are also expected to be present in molten alloy. We believe that some Mn-Al compounds are closely related to the superheating effect. However, it is not clear specifically what compounds exist in molten alloy and how contribute to grain refinement by superheating. In order to study this subject, we utilized a diffusionless process based on rapid solidification. Two grams of AZ91 alloy was melted in a stainless steel tube and then injected onto a copper wheel rotating at high-speed under various conditions to obtain cast ribbons. Cast ribbon was analyzed by an X-ray diffractometer, an electron probe micro-analyzer and a transmission electron microscope. These analyses indicated that the cast ribbons consist of single phase and that the structure is quite homogeneous, i.e., diffusionless solidification occurs due to rapid cooling. Manganese-bearing particles completely disappear in the melt around 963 K and superheat temperatures, which is inconsistent with presently accepted superheat mechanisms, the temperature-solubility nucleation theory and the temperature-phase relationship theory. In the meantime, cross-shaped Mn-bearing particles are often observed in the ribbons when the melt is cooled from superheat temperatures to the injecting temperature (973 K) before injecting. This treatment may facilitate the formation of these particles.

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Section: Introductionmentioning

confidence: 99%

Observation of Manganese-Bearing Particles in Molten AZ91 Magnesium Alloy by Rapid Solidification

et al. 2003

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“…None, not practical [4,15,18,89,90,92,93,136,196,205,207,208,214,[223][224][225][226][227][228][229] Carbon Based Grain Refiners (C, Al-C, Mg-Al-C, SiC, etc. )…”

Section: Carbides or Duplex Particlesmentioning

confidence: 99%

“…Optimization of refiner preparation and addition [2,4,5,9,15,17,18,[87][88][89][90]92,94,95,106,107,109,110,115,119,121,132,135,[137][138][139][140]178,182,185,193,194,200,201,205,207,208,216,223, Melt superheating was first described in a 1931 British patent [195] and involves heating the melt to 150 to 260°C (or 180 to 300°C [18]) above the liquidus temperature [196] and holding the melt at this temperature for an extended period of time depending on crucible size and Al content [92] with higher superheating temperatures shortening refining time [195]. The original patent [195] provided no mechanism but it has been found that Al (beyond 1 wt.% [26]...…”

Section: Carbides or Duplex Particlesmentioning

confidence: 99%

“…Too much bubbling of CO or CO 2 reduced mechanical properties by an unknown mechanism and bubbling Ar, He, H 2 , HCl, N, O 2 and dried air gave no significant refinement [196]. The bubbling of CO 2 into Mg is proposed to follow Equation 21 [136] [136,207,225,226] or MgCO 2 -other C source mixtures [227] have been used with success by many researchers. The addition of MgCO 3 releases CO 2 according to Equation 22 [227] and was just as effective as superheating and CO bubbling [207].…”

Section: Carbonaceous Gases and Carbonatesmentioning

confidence: 99%

“…[4,10,15,18,26,89,90,92,111,119,121,160,178,[195][196][197][198][199][200][201][202][203][204][205][206][207][208] …”

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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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Observations on the control of grain size in magnesium casting alloys

Cited by 2 publications

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Observation of Manganese-Bearing Particles in Molten AZ91 Magnesium Alloy by Rapid Solidification

Observation of Manganese-Bearing Particles in Molten AZ91 Magnesium Alloy by Rapid Solidification

Inclusion removal and grain refinement of magnesium alloy castings

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