Precipitation of ScAl₃ Phase during Solutionizing and Ageing of Hypoeutectic Al-Sc Alloys and its Impact to Mechanical Properties

Abstract:

In this paper, precipitation of ScAl₃ phase during solutionizing and ageing and its impact to mechanical properties of hypoeutectic Al-Sc alloy and effect of Sc addition amount were investigated by TEM and SEM microstructure observation and mechanical property testing. During solutionizing at 640^oC for 24h, for Al-0.2wt.%Sc and Al-0.4wt.%Sc alloy, ScAl₃ particles formed in the course of solidification become smaller, indicating, as a whole, Sc is partially dissolved into Al solution. Simultaneously, precipitation of two types of ScAl₃ particles are observed by TEM. One has a size of 200~300nm, and the other is much small, 5~20nm in size. Though re-dissolution of Sc solute into Al solution and precipitation of large and fine ScAl₃ particles occur in the solutionizing course, but the strength and hardness are decreased. The key reason for it is thought to be the softening effect of high level of vacancies in matrix lattice from the high solutionizing temperature. After further aging at 300^oC for 3h, a great number of fine ScAl₃ particles are precipitated in the Al matrix, which leads to a considerable precipitation hardening effect, thus the strength and hardness are increased obviously. Increasing the Sc content in the alloy results in a considerable rise in as-cast and as-aged strength and hardness, due to the solution strengthening and precipitation hardening respectively.

• Periodical: Materials Science Forum (Volume 877)
• Pages: 581-586
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.877.581
• Online since: November 2016
• Authors: Yun Yi Tang, Hengcheng Liao*, Ye Liu
• Keywords: Al-Sc Alloy, Hardness, Precipitation, ScAl₃

References

[1] A.F. Norman, P.B. Prangnell, R.S. McEwen, The solidification behaviour of dilute aluminium-scandium alloys. Acta Materialia, 1998. 46(16) 5715-5732.

DOI: 10.1016/s1359-6454(98)00257-2

[2] P. Li, Y. Ye, L. He, Valence electron structure analysis of refining mechanism of Sc and Ti additions on aluminum. Chinese Science Bulletin, 2009. 54(5) 836-841.

DOI: 10.1007/s11434-008-0514-z

[3] G. Thomas, R.H. Willens, Defects in aluminum quenched from the liquid state. Acta Metallurgica, 1964. 12(2) 191-196.

DOI: 10.1016/0001-6160(64)90187-7

[4] J. Royset, N. Ryum, Scandium in aluminium alloys. International Materials Reviews, 2005. 50(1) 19-44.

[5] Y.W. Riddle, T.H. Sanders, A study of coarsening, recrystallization, and morphology of microstructure in Al-Sc-(Zr)-(Mg) alloys. Metallurgical and Materials Transactions a-Physical Metallurgy and Materials Science, 2004. 35A(1) 341-350.

DOI: 10.1007/s11661-004-0135-3

[6] V.I. Elagin, V.V. Zakharov, T.D. Rostova, Scandium-alloyed aluminum alloys. Metal Science & Heat Treatment, 1992. 34(1) 37-45.

DOI: 10.1007/bf00768707

[7] J. Røyset, et al., On the addition of precipitation- and work-hardening in an Al–Sc alloy. Materials Science and Engineering: A, 2008. 483–484 175-178.

DOI: 10.1016/j.msea.2006.09.164

[8] G. Xu, et al., Effects of Micro-Addition of Sc on Microstructure and Properties of Al-Cu Alloy. Transactions of materials and heat treatment, 2004. 25(2) 15-18.

[9] B.A. Chen, et al., Effect of solution treatment on precipitation behaviors and age hardening response of Al-Cu alloys with Sc addition. Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing, 2011. 530 607-617.

DOI: 10.1016/j.msea.2011.10.030

[10] S. Iwamura, Y. Miura, Loss in coherency and coarsening behavior of Al3Sc precipitates. Acta Materialia, 2004. 52(3) 591-600.

DOI: 10.1016/j.actamat.2003.09.042

[11] J. Royset, N. Ryum, Kinetics and mechanisms of precipitation in an Al-0. 2 wt. % Sc alloy. Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing, 2005. 396(1-2) 409-422.

DOI: 10.1016/j.msea.2005.02.015

[12] D. William, J. Callister, Fundamentals of Materials Science and Engineering. John Wiley & Sons, Inc. (2001).