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Cryogenic friction-stir processing of ultrafine-grained Al-Mg-TiO2 nanocomposites

Khodabakhshi, F ; Sharif University of Technology

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  1. Type of Document: Article
  2. DOI: 10.1016/j.msea.2014.10.048
  3. Abstract:
  4. Submerged friction-stir processing under cryogenic conditions was employed to fabricate ultrafine-grained nanocomposites with enhanced mechanical characteristics. Al-Mg alloy sheet with 3vol% TiO2 nanoparticles were processed under air (ambient temperature), a water-dry ice medium (~-25°C), and liquid nitrogen. It is shown that a homogenous distribution of reinforcement particles throughout the metal matrix is attained at a rotational speed of 1400rpm and a traverse velocity of 50mm/min after 4 passes. In situ formation of Al3Ti and MgO nanophases during multi-pass processing is shown by transmission electron microscopy. Under the cryogenic cooling condition, ultrafine grains and cellular structures with sizes smaller than 1μm and 200nm are attained. It is shown that the formation of an ultrafine-grained structure is accompanied with significant improvement (150-200%) in the mechanical strength. The tensile yield strength of ~170MPa, elongation of ~22% and Vickers hardness of ~165HV are attained. A change in the fracture mode from ductile-brittle to fully ductile is presented when the cryogenic processing is employed. A relationship between the grain size and the fracture features is demonstrated. Effects of cooling conditions on the microstructure and mechanical properties of friction stir processed Al-based nanocomposites are addressed
  5. Keywords:
  6. Al-Mg alloy ; Mechanical property ; Nanocomposite ; Submerged friction-stir processing ; Ultrafine-grained material ; Nanocomposites ; TiO ; Ultrafine grained materials ; Ultrafine-grained Al-Mg ; Mechanical properties
  7. Source: Materials Science and Engineering A ; Vol. 620, issue , 2014 , pp. 471-482 ; ISSN: 09215093
  8. URL: http://www.sciencedirect.com/science/article/pii/S092150931401291X