Improving Corrosion Fatigue Performance of AA2219 Friction Stir Welds with Low Plasticity Burnishing

Low Plasticity Burnishing (LPB) has been investigated
as a post-weld surface treatment to improve the
corrosion fatigue performance of friction stir welded
(FSW) AA2219 plate. Welds were fabricated from 9.5
mm thick AA2219-T8751 plate. Residual stress
distributions mapped by x-ray diffraction through the
thickness of the weld indicate zones of tension parallel
to the weld line at the interface of the weld and parent
metal on both the advancing and retreating sides of the
weld stir zone. Maximum tension ranged from 100
MPa at the surface to 200 MPa at mid-thickness. LPB
placed the weld region in high compression on the
order of -400 MPa. Fatigue testing was performed in
four-point bending at R=0.1 under constant stress. The
corrosion fatigue performance after 100 hours in 3.5%
salt fog improved from 175 MPa for a milled surface to
225 MPa after LPB processing. LPB provided nearly
complete mitigation of the pitting corrosion damage,
with comparable fatigue performance regardless of salt
fog exposure. Theoretical predictions of the fatigue life
improvement from LPB are also shown and compared
to the empirical fatigue data. LPB appears to provide a
practical weld post-treatment for improved corrosion
fatigue performance of aluminum alloy FSW's.