OPEN ACCESS
The properties of light alloy castings are strongly affected by their inclusion content, particularly double oxide film defects (bifilms), which not only decrease the tensile and fatigue properties, but also increase their scatter. Recent research has suggested that oxide film defects may alter with time, as the air inside the bifilm would react with the surrounding melt, while the hydrogen dissolved in the melt could diffuse into the bifilm cavity to form hydrogen porosity. The mechanical properties of the casting were shown to be significantly dependent upon the new morphology of its entrained bifilms. In this work, the Weibull moduli of the tensile properties of three Al castings, all expected to contain oxide films of, approximately, the same amount were compared. The first casting was poured into a resin-bonded sand mould while the second and third castings were poured into ceramic moulds with the mould for the third casting being preheated prior to pouring. The results of mechanical property analysis and electron microscopy examination suggested a considerable influence of the type of the mould and the solidification time on the morphology of bifilms and by implication, on the reliability and reproducibility of the tensile properties.
bifilms, castings, mechanical properties, oxide film defects
[1] Campbell, J., Castings, 2nd. ed: Butterworth-Heinemann, 2003.
[2] Campbell, J., Entrainment defects. Materials Science and Technology, 22, pp. 127–145, 2006.https://doi.org/10.1179/174328406x74248
[3] Basuny, F.H., Ghazy, M., Kandeil, A.-R.Y. & El-Sayed, M.A., Effect of casting conditions on the fracture strength of Al-5 Mg alloy castings. Advances in Materials Science and Engineering, 2016, pp. 1–8, 2016.https://doi.org/10.1155/2016/6496348
[4] Nyahumwa, C., Green, N.R. & Campbell, J., Effect of mold-filling turbulence on fatigue properties of cast aluminum alloys. AFS Trans, 106, pp. 215–223, 1998
[5] Raiszadeh, R. & Griffiths, W.D., A method to study the history of a double oxide film defect in liquid aluminum alloys. Metallurgical and Materials Transactions B, 37(6), pp. 865–871, 2006.https://doi.org/10.1007/bf02735007
[6] El-Sayed, M.A., Salem, H.A.G., Kandeil, A.Y. & Griffiths, W.D., Determination of the lifetime of a double-oxide film in al castings. Metallurgical and Materials Transactions B, 45(4), pp. 1398–1406, 2014.https://doi.org/10.1007/s11663-014-0035-x
[7] El-Sayed, M.A., Salem, H.A.G., Kandeil, A.Y. & Griffiths, W.D., A study of the behaviour of double oxide films in Al alloy melts. Materials Science Forum, 765, pp. 260–265, 2013.https://doi.org/10.4028/www.scientific.net/msf.765.260
[8] Griffiths, W.D., Caden, A. & El-Sayed, M., An investigation into double oxide film defects in aluminium alloys. Materials Science Forum, 783–786, pp. 142–147, 2014. https://doi.org/10.4028/www.scientific.net/msf.783-786.142
[9] Griffiths, W.D., Caden, A. & El-Sayed, M.A., The behaviour of entrainment defects in aluminium alloy castings. Proceedings of the 2013 international symposium on liquid metal processing and casting, John Wiley & Sons, Inc., pp. 187–192, 2013.
[10] El-Sayed, M., Hassanin, .H & Essa, K., Effect of casting practice on the reliability of Al cast alloys. International Journal of Cast Metals Research, 29(6), pp. 350–354, 2016.https://doi.org/10.1080/13640461.2016.1145966
[11] El-Sayed, M.A., Salem, H.A.G., Kandeil, A.Y. & Griffiths, W.D., Effect of holding time before solidification on double-oxide film defects and mechanical properties of aluminum alloys. Metallurgical and Materials Transactions B, 42(6), pp. 1104–1109, 2011. https://doi.org/10.1007/s11663-011-9571-9
[12] El-Sayed, M. & Griffiths, W., Hydrogen, bifilms and mechanical properties of Al castings. International Journal of Cast Metals Research, 27(5), pp. 282–287, 2014. https://doi.org/10.1179/1743133614y.0000000113
[13] Weibull, W., A statistical distribution function of wide applicability. Journal of Applied Mechanics, 13, pp. 293–297, 1951.
[14] Green, N.R. & Campbell, J., Statistical distributions of fracture strengths of cast Al-7SiMg alloy. Materials Science and Engineering: A, 173(1–2), pp. 261–266, 1993. https://doi.org/10.1016/0921-5093(93)90226-5
[15] Griffiths, W.D. & Raiszadeh, R., Hydrogen, porosity and oxide film defects in liquid Al. Journal of Materials Science, 44(13), pp. 3402–3407, 2009. https://doi.org/10.1007/s10853-009-3450-7
[16] Dispinar, D., Akhtar, S., Nordmark, A., Di Sabatino, M. & Arnberg, L., Degassing, hydrogen and porosity phenomena in A356. Materials Science and Engineering: A., 527(16–17), pp. 3719–3725, 2010.https://doi.org/10.1016/j.msea.2010.01.088
[17] Dispinar, D. & Campbell, J., Critical assessment of reduced pressure test. Part 1: porosity phenomena. International Journal of Cast Metals Research, 17, pp. 280–286, 2004.https://doi.org/10.1179/136404604225020696
[18] Dispinar, D. & Campbell, J., Use of bifilm index as an assessment of liquid metal quality. International Journal of Cast Metals Research, 19(1), pp. 5–17, 2006. https://doi.org/10.1179/136404606225023300
[19] Dispinar, D. & Campbell, J., Effect of casting conditions on aluminium metal quality. Journal of Materials Processing Technology, 182(1–3), pp. 405–410, 2007. https://doi.org/10.1016/j.jmatprotec.2006.08.021