Mechanical behavior and strengthening mechanisms in ultrafine grain precipitation-strengthened aluminum alloy

Kaka Ma, Haiming Wen, Tao Hu, Troy D. Topping, Dieter Isheim, David N. Seidman, Enrique J. Lavernia, Julie M. Schoenung*

*Corresponding author for this work

Research output: Contribution to journalArticle

407 Scopus citations

Abstract

To provide insight into the relationships between precipitation phenomena, grain size and mechanical behavior in a complex precipitation- strengthened alloy system, Al 7075 alloy, a commonly used aluminum alloy, was selected as a model system in the present study. Ultrafine-grained (UFG) bulk materials were fabricated through cryomilling, degassing, hot isostatic pressing and extrusion, followed by a subsequent heat treatment. The mechanical behavior and microstructure of the materials were analyzed and compared directly to the coarse-grained (CG) counterpart. Three-dimensional atom-probe tomography was utilized to investigate the intermetallic precipitates and oxide dispersoids formed in the as-extruded UFG material. UFG 7075 exhibits higher strength than the CG 7075 alloy for each equivalent condition. After a T6 temper, the yield strength (YS) and ultimate tensile strength (UTS) of UFG 7075 achieved 734 and 774 MPa, respectively, which are ∼120 MPa higher than those of the CG equivalent. The strength of as-extruded UFG 7075 (YS: 583 MPa, UTS: 631 MPa) is even higher than that of commercial 7075-T6. More importantly, the strengthening mechanisms in each material were established quantitatively for the first time for this complex precipitation-strengthened system, accounting for grainboundary, dislocation, solid-solution, precipitation and oxide dispersoid strengthening contributions. Grain-boundary strengthening was the predominant mechanism in as-extruded UFG 7075, contributing a strength increment estimated to be 242 MPa, whereas Orowan precipitation strengthening was predominant in the as-extruded CG 7075 (∼102 MPa) and in the T6-tempered materials, and was estimated to contribute 472 and 414 MPa for CG-T6 and UFG-T6, respectively.

Original languageEnglish (US)
Pages (from-to)141-155
Number of pages15
JournalActa Materialia
Volume62
Issue number1
DOIs
StatePublished - Jan 2014

Keywords

  • Al alloys
  • Atom-probe tomography
  • Precipitation
  • Strengthening mechanism
  • Ultrafine-grained materials

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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