Effect of Melt Cleanliness on the Mechanical Properties and Microstructure on AZ91E Mg Alloy Castings

Elsayed, Abdallah; Ravindran, C.

doi:10.1007/s11665-013-0761-2

Cited by 7 publications

(4 citation statements)

References 12 publications

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“…Closer to the edge of the sample, shrinkage porosity was observed (Figure 6a), furthermore, manganese-rich particles were visible, as well as the structure of the intermetallic β-phase (Mg 17 Al 12 ), [3] which was observed along the grain boundaries. Similar Mn-and Fe-rich particles found in AZ91 were characterized by Øymo et al, [24] describing their composition as Al 8 (Mn, Fe) 5 .…”

Section: Sem Evaluation Of the Az91 Samplessupporting

confidence: 74%

“…The inclusions can be divided into oxide films, lumps, and clusters, as well as intermetallic particles; gas-and shrinkage pores, may also be present. [1][2][3][4][5] While measures are taken to protect and cleanse magnesium melts on industrial scale, such as gas purging treatments by Ar, N 2 , or Cl 2 , the usage of a variety of possible cover gases or fluxes and the optimization of the casting system toward a high grade of enclosure, [1,6] the application of ceramic foam filters is seen as a promising method for cleansing the melt and improving the mechanical properties of the casting. [7][8][9] Ideally, an auxiliary addition of fluxes would be avoided, while delivering the same quality of melt cleanliness.…”

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confidence: 99%

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Immersion Testing of Variously Coated Ceramic Foam Filters in an AZ91 Magnesium Melt

et al. 2021

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Due to its low density, high specific strength, and resource availability, magnesium and its alloys, such as AZ91, have a high potential for various lightweight applications. [1][2][3] A major hindrance for its widespread processing and use is its high reactivity, contributing to high dross-and sludge formation in the melt, which results in the metal being prone to corrosion and containing high quantities of nonmetallic inclusions, if the handling of the melt has not been accurate. The inclusions can be divided into oxide films, lumps, and clusters, as well as intermetallic particles; gas-and shrinkage pores, may also be present. [1][2][3][4][5] While measures are taken to protect and cleanse magnesium melts on industrial scale, such as gas purging treatments by Ar, N 2 , or Cl 2 , the usage of a variety of possible cover gases or fluxes and the optimization of the casting system toward a high grade of enclosure, [1,6] the application of ceramic foam filters is seen as a promising method for cleansing the melt and improving the mechanical properties of the casting. [7][8][9] Ideally, an auxiliary addition of fluxes would be avoided, while delivering the same quality of melt cleanliness. [10][11][12] Wu et al. emphasized the effectiveness of ceramic foam filters made from MgO or Al 2 O 3 in AZ91, improving the elongation-to-failure of cast samples up to relative 58%. [13] In contrast to oxidic, sintered filters, carbon-bonded ceramic foam filters show higher resistance toward thermal shock and creep deformation, as well as lower energy consumption during their manufacture, due to their lower manufacturing temperature. [14] After carbon-bonded alumina filters showed promising results in the filtration of steel melts, [15] short-term immersion tests in AZ91 have been carried out to evaluate their applicability in a magnesium alloy melt. Interface reactions between the AZ91 melt and variously coated ceramic Al 2 O 3 -C filters have been investigated after immersion times of 10-120 s. [16] The investigated filter coatings consisted of Al 2 O 3 , MgO-C, MgAl 2 O 4 , or carbon nanotubes/ alumina nanosheets. The formation of MgO in situ layers was shown on filter surfaces containing Al 2 O 3 or MgAl 2 O 4 . [16] Therefore, the next step toward assessing the applicability of oxidic as well as carbon-bonded ceramic foam filters in the field of magnesium melt filtration is the evaluation of their long-term resistance toward the magnesium melt, with a special regard toward melt contamination and inclusion content.In this study, additional ceramic foam filter materials, namely ZrO 2 [13] and MgAlON, [17] were added to the selected materials

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Section: Sem Evaluation Of the Az91 Samplessupporting

confidence: 74%

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confidence: 99%

Immersion Testing of Variously Coated Ceramic Foam Filters in an AZ91 Magnesium Melt

et al. 2021

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“…During the in-situ neutron experiment, the entire furnace assembly was oscillated to increase the number of grains contributing to the signal and to improve counting statistics. Further details regarding experimental methods for in-situ neutron diffraction experiments are outlined in several recent publications [56,[61][62][63]. Focusing on an angular range for a single peak elucidates many important features of the evolution of its associated phase.…”

