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

摘要

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.