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

AbstractThe 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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INVESTIGATION ON PREPARATION, CHARACTERIZATION AND PROPERTY EVALUATION OF FGM AL-SI ALLOY CASTINGS PRODUCED BY CAST-DECANTCAST (CDC) PROCESS

International Journal of Engineering Applied Sciences and Technology ◽

10.33564/ijeast.2021.v06i05.033 ◽

2021 ◽

Vol 6 (5) ◽

Author(s):

Dr. B. Anandavel ◽

Dr J Anburaj ◽

Dr K Thillairajan ◽

V Devakannan

Keyword(s):

Mechanical Properties ◽

Wear Resistance ◽

Mechanical Testing ◽

Outer Layer ◽

Wear Behavior ◽

Functionally Gradient ◽

Property Evaluation ◽

Microstructural Behavior ◽

Alloy Castings ◽

Metallurgical Characterization

Aim of this research paper is to study the microstructural behavior and mechanical properties of Functionally Gradient (FG) layer of Al-Si alloy castings produced by CDC process. The effect of decantation time on the thickness of functionally gradient castings of Al-4.5 wt % Si alloy as an inner layer and Al-Si alloy with 12.5 wt %Si as outer layers was studied by CDC process. The three different combinations of FGM castings were characterized for microstructural and wear behavior using metallurgical characterization and mechanical testing. From the microstructural and wear behavior of FGM casting at outer layer, FG layer and inner layer, it is observed that the FG layer of FGM casting showed very wear resistance compared to other two layers in the FGM casting.

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The Effect of Inverse Macro-Segregation on Fatigue Behavior of Die-Cast AM60 Magnesium Alloy

Materials Science Forum ◽

10.4028/www.scientific.net/msf.488-489.713 ◽

2005 ◽

Vol 488-489 ◽

pp. 713-716 ◽

Cited By ~ 2

Author(s):

Soon Gi Lee ◽

Gautam R. Patel ◽

Arun M. Gokhale

Keyword(s):

Mechanical Properties ◽

High Pressure ◽

Magnesium Alloy ◽

Fatigue Resistance ◽

Surface Segregation ◽

Fatigue Behavior ◽

Eutectic Phase ◽

Mg Alloys ◽

Die Cast ◽

Alloy Castings

The normal and inverse solute macro-segregation are known to occur in Al and other nonferrous alloy castings and have been well studied and documented. However, these phenomena have not been investigated in the high-pressure die-cast Mg-alloys. Consequently, the effects of macro-segregation on the mechanical properties of cast Mg-alloys have not been characterized. The objective of this contribution is to investigate the effects of inverse macro-segregation and porosity on the fatigue behavior of high-pressure die-cast AM60 alloy. It is observed that the inverse macro-segregation of eutectic phase at the cast surfaces adversely affects the fatigue behavior: the fatigue resistance decreases substantially due to the presence of the surface segregation.

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Effect of Casting Conditions on the Fracture Strength of Al-5 Mg Alloy Castings

Advances in Materials Science and Engineering ◽

10.1155/2016/6496348 ◽

2016 ◽

Vol 2016 ◽

pp. 1-8 ◽

Cited By ~ 4

Author(s):

Fawzia Hamed Basuny ◽

Mootaz Ghazy ◽

Abdel-Razik Y. Kandeil ◽

Mahmoud Ahmed El-Sayed

Keyword(s):

Mechanical Properties ◽

Oxide Film ◽

Oxide Films ◽

Bulk Liquid ◽

Sand Cast ◽

Mould Filling ◽

Surface Turbulence ◽

Film Content ◽

Cast Alloys ◽

Alloy Castings

During the transient phase of filling a casting running system, surface turbulence can cause the entrainment of oxide films into the bulk liquid. Previous research has suggested that the entrained oxide film would have a deleterious effect on the reproducibility of the mechanical properties of Al cast alloys. In this work, the Weibull moduli for the ultimate tensile strength (UTS) and % elongation of sand cast bars produced under different casting conditions were compared as indicators of casting reliability which was expected to be a function of the oxide film content. The results showed that the use of a thin runner along with the use of filters can significantly eliminate the surface turbulence of the melt during mould filling which would lead to the avoidance of the generation and entrainment of surface oxide films and in turn produce castings with more reliable and reproducible mechanical properties compared to the castings produced using conventional running systems.

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A Study of the Behaviour of Double Oxide Films in Al Alloy Melts

Materials Science Forum ◽

10.4028/www.scientific.net/msf.765.260 ◽

2013 ◽

Vol 765 ◽

pp. 260-265 ◽

Cited By ~ 6

Author(s):

Mahmoud El-Sayed ◽

Hanadi G. Salem ◽

Abdel-Razik Kandeil ◽

William D. Griffiths

Keyword(s):

