The Effect of the Addition of Transition Metals on Double Oxide Film Defects in an Al–Si–Mg Alloy

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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Liquid-phase oxidation of transition metals 4. Influence of the nature of the metal, the oxide film, and the components of the medium

Bulletin of the Academy of Sciences of the USSR Division of Chemical Science ◽

10.1007/bf00923556 ◽

1979 ◽

Vol 28 (4) ◽

pp. 664-668

Author(s):

S. N. Kurskov ◽

I. P. Lavrent'ev ◽

M. L. Khidekel'

Keyword(s):

Liquid Phase ◽

Transition Metals ◽

Oxide Film ◽

Liquid Phase Oxidation ◽

Phase Oxidation

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Oxide scale behavior of Al–7.5 mass%Mg alloy containing trace Ca during short-term oxidation

Materials Express ◽

10.1166/mex.2021.2090 ◽

2021 ◽

Vol 11 (11) ◽

pp. 1881-1886

Author(s):

Seong-Ho Ha ◽

Young-Ok Yoon ◽

Bong-Hwan Kim ◽

Hyun-Kyu Lim ◽

Sung-Hwan Lim ◽

...

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Oxide Film ◽

Phase Diagrams ◽

Film Formation ◽

Mg Alloy ◽

Short Term ◽

Spinel Formation ◽

Transmission Electron ◽

Significant Difference

In this study, using transmission electron microscopy and phase diagrams from thermodynamic calculations, we investigated the oxide film formation of Al–7.5 mass%Mg alloy containing Ca traces during short-term oxidation in terms of the thermodynamic stability and multi-element oxides by inter-diffusion based on the results of analysis for the oxide film. For the oxidation test at 515 ˚C, for 1 h, its results showed that there is no significant difference between the Ca-added and Ca-free Al–7.5 mass%Mg alloys was observed, while further exposure caused the Ca-free alloy to gain significant weight. Based on the standard Gibbs free energy for oxide production calculated in this study, CaO was the most preferential product among the single metal oxides examined. As per calculations for MgAl2O4-spinel formation reactions, the spinel formation from MgO was thermodynamically the most favorable. According to the phase diagrams calculated in this study, various multi-element oxides including Ca could possibly form in the oxide layer of Ca-added alloy. The analysis results of transmission electron microscopy confirmed that MgO is the primary oxide in the Al–Mg binary alloys. In oxidation tests conducted for less than 1 h, the spinel was rarely found. The outmost areas of oxide layers correspond to MgO and CaO in Ca-free and Ca-added alloys, respectively. However, in the Ca-added alloy, the inner layer contains certain amounts of Ca, Al, and Mg.

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