Section: 1-2 Empirical Data Generationmentioning

confidence: 99%

Mechanisms of Improving the Thermal and Electrical Conductivity of Aluminum Alloy Cylinder Heads

Vandersluis¹

2023

Preprint

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<p>One of the major causes of premature failure in automotive cylinder heads is the accumulation of thermal stresses, due to their large internal temperature gradients in-service. To ensure mechanical integrity, engine operating temperatures are typically restricted. However, this response reduces fuel efficiency, which increases costs and carbon emissions. A more sustainable solution can involve enhancing alloy conductivity, which improves temperature uniformity in the heads. In aluminum alloys, solidification rate, silicon modification, and precipitation heat treatment have each been reported to influence conductivity. Yet, the mechanisms and interactions regarding these parameters were unclear in the literature. Accordingly, the objective of this dissertation was to provide an in-depth, systematic investigation of the individual and combined effects of these processes on the microstructure and conductivity of automotive 319 aluminum alloy.</p> <p>After performing a baseline characterization of commercial cylinder heads, permanent-mould castings were produced with a range of solidification rates and strontium contents. These castings were analyzed to establish the dominant microstructural factors affecting electron mobility in the as-cast condition. Then, samples were subjected to multiple combinations of solution, natural aging, artificial aging, and direct aging heat treatments, to elucidate the roles of the dissolution, spheroidization and precipitation transformations. Furthermore, this work was complimented by several innovative, state-of-the-art experiments, which were the first to analyze the kinetics of solidification, chemical modification, thermal expansion, dissolution, and precipitation in 319. As a result, this dissertation contributed numerous, novel and meaningful insights regarding heat transfer in aluminum alloys. This included elucidation of the independent, major impacts of porosity, silicon morphology, and the size, distribution and coherency of the aluminum-copper precipitates, despite insensitivity to the dendritic size. The appropriate combination of solidification rate, strontium content, and heat treatment was demonstrated to promote superior conductivity to what was possible through their individual variation. Given low-porosity castings, this research revealed the potential for approximately 40% improvements in thermal and electrical conductivity, compared to the strontium-free, as-cast condition. Overall, the extensive conductivity data generated in this research supports strategic and practical materials processing procedures, demonstrates opportunities for balancing high conductivity with mechanical integrity, and ensures enhanced component performance and environmental sustainability.</p>

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“…[1] However, due to the high affinity of Mg with oxygen, oxidation happens throughout the life cycle of Mg-alloys from the foundry to practical service and recycling. [2,3] Oxidation brings up many problems, such as the presence of oxide impurities in the as-cast products, [4,5] non-protective oxide films for corrosion [6] and a high tendency to ignite and burn when exposed to air at high temperatures. [7] These together with other issues inhibit the widespread application of Mg-alloys.…”

Section: Introductionmentioning

confidence: 99%

The Nature of Native MgO in Mg and Its Alloys

Wang

Ramasse

et al. 2020

Metall Mater Trans A

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Native MgO particles in Mg-alloy melts have been recently exploited as potential substrates for heterogeneous nucleation during solidification, leading to significant grain refinement of various Mg-alloys. However, our current knowledge of the nature of the native MgO particles is still limited. In this work, we study both the physical and chemical nature of the native MgO in commercial purity Mg and Mg-9Al alloy by means of advanced electron microscopy. We found that as oxidation products MgO aggregates exist in the alloy melt in three different forms: dominantly young oxide film, occasionally old oxide film and ingot skin, all consisting of discrete nano-sized MgO particles. Detailed analysis shows that the native MgO particles have an octahedral or cubic morphology, a nano-scale particle size and a log-normal size distribution. The mechanisms underlying the formation of the two types of MgO were investigated, and we found that octahedral MgO is formed by oxidation of Mg melt and cubic MgO by oxidation of Mg vapor. With a large lattice misfit with a-Mg, the native MgO particles are impotent for heterogeneous nucleation, but can be made effective for grain refinement.

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Effect of Melt Cleanliness on the Mechanical Properties and Microstructure on AZ91E Mg Alloy Castings

Cited by 7 publications

References 12 publications

Immersion Testing of Variously Coated Ceramic Foam Filters in an AZ91 Magnesium Melt

Immersion Testing of Variously Coated Ceramic Foam Filters in an AZ91 Magnesium Melt

Mechanisms of Improving the Thermal and Electrical Conductivity of Aluminum Alloy Cylinder Heads

The Nature of Native MgO in Mg and Its Alloys

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