Investigation of the Unloading Yield Effect in Aluminum and Magnesium Sheet Metal Alloys at Room Temperature

Abstract:

The reduction of CO₂-emissions and the lowering of fuel consumption are two main objectives in the automotive industry. To reach these targets, conventional materials like deep drawing steels are substituted by new modern lightweight materials such as aluminum and magnesium alloys. During forming of sheet metal parts, the material experiences a plastic deformation, which can affect the part quality regarding the amount of springback or the occurrence of stretcher strain marks. In this context, a time dependent change of the material behavior can emerge after removing the part from the forming tool. Within this contribution, the influence of pre-strain and the unloading yield effect on the subsequent mechanical behavior of the aluminum alloy AA7020 and the magnesium alloy AZ31B are investigated. Additionally, the time dependency of mechanical properties is analyzed for different aging times from 5 seconds to one week after pre-straining. The results show a significant increase of unloading yield effect with increasing pre-strain during uniaxial tension.

• Periodical: Key Engineering Materials (Volume 716)
• Pages: 331-336
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.716.331
• Online since: October 2016
• Authors: Julia Degner*, Sebastian Suttner, Marion Merklein
• Keywords: Advanced Lightweight Materials, Material Characterization, Unloading Yield

References

[1] J. Geng, F. Nie, Unloading yield effect in a twin-roll-cast Mg–3Al–1Zn alloy, Scripta Mater. 100 (2015) 78–81.

DOI: 10.1016/j.scriptamat.2014.12.018

[2] A.W. Thompson, Yield points during cyclic strain of a Cu-7. 57% A1 Alloy, Phys. Stat. Sol. (a) 25 (1974) 85-91.

DOI: 10.1002/pssa.2210250105

[3] A.L. Titchener, G.J. Davies, Yield phenomena in polycrystalline copper, Philos Mag. 11 (1965) 114 1225-1232.

[4] P. Haasen, A. Kelly, A yield phenomenon in face-centered cubic single crystals, Acta Metall. 5 (1957) 192-199.

DOI: 10.1016/0001-6160(57)90165-7

[5] L.M. Malik, J.I. Dickson, Yield point effects in a-titanium during interrupted tensile tests at 300-496 ° K, Materials Science and Engineering 17 (1975) 67-75.

DOI: 10.1016/0025-5416(75)90032-4

[6] H. K. Birnbaum, Unloading effects in crystals - I the unloading yield point Effect, Acta Metall. 9 (1961) 320-326.

DOI: 10.1016/0001-6160(61)90225-5

[7] H. Çi̇menoğlu and E. Kayali, Yield effects in as-quenched, dual-phase steels, Scripta Metall. Mater. 24 (1990) 122437-2442.

DOI: 10.1016/0956-716x(90)90107-r

[8] T. G. Nieh, W. D. Nix, Unloading yield effects in aluminum alloys, Metall. Trans. A. 17A (1986) 121-126.

DOI: 10.1007/bf02644448

[9] R.W.K. Honeycombe, The Plastic Deformation of Metals, second ed., Arnold, (1984).

[10] J.R. Davis, Tensile Testing, second ed., ASM international, (2004).

[11] A. Deschamps, F- Livet, Y. Bréchet, Influence of Predeformation on Ageing in an Al-Zn-Mg alloy – I. Microstructure evolution and mechanical properties, Acta Mater. 47 (1999) 281-292.

DOI: 10.1016/s1359-6454(98)00293-6

[12] A. S. Argon, W. T. Brydges, Deformation of copper in easy glide, Philos Mag. 18 154 (1968) 817-837.

DOI: 10.1080/14786436808227503