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Title: Modeling of Residual Stresses and Property Distributions in Friction Stir Welds of Aluminum Alloy 6061-T6

Abstract

An integrated thermal-metallurgical-mechanical model is used to analyze and provide insights into the formation of the residual stress and the changes in microstructure and property of Al6061-T6 friction stir welds. The simulations were conducted by means of a three-dimensional finite element model that accounts for the phenomena of frictional heating, weld microstructure and strength changes due to dissolution and reprecipitation of the hardening precipitate particles, and the mechanical workpiece/tool contact during the friction stir welding (FSW) process. The model predictions were confirmed by experimental measurement data from previous studies. For the friction stir welds investigated, it was found that the residual stress distribution is strongly dependent on the welding process parameters and the degree of material softening caused by welding. The recovery of material strength from natural aging does not increase the residual stress in the weld. The failure of friction stir weld under tensile load is controlled by the combination of the reduction in strength and the residual stresses in the heat affected zone (HAZ).

Authors:
 [1];  [1];  [1];  [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); High Flux Isotope Reactor
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
931698
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Science and Technology of Welding and Joining; Journal Volume: 12; Journal Issue: 4
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM BASE ALLOYS; MATHEMATICAL MODELS; WELDED JOINTS; MORPHOLOGICAL CHANGES; FRICTION; HEAT AFFECTED ZONE; MICROSTRUCTURE; RESIDUAL STRESSES; FINITE ELEMENT METHOD

Citation Formats

Feng, Zhili, David, Stan A, Wang, Xun-Li, and Sklad, Philip S. Modeling of Residual Stresses and Property Distributions in Friction Stir Welds of Aluminum Alloy 6061-T6. United States: N. p., 2007. Web. doi:10.1179/174329307X197610.
Feng, Zhili, David, Stan A, Wang, Xun-Li, & Sklad, Philip S. Modeling of Residual Stresses and Property Distributions in Friction Stir Welds of Aluminum Alloy 6061-T6. United States. doi:10.1179/174329307X197610.
Feng, Zhili, David, Stan A, Wang, Xun-Li, and Sklad, Philip S. Mon . "Modeling of Residual Stresses and Property Distributions in Friction Stir Welds of Aluminum Alloy 6061-T6". United States. doi:10.1179/174329307X197610.
@article{osti_931698,
title = {Modeling of Residual Stresses and Property Distributions in Friction Stir Welds of Aluminum Alloy 6061-T6},
author = {Feng, Zhili and David, Stan A and Wang, Xun-Li and Sklad, Philip S},
abstractNote = {An integrated thermal-metallurgical-mechanical model is used to analyze and provide insights into the formation of the residual stress and the changes in microstructure and property of Al6061-T6 friction stir welds. The simulations were conducted by means of a three-dimensional finite element model that accounts for the phenomena of frictional heating, weld microstructure and strength changes due to dissolution and reprecipitation of the hardening precipitate particles, and the mechanical workpiece/tool contact during the friction stir welding (FSW) process. The model predictions were confirmed by experimental measurement data from previous studies. For the friction stir welds investigated, it was found that the residual stress distribution is strongly dependent on the welding process parameters and the degree of material softening caused by welding. The recovery of material strength from natural aging does not increase the residual stress in the weld. The failure of friction stir weld under tensile load is controlled by the combination of the reduction in strength and the residual stresses in the heat affected zone (HAZ).},
doi = {10.1179/174329307X197610},
journal = {Science and Technology of Welding and Joining},
number = 4,
volume = 12,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • The evolution of temperature and thermal stresses during friction stir welding of Al6061-T6 was investigated by means of in situ, time resolved neutron diffraction technique. A method was developed to deconvolute the temperature and stress from the lattice spacing changes measured by neutron diffraction. The deep penetration capability of neutrons made it possible for the first time to obtain the temperature and thermal stresses inside a friction stir weld.
  • The evolution of temperature and thermal stresses during friction stir welding of Al6061-T6 was investigated by means of in-situ, time-resolved neutron diffraction technique. A method is developed to deconvolute the temperature and stress from the lattice spacing changes measured by neutron diffraction. The deep penetration capability of neutrons made it possible for the first time to obtain the temperature and thermal stresses inside a friction stir weld.
  • This study describes a simple model that can predict the evolution of hardness distribution as a function of natural aging time in a heat-treatable 6061-T6 Al alloy plate subjected to friction stir welding (FSW). First, two dimensional thermal distributions were simulated as a function of time in the FSW plate by finite element modeling. Second, the hardness changes during natural aging were measured as a function of aging time for a number of Al specimens that had been previously isothermally heat-treated to different hold temperatures in order to determine the natural aging kinetics. Finally, the simulated temperature profiles and themore » natural aging kinetics were correlated to predict the hardness profiles in the FSW plate. The predicted hardness variations are consistent with measured hardness profiles in that the location of minimum hardness moves away from the centerline as the aging time and/or heat input increases. The hardness variation was also related to the location of failure in cross-weld tensile samples.« less
  • Residual stresses were measured through the thickness of friction-stir processed (FSP) 6061-T6 aluminum-alloy plates using neutron diffraction. Two different specimens were prepared to study the relationship between residual stress distributions through the thickness of the plate and angular distortion: (Case 1) a plate processed with both stirring pin and tool shoulder, i.e., a typical FSP plate subjected to both plastic deformation and frictional heat, and (Case 2) a plate processed only with the tool shoulder, i.e., subjected mainly to the frictional heating. The measured residual stress profiles show relatively small through-thickness residual stress variations in Case 1, while there ismore » a significant through-thickness residual stress variations in Case 2. The main cause of the geometric angular distortion could be related to the non-uniform distribution of the frictional heat generated by the tool shoulder leading to the asymmetric distributions of the residual stress through the thickness of the FSP plate.« less