Structural optimization of nanostructured aluminum for enhancing mechanical properties and formability

Jacob Kidmose

Research output: Book/ReportPh.D. thesisResearch

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Abstract

The aim of this project is i) to optimize processing parameters of accumulative roll bonding (ARB) to produce a nanostructure of a commercial pure aluminium (Al1050), ii) to apply post-ARB process treatments in the form of thermal annealing or plastic deformation to tailor the structure and mechanical properties, iii) to do a detailed experimental investigation of the onset and evolution of strain localization and iv) to investigate the performance of the sheets produced using standard formability tests.
Two processing parameters of ARB, wire brushing and stacking, were carefully improved so ARB processing succeeded in producing nanostructured metal sheets with a width of up to 190 mm, allowing standard formability tests to be performed.
The initial coarse grained Al1050 had a yield strength of 39 MPa and a total tensile elongation of about 45%. The as-ARB processed nanostructured Al1050 sheets showed an enhanced yield strength (135 MPa) but limited tensile ductility (7%). Post-process thermal annealing at a medium temperature (225°C) resulted in a good compromise between strength and ductility. The yield stress (98 MPa) is more than twice that of the initial material and the total elongation was restored to around 28%, which is nearly four times of that of the as-ARB state. Post-process deformation by cold rolling up to 50% thickness reductions led to a small change in strength but gradually and monotonically increase in tensile elongation as compared with the as-ARB state. After 50% post-process cold rolling, the yield strength (138 MPa) was maintained comparable with the as-ARB sheet, while the total tensile elongation was increased to 17%, which is more than twice of the ARB state.
Tensile behavior analysis done by an advanced digital image correlation technique (ARAMIS) showed that the onset of localized deformation occurred at a very low strain for the as-processed nanostructured metal even before the UTS, which had not been observed before. The localized deformation developed into a shear band by further tensile straining. After 50% post-process rolling only small localizations were observed and they did not develop before the very end of the test. Formability testing results showed that the ARB conditions perform much better in the biaxial stress region than in uniaxial tension. In particular the ARB and the medium temperature annealed conditions exhibited biaxial stretching capabilities close to that of initial material while the post process cold rolled sheets perform slightly poorer but still better than the Al1050 sheets conventionally cold rolled to similar thickness reductions.
Original languageEnglish
PublisherDTU Wind Energy
Number of pages175
ISBN (Electronic)978-87-92896-85-8
Publication statusPublished - 2014
SeriesDTU Wind Energy PhD
Number0038(EN)

Keywords

  • DTU Wind Energy PhD-38
  • DTU Wind Energy PhD-0038

Projects

Yield point phenomenon and formability of nanometals

Kidmose, J., Huang, X., Winther, G., Mikkelsen, L. P., Tsuji, N. & Nielsen, K. B.

Institut, samfinansiering

01/01/201020/06/2014

Project: PhD

Cite this

Kidmose, J. (2014). Structural optimization of nanostructured aluminum for enhancing mechanical properties and formability. DTU Wind Energy. DTU Wind Energy PhD, No. 0038(EN)