scholarly journals Modelling the temperature change of bifilm defects in Al cast alloys

2019 ◽  
pp. 13-17
Author(s):  
Mahmoud Ahmed El-Sayed
Keyword(s):  
Oxide Film ◽  
Fatigue Properties ◽  
Al Alloy ◽  
Heat Distribution ◽  
Cfd Model ◽  
Double Oxide ◽  
Cast Alloys ◽  
Alloy Castings ◽  
Film Defect ◽  
Surrounding Liquid

Double oxide films (bifilms) are significant defects in the casting of light alloys, and have been shown to decrease tensile and fatigue properties, and also increase their scatter, making casting properties unreproducible and unreliable. 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. It was suggested that in a pure Al melt, oxygen within the bifilm atmosphere would be consumed first to form alumina, then nitrogen would react to from AlN. A CFD model of the heat distribution associated with the reactions between the interior atmosphere of a double oxide film defect and the surrounding liquid alloy suggested that highly localized increases in temperature, up to 5000, could occur, over a scale of a few hundred micrometers. Such localized increases in temperature might lead to change the nature of the bifilm causing it to be less harmful to the properties of Al cast alloys.

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

2013 ◽  
Vol 765 ◽  
pp. 260-265 ◽  
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.

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

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.

An Investigation into Double Oxide Film Defects in Aluminium Alloys

2014 ◽  
Vol 783-786 ◽  
pp. 142-147 ◽  
Author(s):  
William D. Griffiths ◽  
A.J. Caden ◽  
M.A. El-Sayed
Keyword(s):  
Oxide Film ◽  
Sem Analysis ◽  
Rate Of Change ◽  
Al Alloy ◽  
Double Oxide ◽  
Air Bubble ◽  
Mould Filling ◽  
Analog Experiment ◽  
Alloy Castings ◽  
Mg Content

When the oxidised surface of a liquid metal is folded over onto itself and entrained double oxide film defects are formed, which form crevices or cracks in the solidified casting, of varying sizes and orientations. These defects not only reduce mechanical properties, but also increase the scatter of properties. This paper reports an analog experiment to study the behavior of the interior atmosphere of double oxide film defects in Al alloy melts of varying Mg content. Air bubbles were trapped in melts of liquid Al alloy which were then solidified after holding for varying periods of time. The composition of the bubbles was subsequently measured using mass spectroscopy. This showed the reaction of oxygen from the bubble atmosphere to form oxides, followed by the consumption of nitrogen to form AlN. Simultaneously, hydrogen from the melt diffused into the air bubble. The changes in composition were used to estimate the rate of change in composition of the interior atmosphere of a typical double oxide film defect of an estimated size. This suggested that double oxide film defects may quickly achieve an interior atmosphere that would consist of a mixture of mainly nitrogen and hydrogen, and that this atmosphere could exist for periods of time greater than the typical solidification times of light alloy castings. In other words, oxide film defects created during mould filling should persist into the solidified casting. In addition, SEM analysis of oxide film defects also suggested the presence of oxide whiskers, which seem to have formed during holding in the melt.

scholarly journals Double oxide film defects and the properties of aluminum castings. A review

2019 ◽  
pp. 5-12
Author(s):  
Mahmoud Ahmed El-Sayed
Keyword(s):  
Liquid Metal ◽  
Oxide Film ◽  
Aluminium Alloys ◽  
Oxide Films ◽  
Light Metal ◽  
Metal Alloy ◽  
Double Oxide ◽  
Factors Influencing ◽  
Aluminum Castings ◽  
Alloy Castings

Entrapped double oxide films are known to be the most detrimental defects in cast aluminium alloys. The research reported here was aimed at surveying the results of previous researches studying how these defects develop with time, with the intention of understanding their behaviour in the liquid metal once they have formed. This would give a better understanding of factors influencing the properties of light metal alloy castings which will lead to the development of improved practices by which healthier castings with reliable and more reproducible properties are obtained.

Study of double oxide film defect behaviour in liquid Al–Mg alloys

2013 ◽  
Vol 26 (6) ◽  
pp. 330-338 ◽  
Author(s):  
S. Amirinejhad ◽  
R. Raiszadeh ◽  
H. Doostmohammadi
Keyword(s):  
Oxide Film ◽  
Mg Alloys ◽  
Double Oxide ◽  
Film Defect ◽  
Al Mg Alloys
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