Mechanical Properties ◽

Oxide Film ◽

Average Rate ◽

Oxide Films ◽

Reaction Rates ◽

Fatigue Properties ◽

Al Alloy ◽

Double Oxide ◽

Alloy Castings ◽

Time Required

The mechanical properties of Al castings are reduced by inclusions, particularly double oxide films, or bifilms, which are formed due to surface turbulence of the liquid metal during handling and/or pouring. These defects have been reported not only to decrease the tensile and fatigue properties of Al alloy castings, but also to increase their scatter. Recent research has suggested that the nature of oxide film defects may change with time, as the air inside the bifilm would react with the surrounding melt leading to its consumption, which may enhance the mechanical properties of Al alloy castings. In order to follow changes in the composition of the internal atmosphere of a double oxide film defect within an Al melt, a series of analogue experiments were carried out to determine the changes in gas composition of an air bubble trapped in a melt of commercial purity Al, subjected to stirring. The bubble contents were analysed using a mass spectrometer to determine their change in composition with time. Also, the solid species inside the bubbles solidified in the melt were analysed. The results suggested that first oxygen and then nitrogen inside the bubble were consumed, with consumption rates of 2.5x10-6 and 1.3x10-6 mol m-2s-1, respectively. Also, hydrogen diffused into the bubble from the melt at an average rate of 3.4x10-7 mol m-2s-1, although the rate of H diffusion increased significantly after the consumption of most of the oxygen inside the bubble. Based upon these reaction rates the time required for a typical alumina bifilm to lose all its oxygen and nitrogen was determined to be just under 10 minutes.

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Modification of Double Oxide Film Defects with the Addition of Mo to An Al-Si-Mg Alloy

Metallurgical and Materials Transactions B ◽

10.1007/s11663-020-02038-w ◽

2021 ◽

Author(s):

Qi Chen ◽

W. D. Griffiths

Keyword(s):

Liquid Metal ◽

Oxide Film ◽

Cross Sections ◽

Focused Ion Beam ◽

Spinel Phase ◽

Ion Beam ◽

Transmission Electron Microscopy Analysis ◽

Double Oxide ◽

Alloy Castings ◽

Film Defect

AbstractIn this work, Mo was added into Al melt to reduce the detrimental effect of double-oxide film defect. An air bubble was trapped in a liquid metal (2L99), served as an analogy for double-oxide film defect in aluminum alloy castings. It was found that the addition of Mo significantly accelerated the consumption of the entrapped bubble by 60 pct after holding for 1 hour. 2 sets of testbar molds were then cast, with 2L99 and 2L99+Mo alloy, with a badly designed running system, intended to deliberately introduce double oxide film defects into the liquid metal. Tensile testing showed that, with the addition of Mo, the Weibull modulus of the Ultimate Tensile Strength and pct Elongation was increased by a factor of 2.5 (from 9 to 23) and 2 (from 2.5 to 4.5), respectively. The fracture surface of 2L99+Mo alloy testbars revealed areas of nitrides contained within bi-film defects. Cross-sections through those defects by Focused Ion Beam milling suggested that the surface layer were permeable, which could be as thick as 30 μm, compared to around 500 nm for the typical oxide film thickness. Transmission Electron Microscopy analysis suggested that the nitride-containing layer consisted of nitride particles as well as spinel phase of various form. The hypothesis was raised that the permeability of the nitride layers promote the reaction between the entrapped atmosphere in the defect and the surrounding liquid metal, reducing the defect size and decreasing their impact on mechanical properties.

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Achievement of High Strength and Ductility in Al–Si–Cu–Mg Alloys by Intermediate Phase Optimization in As-Cast and Heat Treatment Conditions

Materials ◽

10.3390/ma13030647 ◽

2020 ◽

Vol 13 (3) ◽

pp. 647 ◽

Cited By ~ 4

Author(s):

Bingrong Zhang ◽

Lingkun Zhang ◽

Zhiming Wang ◽

Anjiang Gao

Keyword(s):

Mechanical Properties ◽

Heat Treatment ◽

Tensile Strength ◽

Ultimate Tensile Strength ◽

Intermediate Phase ◽

High Strength ◽

Mg Alloys ◽

Artificial Ageing ◽

Treatment Conditions ◽

Eutectic Si

In order to obtain high-strength and high-ductility Al–Si–Cu–Mg alloys, the present research is focused on optimizing the composition of soluble phases, the structure and morphology of insoluble phases, and artificial ageing processes. The results show that the best matches, 0.4 wt% Mg and 1.2 wt% Cu in the Al–9Si alloy, avoided the toxic effect of the blocky Al2Cu on the mechanical properties of the alloy. The addition of 0.6 wt% Zn modified the morphology of eutectic Si from coarse particles to fine fibrous particles and the texture of Fe-rich phases from acicular β-Fe to blocky π-Fe in the Al–9Si–1.2Cu–0.4Mg-based alloy. With the optimization of the heat treatment parameters, the spherical eutectic Si and the fully fused β-Fe dramatically improved the ultimate tensile strength and elongation to fracture. Compared with the Al–9Si–1.2Cu–0.4Mg-based alloy, the 0.6 wt% Zn modified alloy not only increased the ultimate tensile strength and elongation to fracture of peak ageing but also reduced the time of peak ageing. The following improved combination of higher tensile strength and higher elongation was achieved for 0.6 wt% Zn modified alloy by double-stage ageing: 100 °C × 3 h + 180 °C × 7 h, with mechanical properties of ultimate tensile strength (UTS) of ~371 MPa, yield strength (YS) of ~291 MPa, and elongation to fracture (E%) of ~5.6%.

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