Abstract
The influence of the stirring pin and pressing tool shoulder on the microstructural softening during friction-stir processing (FSP) and subsequent natural aging behavior was investigated for a 6061-T6 aluminum alloy. The evolution of hardness profiles in various characteristic regions of the FSP plates was investigated as a function of time from 4 to 5760 hours after the FSP through the thickness of the plates and correlated to the microstructure and residual strain profiles measured by a neutron-diffraction technique. The results show that the microstructural softening and the natural aging observed in the dynamic recrystallized zone and thermomechanically affected zone are mainly caused by the frictional heating from the tool shoulder, resulting in dissolution and reprecipitation of strengthening precipitates. On the other hand, the softening in the heat-affected zone is due to the dissolution/growth of the precipitates and is not followed by the natural aging under the current processing condition. The kinetics of the natural aging behavior is also discussed.
| Original language | English |
|---|---|
| Pages (from-to) | 69-76 |
| Number of pages | 8 |
| Journal | Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science |
| Volume | 38 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jan 2007 |
Funding
This work is supported by the NSF International Materials Institutes (IMI) Program under Contract No. DMR-0231320. This work has benefited from the use of the Los Alamos Neutron Science Center, Los Alamos National Laboratory. This research is also sponsored by the Laboratory Directed Research and Development program of Oak Ridge National Laboratory (ORNL), managed by UT\u2013Battelle, LLC for the United States Department of Energy under Contract No. DE-AC05-00OR22725. The authors thank Dr. S.A. David, C.R. Hubbard, P.K. Liaw, Mr. A. Frederick, and Mr. T. Sisneros for their help.