Effect of oxide film defects generated during mould filling on mechanical strength and reliability of magnesium alloy castings (AZ91)

2012 ◽  
Vol 25 (3) ◽  
pp. 188-194 ◽  
Author(s):  
A R Mirak ◽  
M Divandari ◽  
S M A Boutorabi ◽  
J A Taylor
Keyword(s):  
Magnesium Alloy ◽  
Oxide Film ◽  
Mechanical Strength ◽  
Mould Filling ◽  
Alloy Castings

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.

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.

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.

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 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.

Study on Regeneration Ability of Oxidation Film on Ignition-Proof Magnesium Alloy Added with RE

2011 ◽  
Vol 284-286 ◽  
pp. 1665-1670
Author(s):  
Zheng Hua Deng ◽  
Hua Ji Li ◽  
Wei Bin Li
Keyword(s):  
Magnesium Alloy ◽  
Oxide Film ◽  
Room Temperature ◽  
Surface Film ◽  
Surface Oxidation ◽  
Surface Oxide ◽  
Regeneration Ability ◽  
Surface Oxide Film ◽  
Oxidation Performance

The ZM5-0.1%RE magnesium alloy was heated to 800°C, when the surface oxide film was formed, the ZM5-0.1% RE Magnesium alloy which had being oxidized obtained by removing the surface oxidation film on the ZM5-0.1%RE magnesium alloy at room temperature. TGA curve, oxidaxion kinetics curves at constant temperatuers of the alloy and XRD spectrum of the surface film were analyzed in order to investigate the sureface oxidation behavior.The results show that the alloy still has anti-oxidation performance, And the oxide inerease occurred mostly between 400°C and 700°C，a layer of tight oxide film with 4-5.5um and composed of RE2O3, MgO, Al2O3and Mg17Al12was formed on the surface of magnesiurn alloy. The tight surface oxide film prevented the further oxidation of the base magnesiurn alloy, It show that the regeneration ability of oxidation film on ZM5-0.1%RE Magnesium Alloy was good.

scholarly journals The Effect of LFC Process Variables on Solidification and Thermal Response of AZ91E Magnesium Alloy Castings

2021 ◽  
Author(s):  
Lukas Bichler
Keyword(s):  
Thermal Analysis ◽  
Magnesium Alloy ◽  
Magnesium Alloys ◽  
Metal Flow ◽  
Mold Filling ◽  
Second Phase ◽  
Process Variables ◽  
Pyrolysis Products ◽  
Alloy Castings ◽  
Non Equilibrium

Magnesium alloys are gaining in popularity as materials of choice for automotive and aerospace applications. Magnesium alloys have the lowest density of all structural metals, effectively making their specific properties highly attractive. Lost Foam Casting (LFC) is a novel near-net-shape manufacturing process utilizing expanded polystyrene (EPS) as a mold filler. Presence of the EPS in the casting cavity promotes formation of unique casting defects.These include misruns, folds, entrapped polystyrene pyrolysis products and potentially increased levels of gas porosity. There is very little published literature on the feasibility of casting magnesium alloys by the LFC process. This research was an attempt to evaluate the effect of selected LFC process variables on AZ91R magnesium alloy castings produced by the LFC process. In this work, the effect of melt superheat, casting section thickness, EPS foam properties and the application of vacuum during mold filling were investigated and correlated to the casting quality and molten flow behavior. Further, detailed thermal analysis was carried out to determine the solidification history of the castings. The results of the thermal analysis were used to determine the effect of the cooling rate on the development of the casting microstructure. Moreover, the morphology and the mode of second phase (Mg17Al12) precipitation were studied and quantified. The results suggest that application of vacuum during the mold filling process increased the metal flow lengths. However, the casting soundness deteriorated due to the applied vacuum. Variations in the density of the vacuum cast horizontal bars were explained through the presence of partially solidified metal. The molten metal flow was further influenced by the foam density and bead fusion. Greater flow lengths were observed in the high density 1.6 pcf foam castings. in the low density 1.3 pcf foam castings, numerous casting defects were associated with the presence of the liquid-EPS pyrolysis products. In general, the thermal analysis suggested that non-equilibrium alloy solidification promoted the formation of the lamellar non-equilibrium Mg17Al12 precipitate, and this was confirmed by optical microscopy.

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