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

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
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.

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 Influence of Bifilm Defects Generated during Mould Filling on the Tensile Properties of Al–Si–Mg Cast Alloys

Metals ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 160
Author(s):  
Mahmoud Ahmed El-Sayed ◽  
Khamis Essa ◽  
Hany Hassanin
Keyword(s):  
Tensile Strength ◽  
Oxide Film ◽  
Hydrogen Content ◽  
Mould Filling ◽  
Cast Alloys ◽  
Alloy Castings ◽  
Factorial Design Of Experiments ◽  
Position Parameter ◽  
Hydrogen Level ◽  
Full Factorial

Entrapped double oxide film defects are known to be the most detrimental defects during the casting of aluminium alloys. In addition, hydrogen dissolved in the aluminium melt was suggested to pass into the defects to expand them and cause hydrogen porosity. In this work, the effect of two important casting parameters (the filtration and hydrogen content) on the properties of Al–7 Si–0.3 Mg alloy castings was studied using a full factorial design of experiments approach. Casting properties such as the Weibull modulus and position parameter of the elongation and the tensile strength were considered as response parameters. The results suggested that adopting 10 PPI filters in the gating system resulted in a considerable boost of the Weibull moduli of the tensile strength and elongation due to the enhanced mould filling conditions that minimised the possibility of oxide film entrainment. In addition, the results showed that reducing the hydrogen content in the castings samples from 0.257 to 0.132 cm3/100 g Al was associated with a noticeable decrease in the size of bifilm defects with a corresponding improvement in the mechanical properties. Such significant effect of the process parameters studied on the casting properties suggests that the more careful and quiescent mould filling practice and the lower the hydrogen level of the casting, the higher the quality and reliability of the castings produced.

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.

Criterion for oxides silumin castings contamination during chill casting

2021 ◽  
pp. 99-103
Author(s):  
O.A. Zarubina ◽  
A.M. Zarubin
Keyword(s):  
Mechanical Properties ◽  
Aluminum Alloys ◽  
Oxide Films ◽  
Casting Process ◽  
Chill Casting ◽  
Oxidation Processes ◽  
Mould Filling ◽  
Gas Tight ◽  
Cast Products ◽  
Modern Computing

To assess the effect of the mould filling modes on the content of oxide films in castings, special criterion is proposed that provides prediction in the contamination of chill castings mаde of aluminum alloys by using modern computing tools to simulate the moulds casting process on computer. It is noted that decrease in the value of the contamination criterion by using alloys with low content of Mg or without this component reduces the possibility of controlling the distribution of oxides in the casting, other elements of the casting mould and using the concentration of oxides, for example, in washers to control the mechanical properties of cast products. This is due to increase in the duration of oxidation processes in gas-tight mould with such change in the composition of the casting material.

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.

Exfoliation and Fracture Behavior of Oxide Films Formed on Titanium and Its Alloy in High Temperature Environments

2006 ◽  
Vol 522-523 ◽  
pp. 417-424 ◽  
Author(s):  
Yoshinori Isomoto Oka ◽  
Takahiro Yamabe ◽  
Toshinori Tsumura
Keyword(s):  
Mechanical Properties ◽  
Titanium Alloy ◽  
High Temperature ◽  
Oxide Film ◽  
Oxide Films ◽  
Pure Titanium ◽  
Specimen Surface ◽  
Wide Range ◽  
Basic Behavior ◽  
Corrosive Environments

It is very difficult to obtain mechanical properties of oxide films formed on a material in high temperature environments despite its importance of estimating material degradation caused by such as thermal stress. Corrosion/oxidation tests were conducted for pure titanium and titanium alloy in high temperature corrosive environments of wet air and water vapor with hydrogen chloride at temperatures from 673 K to 973 K to look into basic behavior of degradation and the growth of titanium oxide films. It was found that oxide films were usually formed on the specimen surface and the growth was accelerated by the corrosiveness of the environment. In order to examine mechanical properties and exfoliation of corrosion products or oxide films formed on titanium and its alloy, tests of single particle impact on the specimen surface with a glass bead were performed in high temperature corrosive environments. The piling-up surfaces around impact craters were formed and plastically strained. The oxide film formed on the metal surface was detached in a wide range of the circumference and fractured a little far from the rim of the crater. Then fracture and exfoliation stress of the oxide film were estimated by the calculation of impact energy and fractured and detached areas. It was found that both the fracture and exfoliation stress of the oxide films were different depending on the corrosive environment and chemical composition of titanium alloy.

Modelling of the Effects of Entrainment Defects on Mechanical Properties in a Cast Al-Si-Mg Alloy

2013 ◽  
Vol 765 ◽  
pp. 225-229 ◽  
Author(s):  
Yang Yue ◽  
William D. Griffiths ◽  
Nick R. Green
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Mechanical Strength ◽  
Aluminium Alloy ◽  
Defect Concentration ◽  
Mg Alloy ◽  
Filling Process ◽  
Double Oxide ◽  
Mould Filling ◽  
Alloy Castings

Entrainment defects such as double oxide films and entrapped bubbles occur frequently in aluminium alloy castings during the mould-filling process, and are very detrimental to both mechanical properties, and reproducibility of casting properties. In this study a modelling algorithm was used to predict the formation and distribution of entrainment defects in Al-Si-Mg alloy castings. The tensile strength of cast test bars was compared with either the number of defects, or the defect concentration within the bars obtained from the simulation. A general relationship between the mechanical strength of the cast test bars and the quantity of estimated defects was apparent.

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

2021 ◽  
Author(s):  
Tian Li ◽  
J. M. T. Davies ◽  
Xiangzhen Zhu
Keyword(s):  
Mechanical Properties ◽  
Oxide Film ◽  
Outer Layer ◽  
Thermodynamic Calculation ◽  
Mg Alloys ◽  
Evolution Mechanism ◽  
Layered Oxide ◽  
Initial Film ◽  
Long Time ◽  
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.

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.

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