W. C. Woo, Z. Feng, C. Hubbard, S. A. David, Oak Ridge National Laboratory, Oak Ridge, TN; X. L. Wang, Spallation Neutron Source, Oak Ridge, TN; B. Clausen, Materials Science and Technology Division, Los Alamos, NM; T. Ungar, Eotvos University, Budapest, Hungary
In-situ Time-Resolved Neutron Diffraction Measurements of Microstructure Variations during Friction Stir Welding in a 6061-T6 Aluminum Alloy
W. Woo1, Z. Feng1, X-L. Wang2, B. Clausen3, T. Ungar4, C. R. Hubbard1, and S. A. David1 1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
2 Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, TN, USA
3 Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM, USA
4 Department of Materials Physics Eötvös University Budapest, Budapest, Hungary
Microstructure changes are one of the most important research areas in friction stir welding (FSW). However, direct observation of microstructure changes during FSW has been extremely challenging and many measurement techniques are inapplicable. Recently developed in-situ neutron diffraction methodology, which drastically improves the temporal resolution of neutron diffraction, enables to observe the transient microstructure changes during FSW. We installed a portable FSW system in the Spectrometer for MAterials Research at Temperature and Stress (SMARTS) at Los Alamos Neutron Science Center. The FSW was performed with a constant welding speed of 0.42 mm/sec and tool rotation speed of 156 rpm on 6.35mm-thickness 6061-T6 Al alloy plate. At the same time, the neutron beam was centered on the mid-plane of the Al plate and the diffraction measurement was continuously experimented during welding. The analysis of the diffraction peak shows the peak broadening as a function of the distance from the tool center. Since the peak broadening phenomenon is related to the grain structure, the peak profile analysis using the modified Williamson-Hall Method provides an insight to understand the grain/crystallite size and dislocation type/density. As a result, we observed the dislocation density is significantly introduced into the stir zone and exponentially decreased from the region during FSW. Furthermore, we will discuss about dynamic recovery, recrystallization, and growth in sub-grain structure during FSW.
Summary: We real-time observed the dislocation density is significantly introduced into the stir zone and exponentially decreased from the region during Friction Stir Welding using in-situ neutron diffraction.
