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Title: Microstructural variation through weld thickness and mechanical properties of peened friction stir welded 6061 aluminum alloy joints

Abstract

The current study examined the effect of microstructure variation on the development of mechanical properties in friction stir welded joints of 6061-T6 aluminum alloy, which were subsequently processed by shot peening (SP). Following to FSW, fatigue specimens were extracted perpendicularly to the welding direction. Surface Skimming to 0.5 mm from crown and root sides of the joint was made and SP was later applied on the two sides using ceramic shots of two different Almen intensities of 0.18 mmA and 0.24 mmA. Microstructural examination by electron back scattered diffraction (EBSD) indicated variation in the grain refinement of the weld zone, with coarsest grains (5 μm) at the crown side and finest grains (2 μm) at the root side. Reduction of microhardness to 60 HV occurred in the weld zone for samples in FSW condition. Application of SP promoted significant strain hardening at the crown side, with Almen intensities of 0.24 mmA providing maximum increase in microhardness to 120 HV. On the contrary, only a maximum microhardness of 75 HV was obtained at the root side. The difference in strain hardening capability at the two sides was strongly dependent on grain size. The two Almen intensities produced similar distribution of compressivemore » residual stresses in the subsurface regions that led to enhance the fatigue strength to the level of base metal for N ≥ 10{sup 5} cycles. Yet, the increase in fatigue strength was more pronounced with increasing Almen intensity to 0.24 mmA, demonstrating further enhancement by strain hardening. - Highlights: • Grain refinement was observed after friction stir welding of AA 6061-T6. • Reduction in microhardness and fatigue strength were obtained after welding. • Variation in grain refinement led to different hardening behavior after peening. • Shot peening induced beneficial compressive residual stresses. • Shot peening and surface skimming markedly improved the fatigue performance.« less

Authors:
 [1];  [2]
  1. Department of Mechanical Engineering, College of Engineering & Petroleum, Kuwait University, P.O. Box 5969, Safat 13060 (Kuwait)
  2. Institute of Material Science and Engineering, Clausthal University of Technology, Agricolastr. 6, 38678 Clausthal-Zellerfeld (Germany)
Publication Date:
OSTI Identifier:
22689735
Resource Type:
Journal Article
Journal Name:
Materials Characterization
Additional Journal Information:
Journal Volume: 126; Other Information: Copyright (c) 2017 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1044-5803
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION SPECTROSCOPY; ALUMINIUM ALLOYS; BACKSCATTERING; CERAMICS; ELECTRON DIFFRACTION; FATIGUE; FRICTION; GRAIN REFINEMENT; GRAIN SIZE; MICROHARDNESS; REDUCTION; RESIDUAL STRESSES; SHOT PEENING; STRAIN HARDENING; STRAINS; SURFACES; THICKNESS; WELDED JOINTS; WELDING

Citation Formats

Abdulstaar, Mustafa A., E-mail: mustafa.abdulstaar@gmail.com, Al-Fadhalah, Khaled J., and Wagner, Lothar. Microstructural variation through weld thickness and mechanical properties of peened friction stir welded 6061 aluminum alloy joints. United States: N. p., 2017. Web. doi:10.1016/J.MATCHAR.2017.02.011.
Abdulstaar, Mustafa A., E-mail: mustafa.abdulstaar@gmail.com, Al-Fadhalah, Khaled J., & Wagner, Lothar. Microstructural variation through weld thickness and mechanical properties of peened friction stir welded 6061 aluminum alloy joints. United States. doi:10.1016/J.MATCHAR.2017.02.011.
Abdulstaar, Mustafa A., E-mail: mustafa.abdulstaar@gmail.com, Al-Fadhalah, Khaled J., and Wagner, Lothar. Sat . "Microstructural variation through weld thickness and mechanical properties of peened friction stir welded 6061 aluminum alloy joints". United States. doi:10.1016/J.MATCHAR.2017.02.011.
@article{osti_22689735,
title = {Microstructural variation through weld thickness and mechanical properties of peened friction stir welded 6061 aluminum alloy joints},
author = {Abdulstaar, Mustafa A., E-mail: mustafa.abdulstaar@gmail.com and Al-Fadhalah, Khaled J. and Wagner, Lothar},
abstractNote = {The current study examined the effect of microstructure variation on the development of mechanical properties in friction stir welded joints of 6061-T6 aluminum alloy, which were subsequently processed by shot peening (SP). Following to FSW, fatigue specimens were extracted perpendicularly to the welding direction. Surface Skimming to 0.5 mm from crown and root sides of the joint was made and SP was later applied on the two sides using ceramic shots of two different Almen intensities of 0.18 mmA and 0.24 mmA. Microstructural examination by electron back scattered diffraction (EBSD) indicated variation in the grain refinement of the weld zone, with coarsest grains (5 μm) at the crown side and finest grains (2 μm) at the root side. Reduction of microhardness to 60 HV occurred in the weld zone for samples in FSW condition. Application of SP promoted significant strain hardening at the crown side, with Almen intensities of 0.24 mmA providing maximum increase in microhardness to 120 HV. On the contrary, only a maximum microhardness of 75 HV was obtained at the root side. The difference in strain hardening capability at the two sides was strongly dependent on grain size. The two Almen intensities produced similar distribution of compressive residual stresses in the subsurface regions that led to enhance the fatigue strength to the level of base metal for N ≥ 10{sup 5} cycles. Yet, the increase in fatigue strength was more pronounced with increasing Almen intensity to 0.24 mmA, demonstrating further enhancement by strain hardening. - Highlights: • Grain refinement was observed after friction stir welding of AA 6061-T6. • Reduction in microhardness and fatigue strength were obtained after welding. • Variation in grain refinement led to different hardening behavior after peening. • Shot peening induced beneficial compressive residual stresses. • Shot peening and surface skimming markedly improved the fatigue performance.},
doi = {10.1016/J.MATCHAR.2017.02.011},
journal = {Materials Characterization},
issn = {1044-5803},
number = ,
volume = 126,
place = {United States},
year = {2017},
month = {4}
}