Improvement of Mechanical Properties by Two-Step Aging in Ultrafine Grained Al-Ag-Sc Alloy

Abstract:

In order to improve limited ductility of ultrafine grained (UFG) Al alloys, mechanical properties of an UFG Al alloy having fine precipitates within grains were investigated. An Al-0.2wt%Sc-4.2wt%Ag alloy was severely deformed by the ARB process at room temperature and subsequently heat-treated by a two-step aging. After the first aging in the two-step aging, fine Al₃Sc precipitates were formed. In the specimen ARB processed by 4cycles, the fine Al₃Sc precipitates were homogeneously dispersed within the grains. On the other hand, in the specimen ARB processed by 8 cycles, Al₃Sc precipitates were linearly-aligned on the grain boundaries that had moved during the heat treatment. After the second aging, fine G.P. zones of Ag as well as Ag₂Al precipitates were observed within the grains in the specimen ARB processed by 4 cycles. Coarse precipitates of Ag₂Al at grain boundaries were observed in the specimen ARB processed by 8 cycles. The difference in the distribution of precipitates was considered to be due to the difference in fraction of high angle grain boundaries in the matrix microstructures. The strength of the solution treated specimen increased by the two-step aging while the tensile elongation decreased. On the other hand, both of the strength and elongation of the specimen ARB processed by 4 cycles increased after the two-step aging. In case of the specimen ARB processed by 8 cycles, the strength decreased slightly and the elongation increased by the two-step aging, and the aged specimen exhibited a good balance between strength and elongation.

• Periodical: Materials Science Forum (Volumes 794-796)
• Pages: 857-863
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.794-796.857
• Online since: June 2014
• Authors: Daisuke Terada*, Yan Zeng, Nobuhiro Tsuji
• Keywords: Age Hardening, Aluminium Alloy, Precipitation, Severe Plastic Deformation

References

[1] N. Tsuji, Y. Saito, S.H. Lee, Y. Minamino, ARB(Accumulative Roll-Bonding) and other new techniques to produce bulk ultrafine grained materials, Adv. Eng. Mater., 5 (2003), 338-344.

DOI: 10.1002/adem.200310077

[2] R.Z. Valiev, M.J. Zehetbauer, Y. Estrin, H.W. Höppel, Y. Ivanisenko, H. Hahn,G. Wilde, H.J. Roven, X. Sauvage, The innovation potential of bulk nanostructured materials , Adv. Eng. Mater., 9 (2007), 527-533.

DOI: 10.1002/adem.200700078

[3] A. Azushima, R. Kopp, A. Korhonen, D.Y. Yang, F. Micari, G.D. Lahoti, P. Groche, J. Yanagimoto, N. Tsujii, A. Rosochowski, A. Yanagida, Severe plastic deformation (SPD) processes for metals, CIRP Annals - Manufacturing technology, 57 (2008).

DOI: 10.1016/j.cirp.2008.09.005

[4] Y. Estrin, A. Vinogradov, Extreme grain refinement by severe plastic deformation: A wealth of challenging science, Acta Mater., 61 (2013), 782-817.

DOI: 10.1016/j.actamat.2012.10.038

[5] E.W. Hart, Theory of the tensile test, Acta Metall,. 15 (1967), 351-355.

[6] M.F. Ashby and L.M. Brown, On diffraction contrast from inclusions, Phil. Mag. B, (1963), 1083-1103.