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Title: Microstructure characterization of the stir zone of submerged friction stir processed aluminum alloy 2219

Aluminum alloy 2219-T6 was friction stir processed using a novel submerged processing technique to facilitate cooling. Processing was conducted at a constant tool traverse speed of 200 mm/min and spindle rotation speeds in the range from 600 to 800 rpm. The microstructural characteristics of the base metal and processed zone, including grain structure and precipitation behavior, were studied using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Microhardness maps were constructed on polished cross sections of as-processed samples. The effect of tool rotation speed on the microstructure and hardness of the stir zone was investigated. The average grain size of the stir zone was much smaller than that of the base metal, but the hardness was also lower due to the formation of equilibrium θ precipitates from the base metal θ′ precipitates. Stir zone hardness was found to decrease with increasing rotation speed (heat input). The effect of processing conditions on strength (hardness) was rationalized based on the competition between grain refinement strengthening and softening due to precipitate overaging. - Highlights: • SZ grain size (∼ 1 μm) is reduced by over one order of magnitude relative to the BM. • Hardness in the SZ ismore » lower than that of the precipitation strengthened BM. • Metastable θ′ in the base metal transforms to equilibrium θ in the stir zone. • Softening in the SZ results from a decrease of precipitation strengthening.« less
Authors:
 [1] ;  [2] ;  [3] ;  [1]
  1. Welding Engineering Program, Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43221 (United States)
  2. (China)
  3. State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001 (China)
Publication Date:
OSTI Identifier:
22285068
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Characterization; Journal Volume: 82; Other Information: Copyright (c) 2013 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM ALLOYS; CROSS SECTIONS; FRICTION; GRAIN REFINEMENT; GRAIN SIZE; METALS; MICROHARDNESS; OPTICAL MICROSCOPY; PRECIPITATION; SCANNING ELECTRON MICROSCOPY; TRANSMISSION ELECTRON MICROSCOPY