Light Metals 2019 pp 143-151 | Cite as
Understanding the Role of Cu and Clustering on Strain Hardening and Strain Rate Sensitivity of Al-Mg-Si-Cu Alloys
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Abstract
Increased demand for light-weighting in passenger vehicles has created a need for strong, light, ductile materials to be used in body-in-white applications. The AA6xxx-series of aluminum alloys are suitable candidates meeting most requirements but can fall short of the formability demands of designers, necessitating an understanding of what controls the formability in this alloy series. This work examines the effect of copper alloying in AA6xxx on the pre-ageing and natural ageing responses of the microstructure and mechanical properties. The changes in microstructure observed by differential scanning calorimetry and hardness testing are related to the work-hardening and strain-rate sensitivity parameters for these alloys measured by tensile testing. An observed asymmetry in the measured strain-rate sensitivity associated with increasing versus decreasing strain rate changes suggests that a different mechanism operates for the two conditions. It is postulated how this asymmetry in strain-rate sensitivity will impact the necking and ductility behaviour of these alloys.
Keywords
Al-Mg-Si-Cu Clusters Ductility Natural ageing Strain-rate sensitivity Tensile test Work-hardeningNotes
Acknowledgements
The author would like to thank the Association Nationale Recherche Technologie (ANRT) for co-funding the project and Devang Sejani for performing the extensive hardness testing found in this work. This paper was first published in the proceedings of the 16th International Aluminum Alloys Conference (ICAA16) 2018 ISBN: 978-1-926872-41-4.
References
- 1.J. Hirsch, “Automotive trends in aluminium-The European perspective,” in Materials Forum, 2004, vol. 28, pp. 15–23.Google Scholar
- 2.J. Hirsch, “Recent development in aluminium for automotive applications,” Trans. Nonferrous Met. Soc. China, vol. 24, no. 7, pp. 1995–2002, Jul. 2014.Google Scholar
- 3.M. Murayama and K. Hono, “Pre-precipitate clusters and precipitation processes in Al–Mg–Si alloys,” Acta Mater., vol. 47, no. 5, pp. 1537–1548, 1999.Google Scholar
- 4.M. Murayama, K. Hono, W. F. Miao, and D. E. Laughlin, “The effect of Cu additions on the precipitation kinetics in an Al-Mg-Si alloy with excess Si,” Metall. Mater. Trans. A, vol. 32, no. 2, pp. 239–246, 2001.Google Scholar
- 5.S. Esmaeili, X. Wang, D. J. Lloyd, and W. J. Poole, “On the precipitation-hardening behavior of the Al-Mg-Si-Cu alloy AA6111,” Metall. Mater. Trans. A, vol. 34, no. 3, pp. 751–763, 2003.Google Scholar
- 6.S. Wenner, C. D. Marioara, S. J. Andersen, and R. Holmestad, “Effect of room temperature storage time on precipitation in Al–Mg–Si (–Cu) alloys with different Mg/Si ratios,” Int. J. Mater. Res., vol. 103, no. 8, pp. 948–954, 2012.Google Scholar
- 7.G. H. Tao, C. H. Liu, J. H. Chen, Y. X. Lai, P. P. Ma, and L. M. Liu, “The influence of Mg/Si ratio on the negative natural aging effect in Al–Mg–Si–Cu alloys,” Mater. Sci. Eng. A, vol. 642, pp. 241–248, Aug. 2015.Google Scholar
- 8.J. H. Kim and T. Sato, “Effects of Cu Addition on Nanocluster Formation and Two-Step Aging Behaviors of Al–Mg–Si Alloys,” J. Nanosci. Nanotechnol., vol. 11, no. 2, pp. 1319–1322, Feb. 2011.Google Scholar
- 9.B. J. Diak and S. Saimoto, “Role of Strain Rate Sensitivity on Diffuse Necking,” in Dynamic Plasticity and Structural Behaviours, 1995, pp. 5–8.Google Scholar
- 10.A. H. Cottrell and R. J. Stokes, “Effects of Temperature on the Plastic Properties of Aluminium Crystals,” Proc. R. Soc. Math. Phys. Eng. Sci., vol. 233, no. 1192, pp. 17–34, Dec. 1955.Google Scholar
- 11.B. J. Diak, K. R. Upadhyaya, and S. Saimoto, “Characterization of thermodynamic response by materials testing,” Prog. Mater. Sci., vol. 43, no. 4, pp. 223–363, 1998.Google Scholar
- 12.B. J. Diak, Microplastic bases for constitutive characterization of aluminum alloys and their correlation to sheet formability. 1997.Google Scholar
- 13.F. R. N. Nabarro, “Cottrell-Stokes law and activation theory,” Acta Metall. Mater., vol. 38, no. 2, pp. 161–164, 1990.Google Scholar
- 14.R. C. Picu and R. Li, “On the relationship between the Cottrell–Stokes law and the Haasen plot,” Mater. Sci. Eng. A, vol. 527, no. 20, pp. 5303–5306, Jul. 2010.Google Scholar
- 15.S. Saimoto, “Dynamic dislocation–defect analysis,” Philos. Mag., vol. 86, no. 27, pp. 4213–4233, Sep. 2006.Google Scholar
- 16.A. S. Argon, Strengthening Mechanisms in Crystal Plasticity. 2007.Google Scholar
- 17.M. Carlone and S. Saimoto, “Precision strain rate sensitivity measurement using the step-ramp method,” Exp. Mech., vol. 36, no. 4, pp. 360–366, 1996.Google Scholar
- 18.Y. Aruga, M. Kozuka, Y. Takaki, and T. Sato, “Formation and reversion of clusters during natural aging and subsequent artificial aging in an Al–Mg–Si alloy,” Mater. Sci. Eng. A, vol. 631, pp. 86–96, Apr. 2015.Google Scholar
- 19.B. J. Diak and S. Saimoto, “Assessment of decomposition products in an Al–Mg–Si alloy by instrumented micro-indentation,” Mater. Sci. Eng. A, vol. 319, pp. 909–913, 2001.Google Scholar
- 20.S. Saimoto and M. S. Duesbery, “Strain rate sensitivity: the role of dislocation loop and point defect recovery,” Acta Metall., vol. 32, no. 1, pp. 147–155, 1984.Google Scholar