A Study on the Effect of Mg and Ag Additions and Age Hardening Treatment on the Properties of As-Cast Al-Cu-Mg-Ag Alloys

Authors: Ahmed. S. Alasmari, M. S. Soliman, Magdy M. El-Rayes

Abstract:

This study focuses on the effect of the addition of magnesium (Mg) and silver (Ag) on the mechanical properties of aluminum based alloys. The alloying elements will be added at different levels using the factorial design of experiments of 2²; the two factors are Mg and Ag at two levels of concentration. The superior mechanical properties of the produced Al-Cu-Mg-Ag alloys after aging will be resulted from a unique type of precipitation named as Ω-phase. The formed precipitate enhanced the tensile strength and thermal stability. This paper further investigated the microstructure and mechanical properties of as cast Al–Cu–Mg–Ag alloys after being complete homogenized treatment at 520 °C for 8 hours followed by isothermally age hardening process at 190 °C for different periods of time. The homogenization at 520 °C for 8 hours was selected based on homogenization study at various temperatures and times. The alloys’ microstructures were studied by using optical microscopy (OM). In addition to that, the fracture surface investigation was performed using a scanning electronic microscope (SEM). Studying the microstructure of aged Al-Cu-Mg-Ag alloys reveal that the grains are equiaxed with an average grain size of about 50 µm. A detailed fractography study for fractured surface of the aged alloys exhibited a mixed fracture whereby the random fracture suggested crack propagation along the grain boundaries while the dimples indicated that the fracture was ductile. The present result has shown that alloy 5 has the highest hardness values and the best mechanical behaviors.

Keywords: Precipitation hardening, aluminum alloys, aging, design of experiments, analysis of variance, heat treatments.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.3607747

References:

[1] X.Y. Liu, Z.P. Wang, B.G. Fu, L. Long, X.L. Zhang, H.X. Cui Effects of Mg content on the mechanical properties and corrosion resistance of Al–Cu–Mg–Ag alloy J. Alloys Compd., 685 (2016), pp. 209-215.
[2] Q Xia, Z Liu, Y Li Microstructure and properties of Al–Cu–Mg–Ag alloy exposed at 200 °C with and without stress (J) Transactions of Nonferrous Metals Society of China, 18 (2008), pp. 789-794.
[3] S. Bai, P. Ying, Z. Liu, J. Wang, J. Li Quantitative transmission electron microscopy and atom probe tomography study of Ag-dependent precipitation of Ω phase in Al–Cu–Mg alloys Mater. Sci. Eng. A, 687 (2017), pp. 8-16.
[4] S.P. Ringer, K. Hono, I. J .Polmear, T. Sakurai. Nucleation of Precipitates in Aged Al-Cu-Mg-(Ag) Alloys with High Cu:Mg Ratios. Acta Materialia, 44(5) (1996), pp. 1883-1898.
[5] R.K. Wyss, R.E. Sanders Jr. Microstructure-property relationship in a 2XXX aluminum alloy with Mg addition Metall. Trans. A, 19 (1988), pp. 2523-2530.
[6] D. Bakavos, P.B. Prangnell, B. Bes, F. Eberl The effect of silver on microstructural evolution in two 2xxx series Al-alloys with a high Cu:Mg ratio during ageing to a T8 temper Mater. Sci. Eng. A, 491 (2008), pp. 214-223.
[7] S. Bai, Z. Liu, Y. Gu, X. Zhou, S. Zeng. Microstructures and fatigue fracture behavior of an Al–Cu–Mg–Ag alloy with a low Cu/Mg ratio. Mater. Sci. Eng. A, 530 (2011), pp. 473-480.
[8] Li. Qiong, F.E Wawner., Characterization of a cubic phase in an Al-Cu-Mg-Ag alloy. Journal of Materials Science, 32 (20) (1997), pp. 5363-5370.
[9] Y. Deng, Y. Zhang, L. Wan, A.A. Zhu, X. Zhang, Three-stage homogenization of Al-Zn-Mg-Cu alloys containing trace Zr Metall. Mater. Trans. A., 44 (2013), pp. 2470-2477, 10.1007/s11661-013-1639-5
[10] Y.-T. Chen, et al. Effects of Cu/Mg ratio and heat treatment on microstructures and mechanical properties of Al-4.6Cu-Mg-0.5Ag alloys Mater. Chem. Phys., 162 (2015), p. 7
[11] P. Priya, D.R. Johnson, M.J.M. Krane Modeling phase transformation kinetics during homogenization of aluminum alloy 7050 Comput. Mater. Sci., 138 (2017), pp. 277-287.
[12] J. C. Williams and E. A. Starke Jr., “Progress in structural materials for aerospace systems,” ActaMaterialia, vol. 51, no. 19, pp. 5775–5799, 2003.
[13] R. N. Lumley and I. J. Polmear, “The effect of long-term creep exposure on the microstructure and properties of an underaged Al-Cu-Mg-Ag alloy,” ScriptaMaterialia, vol. 50, no. 9, pp. 1227.
[14] X. Y. Liu, Q. L. Pan, X. L. Zhang et al., “Creep behavior and microstructural evolution of deformed Al-Cu-Mg-Ag heat resistant alloy,” Materials Science and EngineeringA, vol. 599, pp.160–165, 2014.
[15] A. M. Al-Obaisi, E. A. El-Danaf, A. E. Ragab, and M. S. Soliman, “Precipitation Hardening and Statistical Modeling of the Aging Parameters and Alloy Compositions in Al-Cu-Mg-Ag Alloys,” Journal of Materials Engineering and Performance, pp. 1–13, 2016.
[16] J. S. Robinson, R. L. Cudd, and J. T. Evans, “Creep resistant aluminium alloys and their applications,” Materials Science and Technology, vol. 19, no. 2, pp. 143–155, 2003.
[17] S .Bai , X .Yi , Z . Liu, J . Wang, J. Zhao, P. Ying “The influence of preaging on the strength and precipitation behavior of a deformed Al-Cu-Mg-Ag alloy,” Journal of Alloys and Compounds, Vol. 764, pp 62-72, 2018.
[18] X.Y. Liu, Z.P. Wang, B.G. Fu, L. Long, X.L. Zhang, H.X. Cui “Effects of Mg content on the mechanical properties and corrosion resistance of Al–Cu–Mg–Ag alloy,” J. Alloys Compd., 685 (2016), pp. 209-215.
[19] I.Zuiko, R. Kaibyshev “Al–Cu–Mg–Ag Effects of Mg content on the mechanical properties and corrosion resistance of alloy,” Materials Science and Engineering