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JOM

, Volume 64, Issue 2, pp 234–238 | Cite as

Tailoring Microstructure and Properties of Hierarchical Aluminum Metal Matrix Composites Through Friction Stir Processing

  • Y. H. SohnEmail author
  • T. Patterson
  • C. Hofmeister
  • C. Kammerer
  • W. Mohr
  • M. van den Bergh
  • M. Shaeffer
  • J. Seaman
  • K. Cho
Article

Abstract

The fabrication of hierarchical aluminum metal matrix composites (MMCs) begins with the cryomilling of inert gas-atomized AA5083 Al powders with B4C particles, which yields agglomerates of nanocrystalline (NC) Al grains containing a uniform dispersion of solidly bonded, submicron B4C particles. The cryomilled agglomerates are size classified, blended with coarse-grain Al (CG-Al) powders, vacuum degassed at an elevated temperature, and consolidated to form the bulk composite. This hierarchical Al MMCs have low weight and high strength/stiffness attributable to the (A) Hall–Petch strengthening from NC-Al (5083) grains, (B) Zener pinning effects from B4C particulate reinforcement and dispersoids in both the NC-Al and CG-Al, (C) the interface characteristics between the three constituents, and (D) a high dislocation density. The hierarchical Al MMCs exhibit good thermal stability and microstructural characteristics that deflect or blunt crack propagation. A significant change in the microstructure of the composite was observed after friction stir processing (FSP) in the thermomechanically affected zone (TMAZ) due to the mechanical mixing, particularly in the advancing side of the stir zone (SZ). The NC-Al grains in the TMAZ grew during FSP. Evidence of CG-Al size reduction was also documented since CG-Al domain was absent by optical observation. Given the proper control of the microstructure, FSP has demonstrated its potential to increase both strength and ductility, and to create functionally tailored hierarchical MMCs through surface modification, graded structures, and other hybrid microstructural design.

Keywords

Friction Stir Weld Friction Stir Processing Boron Carbide Stir Zone Powder Metallurgy Technique 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgements

Research was sponsored by U.S. Army Research Laboratory and was accomplished under Cooperative Agreement W911NF-08-2-0026. The views, opinions, and conclusions made in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of Army Research Laboratory or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein. Use of the Materials Characterization Facility at UCF is gratefully acknowledged.

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Copyright information

© TMS 2012

Authors and Affiliations

  • Y. H. Sohn
    • 1
    Email author
  • T. Patterson
    • 1
  • C. Hofmeister
    • 1
  • C. Kammerer
    • 1
  • W. Mohr
    • 2
  • M. van den Bergh
    • 3
  • M. Shaeffer
    • 4
  • J. Seaman
    • 2
  • K. Cho
    • 5
  1. 1.Advanced Materials Processing and Analysis Center, and Department of Mechanical, Materials and Aerospace EngineeringUniversity of Central FloridaOrlandoUSA
  2. 2.Edison Welding InstituteColumbusUSA
  3. 3.DWA Aluminum CompositesChatsworthUSA
  4. 4.Department of Mechanical EngineeringJohns Hopkins UniversityBaltimoreUSA
  5. 5.Weapons and Materials Research Directorate, U.S. Army Research LaboratoryAberdeen Proving GroundUSA

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