Publication Date:
2012-02-13
Description:
The fabrication of hierarchical aluminum metal matrix composites (MMCs) begins with the cryomilling of inert gas-atomized AA5083 Al powders with B 4 C particles, which yields agglomerates of nanocrystalline (NC) Al grains containing a uniform dispersion of solidly bonded, submicron B 4 C 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 B 4 C 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. Content Type Journal Article Pages 1-5 DOI 10.1007/s11837-012-0249-9 Authors Y. H. Sohn, Advanced Materials Processing and Analysis Center, and Department of Mechanical, Materials and Aerospace Engineering, University of Central Florida, Orlando, FL 32816, USA T. Patterson, Advanced Materials Processing and Analysis Center, and Department of Mechanical, Materials and Aerospace Engineering, University of Central Florida, Orlando, FL 32816, USA C. Hofmeister, Advanced Materials Processing and Analysis Center, and Department of Mechanical, Materials and Aerospace Engineering, University of Central Florida, Orlando, FL 32816, USA C. Kammerer, Advanced Materials Processing and Analysis Center, and Department of Mechanical, Materials and Aerospace Engineering, University of Central Florida, Orlando, FL 32816, USA W. Mohr, Edison Welding Institute, Columbus, OH 43221, USA M. van den Bergh, DWA Aluminum Composites, Chatsworth, CA 91311, USA M. Shaeffer, Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218, USA J. Seaman, Edison Welding Institute, Columbus, OH 43221, USA K. Cho, Weapons and Materials Research Directorate, U.S. Army Research Laboratory, Aberdeen Proving Ground, MD 21005, USA Journal JOM Journal of the Minerals, Metals and Materials Society Online ISSN 1543-1851 Print ISSN 1047-4838
Print ISSN:
1047-4838
Electronic ISSN:
1543-1851
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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